FREQUENCY OF VITREO MACULAR TRACTION IN DIABETIC MACULAR EDEMA ON OPTICAL COHERENCE TOMOGRAPHY.
Objective: To determine the frequency of vitreo macular traction (VMT) in patients of diabetic macular edema (DME) as detected on spectral domain optical coherence tomography (SD-OCT).
Study Design: Cross-sectional study.
Place and Duration of Study: Armed Forces Institute of Ophthalmology (AFIO) Rawalpindi, from May 2013 to Jan 2014.
Patients and Methods: Diabetic patients of 18 years of age with DME and central macular thickness (CMT) of >250 um were included. The patients with idiopathic VMT, history of vitreoretinal surgery, eyes with vitreomacular adherence without signs of traction and eyes with history of other retinal vascular diseases like retinal vein occlusion were excluded from study. After taking history and visual acuity Tropicamide 1% eye drop was instilled one in each eye. For poorly dilating pupils 2.5% Phenylephrine eye drop was also instilled. Fundus was examined using 90 D lens on a slit lamp bio microscope.
The patients with diabetic retinopathy changes and DME were subjected to OCT examination. SD OCT examination was carried out by using Topcon 3-D OCT 1000 (Topcon Corporation). Macular scan was selected and the image was captured using standard 6x6 mm protocol, in which the 3-D acquisition consisted of 64 B-scan slices. Axial resolution was 6 um while transverse resolution was 20 um. A fundus photograph was also obtained at the same time. The image quality index was provided on the screen by the OCT software. Confidentiality of the patient record was maintained. All the findings were endorsed on a pre devised proforma. Evidence of traction was shown as vitreous adherence to the retina associated with tissue elevation and deformity at the traction site. The shape of the inner retina at the site of traction was changed and thus was typically thicker than that of the adjoining edematous retinal tissue.
OCT results were related into three groups (1) Vitreo foveal traction: at the center of macula (fig-1a) (2) Extra foveal traction: vitreoretinal traction elsewhere at the posterior pole in between vascular arcades (3) Epi retinal membrane: diagnosed as difference in the brightness of surface tissues (fig-1b).
Data were analyzed using SPSS version 14. Descriptive statistics were used to calculate mean and standard deviation of age, number of diabetic years and CMT. Percentage was calculated for the presence or absence of VMT and gender.
Seventy one eyes of 68 patients who were fulfilling the inclusion criteria were included in final analysis. Out of them 36 (50.7%) were male and 35 (49.29%) were female. Right eye was involved in 31 (45.5%) patients, left eye was involved in 34 (50%) patients and bilateral involvement was present in 3 (4.5%) patients. Mean age of study population was 53.17 +- 8.79 years (range: 35-70 years) with majority of patients were in their 6th decade of life. Mean duration of diabetes mellitus was 8.5 years +- 3.5 years (range: 2-19 years). Mean CMT was 361.8 +- 109 um. Minimum CMT was 254 um and maximum CMT was 652 um. All the patients had CMT > 250 um.
VMT was detected on OCT examination in 17 (23.9%) eyes. Out of these 17 cases vitreo foveal traction was found in 2 (12%) cases, epi retinal membrane was found in 4 (23%) cases and 11 (65%) cases had extra foveal vitreo macular traction bands (fig-2). Mean CMT in cases with VMT was 386 +- 92 um while mean CMT in cases with no VMT was 355 +- 114 um.
Conventional methods of accessing DME include contact and non-contact slit lamp biomicroscopy, indirect ophthalmoscopy, fluorescein angiography and fundus stereo photography. However, with the advent of OCT, the diagnosis and management of DME has been revolutionized. The relationship between vitreous/posterior hyaloid and macular surface in diabetic retinopathy is very complex. OCT identifies VMI abnormalities including epi retinal membrane and/or VMT with precision. Ghazi et al evaluated OCT characteristics of 48 eyes with persistent clinically significant DME after focal laser treatment and found definite VMI abnormalities in 52.1% of eyes and OCT was found to be 1.94 times more sensitive than traditional techniques in detecting VMI abnormalities7.
