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Glaucoma

DESCRIPTION: A condition of the eye characterized by intraocular pressure (i.e., the production of aqueous fluid by the ciliary body exceeds the drainage rate through the trabecular system and Canals of Schlemm). Classification includes three basic types: primary glaucoma (both open-angle or simple glaucoma, the most common type, and closed-angle or acute/chronic type), congenital glaucoma (buphthalmos or hydrophthalmos and juvenile types associated with congenital anomalies), and secondary glaucoma (due to changes in the lens or uveal tract, trauma, rubeosis, surgical procedures, or topical corticosteroids). Heredity seems to predispose individuals to glaucoma, although it may also be related to medications and/or surgical procedures in other parts of the eye. If untreated, the effects can cause damage to the optic disk, restricted visual fields, and corneal edema; cataracts also often develop. Complete blindness can result. When treated early, the condition can be successfully managed medically. Because its onset is so gradual, all adults should be checked regularly for glaucoma.

TREATMENT: Glaucoma cannot be "cured" - only controlled. Miotics help to facilitate aqueous drainage, and other medications (also in eyedrop form) decrease aqueous production. When these measures do not halt the advancing damage to visual fields or optic nerve, surgery (to clear or enlarge the drainage system) is indicated; it is a procedure of last resort. Trabeculectomy and trabeculotomy are microsurgical techniques with high success rates.

Educational note: There may be periods of fluctuating vision if medication level also fluctuates. Fatigue may be a factor in regulating assignments.

IMPLICATIONS: There is some evidence to suggest that stress tends to exacerbate glaucoma; therefore, emotional upset should be avoided. Excessive fatigue should also be avoided. Optical aids and illumination control (e.g., sunglasses) are recommended as needed, since photophobia and decreased visual acuity are symptoms of glaucoma. A unique characteristic of this disorder is the observation by the patient of halos around lights. Early identification and ongoing control are essential if visual function is to be maintained.

Genetic counseling may be indicated.

Halos around lights may also be a sign of incipient cataracts.

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Muscle Imbalances

DESCRIPTION: Strabismus is a term used to describe defects of the eye muscle system. It includes "phorias" (tendencies, or latent muscle imbalances which are controlled by the brain's efforts toward binocular vision) and "tropias"Muscle Imbalances graphic (observable deviations which the brain cannot resolve). Esotropia is the deviation of one eye toward the nose. Exotropia is the deviation of one eye toward the temporal side of the face. Hypertropia is the deviation of one eye upward. Deviations downward are very rare. Deviations may occur with either eye, alternately (e.g., alternating esotropia or alternating exotropia) or may be monocular (always the same eye). Esotropia is the most common defect, is often present at birth, but may appear as late as 4 years of age if due to accommodation; exotropia is less common in infancy and childhood and is usually intermittent. Hypertropia is the least common; and is often compensated for by head tilting. Strabismus is commonly an inherited defect (autosomal dominant) but may also be caused by paresis or secondary to other body defects.

TREATMENT: The goals of correcting strabismus are: good acuity in both eyes, good cosmetic appearance, and binocular vision. Occlusion ("patching") of the good eye forces the deviating eye to develop acuity, and should be initiated as early as possible. It is most effective before age 1, and becomes more difficult by age 5; it is ineffective beyond age 7. Early diagnosis and occlusion are the best first steps in preventing amblyopia. When no further improvement of acuity can be accomplished by patching, surgical realignment of the eye muscles is indicated (occlusion does not straighten the eyes, only improves acuity). Surgery repositions eye muscles through recession (repositioning a muscle to make it "longer") or resection (essentially "shortening" a muscle). Strabismus surgery is rarely precise; more than one opinion may be needed to achieve optimal results. Orthoptics (eye exercises) are sometimes prescribed before or after strabismus surgery, to help improve fusion; an amblyoscope may be used to measure fusion as well as to induce it.

