ABSTRACT

Corresponding Author:
Vaikkakara Sudha,
Associate Professor,
Department of Ophthalmology,
Government Medical College, Thrissur.
E-mail: ajisudha@gmail.com

ABSTRACT

BACKGROUND

The aim of this study is to identify, categorise and analyse the Optical Coherence Tomography patterns of Diabetic Macular oedema.

MATERIALS AND METHODS

In this observational study, 43 eyes of 25 patients with Diabetic Macular oedema (DME) were evaluated. DME was defined as the retinal thickening due to fluid leakage and pooling in the macular area in patients with Diabetes Mellitus. Macular oedema due to other ocular illness was excluded. All patients underwent best corrected visual acuity assessment by Snellen’s visual acuity chart, dilated slit-lamp Biomicroscopic examination, Fundus Fluorescein Angiography(FFA) and Optical Coherence Tomography (OCT) by the same examiner. OCT patterns were analysed. Central foveal thickness was also measured by OCT and macular oedema classified into mild (201 µm-300 µm,) moderate (301 µm-400 µm) and severe (≥400 µm).

RESULTS

Of the total 25 patients in the age group 35-75 years (Mean age 54.08), males predominated in this study (M: F ratio of 2.6:1). OCT examination revealed that 30% eyes had Cystoid macular oedema and 26% had Sponge-like retinal thickness. Mixed cystoid and spongiform pattern w

as observed in 28%, Epiretinal membrane (ERM) in 9%, Plaque of hard exudates in 7%, Serous macular detachment in 9%, and Vitreomacular traction in 5%. 32% eyes had mild macular oedema, 21% had moderate and 35% had severe forms.

CONCLUSION

Various patterns can be easily identified by OCT and treatment may be modified accordingly. Cystoid macular oedema was the predominant form of DME according to this study. Both eyes of a same patient can present with different DME patterns.

KEYWORDS

Optical Coherence Tomography, Diabetic Macular oedema, Cystoid Macular Oedema, Epiretinal Membrane, Central Foveal Thickness, Vitreomacular Traction.

BACKGROUND

Diabetic Macular Oedema (DME), a microvascular complication which is caused by the breakdown of the blood-retinal barrier, promotes neuroglial dysfunction and concomitant visual disturbance.¹ It is the commonest cause of visual loss in patients with non-proliferative diabetic retinopathy and a common cause of visual loss in proliferative diabetic retinopathy.

Diabetic macular oedema is diagnosed stereoscopically as retinal thickening in the macula using slit-lamp biomicroscopy. The ETDRS defined DME as retinal thickening or presence of hard exudates within 1 DD of the centre of the macula. To characterise the severity of macular oedema, and for treatment guidelines the term Clinically Significant Macular Oedema (CSME) is used. Macular oedema is clinically

significant, if one of the following conditions is present: 1. Retinal thickening at or within 500µ of the centre of the macula. 2. Hard exudates at or within 500µ of the centre of the macula if associated with thickening of retina. 3. A zone or zones of retinal thickening one disc area or larger, any part of which is within one disc diameter of the centre of the macula.²

Diabetic macular oedema tends to be a chronic disease. Although spontaneous recovery is not uncommon, 24% of eyes with CSME and 33% of eyes with centre involving CSME will have a moderate visual loss (15 or more letters on the ETDRS chart) within 3 years if untreated.³

The incidence of DME over a 10-year period was 20.1% among patients diagnosed before age 30 years (younger onset) and 39.3% among patients diagnosed after 30 years.⁴ Asthe severity of overall retinopathy increases, the proportion of eyes with macular oedema also increases. 3% in eyes with mild non-proliferative diabetic retinopathy (NPDR), 38% with moderate-severe NPDR and 71% with proliferative diabetic retinopathy (PDR) develop DME.⁵

Optical coherence tomography (OCT) is a fast and noninvasive tool for examining the retina in cross sectional images that correlate reasonably with the retinal histology. It is not only helpful in detecting DME early, but has the added advantage of being able to reveal not only the presence of cystoid macular oedema, but subfoveal serous retinal detachment, vitreomacular traction or an epiretinal membrane which cannot be detected in FFA.

Moreover, the macular thickness map gives us a very accurate idea of central retinal thickness and can quantify the degree of improvement or worsening following therapy.

Aim of Study

The aim of the study was to identify, categorise, and analyse the OCT patterns of Diabetic Macular Oedema.

MATERIALS AND METHODS

This was an observational study done between October 2010 and March 2011 in patients who attended the retina clinic of Govt. Medical College, Thrissur. 43 eyes of 25 patients with Diabetic Macular Oedema were evaluated. The study group included both insulin dependent and non-insulin dependent proliferative diabetic retinopathy and non-proliferative diabetic retinopathy between the ages of 35-75 years.

None of the patients in our study had undergone previous focal laser or pan-retinal photocoagulation, or ocular surgery in the past six months. Other exclusion criteria were dense cataract, macular oedema owing to other ocular illness and advanced diabetic retinopathy.

Diabetic macular oedema is diagnosed stereoscopically as retinal thickening in the macula. The patients were diagnosed as having Diabetic Macular Oedema by slit-lamp biomicroscopic examination with 90D lens. A detailed history regarding onset of visual loss and duration of diabetes, treatment taken, etc was taken and recorded. All these patients underwent best corrected visual acuity assessment by Snellen’s visual acuity chart, and dilated slit-lamp biomicroscopic examination. Fundus photographs were taken and macular oedema was confirmed by Fundus Fluorescein Angiography. Spectral domain OCT (OPKO) was taken on the same day, by the same examiner. OCT was done in all eyes, a line scan program was chosen and the image processed and analysed for pattern characterisation. Central macular thickness was measured with the retinal thickness map. Macular oedema was categorised into mild (with a thickness of 201-300µ), moderate (301-400µ) and severe (≥400µ).

RESULTS

Of the 25 patients we analysed, there were 3 (12%) patients in the age group 30-39 years, 2 (8%) in 40-49 years age group, 11 (44%) in 50-59 years age group, 8 (32%) in 60-69 age groups and 1 (4%) in 70-79 age group. Males predominated with M: F ratio of 2.6:1. 67.3% had NPDR and 32.7% PDR. Mean diabetic age was 14.08 years.

Figure 1. Age Distribution of  the Patients in the Study

Figure 2. Fundus Picture of DME

Biomicroscopic examination of all the patients showed Diabetic macular oedema. 11% patients showed DME associated with cystoid macular oedema (CME), and 2% had DME with vitreomacular traction (VMT). No patients had Epiretinal membrane (ERM) or Serous Macular Detachment with Subretinal Fluid (SRF) clinically.

Ocular Coherence Tomography analysis showed seven patterns of macular oedema in our patients.

Spongiform Pattern

Eyes with spongy oedema showed diffuse thickening of macula. It mostly involved the outer retinal layers, while the internal layers maintained their normal reflectivity. Cross sectional scans show swelling of the retina giving it a spongy appearance with increased retinal thickness.

Figure 3. Spongiform Oedema on OCT

Figure 4. CME on OCT

Cystoid Pattern

Eyes with CME showed large cystic spaces in the foveolar and parafoveal region. It involves various depth of retina and has intervening septa in between.

Mixed Pattern

Some eyes showed both spongiform thickening of outer retinal layers and cystoid spaces in the inner retina.