Strabismus - Introduction, Symptomatology, and Evaluation MCQs

AMBLYOPIA Amblyopia is a unilateral or bilateral reduction of best corrected visual acuity in the absence of any organic cause. Clinical Features: Unilateral or bilateral reduced vision Crowding phenomenon may be seen: The patient is able to identify a Snellen's chart character with the amblyopic eye when the character is presented in isolation. If the character is shown along with other letters, the patient may not be able to recognize it. Neutral Density Filter Test(NDF): When the patient is asked to read through a NDF, the amblyopic eye shows no change, while in the normal eye, there is a drop in visual acuity Amblyopia treatment should be tried till the child is 12 years old. Best results are seen between 5-8 years of age. Reference: Kanski, 8th Edition, Page no. 746.

Angle evaluation is clinically done with Gonioscope but there are machines available for the same They are Anterior Segment OCT Ultrasound Biomicroscopy(UBM) Reference: Yanoff and Duker 4th Edition, Pg No. 1024

Visual field defects are best detected by Goldmann kinetic perimetry (full field) and Humphrey automated threshold perimetry (30-2 programme for central field or neurological programmes). 10-2, 24-2 are used in evaluation of fields in glaucoma. 120-2/ full fields can be used for neurological evaluation but very time consuming/ poor compliance by patients due to attention fatigue. Reference: Parson's diseases of the Eye 23rd edition-Chap 18 - Diseases of the Optic Nerve

Agonist-antagonist: Muscles of same eye which have opposite functions, e.g. MR and LR of the same eye. Synergist: Muscles of the same eye which move the eye in the same direction, e.g. SR and IO of the same eye are synergists in elevation. Yoke muscles: A pair of muscles of opposite eyes which produce a conjugate ocular movement, e.g. LR of right eye and MR of left eye are yoke muscles for dextroversion. Reference: Yanoff and Duker, 4th edition, Pg no. 1186.

Computerized tomography is superior for evaluation of bone disorders. Magnetic resonance imaging and orbital ultrasound would be of less utility and nerve conduction is not commonly done in the setting of acute orbital trauma. Reference: Kanski 8th edition/865

Cover test: The occluder is held in front of the eye for a few seconds and then removed. When the fixing eye is occluded, the examiner will observe the non-occluded eye move to pick up fixation if a tropia is present. If no tropia is present, the non-occluded eye will remain stationary. Uncover test: To assess for a phoria or latent deviation, the examiner observes the eye behind the occluder. If a phoria is present, the uncovered eye does not move, however the eye that is behind the occluder will deviate and return to a straight position when the occluder is removed. Alternate Cover Testing(ACT) determines the total amount of manfiest and latent deviation of the eye. A cover-uncover test is done before moving on to alternate cover testing. Reference: AAO basics by Kara M. Cavuoto, M.D. 2023.

Cycloplegic refraction is used to determine the objective determination of refractive error by relaxing accommodation. It is especially important in young children and patients with strabismus. Dry retinoscopy, manifest refraction and autorefraction are not satisfactory techniques to fully assess refractive errors in young children or patients with strabismus. Reference: Kanski, 6th edition, Pg no. 756.

V-pattern strabismus is a pattern in which the eyes are more abducted in downgaze than in upgaze. The etiology is unknown except in cases of extraocular muscle palsies. Multiple theories suggest primary or secondary muscle dysfunction, which can involve inferior oblique muscle overaction, superior oblique muscle underaction, horizontal rectus muscle dysfunction or extorsion of the globe and bony orbit which may lead to a V- or A- pattern. Infantile esotropia usually presents with a V-pattern. Refractive esotropia, intermittent exotropia and sensory exotropia are not commonly V-patterned. Reference: Yanoff and Duker, 4th edition, Pg no. 1221.