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Anna McKinney, William Miller, Norman Leach, Cristina Polizzi, Eef van der Worp, Jan Bergmanson; The Cause of Midday Visual Fogging in Scleral Gas Permeable Lens Wearers. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5483.
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© ARVO (1962-2015); The Authors (2016-present)
Scleral gas permeable contact lens (SGP) patients may report midday foggy vision, necessitating lens removal. The present study attempts to determine causative factors.
Fifteen SGP wearers were enrolled after obtaining informed consent and divided into two groups - those able to wear lenses 8 hours per day or more (uninterrupted) and those that have to remove lenses temporarily before 8 hours (interrupted). The Texas Eye Research and Technology Center Dry Eye Questionnaire (DEQ) was completed and lens fit was assessed with biomicroscopy and Visante OCT imaging. Tear exchange was measured using a fluorophotometer (Ocumetrics FM-2 Fluorotron). Two microliters of high molecular weight fluorescein (FITC Dextran) was added to the lens bowl and then carefully inserted. Fluorescence was measured immediately and every 10 minutes for 1 hour. The amount of fluorescein present after 60 minutes (T60) was compared between patients.
Of the 15 patients, 5 (33%) were interrupted wearers averaging 4.45 hours. Wearing time for uninterrupted patients (67%) averaged 11.75 hours. Uninterrupted wearers had an average DEQ score of 28±22 while the interrupted wearer’s averaged 54±11. There was a moderate correlation between DEQ scores and average daily wear times (r = -0.528). Sixty percent of both groups exhibited an alignment fit. However, 80% of interrupted wearers exhibited a tight fitting edge compared to 40% of uninterrupted wearers. The average corneal vault for uninterrupted lens wearers was 0.29±0.24 mm while interrupted wearers averaged 0.71±0.44 mm. There was a moderate correlation between corneal vault and average daily wear times (r = -0.509). Fluorophotometry was conducted on 12 of the 15 patients. All patients had residual fluorescein remaining in the post-lens tear film. The T60 for the uninterrupted wearers was slightly lower than in the interrupted wearers (0.6671; 0.7539; p=0.23). However, the tear exchange decay rate was not statistically different.
Foggy vision, occurring in 33% of SGP lens wearers in this study, is a multifactorial phenomenon unique to these devices. Important factors include a predisposition to dry eye and significantly greater central corneal vault combined with lens edge tightness. This study documents, for the first time, post lens tear exchange in SGP lens wearers. Foggy vision is best countered by reassessment of lens edge fit and adjusting corneal vault.
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