Fleck vs. Pre-Descemet's
Membrane Corneal Dystrophy

BY DOROTHY J. BAZZINOTTI, O.D., F.A.A.O.
SEPT. 1996

Corneal dystrophies don't necessarily contraindicate contact lens wear, and an accurate diagnosis can help you determine the best lens to use.

Corneal dystrophies are inherited, bilateral disorders that affect visual function depending on the layers involved, age of onset, pattern of progression and potential for disrupting epithelial and endothelial function. Posterior stromal and Pre-Descemet's dystrophies generally have little effect on vision or comfort and are usually not contraindications to contact lens wear.

CASE PRESENTATION

A 21-year-old male presented for a routine eye exam and first-time contact lens evaluation. He was happy with his spectacle correction and had no visual or ocular complaints. His ocular and medical history were negative for trauma or disease and he denied taking any medications or having any allergies. His family history was positive for hypertension.

Best corrected visual acuity was 20/20⁺ OD and 20/15 OS with -2.00 -0.75 x 85 and -2.25 sphere, respectively. Near vision was 20/20 OU. Color vision, confrontation fields and extraocular muscle tests were normal. Keratometric readings were 46.00 @ 180/45.75 @ 90 OU.

Slit lamp biomicroscopy revealed normal lids, lashes, conjunctiva, anterior chambers, irises and lenses. However, corneal assessment showed diffuse fleck-like opacities throughout the cornea at the level of the posterior stroma or Descemet's membrane equal in both eyes. The epithelium and the endothelium appeared intact. Intraocular pressures on applanation tonometry were 17mmHg OU. Dilated fundus evaluation revealed healthy posterior pole and periphery with clear macula OU and optic nerve head cupping of 0.25 OD and 0.30 OS.

Coincidentally, the patient's younger brother was also in our office that day for a contact lens evaluation. This 17-year-old male had tried soft contact lenses before, but found them uncomfortable. He had no ocular or visual complaints and wanted to try contact lens wear again. He denied any significant medical history except hay fever and allergy to pollen for which he occasionally took Sudafed (pseudoephedrine hydrochloride).

The younger brother's best corrected distance visual acuity was 20/20 OU with -5.50 -0.50 x 15 and -5.25 -0.50 x 168, respectively. Near vision was 20/20 OU. Color vision, confrontation fields, pupils and extraocular muscle testing were normal. Keratometric readings were 41.37 @ 180/42.25 @ 90 OD and 41.37 @ 180/42.50 @ 90 OS.

Slit lamp biomicroscopy revealed normal lids, lashes, conjunctiva, anterior chambers and irises. There appeared to be congenital cortical lenticular opacities OU. Initially, both corneas appeared normal and clear with intact epithelium and endothelium. Intraocular pressures on applanation were 12mmHg OD and 13mmHg OS. Dilated fundus evaluation revealed clear macular and posterior pole OU with myopic, sloping optic nerve cupping of 0.45 OU. There was moderate white without pressure OU but no retinal holes, tears or detachment. On dilated retroillumination of the cornea, we detected fleck-like opacities throughout the cornea at the posterior stroma or Descemet's membrane. This was similar to, but more subtle than the findings in his older brother.

Both brothers were tentatively diagnosed with Fleck dystrophy versus Pre-Descemet's dystrophy. Since there is no contraindication to soft contact lens wear in either corneal dystrophy, we prescribed soft daily wear contact lenses for both patients. We counseled the brothers on the corneal dystrophy which, though unlikely to produce contact lens complications, should prompt them to seek consultation if any unusual symptoms of pain, redness, photophobia or decreased vision occur.

During three months of contact lens follow-up, both patients continued to have good vision and comfort with their lenses. The lenses fit well with good coverage and movement on blinking. We detected no changes in the appearance of the corneal opacities. We recommended a routine follow-up exam in nine months.

CORNEAL DYSTROPHIES: AN OVERVIEW

Most corneal dystrophies can be diagnosed and classified by:

1.) the level of the cornea in which they occur;

2.) the appearance of the lesions;

3.) a generally bilateral presentation;

4.) the patient's age at onset;

5.) a hereditary association.

Some dystrophies have a pronounced effect on visual acuity and ocular comfort and can disrupt corneal function to the extent that the patient needs a lamellar or penetrating corneal transplant. In most transplant cases, the dystrophy eventually presents within the donor graft tissue. Other dystrophies remain asymptomatic with little effect on comfort or vision. Using these criteria, we ruled out all but Fleck and Pre-Descemet's corneal dystrophy in these cases.

