Correlation Between HBA1c Level and Thickness of Both Macula and Choroid in Patients With Type 2 Diabetes Mellitus

Overview

Diabetic retinopathy (DR) is a frequent cause of visual impairment, and the leading cause of blindness in those of working age, but it develops silently along years, producing symptoms only in late stages.

The risk of sight-threatening consequences can be reduced if the lesions are detected before irreversible damage to retinal function has developed .Patients with diabetes mellitus (DM) have many pathological changes in their macula as diabetic macular edema (DME), exudates, cysts, detachment and ischemia that cause impairment of vision. DME is characterized by increased vascular permeability and deposition of hard exudates at the macula and can occur at any stage of DR. With the help of OCT, it is possible to quantify the macular thickness objectively and to follow the progression of DME quantitatively. Currently, DME is classified as 'center involved' or 'non center involved' (referring to whether or not there is oedema i.e., CMT\>250 μm at the fovea) based on OCT. Non-centre involved macular oedema is rarely symptomatic. However, as the oedema spreads to the central macula, patients usually experience progressive vision loss and treatment with anti-VEGF is recommended. Also, DM can cause many pathological changes in the choroid as increased tortuosity, focal vascular dilatation, microaneurysms and nonperfused areas. Studies have analyzed choroidal thickness changes in DR using spectral domain optic coherence tomography. A number of studies have shown that choroidal thickness decreases as the diabetic retinopathy progresses. Swept-source (SS) OCT is a variation of OCT that offers improvements in visualizing the vitreous, retina, and choroid at one image. The increased scan speeds, decreased signal attenuation, more comprehensive imaging, and deeper tissue penetration make SS-OCT ideal for capturing a wide range of views and studying structures below the retinal pigmented epithelium (RPE), especially the choroid. Glycated haemoglobin (HbA1c) is measured primarily to identify the average plasma glucose concentration over prolonged periods and reflect the long-term control of hyperglycaemia. Higher levels of HbA1c increase the incidence of DME over a 10-year period in Wisconsin Epidemiology Study of Diabetic Retinopathy (WESDR). The Diabetes Control and Complication Trial (DCCT) and the UK Prospective Diabetic Study (UKPDS) both of which were randomized prospective studies showed that intensive glycaemic control and thus reduction of HbA1c levels are associated with a decrease in the rates of development and progression of DR and DME. The use of HbA1c for the diagnosis of DM has been approved by the WHO based on a number of epidemiological studies showing that a threshold for increased prevalence of microvascular complications can be observed at HbA1c level of 6.5% . Aim of the work To investigate the correlation between HbA1c levels in patients with type II diabetes mellitus on central macular thickness as well as central choroidal thickness using swept source optical coherence tomography.

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