Chronic Diabetes Mellitus problems can affect a variety of organs and systems, including the eyes. The ophthalmologic consequences include cataracts, glaucoma, macular edema, iris rubeosis, non-proliferative or proliferative diabetic retinopathy, and unstable refraction [1].

The most common cause of visual impairment in diabetics, especially type 2 people, is diabetic maculopathy (fovealedema, exudates, or ischaemia). Traditional methods for determining macular edoema include slit-lamp biomicroscopy, stereoscopic photography, and fluorescein angiography. These methods are, at best, qualitative and relatively insensitive to minute variations in retinal thickness. Since the invention of optical coherence tomography (OCT), medical professionals have been able to objectively evaluate the efficacy of various treatment methods and reliably spot and quantify slight variations in retinal thickness [2-3].

We conducted this study in our setup to evaluate the Correlation between Central Macular Thickness (CMT) & Best Corrected Visual Acuity (BCVA) in Patients of Type 2 Diabetes Mellitus Present at Ophthalmology OPD of Tertiary Care centre due to the conflicting reports in the literature and paucity of studies relative to the existing case load in the Indian population.

Aims and Objectives

The aim of this study was to evaluate the Correlation between Central Macular Thickness (CMT) & Best Corrected Visual Acuity (BCVA) in Patients of Type 2 Diabetes Mellitus present at Ophthalmology OPD of Tertiary Care center.

• Study Area: The study was conducted in Department of Ophthalmology, Indira Gandhi Medical College, Shimla, Himachal Pradesh.

• Study Period: The study was conducted for 12 months after approval from Institutional Ethics Committee from July 2018 to June 2019.

• Study Design: It was a cross-sectional descriptive study of diagnosed patients of Diabetes mellitus attending eye OPD of Indira Gandhi Medical College, Shimla, Himachal Pradesh. 

• Study population: Patients with Type II diabetes mellitus with and without fundus changes of Non-Proliferative Diabetic Retinopathy (NPDR) of any severity.

Selection Criteria

Inclusion criteria

• Patients with Type II Diabetes Mellitus on or off treatment within age group of 40-70 years reporting in the OPD after the start of the study. 

• Patients who gave their consent for participation in the study.

Exclusion criteria

• Patient with pre-existing macular pathology such as ARMD, hereditary maculopathy.

• Patient who have undergone any laser surgery in retina.

• Hypertensive retinopathy more than grade II.

• Uveitis.

• Media haze grade 3 or 4.

• Patient who have undergone cataract surgery.

• Patients with history of ocular trauma.

• Patients with proliferative diabetic retinopathy.

• Patients taking retino toxic drugs.

• Type I Diabetes Mellitus.

• Not willing for study.

Materials

After taking history each patient underwent ophthalmic examination as given below: 

For Visual acuity:

• Snellen’s chart for distant vision. 

• Jaeger’s chart for near vision.

Refraction

• To rule out any refractive error

   

For Complete Anterior Segment Examination

Slit Lamp Biomicroscopy (HAAG STREIT-BQ 900 WITH IMAGING MODULE IM 900 made in Switzerland) examination to see anyopacity in the media, lens for evidence of cataract, pseudophakia, aphakia and anterior vitreous for pigment and cells.

For Intra Ocular Pressure

Schiotz tonometer/Goldmann’s applanation tonometer/NCT.

For Colour vision

Ishihara’s pseudo isochromatic plates

Amsler’s Grid Test for Both Eyes

For Fundus Examination: The pupil was dilated by instilling one to two drops of 5% Phenylephrine Hydrochloride with 0.8% Tropicamide, in patients with normal IOP and normal anterior chamber depth. After 45 minutes when the pupil was fully dilated, the patient was examinedwith:

• Direct ophthalmoscope (HEINE Beta 200S) 

• Volk’s +90 D aspheric lens under slit lamp

• Indirect ophthalmoscope (AAIO WIRELESS)

For Central Macular Thickness

SD-OCT volume scan with TOPCON 3D OCT-1 Maestro (Version 8.42) under dilation with 5% Phenylephrine Hydrochloride with 0.8% Tropicamide in every patient. Using the retinal thickness map analysis protocol, macular thickness was determined and compared with normative data. It consists of a macular cube 512 × 128 (vertical × horizontal) axial scans covering an area of 6 × 6 mm in the macular region. The macula was divided into 3 concentric circles centered at the fovea. This division is a superimposition of the ETDRS map over the OCT map of the macula. It consists of 3 zones; the fovea (less than 1 mm diameter), the inner macula (1 to 3 mm) and the outer macula (3 to 6 mm). Foveal or central macular thickness is defined as the average thickness in the central 1 mm diameter. The central macular thickness was measured thrice and average was calculated. 

