Dr.Shroff Rahul Ashok, S05342, Dr.Shroff Ashok C, Dr.Anand A Shroff
Introduction
Diabetic retinopathy is an important cause of blindness. Fluorescein angiography is the current gold standard to detect vascular lesions in diabetic retinopathy like microaneurysms, IRMA, capillary non-perfusion and neovascularization. However, it needs intravenous dye injection and has to be carefully performed since patients with severe diabetic retinopathy have comorbidities like diabetic nephropathy and cardiovascular disease, and fluorescein can rarely cause anaphylactic shock. Also fluorescein angiography cannot separately visualise images of the superficial and deep plexus. OCT Angiography is a new non-invasive imaging modality used for mapping the retinal microcirculation that uses split spectrum amplitude decorrelation algorithm. It allows vascular changes to be seen separately in different layers of the retina.
Purpose
To compare the clinical features of OCT Angiography of diabetic maculopathy microaneurysms, capillary non-perfusion, capillary tortousity, neovascularization, capillary loops, size and symmetry of foveal avascular zone(FAZ) in non-proliferative diabetic retinopathy(NPDR) vs proliferative diabetic retinopathy(PDR).
Methods
Retrospective analysis of 26 eyes of 17 patients with non-proliferative diabetic retinopathy and 21 eyes of 13 patients with proliferative diabetic retinopathy. 18 patients were female and 29 patients were male. Exclusion criteris was prior anti-vegf or steroid treatment and any ocular comorbidity like RVO or ARMD. All patients underwent BCVA,78D fundoscopy, SD-OCT and OCT Angiography. OCT Angiography scanning area was 6X6mm section centered around the fovea. Vessel density and FAZ size was calculated using the automated software. Microaneurysms were seen as saccular capillary ends. Capillary non-perfusion was traced as border in which no or few capillaries were observed surrounded by area of normal capillary perfusion. IRMA were seen as irregular superficial capillaries anatomizing with deeper capillaries. Neovascularization was seen at border of inner retina and vitreous cavity. Evaluation was done by a single observer.
Results
The central macular thickness was 327 microns in NPDR group and 334 microns in PDR group. There was no significant difference in the FAZ between the two groups with the with NPDR group being 630 microns and PDR group being 590 microns. Asymetry of FAZ was seen in 23 of 26 (88%) eyes in NPDR group and 17 of 21(80%) eyes in PDR group. However the vessel density was better in the NPDR group with NPDR group having 15%(+/-2) compared with 13%(+/-2) in PDR group suggesting that capillary non-perfusion was greater in the PDR group. Microaneurysms were similar in both group with 24 of 26(92%) eyes in NPDR group and 18 of 21(85%) eyes in PDR group showing microaneurysms. Capillary tortuosity was more common in PDR with 17 of 21 (81%) eyes in PDR group showing tortuosity compared to 11 of 26(42%) eyes in NPDR. IRMA was aslo more common in PDR with IRMA seen in 12 of 21 eyes(57%) in PDR group compared to 4 of 26(15%) eyes in NPDR group. Neovascularization was seen in only 3 of 21(14%) eyes in PDR group. Intraretinal pockets of fluid of hyporeflective cysts were not seen on OCT angiography. Logistic regression showed that the presence of dilated capillaries and IRMA increased the odds of PDR significantly.
Discussion
The current study suggests that OCT Angiography is able to help visualize vascular lesions in different layers of the retina using segmentation. Lesions like IRMA where there is anastomoses between the superficial and deep capillary plexuses can be well seen on OCT angiography. However, neovascularization can only be seen in a small number of eyes with PDR. Eyes with PDR characteristically show more vessel tortuosity and greater areas of capillary non-perfusion.
Conclusion
OCT angiography can visualize characteristic lesions like capillary non-perfusion, vessel tortuosity and neovascularization and give an indication of whether the eye is more likely to have non-proliferative or proliferative diabetic retinopathy. Dilated capillary segments and IRMA were more commonly seen in proliferative diabetic retinopathy.
References
1) Am J Ophthalmol. 2015 Jul;160(1):35-44.e1. doi: 10.1016/j.ajo.2015.04.021. Epub 2015 Apr 18. Optical Coherence Tomography Angiography in Diabetic Retinopathy: A Prospective Pilot Study. Ishibazawa A1, Nagaoka T2, Takahashi A2, Omae T2, Tani T2, Sogawa K2, Yokota H2, Yoshida A2.
2) Ophthalmic Surg Lasers Imaging Retina. 2015 Sep;46(8):796-805. doi: 10.3928/23258160-20150909-03. Optical Coherence Tomography Angiography of Diabetic Retinopathy in Human Subjects. Matsunaga DR, Yi JJ, De Koo LO, Ameri H, Puliafito CA, Kashani AH.
3) ENLARGEMENT OF FOVEAL AVASCULAR ZONE IN DIABETIC EYES EVALUATED BY EN FACE OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY. Takase N, Nozaki M, Kato A, Ozeki H, Yoshida M, Ogura Y. Retina. 2015 Nov;35(11):2377-83. doi: 10.1097/IAE.0000000000000849. PMID:26457396
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