Visual problems and useful information on the eye and vision |
Myopia: Myopia is the manifestation of blurred vision at a distance. This term defines an eye is not able to see at a distance defined as a normal eye and which has a visual acuity of 10/10. Therefore, a myopic eye can see well shorter distances, but can not do that at distances greater than 4 meters. In fact, the point of focus of a myopic eye (remote point) is represented by the inverse of the value in meters diopter of its myopia. to eg. a myopic eye of 2.50 Dt has its farthest point (maximum distance is able to focus on a target smaller than 10/10) to 40 cm. Beyond this limit begins to see blurry. From the physical point of view, not a myopic eye focuses the rays coming from infinity on his retina, but in front of it. In this way, the rays coming out of focus on the retina and are necessary lenses negative back-fire rays up to take on the retina. myopia slight arrive up to a value of 4-5 Dt, myopias medium are those between 5-6 Dt Dt and 8, medium-high myopia are between 8 dt. Dt and 14-15 and myopia higher than those over 15 dt. Rarely found myopia than 30 Dt
Hyperopia: Hyperopia, Instead of myopia, means that the subject see well at all distances, even if it is much harder to short distances, depending on the degree of hyperopia. In fact, the hyperopic eye would focus the rays from from infinity behind his retina and forms an image on it is blurred fixed object. In this case, unlike the myopia, comes into operation accommodative system that carries out the positioning image on the retina. In this way, the image becomes sharp. Up close, the effort must be increased and that is why I support it becomes increasingly difficult, sometimes impossible. Patients often complain farsighted astenopeici symptoms (sore head, eyes red, burning, watery, etc..) rather than blurred vision and why some call for hyperopic glasses "sunglasses rest ".
Diagram of the ray path from infinity. Diverging lenses are used in the case of myopia and converging one in case of hyperopia. |
Astehnopia: is a set of symptoms and signs which indicates a pain in the visual system. It is often the alarm bell that stands out in the presence of visual stress. The signs and symptoms of asthenopia are most common: Headache localized on the forehead or the temples with late onset and absent during the day holiday. Again you can have burning eyes, eye redness, tearing, photophobia, transient sfocamenti image to close, nausea, dizziness, double vision, etc.. The best treatment is dealt with by the method S.C.S. that in an active way eliminates the problem. The eye strain is divided into Simple and Complex. The first occurs in the absence of ametropia, the second in their presence.
Visual Acuity: è l'unità di misura della capacità visiva. In Italia si misura in decimi e viene considerata normale un'A.V. di 10/10. In realtà è piuttosto facile trovare valori di A.V. superiori, spesso intorno ai 12/10 ed anche ai 15/10. L'ottotipo, che rappresenta il test con un insieme di lettere, simboli, numeri o disegni a grandezza angolare decrescente, viene solitamente proiettato ad una distanza di 5 o 6 metri. Lo studio dove viene eseguito il test deve avere sempre le stesse condizioni: distanza, luce, contrasto, tempo di presentazione del test. Infatti, variando i parametri su detti, varia anche il risultato finale ottenuto. Nei paesi anglosassoni l'acutezza visiva viene misurata in sesti, mentre negli U.S.A. in piedi. Di seguito inseriamo una tabella comparativa dei tre sistemi. Vedi ottotipo
Dynamic Visual Acuity: represents the evaluation the AV, of view, in a dynamic way simulating the movement. In fact it is very usual that the eyes are used in a dynamic, rather that only in a static, sitting comfortably watching a series of characters with a decent time to do so. The A. V.D. is evaluated projecting a series of numbers or a word at a time, allowing the examinee a very short time to recognize what is projected. The times used are usually 1/10 second, 1/25, 1/50 and 1/100 of a second. only a few Optometrists are able to evaluate the dynamic visual acuity. It is often used during training and visual can be trained to improve. The dynamic visual acuity, as opposed to the static measures the time necessary for recognizing a character often fixed in size and AV average (about 0.6). Sometimes you can also change the font size. The spirit of this measure is to assess not the maximum capacity of AV already seen with the static measure, but the eye's ability to discriminate characters that appear for a very short period of time. as we seen previously, the exposure time does decrease the AV and therefore not characters are used to A.V. very high. The dynamic assessment tends to simulate the daily life, especially the conditions of movement. such Evaluation is crucial for athletes and all evaluations in which known difficulty of increase of A.V. static. This will serve to indicate a Proper visual training. Also, we need to train for an A.. V. pushing to the extreme high dynamic capabilities and ocular oculo-motor.
Aphakia: is the lack of crystalline within the eye. The crystalline lens is that allows the biological vision at all distances (autofocus). This observation can be congenital, traumatic or subsequent to cataract surgery. if congenital, the / the child / a is born without one or both crystalline. Then the eye is not able to correctly focus the images on the retina As the lens has about 12-18 Diopters. In such a case can be applied a contact lens which returns the functionality to the eye, for allow a normal neuro-physiological development of the child / y. If traumatic, aphakia occurs in susseguenza of a trauma that makes dislocate or even out the lens from its housing. Following an intervention of cataract clouding of the lens, it can be removed for eye to regain the necessary transparency to the vision. Today, the lens removed or missing, is almost always replaced by a lens intra-ocular, avoiding the need to use contact lenses or glasses considerable thickness.
Amblyopia: sometimes called "lazy eye" identifies a vision reduced compared the norm. It is usually unilateral (against only one eye), rarely bilaterally. Amblyopic eye is considered that despite the best correction does not reach 7/10 of A.V. The treatment is the most modern active stimulation by specific stimulators and exercises carried out at home. Still use the antiquated system of Orthoptists almost perpetual bandage as the sole remedy, with the major risk of damaging better than the eye is patched for a long time. The bandage, if well done and if supported by other methods can result in 30 days of use. If after this period were not achieved significant results is better abandon treatment and refer to your Optometrist. the chances recovery are related to age of the child. Before you start the better. Difficult are the results after the ninth year of age.
