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S. Fan, C.B. Camras, C.B. Toris; Effects of Central Corneal Thickness on the Efficacy of Ocular Hypotensive Drugs . Invest. Ophthalmol. Vis. Sci. 2003;44(13):86.
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Purpose: To determine the effects of central corneal thickness (CCT) on the efficacy of intraocular pressure (IOP) lowering drugs in patients diagnosed with ocular hypertension (OHT) for at least six months. Methods: This is a retrospective study of 109 patients with OHT on no ocular medications and 97 ocular normotensive (ONT) volunteers with no ocular diseases or abnormalities. At baseline, CCT was measured by slit-lamp pachymetry and IOP was determined by pneumatonometry. The patients and volunteers were divided on the basis of CCT. The Thin Cornea Groups had CCTs of ≤540 µm (OHT n=57, ONT n=63) and the Thick Cornea Groups had CCTs of >540 µm (OHT n=52, ONT n=34). In the OHT patients, measurements were repeated at one week of unilateral treatment with either latanoprost 0.005%, dorzolamide 0.2%, brimonidine 0.2%, apraclonidine 0.5%, timolol 0.5%, pilocarpine 2% or unoprostone 0.15%. The fellow eyes received the appropriate vehicle. IOP and CCT were compared between corneal thickness groups and between OHT and ONT groups with unpaired t-tests, and between eyes within groups with paired t-tests. A correlation between IOP and CCT was evaluated with linear regression. Results: At baseline, the IOPs of OHT patients were not different between corneal thickness groups or between treated and control eyes. After one week of drug treatment to one eye, IOPs were significantly (p=.04) lower in the Thin Cornea Group (16.3±2.6 mmHg, mean±SD) than in the Thick Cornea Group (17.4±2.8 mmHg) and lower in the treated eyes versus the control eyes within each group (p<.001). There was a positive correlation between IOP and CCT (R2 =0.07, p=.008) in the treated eyes after treatment. This correlation did not exist in the treated eyes at baseline, in the contralateral control eyes at any time, or in eyes of ONT subjects. The CCT in the OHT and ONT subjects averaged 541±34 and 532±34 µm, respectively (p=.07). Conclusion: Following treatment with an ocular hypotensive drug, patients with thicker corneas had less of an IOP reduction than patients with thinner corneas. Of several possibilities to account for these findings, corneal thickness may affect bioavailability of topical drugs to their target tissues.
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