Neuro-ophthalmology examination

Written and Edited by Khalil AL-Salem M.D

History :

Ask about past medical history, drug history, family history, and occupation. Smoking, alcohol use and diet may be particularly important. The history is guided by the presenting complaint.

Examination:

The basic neuro-ophthalmic examination includes: near and distance VA, color vision, confrontation field tests, pupil tests, cover tests, eye movements, cranial nerves, fundoscopy including optic nerve examination, and other tests as indicated.

A full neurological examination may be required.

■ Cover test and eye movements:

■ Pupils:

1. Observe: look for anisocoria, ptosis, and iris abnormality (heterochromia, Rubeosis, posterior synechiae, coloboma).

2. Check the near response using an accommodative target (some patients find it easier to converge on their own finger).

3. Test pupillary constriction to light: dim the lights and ask the patient to look at a distance target. Check the direct response (pupil constriction in the same eye) and consensual response (fellow eye constriction). Use a very bright light such as an indirect ophthalmoscope.

4. Look for a relative afferent pupillary defect (RAPD) using the swinging light test. Ask the patient to fix on a distant object. Shine light in one eye for 3 seconds, then moves to the other for the same interval. Repeat as required but do not spend longer on one eye than the other as this may bleach the retina and create an artificial RAPD. If the left optic nerve is damaged, shining the light in the right eye will produce a normal efferent response in the right and left pupil. Moving the light to the left eye then causes a paradoxical dilatation of both pupils as the stimulus intensity is effectively diminished (left RAPD).

Retinal disease, if extensive enough, will also impair the pupil light reflex. Only one functioning pupil is required to test for an RAPD; for example, in a patient with a 3rd nerve palsy with a fixed dilated pupil the test can be carried out as above but only the active pupil is observed. Remember that in bilateral symmetrical optic nerve disease the pupil deficit will be balanced and no RAPD will be elicited.

■ Confrontation visual field testing:

1. Establish the VA and explain that you are testing peripheral vision.
2. Ask the patient to cover one eye with the palm of their hand: ‘Look at my nose: are any parts of my face missing or blurred? Can you see both my eyes?’
3. Hold up both your palms, one in each hemifield and ask, ‘Is each hand equally clear, are there any differences or does each hand look the same?’
4. Now ask the patient to fix on your eye. Always begin by testing for a defect to hand movements. Advance your hand, with fingers moving, from the periphery towards fixation, asking the patient to report when they see movement. A patient will not be able to count fingers in visual field region in which he or she cannot detect hand movements.
5. Ask the patient to fixate on your eye and hold up a finger in one quadrant; ask how many fingers can be seen.
Repeat in each quadrant, presenting 1, 2, or 5 fingers (3 or 4 is too difficult). This will identify areas where vision is better than hand movements.
6. In visual field areas where finger-counting vision has been established look for red desaturation using a red target such as a 4 mm hat pin (a red bottle top may also be used but it is too large for the blind spot or small scotomas). Compare subjective color intensity in four quadrants whilst fixating your eye. Simultaneously holding two red pins either side of the vertical mid-line (in each eye separately) may help detect bi-temporal red desaturation from pituitary tumors or a relative homonymous hemianopia.
7. Test the mid-peripheral and central field with the red target. ‘Tell me when you first see the red color, rather than the pin, and tell me if it then disappears or the color changes at any point.’ Move obliquely in each quadrant from periphery to fixation, equidistant between you and patient. Compare to your own monocular visual field. Look for scotomas.
8. Consider comparing the blind spot size with your own using the red target.
9. It is possible to ascertain the isopter to a small white target such as a 4 mm white hat pin. Failure to detect the white target indicates greater severity of loss than is revealed by the ‘red desaturation’ technique. Similarly, the white target can also be used to plot scotomas and the blind spot.
10. Test the fellow eye.
11. If any defect is detected, draw fields and arrange formal testing. Document the left eye visual field on the left side of the page; the right visual field on the right side of the page (opposite convention to VA).

■ Colour vision.

