Patients Claiming No Light Perception

Determine whether each pupil reacts to light (U or B): The presence of a normal pupillary reaction suggests that anterior visual pathways are intact but do not prove nonorganic visual loss (pupillary response is maintained in cortical blindness). When only one eye has no light perception, its pupil will not react to light. The pupil should not appear dilated unless the patient has bilateral lack of light perception or third cranial nerve involvement. If a patient responds aversely to light stimulus, one can establish some level of afferent input.

Patients Claiming Counting Fingers to No Light Perception

1. Test for an afferent pupillary defect (U): A defect should be present in unilateral or asymmetric visual loss to this degree. If not, the likelihood of nonphysiologic visual loss substantially increases.
2. Mirror test (U or B): If the patient claims unilateral visual loss, cover the better-seeing eye; with bilateral complaints leave both eyes uncovered. Ask the patient to hold eyes still and slowly tilt a large mirror from side to side in front of the eyes, holding it beyond the patient’s range of hand motion vision. If the eyes move, the patient can see better than hand motion.
3. Optokinetic test (U or B): Patch the uninvolved eye when unilateral visual loss is claimed. Ask the patient to look straight ahead and slowly move an optokinetic tape in front of the eyes (or rotate an optokinetic drum). If nystagmus can be elicited, vision is better than counting fingers. Note: Some patients can purposely minimize or suppress an ocular response by diverting focus past the drum.
4. Base-out prism test (U): Place a 4 to 6 diopter prism base-out in front of the supposedly poorly seeing eye. If there is an inward shift of the eye (or a convergent movement of the opposite eye), this indicates vision better than what the patient claims.
5. Vertical prism dissociation test (U): Hold a 4 diopter prism base-down or base-up in front of the supposedly good-seeing eye. If the patient sees two separate images (one above another), this suggests nearly symmetric vision in both eyes.
6. Worth four-dot test (U): Place red-green glasses on patient and quickly turn on four-dot pattern and ask the patient how many dots are seen. If the patient closes one eye (cheating), try reversing the glasses and repeating test. If all four dots are seen, vision is better than hand motion.

Patients Claiming 20/40 to 20/400 Vision

1. Visual acuity testing (U or B): Start with the 20/10 line and ask the patient to read it. When the patient claims inability to read it, look amazed and then offer reassurance. Inform the patient you will go to a larger line and show the 20/15 line. Again, force the patient to work to see this line. Slowly proceed up the chart, asking the patient to read each line as you pass it (including the three or four 20/20 lines). It may help to express disbelief that the patient cannot read such large letters. By the time the 20/30 or 20/40 lines are reached, the patient may in fact read one or two letters correctly. The visual acuity can then be recorded.
2. Fog test (U): Dial the patient’s refractive correction into the phoropter. Add +4.00 to the normally seeing eye. Put the patient in the phoropter with both eyes open. Tell the patient to use both eyes to read each line, starting at the 20/15 line and working up the chart slowly, as described previously. Record visual acuity with both eyes open (this should be visual acuity of supposedly poorly seeing eye) and document the vision of the “good eye” through the +4.00 lens to prove the vision obtained was from the “bad eye.”
3. Retest visual acuity in the supposedly poorly seeing eye at 10 feet from the chart (U or B): Vision should be twice as good (e.g., a patient with 20/100 vision at 20 feet should read 20/50 at 10 feet). If it is better than expected, record the better vision. If the vision is worse, this suggests nonphysiologic visual loss.
4. Test near vision (U or B): If normal near vision can be documented, nonphysiologic visual loss or myopia has been documented.
5. Visual field testing (U or B): Goldmann visual field tests often reveal inconsistent responses and nonphysiologic field losses.

Children

1. Tell the child that there is an eye abnormality, but the strong drops about to be administered will cure it. Dilate the child’s eyes (e.g., tropicamide 1%) and retest the visual acuity after approximately 30 minutes. Children, as well as adults, sometimes need a “way out.” Provide a reward (bribe them).
2. Test as described previously.