Visual Analisys: is the method used Optometrists by behaviorists to diagnose any problem vision. Visual analysis allows to verify all system functions visual refractive error as a function of their needs, abilities fusional, fusional reserves, acceptance of the lenses prescribed and their effectiveness over time, age of the vision problem, accommodative amplitude, and absolute relative degree of deterioration of the visual problem, etc.. So is the only means of being able to prescribe corrective lenses properly taken into account because all variables in the visual system. Who does not perform a visual analysis is able to assess the visual system and therefore it is best that you devote to other uses. The Optometrist, only professional able to undertake a visual, delivers a complete file of all data in order to allow the patient data to preserve the heritage of its visual system, for allow any future checks for other Optometrists.
Cornea: consists of 5 layers: epithelium (5 layers of cells with a total thickness from 50 to 100 microns), membrane bowman (about 12 microns thick), stroma (thickness of about 470-600 microns), Descemet's membrane (thickness of about 6 microns), endothelium (composed of a only cell layer of about 10 microns thick). The cornea has a thickness of about 0.6-0.7 mm. at the center and 0,9-1.0 mm. the limbus. It has a average diameter of 11.00 mm. and more innervated tissue and therefore sensitivity of our body. |
Sclera: is the "white tissue" of the eye and has the purpose of wrapping in a tough fibrous covering and all the internal structures of the eye. E 'attached to the cornea, before, that the limbus represents the transition zone. |
Conjunctive: is the transparent membrane that covers the sclera and arrives at the limbus, where part of the fabric corneal epithelium. Covering the sclera, is folded back and also holds the inner part of the upper and lower eyelids. It aims to defending the eye from microbial attacci and his irritation rise conjunctivitis in various forms: bacterial, viral or allergic. |
Lens: It is a slow biological officer biconvex shape to focus the rays onto the retina. his form varies depending on how does the ciliary muscle to which it is attached via the zonule of Zinn. During the accommodative act, the zonule is released and the lens assumes a more spherical shape. When the ciliary muscle is relaxed, instead, the zonula tends the reducing the power crystal. Aging, tends to turn yellow and to become opaque with cataracts in the epilogue. Not always what happens and not equally in all people. | |
Crystalline lamellae visible with slit lamp 10x | Opacity / Adhesion of Crystalline |
Ciliary muscle: is located at the front end and a width of the body ciliary and is constituted by a mass of fibers or involuntary muscle smooth. And 'composed of circular fibers, or muscle of Muller, and fiber radial. The contraction of the ciliary muscle does bring the processes ciliary the crystalline lens, allowing the increase of curvature and thus the accommodative process. And 'the muscle MEP to accommodation, activity that allows us to read all distances. |
Retina: Is the more important tissue as it can be considered as a true protrusion of the brain. Has a thickness of about 0.1 mm. and is a transparent fabric reversed. The receptors are on the opposite side to that of the light must traverse the entire thickness for achieve them. The retina covers the whole inner part of the eye behind the iris and ciliary muscle. And 'leaning against the choroid and site supported by the vitreous body. The only strong points are the nerve Optical and time locked. E 'consists of 10 layers, in the order: epithelium pigmented, cones and rods, external limiting membrane, layer outer nuclear, outer layer plexiforme, inner nuclear layer, Plexiforme inner layer, ganglionarie cells, layer of fibers nerve, the inner limiting membrane. The retina is full of receptors with maximum density of only cones in the fovea (the area of sharp vision), rods and cones in the intermediate zone and only rods proceeding to tight time. |
Choroid: covers the entire rear half of the globe, except the optic nerve and extends up the front half at the beginning of the ciliary body, about 3 mm. front of the equator. the Choroidal thickness is 0.2 mm post-mortem. about, but is thought to be more alive when the vessels are distended with blood. It 'a tissue vasculature with the task of supplying the eye in many of its need. The structure has five layers: Supracoroide, Strado of large vessels, average vessel layer, layer of small vessels or capillaries, Yaloide membrane. |
Extra Ocular muscles: each eye has six extra-ocular muscles which allow all movements. There are four right: Interior, Outside, Upper and Lower, stuck in the four cardinal points of the eye. Other two are called oblique because it allows all movements composed of oblique meridians. The paralysis or pain operation of one or more muscles of an eye, do not allow the two eyes to fix together in all directions. In this way produces permenente a squint or in some specific directions of gaze. |
Aqueous humor and vitreous humor: the first is a liquid that fills the space of the anterior chamber, between the corneal endothelium and crystalline. the anterior chamber depth is about 3 mm. The vitreous humor fills instead the cavity between the rear surface of the lens and retina. And 'a transparent gel-like white egg. |
The eyeball | From the Eyes to the visual cortex |
Astigmatism: is an ametropia that influence the vision of about half of the same degree of myopia or Hyperopia is not compensated. Usually, an astigmatic eye sees or malino pretty well (in Depending on your point of view) is close, but here looks better, that far. Astigmatism has three broad categories: myopic astigmatism (simple or compound) where the line or lines are located focal front of the retina; hyperopic astigmatism (simple or compound) where the line or two lines Focal are located behind the retina; mixed astigmatism where a focal line is located in front of the retina and the other is located behind the retina itself. the myopic astigmatism are indicated in the recipe by a minus sign, those hypermetropic by a plus sign, those mixed by a minus sign and another one. Here are five examples, the numbers of the proposed:
Astigmatism always has an axis on which acts in As the astigmatic eye is like an oval (more like a ball that to a rugby football). In this case there is a more curved meridian of the other and the corrective lens must necessarily have two values, one for adjusting the more curved, the other for adjusting the more flat. Usually, astigmatism is against the cornea, the lens at times, more sometimes the vitreous or retina. Rarely is a mixture of the said.
Cataract: is represented by opaque lens, which does not allow the passage of light sufficiently. If the total makes the eye totally blind, partially reduces the visual acuity in direct proportion all'opacamento. This is usually aging of the lens, which in senescence becomes gradually more Matt. Extraction of cataract in the elderly is becoming increasingly daily. The lens may become opaque for other causes such as trauma violent, a strong dose of radiation, both U.V. that I.R. (it is typical cataract of glass blowers), misuse or overdosing of substances pharmacological, etc.. When the cataract is opaque so that prevents the person to conduct his life as he did until a short time before, especially it abolishes the autonomy (not that there are other important causes side), then it will be appropriate to take an ophthalmologist in consider the possibility of extracting the cataract and replaced it with a intraocular lens.