Optic nerve damage can result in loss of color saturation and poor color discrimination before significant acuity loss is present. This is very helpful in determining the likely cause of visual loss (i.e. refractive, lenticular, retinal, optic nerve, postchiasmal) and is usually tested with Ishihara plates. The procedure is as follows:
1. Patients should wear reading correction if required.
2. Cover one eye and ask patient to read through the book. Allow 2 or 3 seconds per plate only.
3. Patients with VA better than 6/60 can usually complete the test, but do not proceed if they cannot see the first test plate. Test patients before examining them with bright lights
(e.g. fundal examination or RAPD check) or allow them several minutes to recover after such examination. Patients who have had dilating drops can still perform the test but  may need to use a +1.00 or +2.00 lens. Consider testing red desaturation instead if VA is very poor.
4. Score the number of plates read out of 13, 17, or 21 depending on which book is used (1/17 or ‘control only’ if only the test plate was read). Record the reading distance and any refractive correction.
5. There are some plates which only some patients with congenital anomalous color vision (Daltonism) will be able to read. Do not include these when testing for acquired visual loss unless the patient has Daltonism.
6. Patients who cannot identify numerals (e.g. small children) can be asked to trace the outline of the numbers with their finger or trace the wiggly line across the page in the color plates at the end of the book.
7. The Ishihara book comes with instructions on how to interpret performance on the missed plates in cases of Daltonism. The missed and misread numbers should be the same using each eye.

■ Red desaturation.

Ask the patient to report any difference in the appearance of a red target viewed with each eye in turn.

■ Cranial nerves.

II. Test VA, pupil reactions, visual field and color vision. III, IV, VI. V. Warn the patient then test corneal sensation by lightly touching a wisp of cotton-wool on the peripheral cornea. Sensation may be decreased in contact lens wearers, recurrent herpetic keratitis, or if anaesthetic drops have been instilled to check IOP. Check skin sensation to light touch and pin prick on the face. Ask the patent to clench the teeth together and feel for contraction of the masseter muscles. Ask the patient to open the mouth against the resistance of your hand and look for jaw deviation towards the weaker side. VII. Ask the patient to show their teeth (smile), purse lips, blow out cheeks against the resistance of your fingers, raise eyebrows (forehead wrinkling is spared in central/upper motor neurone lesions) and screw up eyes (assess Bell’s phenomenon). Look for loss or asymmetry of nasolabial folds. Assess for lagophthalmos and corneal exposure by asking the patient to close the eyes lightly. VIII. Ask about hearing loss and vertigo. Cover one ear and whisper a number in the other for the patient to repeat. To test more formally, check that a 256 Hz or 512 Hz tuning fork held on the midline forehead (Weber’s test) is heard equally in both ears, and that air conduction persists after audible bone conduction (with the tuning fork held on mastoid) ceases (Rinné’s test). IX, X. Ask the patient to open their mouth and say ‘Ahhh!’. Look for symmetrical elevation of the uvula, or deviation away from the affected side. Ask about any choking or problems swallowing. Test the gag reflex with an orange dressed stick if concerned. XI. Ask the patient to lift both shoulders and press down to check power. Ask the patient to turn the chin towards one shoulder and press against this action with your palm. With the other hand, feel the muscle bulk of sternocleidomastoid. XII. Observe the patient’s tongue when it is in their mouth for fasciculations or wasting. Ask the patient to stick out their tongue (deviates to the weaker side).

Investigations

CT Scan

Computed tomography (CT) Q & A

Magnetic Resonance Imaging (MRI)

Useful for imaging the anterior and posterior visual pathways (including optic nerve, chiasm, optic tracts, optic radiation and visual cortex), brain, soft tissue or vascular masses, and nonorganic, nonmetallic foreign bodies (FB). Does not show bone or calcium well. More expensive and less readily available than CT, and less useful for some orbital disease. Contraindications include a pacemaker and possible metal FB. Patients with clipped intracranial aneurysms need documentation to show that their clip is not ferromagnetic.

■ Commonly used sequences:
a. T1 image: best for structural defi nition of anatomy. Water (vitreous and CSF) appears black (hypointense), fat is hyperintense, which degrades orbital images.

b. T2 image: best for identifying diseased tissue. Water appears white, so pathological oedema shows as a high signal; fat is also hyperintense.

c. Fat suppression: Suppression of high signal from orbital fat allows clear defi nition of the optic nerve and extraocular muscles

d. Fluid-attenuated inversion recovery sequence (FLAIR): CSF appears dark, making it easier to detect small T2- hyperintense lesions (e.g. MS plaques) adjacent to the lateral ventricles.

e. Short tau inversion recovery sequence (STIR): ideal for imaging the intraorbital optic nerve as orbital fat is supressed but water (infl ammatory oedema) can still be seen as high signal.

f. Gadolinium contrast: useful when looking for lesions with disrupted vessel permeability. Consider if suspected meningioma, acoustic neuroma, lymphoma, metastatic disease, optic neuropathy (e.g. sarcoid), or active MS plaques. Contrast enhancement can be seen on T1 weighted images but not on T2 weighted images.

How structure appear of different MRI

Q & A on MRI