IMPLICATIONS: Since the muscles of the eyes are responsible for coordinated movements and binocular vision, strabismus should be identified and treated as early as possible. The younger a child is, the better the prognosis. Strabismus is never "outgrown" and vision may be permanently lost if strabismus is left untreated. (see Amblyopia)

School vision screening usually happens too late to help most children with strabismus. Preschool vision screening is highly desirable. Alert parents and/or pediatricians can also recognize strabismus and should follow-up with a professional eye examination.

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Enucleation

DESCRIPTION: The surgical removal of the eyeball from its orbit. Indications for removal include:

  • When trauma is so extensive that the form of the eyeball cannot be preserved;
  • Prevention or treatment of sympathetic ophthalmitis;
  • Severe pain in a blind eye;
  • Iridocyclitis, phthisis bulbi, and glaucoma when accompanied by severe pain or inflammatory symptoms;
  • Malignant tumors;
  • Anterior staphyloma, if the eye is blind, troublesome and disfiguring;
  • Early panophthalmitis;
  • Intraocular foreign bodies which cannot be removed and which cause irritation;
  • Cosmetic improvement in blind and disfigured eyes;
  • Unilateral retinoblastoma.

TREATMENT: Artificial eyes are worn after enucleation, for cosmetic purposes and to fill the cavity left between the eyelids. In addition, a prosthesis prevents the eye lashes from turning in and irritating the conjunctiva. A prosthesis can be worn as soon as the socket is free from inflammation (about 1 month). It is usually made of plastic material, which is more expensive than glass, but is unbreakable and needs replacement less often. A prosthesis should be cleaned often.

IMPLICATIONS: If only one eye has been removed (and the other eye has normal visual function), the only impairment in visual abilities will be lack of depth perception. A protective lens for the good eye may be indicated; Orientation & Mobility instruction may also be needed, to orient to the loss of the 90° periphery.

If both eyes have been removed (or if the remaining eye is impaired), adaptive measures will be needed. These could include training in communication skills and daily living skills, Orientation and Mobility instruction, and vocational guidance. Since extreme changes in visual functioning involve elements of emotional reactions, psychological counseling may also be indicated.

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Dislocated Lens

DESCRIPTION: Lens dislocation may be partial or complete, and may be hereditary or result from trauma. If hereditary, it is usually bilateral and associated with other disorders (e.g., aniridia, Marfan's syndrome). It may be complicated by cataract formation. Vision is blurred if the lens is dislocated out of the line of vision. If dislocation is partial and the lens is clear, visual prognosis is good. Traumatic lens dislocation can follow a blow to the eye. If the dislocation is partial, the eye may be asymptomatic, but if the lens has become totally detached and is floating in the vitreous, there is blurred vision. A quivering iris may be a symptom of lens dislocation, due to the lack of lens attachment and support. Iritis and glaucoma are common complications.

TREATMENT: Dislocated lenses are best left untreated when there are no complications.

If a dislocated lens becomes opaque, surgical removal should be delayed as long as possible because vitreous loss and subsequent retinal detachment are common complications of such surgery. If uncontrollable glaucoma occurs, lens extraction is necessary, in spite of the risks involved.

Reading lenses and/or aphakic lenses may be needed.

IMPLICATIONS: (see also description for Aniridia) The child with a dislocated lens may need extra time for tasks requiring clear vision, and may exhibit unusual head positions as he exerts extra energy to see.

 

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Diabetic Retinopathy

DESCRIPTION: The adult-onset form of diabetes is a metabolic disease which ultimately affects retinal blood vessels, causing intraretinal hemorrhaging and abnormal growth of new vessels into the vitreous; the vitreous then pulls away from the retina, and the vessels hemorrhage into the vitreous. This bleeding blocks the transmission of light through a normally transparent vitreous, and functional visual interference results (ranging from "floaters" to blindness). Symptoms of ocular involvement include: sensitivity to glare, diplopia, lack of accommodation, fluctuating acuity, diminishing of color vision, and lessening of visual fields; retinal detachment may follow; secondary complications include glaucoma and cataracts. Other associated systemic conditions include cardiovascular, skin, and kidney problems. If diabetes is well controlled in its early years, the onset of retinopathy is delayed, and its severity is reduced; ocular complications occur about 20 years after the onset, even when it is well controlled. Once retinopathy is established, it is little affected by the day-to-day control of diabetes. High blood pressure should be vigorously treated. In juvenile diabetes, severe retinopathy develops within 20 years in 60%-70% of the cases, even when the diabetes is well controlled. Cataracts are rare in juvenile diabetes, but form rapidly (within several weeks) if they occur. Senile cataracts are common in older diabetics.

