The Central Corneal Thickness in Normal Tension Glaucoma, Primary Open Angle Glaucoma and Ocular Hypertension

Abstract

To compare the Central Corneal Thickness (CCT) of Normal Tension Glaucoma (NTG) with those of Primary Open Angle Glaucoma (POAG) and Ocular Hypertension (OHT) and to study the effect of CCT on the diagnosis and management of glaucoma patients. A total of 99 patients [35(35.35%) females and 64(64.65%) males] were included in the study with four study groups-37 controls (males-24 and females-13), 22 NTG (males-11 and females-11), 28 POAG (males-21 and females-7), and12 OHT (males-8 and females-4). The CCTs of all the participants were measured by using ultrasonic pachymetry. The IOPs were measured by using applanation tonometry. The measured IOPs were corrected by using a linear correction formula. The measurement significant changes (>=1.5) and outcomes significant changes (>=3.0) for the study groups were calculated. The mean CCT of the normals was 527.65± 21.90 μ, the mean NTG was 503.91 ± 11.31 μ, the mean POAG was 525.25± 23.59 μ and the mean OHT was 572.25± 22.71 μ. The difference which was observed in the mean CCT among the groups was statistically significant (p<0.05). The measurement significant change (>=1.5) after correcting the IOP for CCT was observed in 32.258% of the total glaucoma patients, with 27.3% patients ( 6 out of 22) in the NTG, 66.7% patients (8 out of 12) in the OHT and 21.4% patients ( 6 out of 28) in the POAG groups showing it. The difference which was observed was statistically significant (p<0.05). The outcomes significant change (>=3.0) after correcting the IOP for CCT was seen in 6.45% of the total glaucoma patients, with none of the NTG group patients showing outcomes significant changes, whereas 3.57% patients (1out of 28) in the POAG and 25% patients ( 3out of 12) in the OHT groups showed these changes. The difference which was observed was statistically significant (p<0.05). This study confirmed that the central corneal thickness was significantly lower in the normal tension glaucoma patients as compared to those in the controls and in the primary open angle glaucoma patients, whereas the ocular hypertension patients had significantly higher central corneal thicknesses than the controls and the primary open angle glaucoma patients. No significant difference was found between the primary open angle patients and the controls. Due to the effect of CCT on the measurement of the IOP by using an applanation tonometer, which is the main parameter in the diagnosis and the follow up of the glaucoma patients, many POAG patients are misdiagnosed as NTG patients and the normals are misdiagnosed as OHT patients and they are improperly managed. Measurement of the central corneal thickness aid the ophthalmologist in making a correct diagnosis and in a better management of glaucoma and the glaucoma suspects, especially when their corneal thickness differs markedly from the normal thickness.