disorders of cones, visual function is worse in bright light (hemeralopia), and complaints of photophobia and glare are common. Visual field loss may initially reflect rod dysfunction (mid-peripheral defects and ring scotomas) but central loss soon ensues. The ERG is uniformly abnormal in CAR syndrome, usually showing loss of a- and b-waveforms under photopic and scotopic conditions. Even when central acuity is relatively preserved, the ERG may be surprisingly flat. While the electrophysiologic abnormalities in CAR are indistinguishable from those of some hereditary retinal dystrophies, the more rapid progression and older age at onset are features favoring a diagnosis of CAR syndrome.

As in the above case, the normal fundus appearance and fluorescein angiogram create the impression of neurologic visual loss. The abnormal ERG localizes the visual loss to the retina. The presence of auto-antibodies confirms the diagnosis, although such antibodies are not present in all cases. If the clinical findings suggest CAR, screening tests for occult malignancy should be undertaken, even in the absence of a positive antibody test. Treatment is aimed at eradicating or controlling the primary malignancy though corticosteroids, and other immunomodulatory therapies have also been used in an effort to prevent additional visual loss. In most cases reversal of visual loss is not possible.

Diagnosis: Cancer-associated retinopathy

Tip: Prominent degradation of vision in bright light (hemeralopia) suggests underlying retinal disease, particularly affecting cone function.

Episodic monocular blur

Case: This 65-year-old retired accountant described a one-month history of episodic visual loss in the right eye. Specifically, he noted blurring of vision lasting several hours, often present immediately upon awakening. After each episode his vision returned to baseline. There was no associated pain, photophobia or positive visual phenomena. He had undergone uncomplicated cataract extraction with intraocular lens implant in each eye one

year earlier. Ophthalmic and neurologic examination showed only mildly decreased visual acuity of 20/30 OU, attributed to capsular fibrosis and mild corneal guttatae. Subsequent evaluation included carotid Dopplers, MR angiography of the cervical vessels, erythrocyte sedimentation rate (ESR), C- reactive protein (CRP) and complete blood count (CBC), all of which were normal.

This patient’s work-up addressed the possibility of retinal vascular disease as the cause of his transient monocular visual loss (TMVL). Is there something about his history, however, to suggest a different mechanism for his episodes?

This patient’s history of visual loss that was present upon awakening even before arising from bed would be highly atypical for ischemia but quite characteristic of a particular corneal disorder. Corneal decompensation is often worse first thing in the morning because lid closure during the night prevents normal oxygenation and evaporation. This patient was asked to return for evaluation early in the day while experiencing the blurred vision. Examination of the right eye during an episode showed moderate edema of the corneal stroma with macrocystic epithelial changes. More detailed investigation showed his corneal thickness was increased at 670 µm and endothelial photography confirmed a reduced cell count of 500/mm. A diagnosis of Fuchs corneal dystrophy was made.

Discussion: A history of episodic visual loss prompts consideration of a neurovascular mechanism. The most common vascular cause of transient monocular visual loss (TMVL) is retinal embolism. Transient visual disturbance due to retinal emboli (also termed amaurosis fugax) typically has an abrupt onset and offset, often described as a curtain or shade descending over vision. Similar to hemispheric transient ischemic attacks, most episodes of TMVL due to embolic retinal ischemia last for just 5 to 10 minutes. Episodes are usually spontaneous and are not accompanied by pain. The source of