Swept-Source OCT Analysis of the Margin of Choroidal Coloboma

Journal Pre-proof Swept Source Optical Coherence Tomography Analysis of the Margin of Choroidal Coloboma : New Insights Dr Shreyans Jain, MD, FRCS, Dr Vinod Kumar, MS, FRCS, Dr Nitesh Salunkhe, MBBS, MD, Dr Ruchir Tewari, MBBS, MD, Dr Parijat Chandra, MBBS, MD, Dr Atul Kumar, MD, FRCS PII:

S2468-6530(19)30537-8

DOI:

https://doi.org/10.1016/j.oret.2019.08.010

Reference:

ORET 611

To appear in:

Ophthalmology Retina

Received Date: 23 April 2019 Revised Date:

7 August 2019

Accepted Date: 18 August 2019

Please cite this article as: Jain S., Kumar V., Salunkhe N., Tewari R., Chandra P. & Kumar A., Swept Source Optical Coherence Tomography Analysis of the Margin of Choroidal Coloboma : New Insights, Ophthalmology Retina (2019), doi: https://doi.org/10.1016/j.oret.2019.08.010. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © YEAR Published by Elsevier Inc. on behalf of American Academy of Ophthalmology

Title Page Original full-length article Title: Swept Source Optical Coherence Tomography Analysis of the Margin of Choroidal Coloboma : New Insights Short Title: Choroidal Coloboma Authors’ information : 1. Dr. Shreyans Jain1 MD, FRCS 2. Dr. Vinod Kumar1 MS, FRCS 3. Dr. Nitesh Salunkhe1 MBBS, MD 4. Dr. Ruchir Tewari1 MBBS, MD 5. Dr. Parijat Chandra1 MBBS, MD 6. Dr. Atul Kumar1 MD, FRCS Institution: Dr. RP Centre for ophthalmic sciences, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India 110029 Corresponding author :Vinod Kumar Address:Dr RP Centre for ophthalmic sciences, All India Institute of Medical Sciences, Ansari Nagar, New Delhi, India 110029 Phone no.: 91-9868420620 E-mail: [email protected] The study was conducted at Dr. Rajendra Prasad Centre for Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi – 110029, India Conflict of Interest: No conflicting relationship exists for any author.

1

Abstract

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Title: Swept Source Optical Coherence Tomography Analysis of the Margin of

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Choroidal Coloboma : New Insights

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Purpose: To study the retinal architecture and vitreo-retinal interface at the edge of choroidal

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colobomata using swept source optical coherence tomography (SS-OCT).

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Design: Prospective observational case series at a tertiary eye care center.

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Participants: Patients of choroidal coloboma presenting to ophthalmology department and

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fulfilling the inclusion criteria of the study.

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Testing: SS-OCT was done in 30 eyes of 20 patients of choroidal coloboma.

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Main Outcome Measures: The primary objective was to describe the OCT features at the

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margin of coloboma.

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Results:

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previously described findings. Two types of transition from normal retina into intercalary

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membrane (ICM) were noted i.e. abrupt (73.33%) and. gradual (26.67%). Outer retinal layers

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(interdigitation zone and ellipsoid zone) terminated at a variable distance before the RPE in

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56.67% of eyes. Cystic spaces in ICM (46.67%), schisis like spitting of ICM (30%) and

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breaks in ICM (6.67%) were seen as well. Subclinical retinal detachment was also noted in

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one eye. The peculiar features noted at vitreo-retinal interface included vitreous attachment at

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coloboma margin (23.33%), vitreous condensation (6.67%) and hill like projections of ICM

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into the vitreous cavity (26.67%). In the region of coloboma, sclera and tenon’s capsule could

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also be analyzed as a hyper-reflective lamellar structure and irregularly arranged less hyper-

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reflective structure.

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Conclusion: SS-OCT of the coloboma margin has revealed various new features in addition

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to those previously described. The detection of subclinical retinal detachment or early

SS-OCT of the coloboma margin revealed new features in addition to the

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termination of outer retinal layers in selected cases may be helpful in guiding new

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management protocols.

