Unexplained visual loss requires thorough exam

Chicago-Patients with unexplained visual loss are often referred to neuro-ophthalmologists to determine if the problem is associated with the optic nerve or visual pathways. Surprisingly, this is not always the problem, reported Karl C. Golnik, MD, MEd, who spoke during the subspecialty neuro-ophthalmology day at the American Academy of Ophthalmology annual meeting.

"I am surprised at how many patients are referred to me with refractive problems, such as irregular astigmatism or oil-droplet cataracts, and occult corneal disease," explained Dr. Golnik, professor of ophthalmology, neurology, neurosurgery, University of Cincinnati and the Cincinnati Eye Institute, Cincinnati, OH.

Referral for blurriness

A 60-year-old man with hypertension was referred after complaints of gradual bilateral blurriness. He had tobacco-alcohol amblyopia diagnosed and had been told to stop drinking, although his symptoms did not improve. His distance visual acuity was 20/60 in both eyes and his near vision was J2. His examination revealed normal pupils with no relative afferent pupillary defect (RAPD), normal visual fields, and normal fundus examination. The color vision test revealed no problems.

"As soon as I saw this, I knew that this was not tobacco-alcohol amblyopia," Dr. Golnik said. So he did further testing using the direct ophthalmoscope and repeated the slit-lamp exam and discovered the culprit-oil-droplet cataracts. With the potential acuity meter (PAM) test, the patient could see 20/20 OU.

"PAM is another test that you can use to try to determine unexplained refractive media problems," Dr. Golnik continued. Clinicians should remember to utilize these simple tests before making the referral to the neuro-ophthalmologist, he said.

Unexplained vision loss could be the result of retinal/choroid problems. Patients with a history of metamorphopsia usually have macular disease. A small paracentral scotoma also indicates a retinal problem, he said.

A number of tests can be employed to determine if the retina/choroid are involved in vision loss. Usually there is no or a small RAPD. The Amsler grid is useful for detecting central visual field distortions or defects. The photostress test may show signs of early macular degeneration. During the exam, the patient looks at a bright light for 10 seconds and then the clinician measures how quickly visual acuity recovers within 1 line of baseline. If visual acuity takes more than 50 seconds to recover, retinal or macular disease could be present, he said.

Other ancillary tests may also be helpful in the retinal evaluation, such as fluorescein angiography, indocyanine green angiography, ocular coherence tomography, and electroretinography, Dr. Golnik said.

Optic nerve or visual pathways may be affected in patients who present with vision loss. "Be sure to check for RAPD and don't delegate it to your technician," he emphasized.

"Also, don't forget the secret weapon when checking for optic nerve problems-the color vision test," he said. Color vision will be affected if central vision loss occurs because of optic neuropathy.

The correct visual field test is also important in order to identify small scotomas. Dr. Golnik consulted on a case of a 75-year-old woman who reported having difficulty reading. Her distance and near vision was excellent with a visual acuity of 20/20 and J1+ OU. She had good color vision and the visual field examination looked normal.