Abstract
Abstract: :
Purpose:Several landmark studies, including OHTS, have highlighted the importance of the measurement of central corneal thickness (CCT) in the assessment of patients with ocular hypertension or glaucoma. An increase in CCT can lead to an over–estimation of intraocular pressure (IOP) by Goldmann tonometry and vice versa. Many ophthalmologists measure IOP after, as well as before, pupil dilation with tropicamide. There have been no published studies assessing the effect of tropicamide on central corneal thickness. It is, therefore, not known whether tropicamide could lead to an erroneous IOP measurement due to an effect on CCT. Methods:Patients underwent measurement of CCT using an ultrasound pachymeter (Model 885, Humphrey Systems Inc.) both pre– and 15 minutes post–instillation of G.Tropicamide 1% (Minims, Chauvin Pharmaceuticals Inc.). Patients' eyes were excluded if there was evidence of corneal pathology, previous intra–ocular or corneal surgery, concurrent topical treatment or narrow anterior chamber angles. All patients were of Caucasian origin. IOP was measured, by Goldmann tonometery, pre– and 15 minutes post–instillation of tropicamide. Results: 52 eyes were assessed. The mean CCT (+/–2SD) pre–tropicamide instillation was 553.7 (+/–54.8)µm. The mean CCT post–tropicamide instillation was 554.7 (+/–56.1)µm. This was not a statistically significant difference (t–test: paired two sample for mean). The median CCT remained unchanged at 550.5µm pre– and post–tropicamide instillation. The maximum rise in IOP post tropicamide instillation was 2mmHg. Conclusions: The instillation of G.Tropicamide 1% does not have any significant effect on CCT. Any measured change in IOP after pupil dilation with G.Tropicamide 1% is not therefore due to a change in CCT. CCT can be accurately measured either pre– or post–instillation of G.Tropicamide 1%.
Keywords: drug toxicity/drug effects • cornea: clinical science • intraocular pressure