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Introduction

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Irido-fundal coloboma is a congenital abnormality caused by defective closure of embryonic

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fissure during 5th – 7th weeks of fetal life. The incidence of choroidal coloboma in general

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population has been reported to be 0.14% and these can be sporadic or transmitted as an

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autosomal recessive, autosomal dominant or X-linked trait.1,2 Cataract, microphthalmos and

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anophthalmos are frequent ocular associations of coloboma. The severity of visual disability

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in these cases is dependent on many factors including the size and extent of coloboma,

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associated anomalies of the globe such as microphthalmos and nystagmus and the presence of

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rhegmatogenous retinal detachment (RRD). RRD may occur in 4-40% of the eyes that have

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choroidal coloboma.3,4 The retinal breaks in these cases may occur in the intercalary

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membrane (ICM), at the junction of coloboma and retina and/or in the normal retina outside

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the coloboma.5,6

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Swept-source optical coherence tomography (SS-OCT) is the latest milestone in retinal and

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choroidal imaging. To overcome scattering by the retinal pigment epithelium (RPE), which

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disables visualization of deeper lying structures, a longer wavelength has been adopted for

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this machine (1050 nm vs. 840 nm in SD-OCT). Higher resolution (1 µm) and scanning

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speed (100000 A scans/sec) enables acquisition of wider field B-scans (12 mm vs. 6–9 mm

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with conventional SD-OCT) and more accurate imaging of the vitreous, retina, and choroid

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simultaneously.10,11,

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There are only few studies so far which have evaluated the OCT features at the edge of

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choroidal coloboma. The various OCT features described by these studies include type of

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transition, subclinical retinal detachment, cystoid spaces, hump effect, noticed ‘Y’ shaped

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intercalary membrane, cystic spaces, vitreous adhesions, etc.7,8,9

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The purpose of this study was the detailed assessment of vitreo-retinal and chorio-retinal

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interface at the edge of choroidal coloboma using SS-OCT platform which allows better

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visualization of the deeper layers as described above.

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Materials and methods

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This is a prospective observational case series conducted at Dr. Rajendra Prasad Centre for

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Ophthalmic Sciences, All India Institute of Medical Sciences, New Delhi, India during the

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period January 2017 to June 2018. The study adheres to the tenets of the Declaration of

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Helsinki and approval was obtained from the Institutional Ethics Committee of the All India

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Institute of Medical Sciences. Informed consent was obtained from all the patients.

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Patients of choroidal coloboma were recruited from the Retina Services and outpatient

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department of Dr. Rajendra Prasad Centre for Ophthalmic Sciences. Patients with history of

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previous intervention in the form of laser or surgery were excluded. Patients with retinal

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detachment and those who were unable to fixate e.g. nystagmus were also excluded. Detailed

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ophthalmic workup was performed including best-corrected visual acuity (BCVA), slit lamp

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examination, intraocular pressure (IOP) and dilated fundus examination. Type of coloboma

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was also noted according to Ida Mann classification.13 Color fundus photographs and SS-

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OCT were performed using DRI OCT Triton (Topcon Medical Systems, Oakland, NJ, USA)

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by a single Investigator (VK). In all the patients, twelve radial line scans (12 × 12 mm)

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passing through the coloboma margin were obtained, which were analyzed for qualitative

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features at the edge of the coloboma.

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Results

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On the basis of inclusion and exclusion criteria, 30 eyes of 20 patients with choroidal

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coloboma were included in the study. The mean age of the patients was 26.79 ± 18.97 years

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(range 9-72 years). There were 13 males (65%) and 7 (35%) females. Three patients had

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coloboma affecting only one eye. 17 patients had bilateral coloboma but in 7 patients OCT

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images of one eye could not captured due to poor fixation.

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Type of coloboma

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As per Ida Mann classification13, 8 eyes had type 1 coloboma, 9 eyes had type 2 coloboma

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and 8 eyes had type 3 coloboma. Type 5 coloboma was also found in 4 eyes while one eye

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had both type 3 and 5 coloboma.

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The following important features were observed after correlating clinical photographs with

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SS-OCT images:

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1. Transition Zone (coloboma margin)

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Two characteristic types of transition from normal retina to intercalary membrane were

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noted:

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a. Abrupt: It was characterized by sudden transformation from normal layered

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architecture of retina at coloboma margin to featureless intercalary membrane

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(Figure 1 a,c). It was not possible to differentiate any of the retinal layers in the

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intercalary membrane.This feature was noted in 22 eyes (73.33%).