Mature Cataract | Cataract extraction with Criod |
Keratoconus: is a conformation corneal which presents itself in the shape of a cone with the apex facing the outside, often a little 'below. This clinical picture is often evolutionary and during its course tends to greatly increase the corneal curvature, thinning the center of the cornea more and more. This event creates a corneal distortion of the fibers with opacamenti interior. The cornea becomes increasingly astigmatic, often with irregular astigmatism, and more and more thin. To date we do not know the underlying causes of keratoconus, which usually occurs after 15 years of age, there is a correlation family sometimes skips a generation and is usually localized to areas geografiche.Il treatment is only donated to an optimal application of gas permeable contact lenses (also called semi-rigid erroneously) that in 80% cases stops the progression of the cone. The importance of early diagnosis is intuitive, as it is certainly easier to act on a cone little pronounced.
Cheratocono Pronunced |
Toric CL (7.05/7.50) on KE (7.45/6.40) | Epithelial Erosion x little watery |
Keratomileusis (Lasik): is a method surgery that allows the treatment of myopia and hyperopia untreatable with the excimer laser. From the corneal surface is wiped away a thin lamella of tissue using a precise microkeratome. The cover is removed, the surgeon attempts to model the inner face of the laser by changing the thickness. Finally repositions the surface layer removed earlier that ricicatrizzerà without the need for sutures. This operation is performed in topical anesthesia using eye drops. The surgery is indicated in patients with ametropia (myopia or hyperopia) stable for at least 5 years and with a thickness corneal greater than 500 microns. Are excluded in all cases of keratoconus and cases with corneal diseases, especially if chronic, or with other ocular pathologies. Is carried out to compensate for refractive errors between 1 and 12 diopters, while it is not recommended for higher values. The action is certainly prefer the excimer laser (PRK) because it does not affect Bowman's membrane (removed with corneal epithelium and then repositioned) often cause more or less intense opacification of the cornea.
Asymmetric keratotomy: such surgical technique is used for the treatment of keratoconus in order to reduce the prolapse corneal and facilitate the correction with glasses or lenses hydrophilic contact. The first phase is characterized by the asymmetric keratotomy prior study topographic and pachimetrico scheimpfug room. the incisions asymmetric prolapse must make the cone as much as possible, flattening the corneal surface. The operation is performed under topical anesthesia based eyedrops. It 's indicated for patients with keratoconus initial species unless tolerate the use of contact lenses. The major problem of this technique is that has not been standardized while only the inventors are able to confer the necessary security to the success of the intervention. In fact, if the wrong performed, you could create complications that favor a bulging total of the cone.
Radial and Curve keratotomy: are techniques surgical to reduce the power myopic eye. The first part practiced a series of radial incisions (RK) from a central area of about 3 mm. in diameter towards the periphery. The curve keratotomy (AK) is concentric to the pupil in making curved cuts, freeing up the optical zone to flatten the meridian curve. The latter is shown in correction of myopic astigmatism. In both techniques is used local anesthetic-based eye drops. Is based on subjects with myopia stable for over 5 years and the absence of eye diseases. The RK is suitable for myopia between 1 and 6-7 Dt Dt The main disadvantages are the unpredictability of the outcome and the weakening of the structure constant corneal epithelium. Subsequently will be more difficult the use of contact lenses in the case of sub-corrections.
Radial keratotomy | Radial keratotomy |
Colours: the colors are seen as these just because some retinal receptors (cones) play the three lengths fundamental wavelength of light: Red, Green, Blue Using these appropriately three bands you can see all the other colors we know. when the cones are not able to recognize certain color determines the color blindness, better said dyschromatopsia. There are three basic classes of discromatopsici: Protanopi, and Deuteranopi Tritanopi. The first two types merge among them the red with green, albeit with different nuances, eg. the protanope confuses red with blue, while the deuteranope not. The tritanopi mixed yellow and blue. There are specific tests to determine the Ocular ability to see colors well and often, with appropriate filters, and possible to restore the ability to differentiate colors also discromatopsici. The Color Blindness is often hereditary and affects mainly the male population. Is not a disease and does not cause other problems visual.
Colour triangle according to CIE |
Macular degeneration: there are various forms of macular degeneration, but almost all greatly reduce the activity retina, compromising visual acuity. Of the various forms include: degeneration senile a> (of which we give a more detailed description in the link and list of centers where you pubbici Italian photodynamic therapy), circinnata retinitis, capillarosi macular hole, macular degeneration hereditary- Cerebro-retinal (like Tay-Sachs, Bielchowsky, Spielmeyer-Vogt, Kufs, etc..) Best type degeneration, Stargardt's type, such as Behr, Waardenburg type, type Sorby.
Tapestry-Retinal Degeneration |
Diabetes and Retina: there is a a simple and proliferative diabetic retinopathy. The first shows signs starting at the posterior pole, the area between the temporal retinal vessels upper and lower. Consist of micro aneurysms retinal hemorrhages point round (deep) and hard exudates. Initially they are small, multiple and scattered, then become extended to form spots large and confluent. Are highlighted and sometimes vascular factors obstructive. These manifestations include obstructive soft exudates, large hemorrhagic spots, dilated veins or venous segmented nodes. Progresses slowly over the years and if the macula is affected also spoken of maculopathy. The proliferative diabetic retinopathy develops in approximately 10% patients with diabetic retinopathy. In this case new capillaries tend to form in the retina, and on the lua surface to the papilla. these new blood vessels to proliferate and tend to bleed into the vitreous, leading to formation of scar tissue and to a traction retinal detachment. Diabetic Retinopaty, useful link
Diabetic Retinopaty |
Dyplopia: is the double vision. when the two eyes do not look the same stimulus and the brain still uses both images, the subject sees double. The cause can be found in muscle misalignment of the eyes. If diplopia persists, the brain will try to defend themselves by eliminating one eye vision (abolition).
