AMBLYOPIA/STRABISMUS KEHINDE, A. V., MB;BS, FWACS, FICS Senior Ophthalmic Surgeon

Amblyopia refers to a decrease of vision, either unilaterally or bilaterally, for which no anatomical cause can be found.

TERMINOLOGIES Functional amblyopia often is used to describe amblyopia, which is potentially reversible by occlusion therapy. Organic amblyopia refers to irreversible amblyopia. Amblyopia-ex-anopsia Amblyopia

Pathophysiology Amblyopia is believed to result from ‘disuse atrophy’ from inadequate foveal or peripheral retinal stimulation, (typically due to refractive errors) and/or abnormal binocular interaction that causes different visual input from the foveae.

SENSITIVE PERIODS The development of visual acuity from the 20/200 range to 20/20, which occurs from birth to age 3-5 years. The period of the highest risk of deprivation amblyopia, from a few months to 7 or 8 years. The period during which recovery from amblyopia can be obtained, is from the time of deprivation up to the teenage years or even sometimes the adult years.

EPIDEMIOLOGY Range from 1-3.5% in normal children to 4-5.3% with ophthalmic problems. Most data show that about 2% of the general population has amblyopia. It is the leading cause of monocular vision loss in adults aged 20-70 years or older.

EPIDEMIOLOGY (Contd.) Mortality/Morbidity Amblyopia is an important socioeconomic problem. Studies have shown that it is the number one cause of monocular vision loss in adults. Persons with amblyopia have a higher risk of becoming blind because of potential loss to the sound eye from other causes. Race/Sex No racial /gender preference is known. Age Amblyopia occurs during the critical periods of visual development. An increased risk exists in those children who are developmentally delayed, were premature, and/or have a positive family history.

CAUSES OF AMBLYOPIA Anisometropia Strabismus Visual deprivation Small amounts of hyperopic anisometropia, such as 1-2 diopters, can induce amblyopia. In myopia, mild myopic anisometropia up to -3.00 diopters usually does not cause amblyopia. Strabismus Incidence of amblyopia is greater in esotropic patients than in exotropic patients. Visual deprivation Amblyopia results from disuse or understimulation of the retina. This condition may be unilateral or bilateral. Examples include cataract, corneal opacities, ptosis, etc. Organic Structural abnormalities of the retina or the optic nerve may be present.

MANAGEMENT OF AMBLYOPIA

HISTORY Elicit any previous history of patching or eye drops as well as past compliance with these therapies. Document previous ocular surgery or disease. In addition to the routine information, obtaining a family history of strabismus or other ocular problems is important because the presence of these ocular problems may predispose a child to amblyopia.

DIAGNOSIS Visual acuity Crowding phenomenon Usually requires a 2-line difference of visual acuity between the eyes. Crowding phenomenon There is difficulty in distinguishing optotypes that are close together. VA is better when the patient is presented with single letters rather than a line of letters.

DIAGNOSIS (Contd.) Contrast sensitivity Neutral density filters Strabismic and anisometropic amblyopic eyes have marked losses of threshold contrast sensitivity; this loss increases with the severity of amblyopia. Neutral density filters Patients with strabismic amblyopia may have better visual acuity or less of a decline of visual acuity when tested with neutral density filters compared to the normal eye. Binocular function Amblyopia usually is associated with changes in binocular function or stereopsis. Eccentric fixation Some patients with amblyopia may consistently fixate with a nonfoveal area of the retina under monocular use of the amblyopic eye, the mechanism of which is unknown. This can be diagnosed by holding a fixation light in the midline in front of the patient and asking them to fixate on it while the normal eye is covered. The reflection of the light will not be centred.

Testing in preverbal children Cover/Uncover test. Fixation preference may be assessed, especially when strabismus is present. Induced tropia test may be performed by holding a 10-prism diopter before one eye in cases of an orthophoria or a microtropia. Cross-fixation

Occlusion therapy/Patching TREATMENT Refraction Cycloplegic refraction must be performed on all patients, using retinoscopy to obtain an objective refraction. Occlusion therapy/Patching Rule-One week/Year of age Full time Part time Referral Perform a full eye examination to rule out ocular pathology.

STRABISMUS (DEFN.) A visual defect in which one eye cannot focus with the other on an object because of imbalance of the eye muscles. A mis-alignment of the visual axes of the two eyes

CLASSIFICATION Apparent Squint (Pseudostrabismus) Latent squint (Heterophoria) Manifest squint (Heterotropia) a. Concomitant b. Inconcomitant (paralytic, A &V patterns, Restrictive squint)

Pseudostrabismus Pseudoexotropia Hypertelorism Pseudoesotropia Prominent epicanthal folds

CAUSES INVESTIGATION VA/REFRACTION COVER/UNCOVER TEST PRISM COVER TEST HETEROPHORIAS CAUSES ORBITAL ASYMMETRY ABNORMAL IPD FAULTY INSERTION OF EOM EOM WEAKNESS MALPOSITION OF MACULA IN RELATION TO THE OPTICAL AXIS INCREASED ACCOMMODATION INVESTIGATION VA/REFRACTION COVER/UNCOVER TEST PRISM COVER TEST MADDOX ROD TEST

CONCOMITANT STRABISMUS A manifest squint in which the amount of deviation is constant in all directions of gaze

CAUSES OF CONCOMITANT STRABISMUS Sensory causes: Refractory errors, prolonged use of incorrect spectacles, media opacities, neuroretinal dxs. Motor causes: Malformed orbits, EOM disorders Central causes: Fusional deficiencies, Cortical deficiencies Clear img –tion wrong positional relationship pry position

TYPES EXOTROPIA ESOTROPIA HYPERTROPIA HYPOTROPIA

1. Infantile esotropias 2. Accommodative Esotropia Refractve Non-refractive 3. Non-accommodative esotropia Stress-induced Sensory deprivation CN VI palsy etc.

Infantile esotropia Presents usually within first 6mos of life Usually alternating Error is usually normal for the age of patient, +1 -+1.50.00DS Correct significant refractive errors and amblyopia Surgery

Accommodative Esotropia Refractive : 6mos-7yrs. Hypermetrope, +3 - +7. correct deviation with specs Non-refractive: Esotrop ia for near. Correct with +3.00 Mixed AE Esotropia for far, worse for near. Correct Hypermetropia with a plus add, (Bifocals) Fundoscopy REF- SAME FAR &NEAR

Exotropias Intermittent Constant Convergence insufficiency Divergence Excess Basic

TREATMENT Spectacle correction Orthoptic treatment Occlusion therapy Surgery/Referral Fusional convergence

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