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b. Gradual: In this type of transition, normal layered architecture of retina continued

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for some distance in ICM beyond coloboma margin before ending up into un-

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stratified ICM (Figure 1 b,d). It was noted in 8 eyes (26.67%).

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2. Outer retinal layers terminated earlier than RPE

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In 17 eyes (56.67%), the interdigitation zone (IZ) and ellipsoid zone (EZ) did not extend

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all the way upto the margin of coloboma and ended at a variable distance before the

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RPE (Figure 2).

3. Subclinical retinal detachment

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Subclinical (not visible clinically) retinal detachment beyond the coloboma margin was

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noted in one eye (3.33%) of a patient (Figure 3). Cystic spaces were also observed in

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outer retinal layers of adjacent normal retina in this patient .

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4. Cystic spaces

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Cystoid spaces were observed in both ICM region as well as normal retina. 14 (46.67%)

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eyes showed cystic spaces in ICM region (Figure 4). In only one eye out of these, the

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location of cystoid spaces could be made out at the level of inner nuclear layer. 2 eyes

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showed cystic spaces in the region of normal retina at the level of inner nuclear/outer

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plexiform layer. In one eye out of these, cystic spaces were associated with subclinical

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RD (Figure 3).

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5. Schisis in ICM vs ICM detachment

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Splitting of ICM into schisis like cavity was noted in 9 eyes (30 %) (Figure5).This was

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associated with cystoid changes in inner leaf of ICM and was associated with splitting

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of ICM at multiple levels.

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6. Break in ICM

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In 2 eyes, break in ICM (6.67%) could be captured on OCT. While one case showed a

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full thickness hole along with schisis of ICM (Figure 6a,b), in the other case full-

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thickness ICM break was characteristically located at macula as it was corresponding

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with yellow pigment observed on clinical examination (Figure 6c,d).

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7. Hump effect

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This feature wascharacterized by sudden inward turning of the eye wall just before

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coloboma margin and was observed in 6 (20%) eyes (Figure 7a,b). In 2 eyes it was

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associated with retinal thickening at the margin.

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8. Vitreoretinal Interface

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The following peculiar features at vitreoretinal interface were observed on OCT images:

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a. Partial Posterior Vitreous Detachment: In 7 eyes (23.33%) PVD was observed over

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the normal retina as well as over coloboma region with vitreous still attached at the

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coloboma margin (Figure 8a).

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b. Vitreous condensation: Two eyes showed localized vitreous condensation over the coloboma region (Figure 8b).

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c. ICM projections / Hill effect: In 8 eyes peak like projections of ICM were observed

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in the coloboma region however no attachments of vitreous were seen over it.

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(Figure 8c).

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9. Scleral lamellae

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On OCT, sclera was observed as a hyper-reflective structure with lamellar arrangement

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while episclera appeared as a uniform but less hyper-reflective tissue (Figure 9a). Fibres

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of Tenon’s capsule demonstrated loose irregular arrangement interspersed with multiple

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hyperreflective dots of orbital fat/ soft tissue (Figure 9b). In one eye, single hypo-

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reflective scleral cleft was observed in between scleral lamellae (Figure 9a).

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Discussion

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The colobomatous region is characterized by the absence of choroid, RPE and outer retinal

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layers. The colobomatous area is covered by an intercalary membrane whose architecture

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may be layered or non-layered. Previous histopathological studies have shown that choroid

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and RPE end at the coloboma margin while there is splitting of neurosensory retina into two

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layers. The inner layer continues as ICM while outer layer fuses with RPE, junction being

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termed as locus minoris resistanae (LMR). The thickness of ICM may vary in different

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patients but usually there is gradual thinning of ICM from coloboma margin towards ora

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serrata.14,15

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Retinal detachments in eyes with choroidal coloboma are commonly the result of breaks in

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ICM with absence of peripheral retinal breaks. This fact strongly supports the communication

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between sub ICM space and subretinal space through LMR. OCT, by providing in vivo cross

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sectional images of retina at coloboma margin, can reveal some important information

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regarding pathogenesis of RD in these eyes; therefore we conducted this study of SS-OCT

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evaluation of edge of coloboma.