Investigations

The results of glycosylated haemoglobin (HbA1c) test, lipid profile and other relevant investigations done were recorded for each patient.

Methodology

• This study was started after clearance from protocol review committee and the ethical committee. Pretesting of the study proforma was carried out and appropriate changes were done.

• For the selection of study population, all the patients who reported in the Eye OPD of Department of Ophthalmology, Indira Gandhi Medical College, Shimla, Himachal Pradesh were included in the study who qualified for the inclusion and exclusion criteria as stated above and who gave their consent.

• The presence of DM in all patients had been confirmed by the corresponding Internal Medicine Department. 

• As per study proforma, each patient were asked history regarding demographic variables like age, gender, occupation, address. The patients were subjected to various biochemical investigations and detailed ophthalmological examination as per proforma enclosed.

• The informed consent was taken from all patients taken up for study.

Defining criteria

• American Diabetes Association (ADA) recommends that diagnosis of diabetes be made when the person is symptomatic with polydipsia, polyphagia, polyuria or weight loss with:

• RBS  ≥ 200mg/dl

• FBS  ≥126 mg/dl.

• RBS is defined as blood glucose level at any time of day without regard to time since last meal.

• FBS is defined as blood glucose with no caloric intake for at least 8 hrs.

• If patient is asymptomatic ,then 2 blood glucose value are mandatory, preferably 1 including FBS value.

•  HbA1c ≥ 6.5%

• Hypertension: BP values of ≥140/90 mm of Hg (JNC-VII criteria)

• Obesity: BMI of ≥25 (JAPI criteria)

• Retinopathy: ETDRS criteria was used and retinopathy was classified according to the most severe changes in the worse eye.

• Dyslipidemia: According to NCEP-ATP III guidelines, hypercholesterolemia is defined as: 

• TC >200mg/dl

• LDL-C as >100mg/dl

• Hypertriglyceridemia as TG >150mg/dl and

• HDL-C <40mg/dl.

• Dyslipidemia is defined by presence of one or more than one abnormal serum lipid concentration.

Patients were assessed for the presence of clinically significant macular edema (CSME) using slit-lamp biomicroscopy assessment with a 90D lens. The definition utilized in diagnosing CSME was the presence of one or more of the following (Early Treatment Diabetic Retinopathy Study Research Group 1991):

• Retinal thickening at or within 500 micron of center of macul

• Hard exudates at or within 500 micron of center of the macula if associated with adjacent retinal thickening

• Zone or zones of retinal thickening 1 disc area in size, at least part of which is within one disc diameter of center of macula

Statistical Analysis

The collected data was entered in Microsoft Excel and then analysed and statistically evaluated using SPSS-PC-20 version. Quantitative data was expressed by mean, standard deviation and while qualitative data was expressed in percentage. Difference between the proportions was tested by chi square test or Fisher’s exact test while difference between quantitative variable between two group were tested by Student ‘t’ test or Fisher Exact test. For comparison of quantitative data between more than two groups, ANOVA or Kruskal Wallis ‘H’ test followed by posthoc test was used. The correlation between Best Corrected Visual Acuity and CMT was analysed using Karl Pearson’s correlation coefficients. A ‘p’ value less than 0.05 was considered statistically significant.

Results

The present study was conducted in the Department of Ophthalmology, Indira Gandhi  Medical College, Shimla H.P. It was a cross-sectional study of diagnosed patients of type 2 diabetes mellitus attending eye OPD of Indira Gandhi Medical College Shimla from July 2018 to June 2019.

Both eyes (260 eyes) of one hundred thirty (130) patients diagnosed with type 2 diabetes with or without diabetic retinopathy within age group of 40-70 years and diabetes duration of at least 1 year served as the study group on the basis of predefined inclusion and exclusion criteria.

