Neuro-ophthalmology

·         The distinction between a preganglionic (i.e., first- and second-order Horner's syndrome) and a postganglionic (i.e., third-order Horner's syndrome) lesion can be made pharmacologically. Cocaine drops dilate normal pupils but not pupils with sympathetic paresis independent of the level of the lesion. Hydroxyamphetamine does not dilate the miotic pupil in Horner's disease if it results from a third-order neuron lesion but does dilate normal and first- and second-order Horner's pupils.

Area of Nerve Lesions	Involved Cranial Nerves
Orbital apex	II, III, IV, VI
Superior orbital fissure	III, IV, V1, VI
Cavernous sinus	III, IV, V1, V2, VI

·         Clinically the function of the extraocular eye muscles is tested using the “H” test with the medial rectus tested by horizontally crossing one’s eyes and the lateral rectus tested by moving the eye laterally (abducing). From either full adduction or abduction the the eye is then moved in a second direction. When fully adducted, gazing below the horizon tests the superior oblique muscle. Remember “SO” look like the edge of the nose “S” forming the ala and “O” the nostril). When fully adducted raising the eye above the horizon tests the inferior oblique muscle. When fully abduced, gazing below the horizon tests the inferior rectus muscles. When fully abduced, raising the eye above the horizon tests the superior rectus muscle.

·         Versions also known as conjugate movements, are synchronous (simultaneous) symmetric movements of both the eyes in the same direction. For example:

Dextroversion is the movement of both eyes to the right.

Levoversion is the movement of both eyes to the left.

·         Vergences, also called as disjugate movements, are synchronous and symmetric movements of both eyes in opposite directions, e.g.:

Convergence is simultaneous inward movement of both the eyes.

Divergence is simultaneous outward movement of both the eyes.

·         Synergists are the muscles which have a similar primary action in the same eye, e.g., superior rectus and inferior oblique of the same eye act as synergistic elevators.

·         Antagonists are the muscles which have opposite actions in the same eye, e.g., superior and inferior recti are the antagonists to each other in the same eye.

·         Yoke muscles (contralateral synergists) are a pair of muscles (one from each eye) which contract simultaneously during version movements.

·         Hering’s law of equal innervations: According to it, an equal and simultaneous innervation flows from the brain to a pair of muscles which contract simultaneously (yoke muscles) in different binocular movements, e.g., during dextroversion, right lateral rectus muscles and left medial rectus muscles receive an equal and simultaneous flow of innervation.

·         Sherrington’s law of reciprocal innervations: According to it, during ocular movements an increased flow of innervation to the contracting muscles is accompanied by a simultaneous decreased flow of innervation to the relaxing antagonists. For example, during dextroversion an increased innervational flow to the right lateral rectus and left medial rectus is accompanied by a decreased flow to the right medial rectus and left lateral rectus muscles.

·         Suppression is a temporary active cortical inhibition of the image of an object formed on the retina of the squinting eye. This phenomenon occurs only during binocular vision (with both eyes open). It can be tested by Worth’s four-dot test.

·         Methods by which angle of squint can be measured:

1.       Hirschberg’s corneal reflex test

2.       Prism bar cover test (PBCT)

3.       By synoptophore (major amblyoscope)

4.       Krimsky’s corneal reflex test

5.       Perimeter method

·         Nystagmus is an abnormal involuntary rhythmic eye movement that may be induced by having the patient follow a rapid finger movement or can occur at rest. It consists of a slow component (vestibular) as the eye deviates in one direction followed by a rapid corrective movement (cerebral) in the opposite direction. Nystagmus is usually named for the rapid component. End-point nystagmus occurs when a person is asked to gaze too far laterally. Asymmetric lateral nystagmus occurs in only one direction of lateral gaze and is seen in patients with vestibular disease. Up-beating, down-beating, and rotary nystagmus are seen in patients with brainstem disease, and congenital nystagmus that typically disappears with convergence is seen in newborns. In pendular nystagmus, movements are of equal velocity in each direction. In jerk nystagmus, the movements have a slow component in one direction and a fast component in the other direction. The direction of jerk nystagmus is defined by direction of the fast component.

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·         direct ophthalmoscopy:

1.       Papillitis

2.       Papilloedema

3.       Optic atrophy

4.       Glaucomatous cupping

·         direct/ indirect ophthalmoscopy:

1. Diabetic retinopathy
2. Hypertensive retinopathy
3. Retinal detachment
4. Retinitis pigmentosa