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 Table of Contents  
ORIGINAL ARTICLE
Year : 2019  |  Volume : 57  |  Issue : 1  |  Page : 21-23

Functional and structural changes in the macula in diabetic retinopathy – A correlative study


Department of Ophthalmology, Mahatma Gandhi Medical College and Research Institute, Sri Balaji Vidyapeeth, Puducherry, India

Date of Web Publication10-Jun-2019

Correspondence Address:
Dr. Krishnagopal Srikanth
Department of Ophthalmology, Mahatma Gandhi Medical College and Research Institute, Sri Balaji Vidyapeeth, Puducherry - 607 402
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/tjosr.tjosr_9_19

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  Abstract 


Aim: The aim is to study the correlation of macular thickness and sensitivity in type 2 diabetes mellitus patients. Materials and Methods: A cross-sectional comparative study was done on 77 eyes with diabetic retinopathy. Patients were divided into three groups as follows: Group 1 – Diabetic retinopathy without maculopathy, Group 2 – Diabetic maculopathy without clinically significant macular edema (CSME), and Group 3 – CSME. Microperimetry was used to assess macular sensitivity, and optical coherence tomography (OCT) was used to measure retinal thickness. Comparison of retinal sensitivity and thickness was done between groups. Correlation of these parameters to duration of diabetes was also done. Results: The mean macular sensitivity (in dB) in Groups 1, 2, and 3 was 11.57, 11.51, and 8.03, respectively. The mean central macular thickness in Groups 1, 2, and 3 was 199.33, 208.62, and 334.25 μm, respectively. There was statistically significant difference in macular thickness and in macular sensitivity between Groups 1 and 3 (P < 0.001) and between Groups 2 and 3 (P < 0.001). This difference was not statistically significant between Groups 1 and 2 (P > 0.09). Macular sensitivity had a moderate correlation with macular thickness, which was statistically significant (P < 0.001). Conclusions: Macular sensitivity was found to decrease with increasing macular thickness.

Keywords: Macular sensitivity, macular thickness, microperimetry


How to cite this article:
Senthil RP, Srikanth K, Jha KN, Rajalakshmi A R. Functional and structural changes in the macula in diabetic retinopathy – A correlative study. TNOA J Ophthalmic Sci Res 2019;57:21-3

How to cite this URL:
Senthil RP, Srikanth K, Jha KN, Rajalakshmi A R. Functional and structural changes in the macula in diabetic retinopathy – A correlative study. TNOA J Ophthalmic Sci Res [serial online] 2019 [cited 2019 Nov 11];57:21-3. Available from: http://www.tnoajosr.com/text.asp?2019/57/1/21/259889




  Introduction Top


The complications of diabetes mellitus in retina ranges from a spectrum of nonproliferative diabetic retinopathy (NPDR) to PDR to diabetic macular edema (DME) to clinically significant macular edema (CSME).

Patients with CSME are a subset of patients with DME who fulfill the criteria defined by early treatment diabetic retinopathy study (ETDRS).

Recent studies suggest that retinal sensitivity decreases even before diabetic retinopathy becomes clinically evident.[1] Microperimetry evaluates the sensitivity of the retina while the fundus is directly visualized, thereby an exact correlation between macular pathology and the corresponding functional defect is established. This study aims to assess the thickness of macula using optical coherence tomography (OCT) in patients with type 2 diabetes mellitus and correlate it with the macular sensitivity evaluated by microperimetry, thus identifying the neuronal damage before vascular damage is seen clinically.

We have studied the correlation of macular thickness and macular sensitivity in the eyes of patients with type 2 diabetes mellitus. The objectives were to quantify macular thickness and sensitivity, to correlate the relationship between the two, and to correlate them with duration of disease, presence of macular edema, and severity of macular edema.


  Materials and Methods Top


A cross-sectional comparative study was performed on the eyes of patients with type 2 diabetes mellitus visiting the ophthalmology department of a tertiary care hospital. The study was approved by the Institutional Human Ethics Committee and adhered to the principles in the Declaration of Helsinki. Informed consent was obtained from each participant. All patients with type 2 diabetics presenting to the ophthalmology department with a minimum visual acuity >2/60 were included. This level of visual acuity ensured fixation during microperimetry. Patients unable to undergo microperimetry, with preexisting retinal diseases, with ocular diseases that affect retinal sensitivity, inadequate ocular media transparency to obtain good quality OCT images and attention disorder were excluded from the study.

All patients included in this study underwent complete ophthalmological examination. Recording of best-corrected visual acuity, intraocular pressure measurement by Goldmann applanation tonometry, and anterior and posterior segment examination by slit-lamp biomicroscopic examination including +90 diopter lens after pupillary dilatation with tropicamide 1% and phenylephrine 2.5% was carried out. Microperimetry was done using a square 5 × 5 pattern, duration of 200 ms, interval of 2 s, and size of Goldmann III and 4–2 strategy (Optos, Florida, USA) and recorded in decibels (dB). Macular thickness was measured by spectral-domain OCT (Optos, Florida, USA) and recorded in microns. The eyes were divided into no maculopathy, diabetic maculopathy, and CSME groups. We followed ETDRS classification for classifying retinal changes.

Eyes with no obvious diabetic retinopathy changes in the macula were categorized into Group 1. Eyes which fulfilled the following criteria of CSME were categorized into Group 3:

  • Retinal thickening within 500 μm of the center of the macula
  • Hard exudates within 500 μm of the center of the macula, if associated with retinal thickening
  • Retinal thickening of one disc area (1500 μm) or larger, any part of which lies within one disc diameter of the center of the macula.