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Though margin of the coloboma has been studied using SD-OCT, we conducted this study using

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SS-OCT as the latter has certain advantages when it comes to studying subtle details in outer

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retina and choroid. It allows deeper penetration into the choroid and sclera with less signal

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decay, thereby providing better visualization of the vitreo-retinal and choroido-scleral

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interface at the same time. Additionally, it is possible to acquire longer scans without image

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inversion or mirror-image artifacts. This is useful in patients with coloboma as there is

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sudden change in the depth at the edge of coloboma. More number of A-scans per second

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(1,00,000/sec) allows good quality images even in patients with nystagmus, which is

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commonly seen in patients with coloboma.

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In this study, we noted two types of transition at the coloboma margin: abrupt and gradual.

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Abrupt transition was characterized by sudden transformation from layered architecture of

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neurosensory retina to featureless ICM while in gradual transition, normal layered

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architecture of inner retina is maintained for some distance before culminating into a

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featureless ICM. These transition types have been described previously as well. Gopal et al7,8

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reported the occurrence gradual transition (63.33%) more often than abrupt transition

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(36.67%).We however found abrupt transition (73.33%) more common than the gradual

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(26.67%). Medrano et al9 in their case series of 5 eyes using SS-OCT, had noticed abrupt

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transition in 3 eyes while gradual transition was seen in 2 eyes.

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As described above, histopathological reports suggest that at the coloboma margin outer

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layers of retina roll back and merge with the RPE.14,15 Contrary to this we noticed two

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entirely different features on OCT. Firstly, outer retinal layers (IZ and EZ)ended up in

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approximation with RPE instead of merging with RPE. Another striking feature was the

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distinct termination of IZ and EZ before the RPE in 17 eyes. This points towards the

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possibility of the absence of photoreceptors at the coloboma margin. This implies that one or

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two rows of prophylactic laser photocoagulation can be done safely at the edge of coloboma,

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without causing any damage to visual function.

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Subclinical RD associated ICM detachment has been reported by Gopal et al in 3 eyes.7,8 We

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also observed subclinical RD along the margin of coloboma in one eye along with ICM

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detachment/schisis. Similar to their cases, in our case too the detached ICM was taut. Gopal

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et al hypothesized that these detachments could be purely tractional. With continued traction,

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a communication between subretinal and sub-ICM space could be formed and progression to

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clinical RD (secondary RRD) would take place. Though ICM was taut in our case as well, the

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configuration of subclinical RD was convex (consistent with RRD). This suggests that their

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theory of taut ICM as cause of break in LMR might be true but RD to be tractional at the

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beginning does not match with configuration and OCT findings. Early detection of RD at the

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coloboma edge and its prophylactic treatment with laser photocoagulation may help to

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prevent visual loss in these eyes. However it is not possible to scan the entire edge of

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coloboma with the present technology.

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We noticed a novel feature in the form of presence of schisis like splitting of ICM in 9 eyes.

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Three eyesin our series were found to have ICM detachment clinically.All three of these eyes

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were actually found to have schisis of ICM on SS OCT. This suggests that all the cases of

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clinically diagnosed ICM detachment may not be pure detachment. Though Medrano et al9

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had not used the term schisis but they noticed “Y” shaped retina in the coloboma region

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simulating schisis like cavity. Gopal et al7 had mentioned about the ICM detachment in their

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series but they did not notice any schisis in ICM. We could detect this schisis due to higher

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resolution images captured by SS-OCT. One possible hypothesis for ICM schisis could be

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traction due to taut ICM or it may be due to ICM degeneration.

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Similar to studies by Gopal et al7,8 and Medrano9et al, cystic spaces were observed in our

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case series. Cystic spaces in attached ICM may represent the early stage of ICM schisis. The

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cause of cystic spaces in ICM may be tissue loss due to degeneration or it may be due to

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traction over ICM as discussed above. The presence of cystic space in subclinical RD may

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due to chronic inflammation.

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Hump effect is caused by inward turning of the eye wall just before the coloboma margin.

