Reading corneal signs
Excerpted from page 48 of the September 2018 edition of AOA Focus.
Unlike other bodily tissues, the cornea isn't laced with blood vessels for nourishment or to ward off infection. Instead, the cornea requires a perfect balance of tear coverage and fluid movement to remain healthy. Disrupt that balance and there's trouble. In the case of corneal diseases or disorders, the normally transparent tissue clouds with abnormal material accumulation, causing blurred or decreased vision, light sensitivity or glares, and pain.
"Corneal dystrophies are usually relatively isolated, though the prevalence—I feel—is probably underreported, and part of the reason for that is it's very easy to overlook corneal dystrophies, in particular, epithelial corneal dystrophies," says Mile Brujic, O.D., AOA New Technology Committee member. That's because not all corneal dystrophies or disorders are immediately noticeable to the patient, or the doctor.
"In many of the mild-to-moderate cases of these corneal abnormalities, you won't be able to see them with a standard slit-lamp evaluation. Place some fluorescein on the eye, look at the eye with a cobalt-blue light, and a Wratten #12 filter literally exposes many of the irregularities we see with these corneal conditions."
Here are a few cases of corneal whorls, sparkles and map-dot fingerprints that could be indicative of something more.
The golden-brown or gray corneal verticillata, radiating outward from the inferior cornea, aren't unique to the rare, inherited disorder. But, when correcting for pharmacological causes—of which the cardiac anti-arrhythmic amiodarone or anti-malarial chloroquine are most common—Fabry disease should be considered, Dr. Brujic says.
A metabolic error that results from the buildup of the glycoprotein globotriaosylceramide (Gb3) in lysosomes of vascular endothelial cells, Fabry disease is a debilitating and life-threatening disorder that progressively affects major organ systems, leading to kidney failure, heart attack or stroke. Occurring in about 1 in 40,000 births, Fabry disease begins in childhood and can be overlooked for years, especially in individuals with milder forms of the disorder. Fabry disease often manifests with other characteristic features, aside from hallmark corneal whorls, including:
- Acroparesthesias, pain in the hands and feet.
- Angiokeratomas, small, dark-red spots on the skin.
- Hypohidrosis, inability to sweat.
- Tinnitus or hearing loss.
- Gastrointestinal problems.
"If you rule out the pharmacological cause, often if the patient is younger and has corneal whorls, that should almost immediately trigger higher on our suspicion scale for Fabry disease," Dr. Brujic says.
Should doctors suspect Fabry disease, a referral to a genetic specialist is recommended to confirm via DNA testing. Although there is no cure, patients may benefit from enzyme replacement therapy.
Epithelial and endothelial dystrophie
Whereas the ocular manifestations of Fabry disease might persist for years unnoticed or without any consequence to visual acuity, that isn't the case with epithelial basement membrane dystrophy (EBMD). One of the more common corneal dystrophies, EBMD is a protrusion of the basement membrane into the epithelium, causing recurrent corneal erosion. This erosion exposes nerve endings and causes severe pain, not to mention blurred vision, light sensitivity and foreign body sensation.
Also known as map-dot-fingerprint dystrophy for the bilateral, opaque clouds, dots and lines on the epithelium, EBMD can cause astigmatism and other higher-order aberrations, says Melissa Barnett, O.D., AOA Contact Lens and Cornea Section (CLCS) member and principal optometrist at UC Davis Eye Center.
"Microcysts appear as oval, oblong or comma-shaped, and rarely appear alone but are typically associated with map and fingerprint patterns," Dr. Barnett writes, adding that such patterns also may appear without dots or individual microcysts.
Management strategies typically include ocular lubricants, bandage contact lenses, topical hyperosmotics, epithelial debridement, autologous serum eyedrops, anterior stromal puncture, phototherapeutic keratectomy and amniotic membranes.
From the posterior cornea, Fuchs' dystrophy is a bilateral, asymmetric condition that manifests most commonly among 50- to 60-year-old patients and presents as painful, recurrent corneal wounds with hazy vision. Essentially the deterioration of "pumper cells," Fuchs' dystrophy results in corneal clouding and swelling that creates painful blisters.
Initially asymptomatic, Fuchs' can threaten vision loss and necessitate a corneal transplant. A transplant patient may be a candidate for scleral lens wear, Dr. Barnett notes.
"When managing these patients with scleral lens wear, it is important to have a baseline endothelial cell count and global pachymetry in order to monitor the cornea carefully," she writes.
In a broad sense, Dr. Brujic argues that eye care practitioners should espouse a holistic approach to patient care—not entrenching themselves solely in eye care—given that corneal issues can be indicative of systemic disorders. An example? Wilson disease.
Here's a genetic disease that prevents the body from removing excess copper, of which a delicate balance is necessary to maintain healthy bodily functions. Too little copper, and muscles weaken, white blood cell counts drop and anemia develops. Too much, and the buildup in the liver, brain and eyes becomes lethally poisonous. It, too, can be caught in the cornea.
"You literally see pigment in the cornea, but it's actually copper deposits in Descemet's membrane," Dr. Brujic says.
Called Kayser-Fleischer rings, the pigmentation appears as a rusty-brown ring around the edge of the iris and rim of the cornea. The National Institutes of Health notes Kayser-Fleischer rings are often indicative of nervous system damage resulting from Wilson disease, while the rings are only present in upward of 66% of those with liver damage alone.
True, such disease and manifestations may be rare, but in each case early detection can be critical not only for improving a patient's quality of life, but also for improving their outlook.
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