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Scleral contact lenses are extensively prescribed in certain centres, especially when the eyes to be fitted are abnormal. The original sealed lens prevented the tear fluid behind it from exchanging with the lacrimal secretion present in the conjunctival sac. In consequence, the corneal epithelium rapidly became depleted of oxygen, and this resulted after a few hours in the misting of vision and the appearance of haloes (Smelser, I952).In order to promote the circulation of the fluid over the cornea, scleral lenses have been designed with fenestrations or with channels. There appear, however, to have been no objective tests of the effectiveness of these procedures. One way to ascertain this is to stain the fluid behind the lens with fluorescein and to measure the rate at which the fluorescence is lost; this rate of loss should represent the rate at which unstained tear secretion replaces the original fluorescein-stained fluid. Fluorescein was used for this purpose in the pioneer experiments of Smelser (1952), but a specially designed lens had to be made to collect the dye for measurement at the end of a test, and repeated tests were required to determine the rate of loss.The availability of the slit-lamp fluorophotometer designed by one of us (Maurice, I963) has made it possible to follow accurately the changes in dye concentration behind a normal lens during a single wearing period. MethodPatients who had been routinely fitted with scleral lenses at the Contact Lens and Prosthetics Department of Moorfields Eye Hospital, High Holborn, were used as subjects for these tests. Three patients (four eyes) wore fenestrated lenses (F) and eight patients (ten eyes) channelled lenses (C). The channels were grooves in the haptic from the zones of corneal clearance to the periphery of the lens. The fenestration was I to I-5 mm. in the limbal clearance zone and was usually sited temporally. The maximum continuous wearing time without misting of vision was noted for each patient. The nature of the test was explained and the lens inserted on to the eye to be tested. Physiological saline buffered to pH 7-2 and warmed to body temperature was used as insertion fluid. A baseline measurement resulting from scattered light and natural fluorescence was made at a point of contact lens clearance from the cornea. The patient then removed the contact lens, filled it with a solution of to-6 g./ml. fluorescein in physiological saline (pH 7.2), and then reinserted it.The patient had previously become accustomed to being observed through the fluorophotometer. The clearance zone behind the lens where measurements could be conveniently carried out was identified as quickly as possible, and readings were made at suitable intervals for a period of an hour or more. Between measurements the patient was allowed normal freedom of movement. At the end of the test the lens was removed, filled with an unstained saline solution, and re-inserted. This allowed a baseline reading to be taken from the same point under the contact lens.Since most of the lense...

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