Detachment of Retina: is the condition in which the retina becomes detached from its natural folds back on itself, or breaks in one or more points. And 'more common in subjects with high myopia and in the elderly. Sometimes tears are caused by injuries. The cause breakage detachment of the retina from the choroid with loss of nutrition the retina and subsequent retinal blindness in that area. The symptoms of rupture are: a view of objects floating in front of the eyes (but if they are unchanged many months are free from danger), floaters appeared suddenly, lightning light even with closed eyes, dark spots peripherals, dark veil that covers much of the visual field, etc.
Retinic detachment |
Visual Training: is an exercise vision (visual training) combined with tips and rules for proper hygiene visual. The visual education is the only active system to improve the visual performance in those subjects who develop a vision problem because the stressors of their environment. For example the difficulty of Learning is not only linked to an intellectual deficiency, but it is often related to incorrect posture and methods of study is not adequate. The apparatus vision, in such conditions, suffer and try to adapt or leave. in this last case, the adjustment will result in a varied symptomatology astenopeica leading to loss of concentration and yield in study. Later cause the onset of myopia as a unique opportunity to improving the skill closely at the expense of vision for distance. The visual education will try to stop this process, reconstructing the organization of the approach at close range. at the same time diminish the problems from a distance and often short-sightedness will be reduced significantly. The miogior way of using the visual education is that of SCS Method font> strong> who plays As to the perfection of that, making the subject focus of the whole process visual and behavioral training. At the end of training, the subject will be so good that you learn to apply the rules will not allow than the onset of his previous problem. In this way, the results will remain stable over time.
Phorias: represents the value of divergence or convergence (as measured horizontally) of the two eyes in dissociated conditions (when there is a merger, and each eye sees a separate aims other eye). If measured vertically, represents the vertical compensation value that the two eyes are to maintain the fusion. The same is done horizontally. Normal values are represented from -0.5 Dpr. (exoforia) for distance and -6.0 dpr. (exoforia) to close. Exoforia means position at rest in a divergence, esoforia is defined for the position at rest in convergence. Iperfora and Ipoforia indicate positions in resting respectively in the top and bottom of an eye (the one in question) respect to each other.
Phoropter: is an innovative tool used by the majority of Optometrists and encloses the All lenses, prisms and accessories enclosed in the most advanced cassette test. Completely replaces the glasses that usually served years ago to support the many lenses during the visual inspection. It 's very practical, does not weigh on the nose, but it is claimed to be only with a special arm. allows measurements very precise and safe. The lenses are all treated and are reflective of high quality. Allows execution of all tests optometric analysis, something sometimes impossible with the old test lorgnette, still in vogue among some older ophthalmologists. There are various versions and some manual where a computer software controls the motors which vary the lenses and the accessories.
Phoropter |
Photophobia: represents a hardship to sometimes comes to light that prevent a normal life to the person who suffers. usually depends on a large sensitivity to light by the receptors retinal, other times a total absence (albinism) or partial epithelial the retinal pigment epithelium, and hereditary causes for pathological reasons. the light most annoying is the Sun, although the most sensitive, the interior light is still very annoying. The only remedy, apart from the treatment pharmacological for some pathological cases, is the use of filters alone or above all, protect against radiation U.V. These filters (sunglasses), cut the U.V. below 400 nm. The absorption of the filters, the white light, must be between 75% and 90%. The color should be selected from case to case, even if the gray color (neutral color) may be indicated in many cases.
Glaucoma: is an eye condition in wherein the intra-ocular pressure rises above the permitted level (approximately more than 22 mm / Hg). The rising pressure squeezes the nerve fibers of the retina. the fibers nerve, if subjected to a long period of excessive pressure, die irreversibly. Glaucoma, therefore, if untreated can lead to blindness the affected eye. Today, thorough checks of Ophthalmologists and some Optometrists graduates almost always possible to avoid complications dangerous, recognizing time and indicating a likely attack glaucomatous subject to the timely appropriate eye care. There are two main types Glaucoma: 1) open angle that develops insidiously and leads to loss of visual acuity, with no or few symptoms, 2) angle-closure that develops leading to sudden sharp pains and a sudden loss of eyesight with congestion of the eye. For this congestion, it often shows an eye Red-sided. In subjects over 40 years was found percentage of 1% -2% greater chance of open-angle glaucoma. There is also a tendency familiar to such pathology. The treatment is relevance of medical ophthalmologist who will administer the right medications in order, usually pilocarpine, timolol maleate, etc.. The treatment may last for many years. Surgery is provided to amplify or recreate the channels of trabecular meshwork that are insufficient to the drainage of aqueous humor, in the cases selected for this intervention.
Glaucomatous cupping of the optic nerve head |
Excimer Laser (PRK): represents a real scalpel guided by their own computer. With it are ablated, ie eliminated, thin layers of fabric (microns). With this technique ablano sections concentric of corneal tissue and the amount of tissue to be ablated is linked to the amount of myopia to be corrected. Modifying the corneal curvature is amending power of the eye. Is performed under local anesthesia. And 'indicated in patients with stable myopia for several years and the correction is moderate. The main drawback is given by the possible appearances of haze (opacamenti) in the eye with a consequent reduction in visual acuity. The hyper-or hypo-correction is a risk you run and you will need a further action to correct any errors. Some cases show a regression results in time, re myopia reduced intervention.
Laser thermal keratoplasty (LTK): this type of Laser works by increasing the dioptric power of the eye. Applying a beam of heat around the cornea, it increases the curvature of the central part. This laser is a Holmium laser emitting an infrared facio and therefore heat. The beam reaches the cornea into 8 small pre-established points on its circumference. The treatment is performed under local anesthesia. And 'indicated in the treatment of hypermetropia up to 3.50 Dt The only complication is given from the corneal opacities that are formed at the points affected by the laser, but not affect vision and subside gradually until it became invisible to the naked eye. Only a few cases show a regression in time, re part of hypermetropia.
Lenti a Contatto: For more information please see Contact Lenses. This topic is widely discussed in the proposed link and therefore we invite you to log on. Additional requests or more will be like, send it by e-mail.