Fleck dystrophy is an autosomal dominant disorder characterized by small, discrete white dandruff-like flecks which may be round, oval or doughnut-shaped and which appear diffusely throughout the cornea, extending axially to peripherally. The lesions, which are best seen on retroillumination, usually involve all layers of the stroma, are rarely progressive, and have no effect on visual function save the possibility of increased glare. This disorder presents early in life and may be congenital. Associated ocular findings include: congenital cataracts, as in the younger brother; central cloudy corneal dystrophy; pseudoxanthoma elasticum; limbal dermoid; and, rarely, decreased corneal sensitivity.

Pre-Descemet's membrane dystrophy is also an autosomal dominant disorder in which gray-white flakes similar to snowflakes appear in the posterior one-fifth of the stroma. They are similar to, but larger and more diffuse than, corneal farinata. The opacities may have six varieties of shape: comma, linear, filiform, circular, boomerang and dendritic. They may appear axially, annularly or diffusely and can extend to the periphery of the cornea. They rarely appear in the anterior four-fifths of the stroma. Pre-Descemet's dystrophy is considered a secondary dystrophy when it is associated with other abnormalities such as anterior membrane dystrophies, posterior polymorphous dystrophy and icthyosis.

Because primary Pre-Descemet's dystrophy usually manifests between the ages of 30 and 70, we did not initially consider it in the diagnosis of these patients. Also, the histopathology of the lesions in this disorder suggests that the abnormal stromal keratocytes contain lipofuscin which is associated with age-related degeneration. Yet, the posterior nature of the lesions in the siblings pointed more to Pre-Descemet's than Fleck dystrophy in which all layers of the stroma are involved. Also, Fleck is not a progressive disease. The fact that the corneal findings were more pronounced in the older brother seemed to suggest a progressive process like Pre-Descemet's dystrophy.

Because both dystrophies manifest more often in women, it may have been helpful to examine the patients' mother. Almost all corneal dystrophies are autosomal dominant which would mean that a carrier's offspring would have a 50 percent chance of having the disorder. Due to variable penetrance, however, this does not always occur.

CORNEAL DYSTROPHIES & CONTACT LENS WEAR

Corneal dystrophies generally do not contraindicate contact lens wear. In fact, the therapeutic use of hydrogel contact lenses in corneal dystrophy has been well documented. Conditions that are predisposed to stromal edema and bullae such as Fuchs' endothelial dystrophy should be fit with a large, loose fitting, high water content soft lens which will protect the cornea from irritation caused by blinking and act as a wick to draw fluid out of the cornea.

Conditions associated with corneal surface irregularity and recurrent corneal erosion such as epithelial basement membrane, Bowman's layer and anterior stromal dystrophies should be fit with a thick, low water content soft lens to discourage erosions and mask irregular astigmatism.

Due to the lack of literature on potential corneal compromise or functional degradation secondary to contact lens wear in patients with benign corneal dystrophies, these new contact lens wearers must be monitored carefully. Progression of the dystrophy could limit contact lens success, and continued contact lens wear could lead to further progression and complications.

CONCLUSION

Even young, healthy patients who seek only routine eye care and cosmetic contact lenses can present with unusual corneal conditions. In evaluating a patient for contact lens wear, practitioners must perform a scrupulous corneal assessment to identify existing disorders that may limit contact lens success and may later be mistaken for a contact lens complication.

While a corneal dystrophy should not necessarily deter practitioners from prescribing contact lenses, the accurate diagnosis of a dystrophy and its potential corneal complications can indicate the best lens to use. Also, some dystrophies are also associated with other ocular complications which should prompt further diagnostic testing. For example, posterior polymorphic and Fuchs' dystrophies have a higher association with glaucoma, and Fleck dystrophy has been linked with congenital lens opacities and decreased corneal sensitivity.

Practitioners should counsel patients with corneal dystrophy on the potential long-term effects of corneal dysfunction, and on the likelihood of family members or offspring also manifesting the disorder. Persons with corneal dystrophies who are fit with contact lenses should be monitored regularly for the development of unusual complications which may have yet to be reported in clinical literature. CLS

Dr. Bazzinotti is director of optometry services at Brighton Marine Uniformed Services Health Center in Boston, and an assistant professor at the New England College of Optometry.