Oman Journal of Ophthalmology

ORIGINAL ARTICLE
Year
: 2014  |  Volume : 7  |  Issue : 3  |  Page : 126--129

Spectral domain optical coherence tomography characteristics in diabetic retinopathy


Laxmi Gella1, Rajiv Raman2, Padmaja Kumari Rani2, Tarun Sharma2,  
1 Department of Optometry, Elite School of Optometry, No. 8, G. S. T. Road, St. Thomas Mount, India
2 Shri Bhagwan Mahavir Vitreoretinal Department, 18, College Road, Sankara Nethralaya, Chennai, Tamil Nadu, India

Correspondence Address:
Rajiv Raman
Consultant, Shri Bhagwan Mahavir Vitreoretinal services, 18, College Road, Sankara Nethralaya, Chennai - 600 006, Tamil Nadu
India

Abstract

Purpose: To report the appearance of diabetic retinopathy lesions using spectral domain optical coherence tomography (SD-OCT). Materials and Methods: A total of 287 eyes of 199 subjects were included. All the subjects underwent complete ophthalmic examination including SD-OCT. Results: The appearance of various lesions of diabetic retinopathy and the retinal layers involved were reported. In subjects with macular edema the prevalence of incomplete PVD was 55.6%. Conclusion: SD-OCT brings new insights into the morphological changes of the retina in diabetic retinopathy.



How to cite this article:
Gella L, Raman R, Rani PK, Sharma T. Spectral domain optical coherence tomography characteristics in diabetic retinopathy .Oman J Ophthalmol 2014;7:126-129


How to cite this URL:
Gella L, Raman R, Rani PK, Sharma T. Spectral domain optical coherence tomography characteristics in diabetic retinopathy . Oman J Ophthalmol [serial online] 2014 [cited 2022 Sep 26 ];7:126-129
Available from: https://www.ojoonline.org/text.asp?2014/7/3/126/142594


Full Text

 Introduction



Diabetic retinopathy (DR) is a major cause of blindness in the working age group worldwide and remains one of the most serious complications of diabetes mellitus. [1] Identification of early changes in cases of DR is important which can help in the diagnosis and management of disease. Newer imaging techniques like spectral domain optical coherence tomography (SD-OCT) with their better resolution are available which aid in assessment of morphological changes. [2]

Ophthalmoscopy, fundus photography and fluorescein angiography (FA) are the common tools to diagnose DR and diabetic macular edema (DME). There is an increasing demand for high-resolution imaging of the ocular tissue to improve the early diagnosis and management of DR. This study aims to report the appearance of various lesions in DR using SD-OCT.

 Materials and Methods



Two hundred and eighty-seven eyes of 199 subjects were included in this study. The study sample includes subjects with diabetes mellitus with or without clinical evidence of DR and normal healthy subjects. This study was approved by institutional review board. Informed consent was obtained from all the subjects after explanation of the nature of the study and details of the procedure. All the subjects underwent a comprehensive eye examination and detailed fundus examination. The severity of DR was graded based on International Clinical Diabetic Retinopathy Disease Severity Scale. [3]

All the patients underwent SD-OCT (Copernicus, Optopol Technologies, Zawierci, Poland). The programs used for the present study were Asterisk scan and 3D scan protocols. For the purpose of this study we used a scan length of 7 mm with 6 B-scans and 3000 A-scans per B-scans through the center of the fovea for the asterisk scan protocol. 3D scan protocol was used with 7 mm scan length with 50 B-scans and 1000 A-scans per B-scan. The structural changes in cases of subjects with different stages of DR were analyzed on grey scale images based on hyper and hypo reflectivity and also the location of the lesions.

We classified the stages of posterior vitreous detachment (PVD) based on the SD-OCT findings. The absence of PVD was diagnosed when the posterior hyaloid was not detected on SD-OCT scan of the macula. Incomplete PVD was diagnosed when the posterior hyaloid remained partially attached to the macula on at least one SD-OCT scan. Complete PVD was diagnosed when posterior hyaloid is visible in the vitreous cavity without any attachment to the macula on all the scans on SD-OCT. Complete PVD was also confirmed with the indirect ophthalmoscopic examination if the posterior hyaloid echo was not visible in the SD-OCT scan.