Design of a tri-curve RGP corneal lens | Fluoresceinic image of the same CL |
Filter lenses: depending on the type of materials and colors used, these lenses can absorb quantities variables rays. The best have a cut at 400 nm. which means which block all wavelengths below this value (under the light blue). The materials that absorb UV are better in sequence: polycarbonate, the organic resin, and finally the crystal. The more optical scrupulous have the machinery to verify the level of absorption of UV and visible light of each filter. The absorption of visible light is given by percentuele darkening of the lens. A filter with absorption 70%, it means that allows the passage of only 30% of light. there are filters selective based on their staining. These filters act on close range of wavelengths for specific uses.
Intraocular Lenses (IOL): are put in place of the lens removed during a cataract operation. In this way eye visual acuity recovers quickly without having to use glasses or lenses contacts. You just need a pair of glasses for reading because the IOL allows good visual acuity for distance, but not near.
Ophthalmic Lenses: there are many types, to meet the needs of ametropic. In a simple table we list the most common terms and their meanings:
Kind of Lens | Meaning |
Sferic | That only corrects nearsightedness or farsightedness |
Toric or Cylindrical | Corrects astigmatism |
Monofocal | Focuses on only one point: Far or Near |
Bifocal | Focuses on two points: Far and Near |
Trifocal | Focuses on three points: Far, Intermediate and Near |
Multifocal | Focuses all points from far to near |
Filter | Reduces the amount of light and UV |
The basic parameters of each ophthalmic lens are: refractive index, denoted by n, (which shows the slowing of the light in between the higher and more subtle will be the lens power parity), costringenza or abbe number (which shows the chromatic dispersion in the material, the higher and the lower the dispersion and the better the quality of lens), visible light transmittance (transparency of the material, the more higher the value the more transparent the material), transmission of UV rays (indicates the ability of the material to cut off UV rays, avoiding that they arrive the eye, the higher the wavelength of cutting and the better the matriale used), transmission curve (indicating the linearity of transmission of light through the material), specific gravity (The weight of matriale: relationship between mass and volume). Other interesting properties are resistance chemical attack and abrasion. There are many material Production From blank with which lenses are constructed and some treatments to be applied to their improve its quality. We summarize below:
Materials | Properties | n | Indications |
Organic resin | Low weight - unbreakable | 1,49 | Mild ametropia up to 4 Dtr. |
Organic resin | Low weight - unbreakable | 1,60 | Ametropia up to 6 Dtr. |
Organic resin | Low weight - unbreakable | 1,67 - 1.74 | Ametropia up to 8-14 Dtr. |
Crystal low index | Lesser thickness of the resin, hard to scratch | 1,50 | Mild ametropia up to 4 Dtr. |
Crystal mid index | Lesser thickness of the resin, hard to scratch | 1,60 | Ametropia up to 6 Dtr. |
Titanium crystal | Lesser thickness of the resin, hard to scratch | 1,70 | Ametropia up to 8-15 Dtr. |
Lantanium crystal | Lesser thickness of the resin, hard to scratch | 1,80 | High ametropia up to 12-18 Dtr. |
Very high crystal index | Extremely thin, hard to scratch | 1,90 | Ametropia over 15 Dtr. |
Tratements | Properties | Indications | |
antireflection | Increases the transmittance of the lens, reduces glare | - | VDT operators, drive, ecc. |
Anti-Scratch | Increases the scratch resistance of the resin | - | Lenses for little boys, frequent damage |
U.V. | Delete the passage of UV rays through the lens | - | Working outdoors |
Anti-fouling | Facilitates cleaning the lens surface | - | All lenses |
Verification process of an ophthalmic lens | Three-dimensional design of a progressive lens of the latest generation |
Tear film: enormous importance for the proper functioning of our insight into what remains efficient and nourishes the cornea. Deficiency of the film creates serious problems for the retinal tear. His absence would make it impossible the life of the cornea and consequently of the vision. Its thickness is from 8-9 miron to 4 microns respectively in front of the cornea and the conjunctiva. It ' consists of 3 distinct layers that corneal epithelium, to the outside are: the mucous layer, water layer and lipid layer. The innermost layer, the mucous is made up of mucin adsorbed corneal epithelium, together with an excess of mucin not yet dissolved covering the layer of mucin adsorbed. The thickness of this layer is from 200 to 400 angrom. the layer intermediate is the most often, 99.7% of all the tear film. The layer surface, the lipid has a thickness ranging from 50 to 5000 angstroms measured at the closed eyelids. The tear film is stable as long as the voltage surface of the tear film is lower than that of the epithelium corneal epithelium. This stability is achieved after about one second a blink. Over time the film thins and lipids can contaminate mucins by creating areas of dry (time Breack Up Time). Appraisal of that time you can make some considerations on the quality the tear film. these assessments are critical in the intention of apply corneal lenses, especially if hydrophilic (also called soft) as absorb liquid. The interaction of the lens must not compromise physiology of the cornea. The tear fluid contains proteins, immunoglobulins, inorganic ions, organic such as glucose, lysozyme, betalisina, mocopolisaccaridi and glycoproteins. Thus creates the conditions for proper nutrition of the cornea and its defense against attack pathogens.
Metamorphopsia: are manifestations of irregular shapes when watching regular shapes. When you look at a straight line and it feels wrong, rounded or oblique is a symptom of metamorphopsia. This can happen when a major alarm bell that could be in place a lifting of the retinal tissue. If the effect is accompanied by flashes of light could be in place a retinal detachment. In such a case is urgent contact an ophthalmologist or otherwise a Optometrist. the Lifting retinal edema caused by an under-payment or retinal another, means that the image is distorted and from here the vision that drift.
