Eye Conditions - PDF

Introduction * Orthophoria  perfect ocular alignment in the absence of any stimulus for fusion (uncommon). * Heterophoria  tendency of the eyes to deviate when fusion is blocked (latent)..slight phoria is present in most normal individuals and is overcome by the fusion re...

Introduction * Orthophoria  perfect ocular alignment in the absence of any stimulus for fusion (uncommon). * Heterophoria  tendency of the eyes to deviate when fusion is blocked (latent)..slight phoria is present in most normal individuals and is overcome by the fusion reflex. * Heterotropia  manifest deviation.  Extra-ocular muscles * There are 6 EOM  4 recti muscles (medial, lateral, superior and inferior) and 2 obliques muscles (superior and inferior). * Innervations  3rd CN, 4th CN and 6th CN (L6 SO4). * 5 of the 6 EOM (inferior oblique excepted) originate at the orbital apex. EOM  Position of gaze * There are 9 diagnostic position of gaze those in which deviations are measured ( primary position , elevation , depression , dextro-version , levo-version , dextro- elevation , levo-elevation , dextro- depression and levo- depression ). * The primary position is defined as the position when the eye and head are both directed straight ahead.  Strabismus adaptation 1. Sensory  the ocular sensory system in children has the ability to adapt to anomalous status (confusion and diplopia) by 2 mechanisms (suppression and abnormal retinal correspondence). 2. Motor  adoption of an abnormal head posture ( face turn / head tilt / chin elevation or depression ).  Amblyopia * It is the developmental defect in the central visual pathways result in unilateral or rarely bilateral decrease in best corrected visual acuity for which there is no identifiable pathology of the eye or visual pathway (absence of organic lesion). * Causes : 1. Strabismus. 2. Anisometropia (difference in refractive error between the eyes). 3. Stimulus deprivation (opacities in the media like congenital cataract). 4. Bilateral ametropia (high symmetrical refractive errors and usually hypermetropia  bilateral amblyopia ). * Diagnosis : 1. Difference in the VA between the 2 eyes by 2 Snellen lines. 2. Crowding phenomenon  reading single letter clearly. * Treatment : ( the sensitive period during which acuity of an amblyopic eye can be improved is usually up to 7-8 years ). (correction of significant refractive errors is an essential preparation for active amblyopia treatment). 1. Occlusion or patching of the better-sighted eye  is the most effective treatment…if there has been no improvment after 6 months of effective occlusion , further treatment is unlikely to be fruitful. 2. Penalization by atropine or fogging  for mild amblyopia 6/24 or better. 3. Low dose of oral Levodopa have been shown to augment the effect of occlusion therapy.  Clinical evaluation of strabismus 1. History (age of onset, …..). 2. Visual acuity (according to age …..). 3. Tests for stereopsis (like titmus fly test). 4. Tests for sensory anomalies (like Worth 4-dot test). 5. Measurement of deviation (like Hirschberg test and cover test). 6. Motility tests (ocular movements). 7. Investigation of diplopia (like Hess chart). 8. Refraction and fundoscopy. * The earlier the onset strabismus, the more likely the need for surgical correction.  Esotropia * It is a manifest convergent squint (inward deviation) which is the most common form of strabismus, either concomitant ( same angle of deviation in horizontal gaze position) or incomitant ( the angle differs in various positions of gaze). A. Accommodative  Refractive (hypermetropia between +2 to +7 DS that presented between age of 18 months till 3 years which is treated by plus glasses) or non-refractive (high AC/A ratio which may require bifocal glasses). B. Non-accommodative : 1. Infantile  within 6 months, no refractive errors, large angle, alternating and no limitation of ocular movement…treatment ideally surgical by age of 1 year(even though bifoveal fusion is not achieved)…(sometime may require further second session of surgical corrections). 2. Microtropia. 3. Convergence spasm. 4. Sensory. 5. Consecutive. 6. 6 cranial nerve palsy. 7. Duane syndrome type 1. 8. Mobius syndrome.  Pseudo-squint * It is a clinical impression of ocular deviation when no squint is present. Causes : 1. Epicanthal folds  may simulate an Esotropia as in Orientals persons. 2. Abnormal interpupillary distance.  Exotropia * It is a divergent squint (outward deviation). * Types : 1. Early onset (constant)  normal refraction, large and constant angle of deviation and usually associated with neurological abnormalities … treatment mainly surgical. 2. Intermittent  around age of 2 years, exophoria breaks down to exotropia under conditions of visual inattention…treated either by over-minus lenses to stimulate accommodation and convergence with near exercise and training or surgical (the exodeviation is rarely completely eliminated by surgery and results found to be unsatisfactory to the patient or physician). 3. Sensory. 4. Consecutive. 5. Duane type 2. 6. 3 cranial nerve palsy.  Special types of strabismus * Duane syndrome  (congenital anomalous innervation of LR by fiber from 3 cranial nerve). d r * Brown syndrome  ( congenital mechanical restriction result in impaired movement of the SO tendon through the trochlea). * Mobius syndrome  multiple bilateral cranial nerves palsy like 7 and 6 ). th th * Paralytic Strabismus : 1. 6 cranial nerve palsy  esotropia. th 2. 3 cranial nerve palsy  exotropia. d r 3. 4 cranial nerve palsy  hypertropia. th  Surgery * To improve appearance and if possible to restore binocular single vision and also be used to reduce an abnormal head posture. 1. Weakening procedures  like recession. 2. Strengthening procedures  like resection. 3. Vector adjustment  like transposition. * Surgical results vary depending on criteria for success and length of follow-up. Cosmetic success is often defined as an esotropia or exotropia of less than 15 prism diopter and functional success is often defined as a small asymptomatic phoria less than 10 prism diopter. * Surgical success rates are dependent upon many variables, some of which are unique to a given clinical situation. * Patients who undergo surgery attain their final alignment within 1 – 6 weeks after surgery.