 Results



The mean age of the study sample was 55.4 ± 8.9 years. The mean duration of diabetes mellitus from diagnosis was 112.1 + 76.6 months. [Table 1] shows the quantitative parameters of various lesions in different stages of DR. Most frequently found lesions in SD-OCT are hard exudates and hemorrhages followed by cystic spaces.{Table 1}

[Table 2] shows qualitative parameters of these lesions in terms of SD-OCT appearance and layers involved. Four morphological patterns of hemorrhages seen on SD-OCT were oval-shaped hyperreflective echos surrounded by hyporeflectivity, medium to high reflective echos causing shadow in the inner retina, high reflective echos at retinal nerve fiber layer and ganglion cell layer causing shadow in case of flame-shaped and organized high reflective membrane at vitreoretinal interface causing shadow in case of subhyaloid hemorrhage.{Table 2}

Prevalence of incomplete PVD was more in subjects with DR [Figure 1]. In subjects with macular edema the prevalence of incomplete PVD was higher i.e, 55.6% and the no PVD was found in 44.4% and we did not see any cases in macular edema with complete PVD.{Figure 1}

 Discussion



In our study we reported appearances of the DR lesions in SD-OCT. Microaneurysms are saccular outpouchings from the sides of cellular capillaries, both on the arteriolar and the venular side. On SD-OCT, they appear as very small medium to high reflective echos causing minimal shadow in the inner retinal layers [Figure 2]a. Hard exudates are lipoprotein deposits and these appear as very high reflective echos [Figure 2]b on SD-OCT which cast a shadow on the posterior layers making us difficult to visualize the underlying layers. These hard exudates are present in inner and outer, nuclear and plexiform layers.

Cystic spaces appear as optically empty spaces [Figure 2]c and these involve the layers from outer nuclear layer (ONL) to the ganglion cell layer (GCL). Histopathologic studies have suggested that the development of macular edema is initiated by fluid accumulation within Muller cells. If the accumulation continues, or remains chronic, then at some point death of the Muller cells occurs and may result in the formation of large cystoid cavities, or cystoid macular edema. [4]{Figure 2}

Hemorrhages can be located pre-, intra- or subretinally. Various patterns of the hemorrhages can be observed by SD-OCT. In our study we observed 4 different patterns. Most commonly observed pattern was oval shaped hyper reflective echo surrounded by hypo reflective echo in the inner retinal layers causing shadow and this involves ONL, outer plexiform layer (OPL), inner nuclear layer (INL), inner plexiform layer (IPL) and GCL [Figure 3]a. This pattern of appearance may be due to the resolving stage of hemorrhages. Another pattern was medium reflective echos causing shadowing in the inner retina. On ophthalmoscopy when the hemorrhages are present in the retinal nerve fiber layer (RNFL) they appear as flame shaped and in SD-OCT these appear as high reflective spots at the RNFL layer causing shadowing. These should not be misinterpreted as the normal blood vessels in the retina which also appear as high reflective echos in the RNFL causing shadowing. In the cases of subhyaloid hemorrhage, the SD-OCT shows the presence of a high reflective lesion consistent with blood which is localized and causing shadowing of the underlying retinal layers which is similar to the findings reported in the case reported by Punjabi et al. [5] Due to the collection of blood in the most dependent position of the subhyaloid space with the gravity, the horizontal level of the blood is seen as the straight line in SD-OCT, beyond which it causes shadowing on the inner retinal layers. In [Figure 3]b small arrow shows a thin bright line above the internal limiting membrane that approximates the organized blood. This could possibly be fibrous tissue that forms a capsule around the blood, but the exact nature of this bright band is unknown.{Figure 3}

On SD-OCT cotton wool spots appear as hyperreflective, nodular or elongated lesion in the RNFL [Figure 3]c and also involving the GCL, which cast shadow on the posterior layers. This appearance is assumed to reflect focal swelling of the nerve fibers, [6] which is due to intracellular fluid and organelles accumulated secondary to interrupted axoplasmic flow.