S.C.S. Method: For further information see SCS Method The S.C.S. Method represents one of the few alternatives to the use of glasses for forced myopia, myopia, especially if it is functional. The treatment takes place at asthenopia which appears as a red flag when a visual stress attempts to undermine the efficiency of near visual and / or far. The method S.C.S. is the only one that employs a simple means of diagnosis and selection, but at the time yet very effective. This is to select only those subjects who beneficerranno surely this method, eliminating all those who hardly get good results. The method provides for a sitting initial selection and explanation of work to do, the following one occurs After 7 days and about 4-5 sessions every 3 weeks after control about. The visual exercises (visual training) are carried entirely at home and this allows to integrate the results in the environment in which the subject experiences routinely and eliminate the many costs of moving. For training machines are not used, but only on paper and aids flipper lenses transparent and color. Another key aspect is that of education posture of the subject who learns not to put a strain on his eyes or during training, nor after. In fact, maintaining entrenched standards behavior and aids in the training data, the results remain to always.
Functional myopia: is defined as the myopia that occurs usually after 14 years of age and whose spring trigger is stress caused by a visual distance of work / study too short. Soventemente the load required to accommodative distances incredible (as 12-20 cm.) to consider, triggers the body's response to support the effort. The body adapts to stress and yield. Myopia in If so, solves the problem closely, while sacrificing the vision for far. In fact, a nearsighted eye uses less accommodating than an eye not myopic, while working to close. The correction of myopia with this glasses or contact lenses is the worst thing you can do, while vision of educational systems and behavior as the SCS Method (see in detail above), solve the problem and eliminate myopia prodottasi. In fact the correction with glasses or L.C. shows the body in conditions pre-myopia and it will develop further to reach a situation of myopia new more comfortable. And 'This is the condition of those guys that increase Their myopia each year. The functional myopia is not pathological.
Eyes and VDUs: The video terminals do not emit harmful radiation to the point of creating visual problems, but create an area of significant eye fatigue due to: reduced working distance, jumps continuous monitor-accommodative, tastieta, the plane of paper, printer, etc.., reflections of the monitor (the room lights, windows, etc..), etc.. all this work, tired eyes that often develop eye strain. such symptoms are treatable with the method S.C.S. SCS Method. Subjects VDT worker after many hours or all day work often show these problems. Things to do are: uniform working distances (monitor, keyboard, etc..), eliminating reflections on your monitor, increase the contrast and adjust the brightness of the display monitor to avoid a few bad pixels resolution, avoid the green phosphor monitor, pause for 5 min. every 30-45 min. work, make jumps of focus by moving the vision and check out the fast focusing, consult a Optometrist if problems persist.
Glasses: the glasses are all of a frame and two lenses. The frames are made of the most used in various metals such as nickel silver, steel, alloys with titanium, etc.., or in materials plastic as the sheet of acetate, injected material Production From blank, carbon fiber, etc.. The choice of the frame is essential for making a good job for unite perfect vision, light weight eyewear final feature of the product, and aesthetic. This consideration should be made by reading data the ophthalmic lens to be used. The optician's advice is important and no one can be replaced as it is the only one to know the materials and the procedures for assembly of the lenses choices. Fashion is important, but soventemente is preferable to follow the right advice rather than find themselves using a which was nice glasses without lenses only. Depending on the materials each frame has its strengths and weaknesses such as elasticity, lightness, anallergia, the robustness, etc.
Glasses Rest: are commonly defined as those glasses which give some "rest" eyepiece. Normally they are always spectacles. In fact there are no glasses resting on their own, the same for everyone. But a person can suffer from symptoms astenopeici (see asthenopia), rather than blurred vision and glasses prescribed, while not raising the level at times visual acuity, relieves symptoms and signs of asthenopia. usually the using lenses of glasses resting low power, usually with positive lenses and / or astigmatism. With regard to the mount can be found under the heading glasses.
Ophthalmologist: is the medical professional specializing in eye care. Its main Skills are the medication and eye surgery. less depth are his studies on the visual refraction (a measure of view). No other substitute for professional medical ophthalmologist pharmacological treatment of the eye and therefore is not to follow recommendations Friends or pharmacists for self-medication an eye condition. however about surgery, surely is a professional who is involved in all where necessary and may need time to evaluate the intervention. also intervenes in cases of corneal modified to reduce a visual problem which the nearsightedness, farsightedness, astigmatism some, etc.. The extraction of the cataract is now a practical technique that safely, even by ambulatory (day hospital).
Optometrist: is the professional specializing in the treatment of visual function. Not limited to verify a possible defect of vision, but making a complete visual analysis is able to prescribe the best corrective system for the end user. In fact, takes into account all the behavioral aspects of the subject (type of work / study, posture, visual effort hours, preceding, hobbies, etc..) and all visual-motor changes that will create new prescription (estimate distances, estimated depth, excess or lack of convergence, accommodative problems, etc.).. In Italy this profession is not yet regulated, but there are already many Optometrists graduates abroad, where Optometry is one of the most popular disciplines, much more than their Eye-Ophthalmologists. The Optometrist is the only professional able to identify effective visual education to combat various problems visual and functional behaviors such as myopia, asthenopia simple or complex, the difficulty of learning, etc.
Orthoptist: is the professional who Ophthalmologist aids the physician in particular in the treatment of strabismus, species before and after surgery strabologico. For this reason work Ophthalmologist with your doctor. Following the visual rehabilitation of persons and operated those in which a functional recovery is attempted to avoid surgery.
Optician: is a category that includes three figures in a single activity: the artisans to create the product starting from semi-finished lenses work, what sells in the commercial different products and finally the finished work as the Royal Decree of 1928 allows him to measure the short-sightedness and presbyopia. it is also able to apply all kinds of contact lenses for all kinds of visual problem. In two words, the Optical is the only expert in all types of vision correction and is able to advise the user in order to receive the best final product in compliance with the technical rules, the pleasantness product aesthetics, lightness, which will be dedicated to the use, etc.. No one can replace the optician to make these choices because no other has studied for this purpose.
