Central Corneal Thickness (CCT) among Glaucoma and Non Glaucoma Patients in a Hospital Based Population

Abstract

Objectives: To estimate the difference in the central corneal thickness among normal tension glaucoma (NTG), primary open angle glaucoma (POAG), ocular hypertensives (OHT) and non glaucomatous patients.

Methods: Intraocular pressure (IOP) (by Goldmann applanation tonometry) and central corneal thickness (CCT) (ultrasound Pachymetry, Ocuscan rxp) were measured in 44 eyes with NTG, 138 eyes with POAG, 16 eyes with OHT and in 202 normal eyes. The CCT was used to obtain a corrected value for the IOP. The data thus obtained was analyzed and statistical calculations were performed using statistical software (SPSS version 16).

Results: Total number of study subjects were 400; among those, 202 were normal subjects, 138 were POAG patients, 44 were NTG patients and 16 were ocular hypertensives. Mean CCT in POAG was 543.37µm with SD 37.39µm, and mean CCT in NTG was 530.43µm with SD 33.43, and mean CCT in ocular hypertensives was 598.06µm with SD 5.92 and normal subjects was 539.78µm with SD 23.95. There was higher CCT in ocular hypertensive patients than other groups which was significant (p value <0.001). There was no significant difference in CCT between normal subjects (539.78 µm) and patients with POAG (543.37 µm), but the CCT in the group with NTG (530.43 µm) was lower than that in the normal subjects or the group with POAG but statistically it was not significant (p value >0.001).

Conclusions: patients with OHT have a thicker CCT than do patients with POAG, NTG and normal subjects. The central corneal thickness of the normal tension glaucoma patients was lower than as compared to that in the primary open angle glaucoma patients and normal subjects. No significant difference was found between the primary open angle patients and the normal subjects. Due to the effect of the CCT on the measurement of the IOP with the use of an applanation tonometer, which is the main parameter in the diagnosis and the follow up of glaucoma patients, many POAG patients may be misdiagnosed as NTG due to thinner corneas and the normal patients may be misdiagnosed as OHT due to thicker corneas. Measurement of the central corneal thickness helps the ophthalmologist in making a correct diagnosis for these patients, as well as in better management of the intra ocular pressure, especially when their corneal thicknesses differ markedly from the normal thickness. The inclusion of a CCT adjusted IOP during the management of glaucoma patients, will prevent the over or under treatment of such patients.