Only in two eyes the SD-OCT was able to pick up the characteristic appearance of capillary non-perfusion (CNP) area. SD-OCT showed a thinning of inner retinal layers [Figure 4]a than the normal retina. This might be due to the reason that the inner retinal layers may be particularly at risk to hypoxic insult because they are supplied with oxygen from the retinal vasculature, which is relatively sparse compared with the choroidal circulation, which supplies most of the outer retina. [7]{Figure 4}

Proliferative DR is characterized by either neovascularization of the disc or elsewhere. Preretinal neovascularization on SD-OCT can be detected as a preretinal high reflective membrane occasionally causing shadow [Figure 4]b. This appearance is due to the presence of some amount of fibroglial tissue. [8]

SD-OCT brings new insights into morphological changes of the retina in DR. It enhances the ability to exactly identify the epiretinal membranes (ERM), vitreomacular traction and the posterior hyaloid status. In our study incomplete PVD i.e, with macular attachment was the most frequent condition found in subjects with macular edema (55.6%) which was similar to the study results of Gaucher et al. [9] On SD-OCT, the posterior hyaloid was thin and minimally reflective. The high prevalence of incomplete PVD might have been induced by the DME itself. The breakdown of inner blood-retinal barrier in cases of DME might have lead to the accumulation of cytokines or other mediators in the posterior vitreous cortex, which might have triggered the PVD. Another reason might be that the incomplete PVD with macular attachment may directly contribute to the development of DME.

In subjects with DR, secondary ERM can develop due to the epimacular proliferating fibroglial tissue. It appears as a hyperreflective band on the inner surface of the retina. In the starting stage it has a global retinal adherence later it causes tractional force on the retina leading to macular edema and due to it discontinuous attachment to the retinal surface causes internal limiting membrane folds.

 Conclusion



Structural abnormalities in diabetic retinopathy can be detected and characterized by SD-OCT. It compliments FA in understanding the pathology and managing it accordingly.

References

1Kristinsson JK. Diabetic retinopathy. Screening and prevention of blindness. A doctoral thesis. Acta Ophthalmol Scand Suppl 1997;223:1-76.
2Nittala MG, Laxmi G, Raman R, Rani PK, Bhargava A, Pal SS, et al. Spectral-Domain OCT and Microperimeter characterization of morphological and functional changes in X-linked Retinoschisis. Ophthalmic Surg Lasers Imaging 2009;40:71-4.
3Wilkinson CP, Ferris FL 3 rd , Klein RE, Lee PP, Agardh CD, Davis M, et al. Proposed international clinical diabetic retinopathy and diabetic macular edema disease severity scales. Ophthalmology 2003;110:1677-82.
4Kim BY, Smith SD, Kaiser PK. Optical coherence tomographic patterns of diabetic macular edema. Am J Ophthalmol 2006;142:405-12.
5Punjabi OS, Flynn HW Jr, Knighton RW, Gregori G, Couvillion SS, Lalwani GL, et al. Spectral domain optical coherence tomography for proliferative diabetic retinopathy with subhyaloid hemorrhage. Ophthalmic Surg Lasers Imaging 2008;39:494-6.
6Bek T, Lund-Andersen H. Cotton-wool spots and retinal light sensitivity in diabetic retinopathy. Br J Ophthalmol 1991;75:13-7.
7Unoki N, Nishijima K, Sakamoto A, Kita M, Watanabe D, Hangai M, et al. Retinal sensitivity loss and structural disturbance in areas of capillary nonperfusion of eyes with diabetic retinopathy. Am J Ophthalmol 2007;144:755-60.
8Lang GE. Diabetic Retinopathy: Optical coherence tomography findings in diabetic retinopathy. Dev Ophthalmol 2007;39:31-47.
9Gaucher D, Tadayoni R, Erginay A, Haouchine B, Gaudric A, Massin P. Optical coherence tomography assessment of the vitreoretinal relationship in diabetic macular edema. Am J Ophthalmol 2005;139:807-13.