A 60 y.o. male with diabetes, obesity and HT comes to the ED with a complaint of "I can no longer see to drive.
The pt had been seen several times for blurry vision and once in the same day of his visit for eye redneess. His vision was 20/25 in both eyes and he did not have a cornea abrasion. What could be wrong?
Does this finding on his retina explain his vision loss?
Our patient had a choroidal nevus , a pigmented tumor of the blood vessel layer beneath the retina. It is benign.and does not explain his blurry vision. He had incomplete homonymous hemianopsia with preserved central vision: an occipital stroke. Macular sparing commonly results from infarcts of the most posterior portion of the occipital cortex in a posterior cerebral artery distribution. The occipital pole manages macular field information and has an anastomotic vascular supply from the contralateral side which can supply the affected macula in the advent of a stroke. Our patient’s MRI is shown below
In terms of ability to drive, a visual field of 120 degrees on the horizontal is necessary by law on the Goldmann field test. Patients with homonymous hemianopsia are not able to drive. A reminder of the visual pathways is shown below.
FUN FACT
While in our case the macula was spared and his central vision was good, in the case of injury from a solar eclipse, the macula is injured by looking directly at the sun. Solar retinopathy causes specific changes to the retina that can be seen on optical coherence tomography (OCT) in the fovea. Solar retinopathy can cause blind spots in central vision. They can occur up to 48 hours after exposure and while some damage resolves after the retina heals; in others the damage is permanent.
Since the injury involves the macula, severe damage can be detected in the ED using an Amsler chart
If the patient looks directly at the center dot with one eye and the chart at 14 inches from the eye some lines will seem wavy if there is macular damage. Blind spots may also be apparent. Those patients need a referral to ophthalmology.
A normal amsler grid
An Amsler grid with macular damage.
Zhang X, Kedar S, Lynn MJ, Newman NJ, Biousse V. Homonymous hemianopias: clinical-anatomic correlations in 904 cases. Neurology. 2006 Mar 28;66(6):906-10.
Bilhotra J, Mitchell P, Healey P, et al. Homonymous visual field defects and stroke in an older population. Stroke 2002;33:2417-20.
Su, Daniel; Greenberg, Andrew; Simonson, Joseph L.; Teng, Christopher C.; Liebmann, Jeffrey M.; Ritch, Robert; Park, Sung Chul (April 2016). "Efficacy of the Amsler Grid Test in Evaluating Glaucomatous Central Visual Field Defects". Ophthalmology. 123 (4): 737–743.