Chart: To construct a optotype is starts from the value of the minimum angle of resolution (MAR) which has been calculated to 1 'of arc. Then between a sign and another great 1 'of arc each of a character considered there must be at least 1 'of arc separation (space) to recognize them as separate. The best optotype in this sense is represented by E oriented in which the value of 10/10 (1.0) is formed from 3 arms of the E and from 2 spaces all having a size of 1 'of arc, for total of 5 'arc of the entire letter. To obtain an increase geometric linear, instead of increasing by 1/10 at a time, increases of 0.1 logarithmic units and therefore the symbols are always 1.259 times larger than the earlier. Indeed, as occurred for old optotypes, an increase of 1/10 at a time is generated a large difference between 1/10 and 2/10, respectively of 10 characters 'and 5' of arc, while very small between 9/10 and 10/10, respectively 1 'and 1.1' of arc). This is critical for low acutezze visual in which an increase of 1/3 of the tenth is much more important than than it is in passing from 9/10 to 10/10. Another case of optotype angular that of Landolt rings in which the opening of the circle is equal to stroke width of the rim. To these optotypes more technical, for reasons of simplicity of communication, were added optotypes morfoscopici that use letters, numbers and symbols or drawings. Although easier to use, they create different problems depending on the characters used (see the book CSO delivered) that is much more difficult to recognize a B instead of an L for a given size. The designs are very easy to recognize under the value of 3/10, while they become very complex over the 4/10. This is due to asymmetry of signs and spaces in each drawing, often without spaces. Factors that influence the results are represented by: LUMINANCE OF FUND: that should be never less than 600 lux and 480 lux LUMINANCE ENVIRONMENT: What should be the same as the fund does not influence of background luminance. CONTRAST: should be around 60% -80%. The VA increases the contrast. TIME OF PRESENTATION: should be a few seconds, maximum 5 since the AV increases with increasing time of presentation. ADAPTATION TO THE ENVIRONMENT : The subject should remain under the same conditions until the beginning of the visit at the end as the adaptation to environmental conditions is related to the time and the greater the adaptation, the greater is the time devoted to adapt. Static visual acuity is measured in decimal notation and is derived by the inverse of MAR between two elements of the test measured in the first arc. The angle subtended by the character of our eye is given by the inverse of tangent that this character represents. Eg. character for a 7 mm high. place to 6 feet away, the angle subtended is: inverse of 7/6000 = 0.06 degrees = 4' and 0.6", about 05 or 12/10. Other systems of measurement are the scale of Snellen with denominator of the 10 values expressed in decimal form, from which 0.1 = 1/10 and 1.0 = 10/10. Still others are those of the Snellen fraction, common in countries Anglo-Saxon. They express the relationship between the distance of observation of the tests and the maximum distance at which the test is actually seen. Eg. if a character of 0.1 to 60 meters and is placed at such a distance is recognized there will be a VA of 60/60 or 6/6 or 20/20. If, however, to arrive at we must recognize up to 30 mt., you will a VA of 30/60 or 0.5 or 12/6 or 40/20.
Series of projection chart |
Eyelids: are useful to defend the eyes from the entrance of foreign bodies, to oxygenate the cornea during sleep (with its blood vessels), to secrete mucous substances necessary for the cornea maintain this perfect. There are, prurtroppo, several problems to which the eyelids may suffer. Li listed below: Ptosis (sag of the upper eyelid), eyelid retraction (muscle hyperfunction lift), entropion (inward folding of the lid margin and cilia), Ectropion (outward folding of the lid margin and cilia), xanthelasma (fat deposit on eyelid skin), Chalazion (occlusive cysts of meibomian glands), hordeolum (a small abscess ciliary follicle), or allergic contact dermatitis, herpes zoster ophthalmic, basal cell carcinoma (locally invasive lesion that does not produces metastases).
Eye disorders: are unfortunately numerous and the specialist in the diagnosis and treatment is your doctor Ophthalmologist. As we point out only some of the following: blepharitis (eyelid and dependents eyelids), conjunctivitis (dependent of the conjunctiva), keratitis (borne by the cornea), scleritis and episcleritis (against the sclera), corioretiniti (a loading of the choroid and retina), endophthalmitis (inflammation of the entire eye), hemorrhage, retrolental fibroplasia (to the retina), glaucoma ( to the retina due to high pressure), and iridocicliti iridodialisi iritis (iris dependents), histoplasmosis (to the retina), myasthenia impairment (charged to the extraocular muscles and eyelids), retrobulbar neuritis (a the optic nerve), papilliti (charged to the optic nerve), retinitis (an load of the retina), uveitis (with load of the iris and ciliary body), etc.
Posture: represents the position of body. Visual analysis is a very important aspect to keep in considered as a wrong posture is often the cause of many problems visual. Studying at very close distances (often many children studying in 15-20 Cm. away from the text) because first astenopeici problems, then, if the condition persists, the individual may develop a delayed learning with probable early school leavers, or a myopic functional development which is needed to tackle the big effort at that distance. This is just one example, but often there are more for a while as: keeping the sheet sideways, holding the scirvere pen in an unusual way, using the wrong light, improper use plans, misusing the time available, etc.
Presbyopia: is the condition in which finds the eye when it is no longer able to focus at a distance close. This normally occurs after 40 years of age and is due to lack of possibility accommodative available to the eye to cope at close quarters. The accommodative amplitude necessary to focus a near object is represented by the inverse of the distance in meters. Ad. eg. a object placed at 40 cm. from the eyes of the observer, forces the latter to make an effort of 2.50 Dt (100/40). To be able to comfortably support a similar effort, the eye must be at least double that capacity. So it may be supported an effort to 40 Inches. when you have at least amplitude Dt 5:00 accommodative. Advancing age produces a reduction in the accommodative power del'occhio and when it becomes lower at 4.00 Dt (focal convenient to 50 Inches.) while staving off the object, it becomes difficult to continue working close, especially if minute or precision. The compensation is always positive that an addition should be calculated taking into account the value dioptric need for far (away although the subject makes a less).
