Retina Quiz

Spelunker’s Central Vision is
Now in the Dark

Interestingly, his history revealed he spent much time as a child spelunking in the hills of West Virginia and Kentucky, where he grew up. He also has a 15-year history of Type II diabetes (noninsulin dependent diabetes mellitus).

On examination, his best-corrected visual acuities were 20/40 O.D., 20/200 O.S. Confrontation visual fields were full to careful finger counting O.U. The pupils were equally round and reactive without an afferent pupillary defect. Amsler grid testing of the right eye showed scotomatous alterations nasally with slight metamorphopsia extending into fixation. As mentioned, the left eye had a large central scotoma. Anterior segment examination of both eyes was unremarkable.

On dilated fundus exam, the vitreous was clear. The optic nerves appeared healthy with moderate-sized cups O.U. There was a slight amount of peripapillary atrophy temporally around both nerves. Two large chorioretinal scars surrounding the fovea — one temporal, the other superior — were observable in the right eye. There was also a smaller inferior scar. 

Of greater concern, however, were two focal areas of subretinal hemorrhage, as seen in the fundus photograph below. The left eye has a large disciform scar involving the macula. A fluorescein angiogram showed early hyperfluorescence in the macula with late leakage.
 

Note the choroidal scarring and subretinal hemorrhage in the macular area.	Fluorescein angiogram shows early hyperfluorescence in the macula with leakage.

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Take the Retina Quiz 1. What explains the chorioretinal scars in the right eye? a.Toxoplasmosis. b.Trauma. c.Previous laser. d.Diabetic retinopathy. 2. Why does this patient have blurred vision? a. Choroidal neovascular membrane. b. Diabetic macular edema. c. Reactivation of toxoplasmosis. d. Neurosensory retinal detachment. 3. What is the overall diagnosis of this condition? a. Diabetic retinopathy. b. Toxoplasmosis. c. Ocular histoplasmosis. d. Macular degeneration. 4. How should this patient be managed? a. Observation. b. Krypton laser. c. Submacular surgery. d. Photodynamic therapy (PDT). Answers

Discussion

This patient has developed a choroidal neovascular membrane involving his fovea, which is surrounded by chorioretinal scars from previous laser procedures. What would predispose him to developing choroidal neovascularization? That he grew up in West Virginia and Kentucky is a clue. Further, if you know what “spelunking” means, it’s even more obvious. 

Spelunking is the term for “caving,” and this patient has many stories of exploring caves as child and young adult. He also had instances of encountering bats and crawling over bat droppings while caving. This points to a diagnosis of ocular histoplasmosis . He may very well have developed this condition had he not been a spelunker, since the area where he grew up is endemic for histoplasmosis.

Histoplasmosis comes from exposure to the fungus Histoplasma capsulatum via the respiratory tract. Geographic areas endemic for this condition include the Ohio and Mississippi River valleys, where more than 60% of the population will have a positive skin test to histoplasmin. It is likely carried via chicken, pigeon and other bird droppings, as well as bat droppings. 

The clinical findings seen in ocular histoplasmosis have been well described. At least two of the following lesions in the fundus indicate the diagnosis:

• Focal, “punched out” atrophic scars in the macula or periphery (“histo-spots”).
• Peripapillary chorioretinal atrophy.
• Choroidal neovascularization (CNV).
• Fibrovascular disciform macular scar secondary to CNV.

When a lesion involves the macula, patients usually complain of blurred vision and metamorphopsia. Evidence of CNV includes the presence of subretinal hemorrhage, exudate, neurosensory retinal detachment or even a gray-green pattern of pigment. The latter does not always appear, depending upon the membrane’s anatomic location. It was not present in our patient because the membrane was below the RPE. These are classified as type I CNVMs. That’s unusual in that the CNV in most patients with ocular histoplasmosis grows above the RPE, within the subsensory retinal space, an anatomical growth pattern referred to as type II. Recent studies show that type II CNVMs do quite well with removal of the membrane because the surgery does less damage to the sensory retina than standard laser treatment does. 

So, now the question is: How should you manage this patient?

Management

The Macular Photocoagulation Study group (MPS) showed a clear benefit with laser photocoagulation to CNVM with ocular histoplasmosis. In our patient, however, laser photocoagulation will certainly destroy the retina and wipe out the central vision in his only good eye. 

Submacular surgery is another treatment option that has been successful, especially in histoplasmosis patients. However the membrane in our patient appeared to be located below the RPE. Submacular surgery has not been as successful in these instances. So what should he do?

The patient strongly considered submacular surgery, but after careful thought, elected to undergo photodynamic therapy (PDT). In PDT, a photosensitizing drug is slowly infused into a patient’s arm for about 10 minutes. The drug seems to have selectivity for neovascular tissue. When the drug collects in the CNVM, a nonthermal light laser activates it. This causes a chemical reaction that activates platelet formation and subsequent thrombosis and occlusion of CNV within the treated area, without the destructive thermal damage to the sensory retina or RPE. 

Studies have shown that PDT causes short-term cessation of fluorescein leakage from the CNV for up to 12 weeks after initial treatment. Subsequent treatments may be necessary. Results of phase III investigations showed successful treatment in 61% of patients undergoing PDT vs. 46% treated with a placebo in AMD patients who had angiographic evidence of “classic” CNV.1 Our patient felt that if PDT ultimately fails, submacular surgery would still be a viable treatment option down the road.
 

1. Bressler NM, Bressler SB. Photodynamic therapy with verteporfin (Visudyne): Impact on ophthalmology and visual science. Invest Ophthalmol Vis Sci, 2000 Mar;41(3):624-8.

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