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Abstract #16913 Published in IGR 9-1
The effect of contact lens induced corneal edema on Goldmann applanation tonometry measurements
Hamilton KE; Pye DC; Hali A; Lin C; Kam P; Ngyuen TJournal of Glaucoma 2007; 16: 153-158
AIM: To determine the effect of small increases in corneal hydration on the accuracy of Goldmann applanation tonometry estimates of intraocular pressure (IOP). MATERIALS AND METHODS: Twenty-five young healthy subjects presented on 3 separate days approximately 1 week apart. On 2 visits, subjects were required to wear a hydrogel contact lens with either a center thickness of 0.3 and 0.7 mm (HEMA 38% water content, parallel surface curve) in 1 eye only under closed-eye conditions for 2 hours to induce corneal swelling. The third visit acted as a control. IOP, corneal thickness, and corneal curvature were measured in both eyes before and after contact lens wear on all visits. RESULTS: There was a statistically significant increase in corneal thickness of 40.2 ± 14.4 μM (P < 0.001) and 41.9 ± 16.4 μM (P < 0.001) after wearing the 0.3 and 0.7 mm thick contact lenses, respectively (2-tailed paired t test). There was an increase in IOP of 2.8 ± 2.2 mmHg (P < 0.001) after wearing the 0.3 mm thick contact lens, and a statistically insignificant difference of 1.3 ± 3.0 mmHg (P = 0.058) after wearing the 0.7 mm thick contact lens (2-tailed paired t test). There was a statistically significant Pearson correlation between the change in corneal thickness and the change in IOP after lens wear (r = 0.500, P < 0.001, 0.3 mm lens and r = 0.399, P < 0.001, 0.7 mm lens). The corneal hydration-induced measurement error was 0.46 mmHg per 10 μM change in corneal thickness (0.3 mm lens) and 0.35 mmHg per 10 μM change in corneal thickness (0.7 mm lens). CONCLUSION: A small increase in corneal hydration and thickness may cause a clinically significant overestimation of IOP when measured using Goldmann applanation tonometry.
Dr. K.E. Hamilton, School of Optometry and Vision Science, University of New South Wales, Sydney, Australia
Classification:
6.1.3 Factors affecting IOP (Part of: 6 Clinical examination methods > 6.1 Intraocular pressure measurement; factors affecting IOP)
2.2 Cornea (Part of: 2 Anatomical structures in glaucoma)
