Abstract
Aim: To measure macular thickness by optical coherence tomography (OCT) in various grades of diabetic retinopathy with no clinically significant macular edema (CSME) and its comparison with non-diabetics.
 Design: Prospective cross–sectional study.
 Methods: Macular thickness was measured by OCT in 72 healthy volunteers (107 control eyes), 45 patients with mild and moderate non-proliferative diabetic retinopathy (NPDR) (78 eyes) and 37 patients with severe NPDR and proliferative diabetic retinopathy (PDR) (66 eyes). Patients with diabetic macular edema (DME) as assessed by stereoscopic evaluation or photographs were excluded. One-way ANOVA test to compare the mean thickness and Tukey's test for multiple comparison between groups were used.
 Results: Central subfield thickness (CST) was 238.57 ± 25.077 µm, 251.22 ± 24.649 µm, and 270.45 ± 28.956 µm in the three groups respectively. As the severity of retinopathy increased, the macular thickness significantly increased (p = < 0.001) in all the nine zones on OCT. There was a significant increase in CST noted in all the grades of retinopathy when compared with non-diabetics (p = 0.004, p = < 0.0001). No significant difference in macular thickness was noted between genders, irrespective of their groups (p = 0.72), or between the three groups in all the nine zones (p = 0.609).
 Conclusion: There is a significant increase in CST in all grades of retinopathy, as well as with increasing severity of retinopathy when compared to non-diabetics. This warrants the need to obtain OCT measurements even in patients with moderate NPDR without CSME to rule out subclinical DME.
Highlights
The most common cause of visual loss in patients suffering from diabetic retinopathy is macular edema
The DRCR.net had primarily used the TD-optical coherence tomography (OCT) in its studies related to measurements of diabetic macular edema (DME) up until 2011.9 They have established a mean Central subfield thickness (CST) of 250 μm as the cut-off value to represent the upper limit of normal macular thickness
Other studies that have compared data obtained using the Stratus OCT and the Cirrus HD-OCT in both normals and patients with DME, have demonstrated that the median difference between Stratus and Cirrus CST was 43 μm,[9] i.e., that Cirrus OCT measured retinal thickening was between 30 to 55 microns thicker compared to the Stratus OCT.[12]
Summary
The most common cause of visual loss in patients suffering from diabetic retinopathy is macular edema. This is a preventable cause of blindness and treatments that reduce diabetic macular edema (DME) can improve or stabilize visual acuity. Macular edema is routinely detected clinically by fundus examination using a contact lens through a biomicroscope. This is dependent on observer skill, patient co-operation, degree of pupillary dilatation, amount of media opacity, and the pattern of retinal edema.[2] optical coherence tomography (OCT) has emerged as the ideal imaging modality in the evaluation and management of DME
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