Figure 1: Errorplot Showing Association of Cmt with Bcva in Right Eye

Figure 2: Errorplot Showing Association of Cmt with Bcva in Left Eye

Total of 130 patients were taken of which 66.9% were male (n = 87) and 33.1% were females (n = 43). The age of the patients in the study ranged from 40 - 70 years. Mean age of study subjects was 56.88±8.26 years. Duration of diabetes in study subjects ranged from 1- 25 years (Mean 8.87±2.34). There were 34.6% (n = 45) of patients who had duration of diabetes equal to or less than 5yrs. There were 34.6% (n = 45) of patients who had duration of diabetes between 6-10 years, 20% (n = 26) patients had duration of diabetes between 11-15 years and 10.8% (n = 14) patients had duration of diabetes >15 years (Table 1).

Table 1: Distribution Of Age, Gender & Duration Of Diabetes Among Study Subjects (N = 130)

In the present study, CMT in right eye ranged from 189–751 μm with mean value of 260.41±101.66. CMT in left eye ranged from 180–561 μm with mean value of 255.69±88.89 (Table 2).

Among 130 study subjects best corrected visual acuity of right eye was 6/9 or better in 68.5% (n = 89), between 6/12–6/24 in 20.0% (n = 26), between 6/36–6/60 in 8.5% (n = 11) and worse than 6/60 in 3.1% (n = 4). 

Table 2: Descriptive Characteristics of Study Subjects

Best corrected visual acuity of left eye was 6/9 or better in 67.7% (n = 88) subjects, between 6/12–6/24 in 20.8% (n = 27), between 6/36–6/60 in 7.7% (n = 10) and worse than 6/60 in 3.8% (n = 5) (Table 3).

Table 3: BCVA in Study Subjects

Increased CMT in right eye significantly correlated with decreased best corrected visual acuity in the same eye which was found to be statistically significant with a ‘p’ value of <0.01 (Table 4).

Increased CMT in left eye significantly correlated with decreased best corrected visual acuity in the same eye which was found to be statistically significant with a ‘p’ value of <0.01.

Table 4: Association of BCVA with CMT in Right Eye

Table 5: Association of Bcva with Cmt in Left Eye

Present study was done to evaluate the Correlation between Central Macular Thickness (CMT) and Best Corrected Visual Acuity (BCVA) in Patients of Type 2 Diabetes Mellitus present at Ophthalmology OPD of Tertiary Care center. Significant correlations were found between greater central macular thickness and worse best corrected visual acuity in our study (p = <0.01). This was found to be true for both right and left eye. The Diabetic Retinopathy Clinical Research Network reported that the relationship between the visual acuity and central retinal thickness measured by OCT was linear [4]. However, Koleva-Georgieva and Sivkova reported no correlation between the BCVA and retinal thickness [5].

Present study concluded that Increased Central Macular Thickness (CMT) was significantly correlated with decreased Best Corrected Visual Acuity (BCVA) in both eyes among Patients of Type 2 Diabetes Mellitus present at Ophthalmology OPD.

1. Fauci, A. et al. Harrison's Manual of Medicine. 19th ed., New York: McGraw-Hill Education LLC, 2016.

2. Raman, R. et al. “Influence of glycosylated hemoglobin on sight-threatening diabetic retinopathy: a population-based study.” Diabetes Research and Clinical Practice, vol. 92, no. 2, 2011, pp. 168–173.

3. Bowling, B. “Retinal vascular diseases.” Kanski’s Clinical Ophthalmology, 8th ed., China: Elsevier Health Sciences, 2016, pp. 520–528.

4. Diabetic Retinopathy Clinical Research Network. “Relationship between optical coherence tomography-measured central retinal thickness and visual acuity in diabetic macular edema.” Ophthalmology, vol. 114, no. 3, 2007, pp. 525–536.

5. Koleva-Georgieva, D. and N. Sivkova. “Assessment of serous macular detachment in eyes with diabetic macular edema by use of spectral-domain optical coherence tomography.” Graefe’s Archive for Clinical and Experimental Ophthalmology, vol. 247, no. 11, 2009, pp. 1461–1469.