Background  
Ocular manifestation is the perhaps one of the most important effects of diabetes in the body. central corneal thickness (CCT) has also been demonstrated to be associated with the onset and progression of glaucoma. 

Aim  
To compare the CCT of subjects with diabetes mellitus with age and sex matched healthy subjects. To determine the correlation of CCT with duration of diabetes mellitus and severity of diabetic retinopathy

Method  
In this cross-sectional, observational study one hundred twenty four(124) subjects with diabetes mellitus and 65 age matched healthy controls who gave consent also enrolled. Eyes of subjects with history of intraocular surgery, history of trauma, contact lens wear, treatment for any topical or systemic diseases, with underlying ocular pathology, malignancy, acute illness and pregnancy were excluded. CCT was measured by pulsair non-contact tonometer. The pupils were subsequently dilated with and fundus examination was done. According to retinopathy status based on the ETDRS (Early Treatment of Diabetic Retinopathy Study) subjects with diabetes were categorized as proliferative diabetic retinopathy (PDR) (Group III), non-proliferative diabetic retinopathy (NPDR) (Group II) and no diabetic retinopathy (Group I). Nondiabetic healthy control subjects were categorized as Group IV.

Results  
A total of 121 patients were included in the study. The mean CCT for the study group was 547.02 ± 2.34 and for the control group was 504.6 ± 3.14 and the difference was significant (p = 0.02). Mean CCT in subjects with diabetes with duration more than 10 years was higher (557.71 ± 19.44) as compared to those having it for less than 10 years (534.05 ± 27.30) but the difference was not significant (p = 0.178). Patients with PDR had higher mean CCT (572.13 ± 17.50) compared to NPDR (553.78 ± 8.80). Patients with diabetes but no diabetic retinopathy had lesser mean CCT than NPDR thus implying positive correlation of CCT with severity of diabetic retinopathy.

Discussion  
In our study we found significantly greater mean CCT in eyes in subjects with diabetes compared with control eyes. Similar results were found by ozdamar et al,1 in their study. But Keoleian et al2 in their study showed no significant difference in corneal thickness in subjects with diabetes. We found a significant positive correlation between mean CCT and severity of diabetic retinopathy. In our study we also found a nonsignificant positive correlation between CCT and HbA1c level. Su et al showed that current HbA1c level was perfect predictor for CCT evaluation. In contrast to our results, Keoleian et al.2 did not report any correlation between HbA1c and CCT. Routine assessment of CCT with a simple non-invasive test like pachymetry along with the usual retinopathy assessment might help in the identification of those patients with diabetes mellitus who could be at higher risk of developing severe ocular complications, thus preventing visual disability by early detection and management.

References  
1. Ozdamar Y, Cankaya B, Ozalp S, et al. Is there a correlation between diabetes mellitus and central corneal thickness? Journal of Glaucoma 2010;19(9):613-616.   
2. Keoleian GM, Pach JM, Hodge DO, Trocme SD, Bourne WM. Structural and functional studies of the corneal endotheliumin diabetes mellitus. Am J Ophthalmol 1992;113:64–70.



Study to find corellation and Severity of Diabetic Retinopathy and Central Corneal Thickness Changes