In a retrospective study, OCT scans of diabetic patients with macular edema were reviewed and 24% of the cases were associated with vitreofoveal or extra foveal vitreous traction, out of which, 56% had vitreofoveal traction and 44% had extrafoveal traction8. Gandorfer et al looked at the vitreoretinal relationship in diabetic patients with and without DME using OCT and reported that 53% of patients with macular edema had peri foveal PVD, while only 11% of patients without DME had peri foveal PVD9. In DME VMT is a contributing factor which not only aggravates the primary pathology but also worsens the prognosis and has an adverse effect on the vision. In our study, 23.9% of eyes had VMT. Ophir et al, while studying the outcomes of grid laser photocoagulation on diffuse DME detected that in 16.7% of the eyes with treatment failure in terms of increase CMT above baseline level, after initial improvement, was due to presence of extra foveal VMT10.
Khan et al evaluated SD OCT evident ERM and/or partial vitreo macular separation (pVMS) in patients undergoing macular laser photocoagulation for center involving DME and found out that ERM or pVMS was present in 25% of eyes11.
According to Diabetic retinopathy clinical research network, there was reduction in CMT in 93% of eyes which underwent vitrectomy for DME associated with VMT12. Diaz-Llopis et al studied that there was reduction in CMT in 100% of cases who underwent enzymatic vitreolysis for DME associated with evident posterior hyaloid adherence to the retinal surface13. It was found by La Heij et al in one of their studies that the visual acuity improvement after vitrectomy for DME was significantly better in the eyes which did not have laser photocoagulation previously. The author suggested that delay in the vitrectomy and harmful effects of the laser are the causes for poor visual outcomes14. Hence the detection of VMT is important in deciding the mode of treatment.
The current study revealed that a considerable number of cases of DME were associated with VMT with extra foveal VMT (62.5%), ERM (25%) and foveal VMT (12.5%) were the common abnormalities. In this study apart from 2-D B-mode imaging, 3-D images were also analyzed. In a retrospective study association between diffuse DME and extrafoveal vitreous traction was observed in 186 eyes of 121 patients andVMT was found in 45 (24%) eyes. Out of those vitreofoveal traction was detected in 25 (56%) eyes and extrafoveal traction in 20 (44%) eyes7. In that study centrally fixated Automatic 6-radial line program and line group OCT-2000 program was used. The results of our study were comparable with that study. However, in our study, extrafoveal VMT was detected in relatively more number of eyes with DME. This could be because of utilization of 3-D imaging modality in our study. In 3-D image whole vitreoretinal field is imaged so the interface can be observed more clearly.
Jackson et al in a meta-analysis of vitreous attachment in DME found the cumulative prevalence of VMT or taut hyaloid being 18%, with 28.7% of eyes undergoing pars plana vitrectomy had VMT as compared to 12% of non-surgical cases2.In another study sole extrafoveal vitreous traction was found in 34.5% of the patients by using 3-D SD OCT, with extrafoveal sites included both retinal as well as the papillary traction15. Vitreopapillary traction was not included in our results.In our study, two (18%) of the 11 eyes with extrafoveal VMT, no association was found between the underlying retinal thickening and the central macular edema. This finding should be kept in mind while planning for an intravitreal therapeutic agent. It was reported by Arevalo et al that the intra vitreal Bevacizumab injection in eyes with proliferative diabetic retinopathy may lead to tractional retinal detachment or its progression16.
The results of this study provide more insight into the VMI abnormalities in our population, hence providing a rationale for deciding between intra vitreal anti VEGF agents or surgical treatment in patients with DME associated with VMI abnormalities. The limitations of this study were relatively smaller sample size that was not necessarily representing the whole population. Further case control studies are required in our set up to provide more detailed understanding of this intriguing aspect of DME.
Detection of VMT in about a quarter of cases reflects that OCT is a viable tool for early detection of vitreomacular interface abnormalities.
CONFLICT OF INTEREST
This study has no conflict of interest to declare by any author.
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|Publication:||Pakistan Armed Forces Medical Journal|
|Date:||Feb 28, 2017|
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