U.V. rays: as shown in Figure relative to the lens filter, UV rays are between 200 and 380 nm. in the spectrum of wavelengths. The UVC range from 200 to 280 nm., UVB from 280 to 315 nm. and UVA from 315 to 380 nm. These radiations are absorbed by ocular media and, if their energy is not massive, causing minor photo-chemical problems in the retina and ocular media. The medium that suffers most is that if the lens under continuous UV radiation, tends to become opaque causing cataract. This drawback is the salvation of retina that avoids all'opacizzarsi be damaged through the lens. In large doses cause severe retinal damage (typical of the welders). It 's important to protect themselves from this radiation, particularly in summer season, when the inclination of the terrestrial allows the arrival of radiation with greater intensity. The use of firltri alone is fundamental and Equally important is to verify the effectiveness of an optical filter qualified and / or of confidence.
Receptors: are the cells that receiving the radiation visual and transform them into impulses nervoli by means of chemical mediators. Continuing with simplicity, there are the rods and cones (2 ° retinal layer). The cones are very dense in the fovea and the macula where it is the point of maximum visual acuity, decrease towards the peripheral retina. The rods have the opposite behavior: there are in the macula and increase in density towards the retinal periphery. The cones are specialized color vision, while rods in night vision and estimation device. are connected to the ganglion cells, amacrine and horizontal of the retina, from which connections the impulse reaches the nerve optical and then the brain.
The 10 layers of the retina |
Retinitis Pigmentosa: is a condition retinal pigment epithelium, and that destroys the effectiveness of the cone it receptors, especially the rod. Has genetic causes, and not yet known an effective treatment for addressing it. Usually begins in a peripheral towards the center. The subject begins to have poor vision night and the vision to become more tubular iniza Make up blindness. You should visit the sites that speak specifically to that problem and can give information on the subject more than any other. Useful link to Retinitis Pigmentosa
Retinitis Pigmentosa |
Prescriptions (interpretation): It is important to understand the data contained in a prescription, below we provide some data to do this:
Part of a classical Optometric prescription | Technical data | Meaning |
Sph. | Spherical value: - = Miopia, + = Hyperopia | |
Cyl. | Astigmatic value: + = Positive, - = Negative | |
Ax | Axis of astigmatism, from 0 to 180 degrees | |
Far | Value to use for far distance, up to 5 metres | |
Near | Value to use for close distance, reading distance | |
FPD | Far Pupillary Distance | |
NPD | Near Pupillary Distance | |
VA | Visual Acuity | |
OCD | Dominant eye | |
STTR | Stereoscopic Threshold |
Contrast sensitivity: is a test useful in the evaluation of the visual contrast conditions variable and therefore closer to the normal life of every person. In fact, the tests are performed dell'ottotipo high contrast, usually black on white and never low contrast. Furthermore, there are diseases that affect much on the response to contrast sensitivity, and therefore this test is very important in early diagnosis. As shown in the figure below, there is a curve defined as normal starting from a low spatial frequency (column A) to the column E of the high spatial frequencies.
Diagram of Contrast Sensitivity |
Sport Vision: is a discipline Optometry which has the purpose of improving the performarces visual-behavioral athletes. The technique works with all stakeholders, but its primary application is on those who practice sports competitive level, where every small improvement may allow achievement of important results. The vision coordinate all our actions and the latter become more difficult during a dynamic activity such as sport. Taking an example of our most popular sport, football, when a player must hit the ball that comes from a mate, his vision should enable him to understand when and on what will be the exact direction step, when the point is to understand where he meets and his speed. If it comes to making a shot, or another transition to a further companion, behavior will adapt to the situation and so on. The technique of sport Vision allows you to identify the weaknesses of Visual-behavior of the athlete and then train these deficiencies with its appropriate exercises of: hand-eye coordination, eye-foot occhio-racchetta/mazza, peripheral perception, discrimination rate, etc.
Strabismus: is the condition of manifests deviation of one of the two eyes from the aims of fixation. watching Figure given below, we find that while the eye is placed to the left staring at the frog's eye to the right sets to the right. In this case the brain can only use the eye fixing. Strabismus can be charged of an eye that is constantly deflected or can be alternating, where the two eyes are used alternately to secure the stimuli, but never together. The angle alpha is the angle of deviation. A detour to the outside, as in proposed case, is called exotropia, if inward is called esotropia. If the vertical strabismus is will ipertropia or ipotropia of an eye compared another. There are other more complex types that fall within that short description.
Visual stress: is the condition of alarm in which they find their eyes when they maintain a job excessive for the structure in question. This happens especially during a job at close range, especially if too close, if prolonged, if aggravated by incorrect posture (sofa, bed, floor, etc..), if carried out with light or reduced poor, etc.. The visual apparatus enters into suffering and stress is the spring that allows the overcoming of the obstacle (positive stress). But if the stress lasts too (negative stress), then it can take over the adaptation and the visual system may stop working, with sonseguente inefficiency, or continue modifying his skills. in the latter case, takes over the functional myopia to allow a work effective at close range.
Toxoplasmosis: The Gondi Toxoplasma is a ubiquitous protozoan whose definitive host is the cat (gut), capable of attacking not only the man, but also almost all mammals. Toxoplasma infection is very common, so that in the population serological positivity is almost the norm. It is usually asymptomatic. When a pregnant woman becomes infected, the protozoa have a tendency very high to hide in nerve cells dl fetus, both in the retina in brain, in the form of sporozoites. At the time of their transformation trophozoites give significant inflammatory processes that occur in the eye borne by the choroid. We distinguish two different aspects of choroiditis Toxoplasma: 1) the scar of choroiditis Child i> which follows an intrauterine inflammation. Then Fundus examination show a broad plate of choroiditis often macular scar and x-rays of the skull are appreciated of calcifications. 2) the evolutionary to choroiditis i> usually found in young and manifests itself as a choroiditis recurrence of outbreaks that wound around a scar. The choroiditis by Toxoplasma responds well to specific therapy based on sulfonamides, pyrimethamine and corticosteroids, but relapses are frequent. the Early diagnosis is crucial for an effective solution and safeguard permanent injury.
Macular chorioretinal scars from presumed toxoplasmosis
NB: Not all subjects were treated with the same depth and news reports are sometimes generic type. For more information and further details, please send us a specific request E-Mail or contact your Optometrist, Ophthalmologist your or your Orthoptist trusted.
Sorry for the English translation sometimes poor because of the large amount of data, it was done mechanically.