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Though it would be difficult to pinpoint the exact cause, we hypothesize it to be caused by

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either the same developmental factors, which are involved in coloboma formation or may be

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due to strong vitreoretinal traction. Gopal et al also observed this feature in 5 eyes with some

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eyes associated with thickening of the retina exaggerating the hump effect.7 Gopal et al

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hypothesized that this feature may have a bearing on the ease with which laser burns can be

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placed on the margin of the choroidal coloboma.

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Partial PVD was noted in 7 eyes. In all the cases vitreous was attached at the margin of

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coloboma with PVD present on both sides of coloboma i.e. over the normal retina as well as

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colobomatous area. Medrano et al9 also observed partial PVD but with strong vitreoretinal

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adhesion to the inner wall of coloboma. This correlates with the strong vitreoretinal adhesion,

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which we usually notice at the time of PVD induction during surgery in coloboma eyes.

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Other two peculiar features noted were the presence of peak like projections of ICM in 8 eyes

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and peculiar whorl like vitreous condensation in the coloboma region in one eye. All these

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findings suggest about abnormal vitreo-retinal interactions in eyes with fundal coloboma that

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could contribute towards increased incidence of retinal detachment in these eyes.

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In our study, we observed the presence of marked posterior bowing of sclera in 10 eyes, a

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feature that is usually seen in high myopia as well.16,17 But contrary to high myopia where

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sclera is thin in most of the cases, thinning was present in only 2 cases in our study. This

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points towards different pathophysiology involved in posterior bending of sclera which may

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be due to decreased eye wall strength caused by loss of outer retina, RPE and choroid. It also

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raises the suspicion that not only the outer retina and choroid, sclera may also be affected in

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choroidal coloboma patients.

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This study has some inherent limitations. Firstly, eyes with retinal detachment were excluded,

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limiting the information acquired regarding the features and pathophysiology of retinal

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detachment in coloboma patients. Secondly, the evaluation of entire margin of coloboma is

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not feasible. Therefore it is highly possible that the features present in some eyes would have

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been missed in other eyes.

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To conclude, high resolution SS-OCT images allow detailed in vivo evaluation of transition

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in various individual layers of retina at coloboma margin. The findings of early termination

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of outer retinal layers can be helpful in formulation of new guidelines for prophylactic laser

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in selected cases. It can be used as an important tool for early detection of subclinical retinal

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detachment. The other features like hill effect, posterior bowing of sclera etc. suggest that

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further studies with larger cohort are required for better understanding of their clinical

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significance.

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Acknowledgment

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We acknowledge the contribution of Ms. Shilky Singh (M. Optom.) and Ms. ZainabJawaid

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(M. Optom.) for the technical help provided.

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References

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1. Jesberg DO, Schepens CL. Retinal detachment associated with coloboma of the choroid. Arch Ophthalmol 1961;65:163-73. 2. Chang L, Blain D, Bertuzzi S, Brooks BP. Uveal coloboma clinical and basic science update. CurrOpinOphthalmol 2006; 17: 447–470.

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3. Jesberg DO, Schepens CL. Retinal detachment associated with coloboma of the choroid. Arch Ophthalmol 1961;65:163-73. 4. Schepens CL: Retinal detachment and Allied diseases. Philadelphia, WB Saunders, 1983, pp.58–62, 615–32 5. Gopal

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6. Gopal L, Badrinath SS, Sharma T, Parikh SN, Shanmugam MS, Bhende PS, Agrawal

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retinal colobomas. Deep penetration Swept Source-OCT

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11. Povazay B, Hermann B, Unterhuber A, et al. Three-dimensional optical coherence

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tomography at 1050 nm versus 800 nm in retinal pathologies: enhanced performance

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tomography. Am J Ophthalmol. 2014;157(6):1272–1281.

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13. MannI. Developmental abnormalities of the eye. London: Cambridge University Press. 1937 65–103. 14. Schubert HD. Schisis-like rhegmatogenous retinal detachment associated with choroidal colobomas. Graefes Arch ClinExpOphthalmol 1995; 233:74–79.

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15. Schubert HD. Structural organization of choroidal colobomas of young and adult

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patients and mechanism of retinal detachment. Trans Am OphthalmolSoc 2005;

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103:457–472.

