Microcysts and Reversed Illumination

BY TERRY SCHEID, O.D., F.A.A.O.
JUNE 1996

Our patient, F.L., is a 78-year-old male who wears aphakic Softcon lenses in both eyes. He has worn these lenses for approximately 18 years with monthly removal and disinfection. F.L. is generally asymptomatic and his corrected distance visual acuity is OD 20/30 and OS 20/300 (due to cystoid macula edema following cataract surgery). At early morning appointments, we observe corneal striae in each eye due to corneal swelling. Microcystic edema is present, especially centrally and mid-peripherally, due to the high plus power contact lens.

We used the slit lamp microscope and marginal retro-illumination to take this photograph. With this technique, the slit beam is separated from the microscope axis by approximately 45 degrees. After locating the microcysts under low magnification, we displaced the slit beam laterally providing an alternate light/dark background for marginal retro-illumination. The iris/pupil border may be used to create the background. We then increased the magnification to 30X and used the Nikon FS/2 biomicroscope and ASA 200 slide film for photography.

MICROCYSTS REPRESENT A DELAYED RESPONSE TO CHRONIC EPITHELIAL HYPOXIA. THE REVERSED ILLUMINATION INDICATES THAT MICROCYSTS ACT AS A CONVERGING LENS DUE TO THEIR HIGHER REFRACTIVE INDEX THAN THE SURROUNDING CORNEA.

Note the reversed illumination evident in the photograph. Microcysts are typically irregular in shape and 15 to 50µm in size. The reversed illumination indicates that microcysts act as a converging lens due to their higher refractive index than the surrounding cornea. They may show a mixture of reversed and unreversed illumination indicating that they have a variable optical density. In contrast, corneal vacuoles and bullae always show unreversed illumination.

Microcysts represent a delayed response to chronic epithelial hypoxia. In the presence of a significant number of microcysts, clinical options are to increase material oxygen transmissibility when possible, or discontinue or decrease extended wear.

In this case, the patient could not insert, remove and handle the lens and had no one available to handle this task at home. In-office and house call removal was performed as often as possible. CLS

Dr. Scheid, Merrick, N.Y, is a diplomate of the AAO Contact Lens Section, and an assistant professor at S.U.N.Y.