Eyes which had either diabetic maculopathy changes or diabetic macular edema which were not present within 500 μm of the fovea or not fulfilling the other criteria of CSME were categorized into Group 2.

Statistical analysis was done by SPSS, version 2.0 (IBM, Armonk, New York, U.S.A). For continuous data, we calculated mean with standard deviation, range, and 95% confidence interval. The central macular thickness (CMT) and retinal sensitivity between the three groups were compared by ANOVA followed by post hoc tests. The correlation between CMT, retinal sensitivity, and duration of diabetes was done using Pearson's correlation. P < 0.05 was considered statistically significant.


  Results Top


Seventy-seven eyes of 40 patients were studied. Twenty-nine (72.5%) males and eleven (27.5%) females were included. The mean age in the study group was 52.72 ± 9.11 years. The retinal sensitivity and macular thickness details are shown in [Table 1]. There was statistically significant difference (P < 0.001) in macular thickness and in macular sensitivity between Groups 1 and 3 and between Groups 2 and 3. This difference was not statistically significant between Groups 1 and 2 (P > 0.09) [Table 2].
Table 1: Macular sensitivity and thickness of study groups (n=77)

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Table 2: P value for macular thickness and sensitivity

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Macular sensitivity had a moderate negative correlation with macular thickness which was statistically significant (P < 0.001). However, duration of diabetes was found to have very weak correlation with both macular sensitivity and thickness, and it was not statistically significant [Table 3].
Table 3: Pearson's correlation

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  Discussion Top


Interventions in diabetic retinopathy depend on the detection of evident changes in the retina. With advances in imaging in functional assessment, clinicians aim to detect anatomical and functional changes before retinopathy manifests clinically. Our study found that macular sensitivity decreased with an increase in macular thickness.

Few studies are available in the literature on OCT-based macular tomography and evaluation of retinal sensitivity using microperimetry in diabetic patients. We have only one such report on Indian population in diabetics. This study reports some evidence of early neuronal damage before the clinical evidence of diabetic retinopathy.[1] Vujosevic et al. found that the thickness of macula gradually increases as the severity of diabetic retinopathy increases and consequently sensitivity of the macula decreases down while progressing from clinically no macular edema to CSME.[2] This finding was in line with our study.

Retinal thickening results from microangiopathic changes in diabetic retinopathy such as basement membrane thickening and selective loss of pericytes leading to endothelial barrier decompensation resulting in serum leakage and retinal edema.[3] Retinal sensitivity decreases because of the neuronal damage that occurs in diabetic retinopathy. Some postulated mechanisms are increased apoptosis, glial cell reactivity, microglial activation, and altered glutamate metabolism. Retinal ganglion cells are affected earliest.[4] Elevated rate of cell death is also seen in the outer nuclear layer, photoreceptors, and retinal pigment epithelium. Increased levels of glutamate and overexpression of the RAS system play an essential role in the neurodegenerative process in diabetic retinopathy.[5]

Okada et al. postulated that the mean sensitivity of the retina in the central 2° and 10° was significantly lower in patients who had developed DME than in normal persons.[6] Our study also concurred similar results. It was also noted that duration of diabetes had no significant effect on retinal thickness and sensitivity. This is in accordance with previous studies.[7]

Small sample size, lack of follow-up, and lack of correlation with visual acuity were the limitations of this study.


  Conclusions Top


Our study shows that the mean macular sensitivity and macular thickness between study populations without CSME and with CSME are statistically significant. Moderate negative correlation exists between macular thickness and sensitivity. Duration of diabetes bears no correlation with macular thickness and sensitivity. Microperimetry is a useful tool in the assessment of macular function in diabetics.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Verma A, Raman R, Vaitheeswaran K, Pal SS, Laxmi G, Gupta M, et al. Does neuronal damage precede vascular damage in subjects with type 2 diabetes mellitus and having no clinical diabetic retinopathy? Ophthalmic Res 2012;47:202-7.  Back to cited text no. 1
    
2.
Vujosevic S, Midena E, Pilotto E, Radin PP, Chiesa L, Cavarzeran F, et al. Diabetic macular edema: Correlation between microperimetry and optical coherence tomography findings. Invest Ophthalmol Vis Sci 2006;47:3044-51.  Back to cited text no. 2
    
3.
American Academy of Ophthalmology. Retina and Vitreous. Vol. 12. San Francisco; American Academy of Ophthalmology; 2017.  Back to cited text no. 3
    
4.
Barber AJ. A new view of diabetic retinopathy: A neurodegenerative disease of the eye. Prog Neuropsychopharmacol Biol Psychiatry 2003;27:283-90.  Back to cited text no. 4
    
5.
Villarroel M, Ciudin A, Hernández C, Simó R. Neurodegeneration: An early event of diabetic retinopathy. World J Diabetes 2010;1:57-64.  Back to cited text no. 5
    
6.
Okada K, Yamamoto S, Mizunoya S, Hoshino A, Arai M, Takatsuna Y. Correlation of retinal sensitivity measured with fundus-related microperimetry to visual acuity and retinal thickness in eyes with diabetic macular edema. Eye Lond Engl 2006;20:805-9.  Back to cited text no. 6
    
7.
Sng CC, Cheung CY, Man RE, Wong W, Lavanya R, Mitchell P, et al. Influence of diabetes on macular thickness measured using optical coherence tomography: The Singapore Indian eye study. Eye (Lond) 2012;26:690-8.  Back to cited text no. 7
    



 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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