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16. Ohno-Matsui K, Fang Y, Morohoshi K, Jonas JB. Optical Coherence Tomographic

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Imaging of Posterior Episclera and Tenon's Capsule. Invest Ophthalmol Vis Sci. 2017

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Jul 1;58(9):3389-3394

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Legends

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Figure 1.Colour fundus photographs of the right eye of a 10‑year‑old male (a) and 12 year

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old female (b) showing type 3 and type 2 coloboma respectively with the green arrow

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indicating the site of the radial SS-OCT line scan. SS-OCT scan of former (c) shows abrupt

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type of transformation of normal layered retinal architecture into featureless ICM while in

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latter (d) it shows normal layered architecture of retina continues for some distance in ICM.

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(SS-OCT- swept source optical coherence tomography, ICM- intercalary membrane)

306

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Figure 2. SS-OCT of the right eye of a 9-year-old female with type 2 coloboma (a) and left

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eye of a 10‑year‑old male with type 3 coloboma (b). Green arrows indicate the termination

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of IZ and EZ before the termination of RPE (red arrow). (SS-OCT- swept source optical

310

coherence tomography, IZ- interdigitation zone, EZ- ellipsoid zone, RPE- retinal pigment

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epithelium)

312 313

Figure 3. SS-OCT of the left eye of a 18-year-old male with type 2 coloboma shows shallow

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subretinal fluid (red arrow) with cystic spaces (blue arrow) present over both attached as well

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as detached retina. (SS-OCT- swept source optical coherence tomography)

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Figure 4. Colour fundus photograph of the left eye of a 60‑year‑old male showing type 2

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coloboma (a) with SS-OCTscan (b) shows cystic changes in ICM (red arrow). (SS-OCT-

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swept source optical coherence tomography, ICM- intercalary membrane)

319 320

Figure 5. Colour fundus photograph of the right eye of a 21‑year‑old male (a) showing type

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2 coloboma. SS-OCT scan (b) shows typical schisis like splitting of ICM (blue arrow). (SS-

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OCT- swept source optical coherence tomography, ICM- intercalary membrane)

323 324

Figure 6. Colour fundus photographs of the right eye of a 21‑year‑old male (a) and left eye

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of a 9-year-old female (c) showing type 2 coloboma. SS-OCT scan of both in (b) and (d)

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shows break in the ICM (red arrow). In the latter, location of break is corresponding with

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yellow pigment, suggestive of it being a macular hole. (SS-OCT- swept source optical

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coherence tomography, ICM- intercalary membrane)

329

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Figure 7. SS-OCT of the right eye of a 9-year-old female with type 2 coloboma (a) and left

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eye of a 10‑year‑old male with type 3 coloboma (b). Red arrow indicates the inward bending

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of the eye wall towards vitreous cavity. (SS-OCT- swept source optical coherence

333

tomography)

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Figure 8. (a) SS-OCT of the right eye of a 60-year-old male with type 3 coloboma. Radial

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scan through coloboma margin shows PVD on either side with vitreous still attached at the

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margin. (b) SS-OCT of the left eye of a 43-year-old female with type 5 coloboma showing

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vitreous condensation over the coloboma region (red arrow head). (c) SS-OCT of the left eye

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of a 11-year-old male with type 1 coloboma shows peak like projections of ICM (red arrow)

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(SS-OCT- swept source optical coherence tomography, PVD- posterior vitreous detachment,

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ICM- intercalary membrane)

342 343

Figure 9. (a) SS-OCT of the right eye of a 12-year-old female with type 1 coloboma. Blue *

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shows sclera as a hyperreflective lamellar structure with blue arrow indicates hyporeflective

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scleral cleft. Yellow bar shows uniform but less hyper-reflective episcleral tissue. (b) SS-

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OCT of the right eye of a 23-year-old male with type 1 coloboma. Red arrow shows tenons

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capsule as a irregularly arranged hyperreflective structure and red * shows orbital fat/soft

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tissue as hyperreflective dots. (SS-OCT- swept source optical coherence tomography)

349

Highlights

Swept-source optical coherence tomography was done to evaluate coloboma margin. Two types of transitions, early termination of outer retinal layers, cystic spaces and schisis in the intercalary membrane and subclinical retinal detachment were noted.