Midday fogging is a frequent complaint among scleral contact lens (ScCL) wearers, and the mechanism and cause of this is unknown. The purpose of this investigation was to understand the relation between midday fogging, ocular surface leukocytes, and ScCL fitting characteristics. Dr. Gerald McGwin, professor in the department of epidemiology at the University of Alabama at Birmingham School of Public Health joined other researchers from UAB to examine the cause of this complaint.
Subjects arrived at a clinical exam having worn ScCLs for at least 4 hours. ScCL were removed, and 150 μL of phosphate-buffered saline (PBS) was used to wash the bowl of the ScCL. Eyes were washed post-ScCL removal with 5 mL PBS per eye. Wash solutions were collected and leukocytes were then isolated and counted, followed by assessment with flow cytometry. Samples from the post-lens tear fluid were stained with fluorescently labeled antibodies to detect leukocyte distributions.
Thirty-nine eyes from 19 adapted, full-time, ScCL wearers were included, and 46 percent presented with midday fogging. ScCL corneal clearance was 246 ± 61 μm for nonfoggers, while it was 308 ± 98 μm for those with fogging (P < 0.05). On average, the number of leukocytes collected from the ScCL bowl (9551 ± 18,926) was greater than the number of leukocytes recovered from the eye wash (2195 ± 4384, P < 0.02). ScCL corneal clearance was associated with the presence of fogging, with an odds ratio of 2.24 (95 percent confidence interval = 1.48–3.38, P < 0.001).
[Photo: Dr. Gerald McGwin]
The authors concluded that leukocytes, predominated by neutrophils, are present in the post-lens tear film of ScCL wearers, and in particular wearers with greater ScCL corneal clearance have greater odds of having midday fogging.