TREATMENT: Control of the diabetes is essential (through diet, exercise, urine testing, and insulin therapy if needed), as is the control of high blood pressure. Photocoagulation may help when vision is affected by a focal area of retinal edema, and may delay the onset of proliferative retinopathy. It may also be used to alleviate drastic complications later, although not necessarily preserving macular function (central acuity). Trans-pars plane vitrectomy helps about 75% of patients who have sustained visual loss due to hemorrhaging. Retinal detachment may be treated with scleral buckling, Photocoagulation, and vitrectomy.

IMPLICATIONS: Low vision aids and increased illumination may be helpful when visual function is maintained.

Diabetic retinopathy is one of the leading causes of visual impairment. It is the most common cause of blindness in younger people throughout the world, although the visual outlook for the adult onset type is better than for the juvenile type. In a random population of diabetics, a little over one third will have some type of diabetic retinopathy, however less than 5% will develop the severest symptoms; 1% of these will become blind.

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Cortical Blindness

DESCRIPTION: A term used to describe an apparent lack of visual functioning, in spite of anatomically and structurally intact eyes. The cause is assumed to be a lack of cortical functioning (i.e., the visual cortex of the brain is non-functional. Children with "cortical blindness" do not exhibit nystagmus, however. Nystagmus may be the way the nervous system responds to bad vision, since it occurs simultaneously with many visual impairments. Neither a CAT scan nor a VEP can confirm cortical function. In the absence of other abnormalities (e.g., optic atrophy, microcephaly, frequent seizuring), the prognosis is good for regaining some degree of visual functioning in children with "cortical blindness."

TREATMENT: Vision stimulation activities of all kinds are appropriate, over a long period of time. However, the potential for improved visual functioning is probably better in the younger child than in the adult. Fibers of the optic tract and their connections (the extrageniculostriate system) may be important in visual recovery, since they are theorized to be 1) important in the maintenance of a stationary optical image on the retina via reflex eye movements; 2) essential for the provision of visual feedback for cerebellar coordination of learned skilled movements; and 3) mediators in visual functioning with the geniculostriate system.

IMPLICATIONS: It is currently believed* that the pliability of the young brain may be a factor in this positive prognosis. The recovery pattern is not easily detected by standard ophthalmic tests, since visual behaviors are unique and somewhat unusual (e.g., many children recover the ability to identify single letters of large print when well isolated; most recover the ability to name colors; most can detect moving targets in the peripheral field better than in the central field). Short term evaluations should not determine visual potential, since progress may take time. Dramatic and significant visual recovery can happen over a long term (a decade or more).

*This information taken from a presentation by Creig Moyt, M.D. (a pediatric ophthalmologist) at the 10th International Seminar on Preschool Blind Children, October 7-10, 1984, Asilomar, California.

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Corneal Scarring

DESCRIPTION: May be caused by injury to the cornea (abrasion, laceration, burns, or disease); depending on the degree of scarring, vision can range from a blur to total blindness Surface abrasions, although extremely painful, heal transparently (do not leave scars). Deeper abrasions and ulcerations/lacerations result in a loss of corneal tissue, which is replaced by scar tissue. Scars left from burns depend on the type and depth of burn: boiling water or a curling iron leave superficial scarring; acids or alkalies cause deeper damage unless neutralized immediately. Scarring from disease (usually an inflammation) is usually the result of a proliferation of new blood vessels into the clear cornea, to assist in the healing process. Diseases which cause vascularization include herpes simplex, syphilis, and keratitis.

TREATMENT: When corneal scarring is dense enough to affect vision, a corneal transplant is indicated. This procedure is 90% successful because of the minimal rejection rate (due to a lack of blood supply in the cornea).

