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Col . RANGACHARI AWARD (Joint Award)

Dr. Mishra Divyansh Kailashcandra, D16793, Dr. Vinaya Kumar Konana, Dr. Rajesh Ramanjulu, Dr. Mahesh Shanmugam P

Introduction

Since its invention, optical coherence tomography (OCT) has made remarkable advancements in both image resolution and acquisition speed. Recent improvements to commercially available OCT systems have also included increasing scan length.The new DRI OCT Triton plus (Topcon, Tokyo, Japan), a commercially available, swept-source OCT system, is capable of producing a 12-mm scan. A novel yet simple technique to expand the scan length on OCT has been reported as an extended field imaging (EFI) technique which involves imaging the posterior pole through trial frames fitted with a +20 diopter lens. 1 Wide-field OCT imaging is advantageous over conventional OCT imaging because a more comprehensive assessment of the posterior pole can be made with a single scan. It also has the ability to detect abnormalities of the vitreomacular interface in great detail. Preoperative OCT assessment of associated vitreomacular interface abnormalities in patients with diabetic retinopathy requiring vitrectomy can assist in decision makingpreoperatively in terms of accurate plane of dissection as they would have, an incomplete posterior vitreous detachment with multiple focal attachments. In this study, we sought to further explore the feasibility of EFI technique in aiding us doing diabetic vitrectomy with minimal complications.

Methodology

This study was a prospective study of thirty eyes from22 patients with Proliferative diabetic retinopathy who visited Sankara Eye Hospital between January 2017 and May 2017. This study was approved by the Institutional Review Board was conducted in accordance with the ethical standards stated in the 1964 Declaration of Helsinki.The eyes with poor quality images due to media opacities or poor fixation wereexcluded from the study.

A set of 12 mm radial scans centered on fovea and another set centered on optic disc were captured in all subjects with standard technique and with a novel EFI OCT technique. OCT images were captured with DRI OCT triton plus. The EFI technique involved imaging the posterior pole through trial frame fitted with a +20.00-diopter lens (planoconvex) with convex surface facing the eye, then the expansion rates were calculated using ImageJ software (NIH) (https://imagej.nih.gov/ij/).

We analyzed the image quality by assessing the visibility of ellipsoid zone in normal area of retina and the lateral edges of OCT scan. The image quality was graded with a scale of 1 to 3 with 1 being the poor quality and 3 being the best. Reflection artifacts and rim artifacts were analyzed. The vitreoretinal interface was analyzed based on the visibility of posterior and anterior attachments. Superotemporal and inferotemporal attachments were assessed in fovea centered scan. Superonasal and inferonasal attachments were assessed in disc centered scan. The above parameters were compared between standard and EFI images.

Results

A total of 30 eyes of 22 patients were included in the study of which were 12 were male and 10 were female. The mean age group was 51 years. A total of 10 patients had vitreomacular traction, 5 patients had taut posterior hyaloids, 8 patients had traction retinal detachment involving macula and 7 patients had traction involving disc and papillo macular bundle.The scan length was increased by a factor of 1.55 when obtained using EFI technique. Of the 30 disc centered scans 6 scans were not centered in standard OCT and 13 scans were not centered in EFI OCT. In the 30 fovea centered scans 7 scans were not centered in standard OCT and 12 scans were not centered in EFI OCT. In standard OCT images 86.6 % were of grade 3 whereas in EFI 58% were of grade 3. No artifacts were seen in standard OCT. Reflection artifacts were absent in standard OCT but 36% of eyes showed reflection artifacts in EFI images. Rim artifacts were absent in standard OCT but 22 % of eyes had rim artifacts in EFI images.

Out of 30 eyes, vitreoretinal separation was noted in 21 eyes in superotemporal and inferotemporal quadrant of which anterior extent of attachments were made out in 15 eyes using EFI technique where as in only 08 eyes it could be made out in standard OCT. In twelve eyes, vitreoretinal separation was seen in superonasal and inferonasal quadrant, of which in 9 eyes anterior extent was noted in EFI technique and in 5 eyes it was noted using standard techniques.

Discussion

A convex lens placed between the eye and the OCT machine theoretically increases the imaging light incidence angle resulting in imaging field expansion. The convex lens causes least angular minification of the target which also increases the field of OCT. Since the eye is a globular structure, the concavity of posterior pole also contributes to increase in the scan length. The field of expansion in EFI technique is increased by a factor of 1.5. Furthermore, EFI results in a decrease in image resolution because EFI does not change the hardware capabilities of the OCT system. It simply magnifies each pixel, so the detailed information is missed, but there is no gross loss of details of the retinal architecture. Reflection and rim artifacts are common with the EFI technique. Reflection artifacts though present did not hamper visualization of details in majority of cases. Assessment of vitreoretinal interface plays an important role in diabetic vitrectomy. Identification of surgical plane is of utmost importance to proceed with a successful surgery.2&3 The EFI technique enables us to identify the anterior extent of attachment thus aiding us in plane of dissection. The colour photo of fundus cannot be seen in detail because of reflection of light produced by the lens but can be compensated by looking into the projection image. The EFI technique has also been employed to OCT Angiography to evaluate the non perfusion areas in retinal vein occlusion.4 Further EFI OCT can also be tried in acquiring images for mid peripheral lesions. The limitations of our present study include the fact that this was a study that only included a limited number of patients. In summary, EFI technique can be used effectively in assessing the vitreoretinal interface abnormalities in diabetic retinopathy and also aiding us in identification of correct cleavage plane in diabetic vitrectomy. The technique is effective, economical, simple to implement, easy to perform, and uses readily available materials.

  • Refrences :Uji A, Yoshimura N. Application of extended field imaging to optical coherence tomography. Ophthalmology. 2015;122(6):1272–1274.
  • Aylward B, Sullivan P, Vote B. The video atlas of eye surgery. Vitreoretinal 1: basic techniques. Surrey, UK: Eye Movies; 2005.
  • Kanski JJ, Gregor ZJ. Retinal detachment: a colour manual of diagnosis and treatment. 2nd ed. London: Butterworth-Heinemann Medical; 1995. p. 161.
  • Kimura M, Nozaki M, Yoshida M, Ogura Y.2016 Jul 13;10:1291-5

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