A simple model for demonstrating abnormal slitlamp findings.

One of the challenges facing the ophthalmologist-teacher is to demonstrate abnormal physical findings to medical students, beginning ophthalmology residents, and general physicians at the time dictated by the students’ schedules rather than by the availability of patients in the clinic. Abnormalities of the ocular fundus and external eye are effectively displayed by goodquality photographs, but abnormal slitlamp findings, particularly “cells” and “flare,” are extremely difficult to capture on film. To solve the problem of demonstrating these abnormal slitlamp findings to students on a “demand” basis, a simple, inexpensive model was constructed using common laboratory and household materials. This model simulates the optical section of the cornea, the presence of cells and flare in the anterior chamber, and the variation of the thickness of the optical section with the varying thickness of the cornea. Our model was constructed using a screw-top glass vial measuring 15 mm in diameter and 45 mm in height (# 03-33921B, Fisher Scientific, Pittsburgh, Pa) (Figure 1). This vial was filled with colorless baking soda flavored mouthwash (Scope, Proctor & Gamble Co, Cincinnati, Ohio) to which a small amount of face powder was added by raking particles from the powder puff into the vial. Lightcolored powder is preferable to a darker shade. The amount of face powder can be varied until the proper effect is obtained, or several vials can be prepared using differing concentrations of particles to simulate 1+, 2+, or 3+ cells. Although the face powder particles are larger than the inflammatory cells they represent, they are some of the smallest insoluble particles commonly available around the house or in the laboratory. These components were chosen for their stability and availability. Our original model has been stable for almost 2 years and does not appear to have become contaminated or allowed bacterial or fungal growth, as some protein compounds, such as gelatin, might have. A control vial may also be prepared using distilled water or alcohol. The vial can be held in front of the slitlamp by the teacher or the student and observed, displaying several different views that simulate clinical observations of abnormal slitlamp findings. An alternate method of support is to use 2 test tube clamps fastened to the uprights of the slitlamp. By positioning the vial horizontally, the student can focus the thin beam of the slitlamp on the outer surface of the vial and view what is equivalent to an optical section of the cornea (Figure2). The vial has a 7.5-mm radius of curvature, which approximates that of the normal cornea. The student can see the anterior surface of the vial, the dark band representing the wall of the vial, and the interface between the inner surface of the vial wall and the liquid contents. By rubbing a finger over the surface of the vial and depositing skin oils there, the outer surface will become more visible and allow From the Department of Ophthalmology, University of Tennessee, Memphis. SPECIAL ARTICLE