IMPLICATIONS: The best treatment is prevention (of disease and injury). Educational needs will vary, according to individual conditions (extent and Iocation of corneal scar tissue in relation to the pupil). The level of illumination and print size may be factors to consider also.

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Color Deficiencies

DESCRIPTION: A defect of the cones which affects color detection; called "achromatopsia" in its most extreme form; X-linked genetic defect occurring in 8% of men and 0.4% of women; may also be acquired as a result of retinal disease (specifically when it affects the macula) or poisoning. Type depends on which cones are affected:

Cone Monochromats have only one type of cone and may be red-green, red-blue, or green-blue blind; occurs one in a million.

Dichromats have two types of cones; this group is further divided into: Protanopes (red-blind; see blue and green), Deuteranopes (green- blind; confuse shades of red, green and yellow), and Tritanopes (blue-blind; see red and green).

Anomalous Trichromats make up the largest group and are similar to the Dichromatic group except in intensity (Protans and Protanopes, Deutrans and Deuteranopes, Tritans and Tritanopes...similar but milder defects.

Rod Monochromatism is very rare; there is complete lack of cone function and accompanying photophobia, nystagmus, and poor visual acuity; visual fields are normal. The photophobia and nystagmus reduce with age.

TREATMENT: There is no treatment for color deficiencies; in the case of achromatopsia, optical aids, sunglasses, and lowered illumination may be helpful.

IMPLICATIONS: Although color blindness is more of a social inconvenience than a handicap, educators should be aware of students with this condition since many educational materials utilize color as an instructional vehicle. Students with color blindness may need to learn compensatory techniques for sorting or selecting clothing or interpreting traffic signals.

Genetic counseling may be indicated.

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Coloboma

DESCRIPTION: Congenital cleft in some part of the eye (commonly the iris, but may also occur in the lid(s) or pigment epithelium and choroid); caused by faulty closure during prenatal development; usually hereditary; secondary complication: cataracts. Associated conditions are: microphthalmia, polydactyly and mental retardation. Depending on the extent and location of the coloboma, there may be decreased visual acuity, nystagmus, strabismus, photophobia, and a loss of visual fields.

TREATMENT: Cosmetic contact lenses and/or sunglasses for colobomas of the iris. Optical aids may be helpful.

IMPLICATIONS: Visual fields measurement is suggested when a coloboma of some-part of the inner eye is suspected (i.e., choroid or pigment epithelium).

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Chorioretinitis

DESCRIPTION: A type of posterior uveitis, almost always affecting the retina; usually follows an active microbial invasion of the tissues by a causative organism which is rarely recovered (definite etiological diagnosis is seldom possible); generally classified as granulomatous. The onset may be in utero when caused by the Toxoplasma gondii, probably the most common cause (see Toxoplasmosis). If granulomatous uveitis is acquired, the onset is insidious: vision gradually becomes blurred, pain is minimal, mild photophobia is present, and the pupil is often constricted and/or irregular in shape. Fresh lesions seen through the ophthalmoscope appear as yellowish-white patches through a hazy vitreous. As healing occurs, the vitreous clears and pigmentation appears at the edges of the lesions. In the healed stage, there is considerable pigmentation (i.e., "scars") and scotomas occur where the lesions are located; these healed areas usually do not result in significant visual loss. If the macula has not been involved, recovery of central vision is complete. The disease can last months to years, sometimes with remissions and exacerbations, and is capable of causing permanent damage with marked visual loss.

TREATMENT: Must be treated medically, usually with anti-infective agents and systemic corticosteroids. Although organisms responsible for toxoplasmosis and tuberculosis (both possible causes of chorioretinitis) may be activated by corticosteroids, they are given as a calculated risk to control the inflammatory response when vision is threatened.

IMPLICATIONS: Functional vision depends on the extent and site(s) of the healed lesions. If the macular area was not involved, central acuity remains normal and the scotomas are usually not significant in terms of visual functioning. However, if the macula was involved, the lowered acuity can result in markedly reduced visual functioning. magnification may be helpful.

 

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