Ophthalmic Surgery, Lasers and Imaging Retina

Clinical Science 

En Face Imaging of Epiretinal Membranes and the Retinal Nerve Fiber Layer Using Swept-Source Optical Coherence Tomography

Margaret A. Greven, MD; Zachary Elkin, MD, MPH; Ryan W. Nelson, BS; Theodore Leng, MD, MS

Abstract

BACKGROUND AND OBJECTIVE:

To describe en face swept-source optical coherence tomography (SS-OCT) imaging of epiretinal membranes (ERMs) and the underlying retinal nerve fiber layer (RNFL).

PATIENTS AND METHODS:

SS-OCT images were captured in nine eyes with ERMs. These SS-OCT en face images were qualitatively compared to spectral-domain OCT (SD-OCT) en face images. Using SS-OCT, en face images of the RNFL were obtained, if possible.

RESULTS:

En face SS-OCT images of ERMs were obtained in all nine eyes of eight individuals with clinically diagnosed ERMs that were superior to SD-OCT images. Clear en face images of the RNFL were acquired in seven of nine eyes (78%) using SS-OCT.

CONCLUSIONS:

SS-OCT is a novel method for generating en face images of ERMs. Compared with SDOCT en face images, SS-OCT could more clearly identify the plaques and folds of ERMs and underlying defects in the RNFL. Such images could be useful for surgical planning and assessment of the integrity of the underlying RNFL.

[Ophthalmic Surg Lasers Imaging Retina. 2016;47:730–734.]

Abstract

BACKGROUND AND OBJECTIVE:

To describe en face swept-source optical coherence tomography (SS-OCT) imaging of epiretinal membranes (ERMs) and the underlying retinal nerve fiber layer (RNFL).

PATIENTS AND METHODS:

SS-OCT images were captured in nine eyes with ERMs. These SS-OCT en face images were qualitatively compared to spectral-domain OCT (SD-OCT) en face images. Using SS-OCT, en face images of the RNFL were obtained, if possible.

RESULTS:

En face SS-OCT images of ERMs were obtained in all nine eyes of eight individuals with clinically diagnosed ERMs that were superior to SD-OCT images. Clear en face images of the RNFL were acquired in seven of nine eyes (78%) using SS-OCT.

CONCLUSIONS:

SS-OCT is a novel method for generating en face images of ERMs. Compared with SDOCT en face images, SS-OCT could more clearly identify the plaques and folds of ERMs and underlying defects in the RNFL. Such images could be useful for surgical planning and assessment of the integrity of the underlying RNFL.

[Ophthalmic Surg Lasers Imaging Retina. 2016;47:730–734.]

Introduction

Epiretinal membranes (ERMs) are fibrocellular proliferations that occur at the vitreoretinal interface; contraction of these membranes can cause meta-morphopsia and vision loss. Management of ERMs consists of observation for mild cases and surgical removal for visually significant cases. Optical coherence tomography (OCT) is an important adjunct to the clinical examination in patients with ERM for confirming the diagnosis, predicting surgical outcomes, and surgical planning.1–4

OCT can aid in surgical planning as it enables the surgeon to visualize edges of the membrane, aspects of the membrane that are elevated off of the retina, and thicker areas of the membrane. This can guide the surgeon's approach to beginning the membrane peel.4 En face OCT images allow physicians to visualize the morphology of ERMs in a different, complementary way to standard cross-sectional OCT imaging of the retina. Spectral-domain OCT (SD-OCT) en face images have demonstrated plaques associated with retinal adhesions to the ERM and folds representing detachments of the membrane from the retinal surface.5

Swept-source OCT (SS-OCT) is a novel imaging tool that has a lower sensitivity roll-off and can be run at a wavelength of 1,060 nm, and which can therefore provide higher penetration into the choroid than commercial SD-OCT instruments, which typically have a central wavelength of 840 nm.6–8 SS-OCT has previously been used to evaluate changes in choroidal thickness in eyes with ERMs following membrane peels.9 SS-OCT en face images have also been used to characterize a host of other retinal conditions, including age-related macular degeneration, polypoidal choroidal vasculopathy, and central serous chorioretinopathy.10–13 To our knowledge, SS-OCT en face images have not been used to describe the vitreoretinal interface and retinal nerve fiber layer (RNFL) with ERMs.

Patients and Methods

The study was approved by the Human Subjects Institutional Review Board of Stanford University School of Medicine, and data collection and reporting were in compliance with all HIPAA requirements. The Declaration of Helsinki and all applicable federal and state laws were complied with during this study.

SS-OCT images were captured in nine sequential eyes with ERM diagnosed by clinical exam and SD-OCT. The SS-OCT device used was a prototype approved for investigational use with a laser wavelength centered at 1,060 nm with an acquisition speed of 100,000 A-scans/sec (Carl Zeiss Meditiec, Dublin, CA). Volume scans of 6 mm × 6 mm centered over the fovea were obtained (512 A-scans/B-scan; 512 B-scans/cube). SD-OCT scans were acquired over 6 mm × 6 mm (512 A-scans/B-scan; 128 B-scans/cube). En face images were created using 4 µm summed voxel projections (slabs) centered on the internal limiting membrane and then moved posterior to image the RNFL. Similar slabs were used to compare en face images from SD-OCT scans. The pixel size and separation of the SS-OCT scans were much better than for the SD-OCT scans (6 µm × 6 µm × 2 µm for SS-OCT as compared to 12 µm × 47 µm × 2 µm for SD-OCT), which was partially enabled by the speed of the SS-OCT instrument compared to the SD-OCT instrument (Cirrus OCT, Carl Zeiss Meditec, Dublin, CA) (27,000 A-scans/sec). The scan time for both scans was similar with approximately 2.8 seconds per scan.

Patient characteristics including age, gender, affected eye, preoperative visual acuity, and other ocular conditions were recorded. The presence of macular pathology in addition to the ERM was recorded. SS-OCT en face images were qualitatively compared to SD-OCT en face images. Using SS-OCT en face imaging, the ability to visualize the RNFL was recorded.

Results

En face images of ERMs were obtained in all nine eyes of eight individuals with clinically diagnosed ERMs. The mean age was 68 years (range: 47 years to 88 years), visual acuity ranged from 20/20 to 20/200, and four patients had additional macular pathology on clinical examination (Table).


Characteristics of Patients Whose Eyes Were Imaged Using SS-OCT

Table:

Characteristics of Patients Whose Eyes Were Imaged Using SS-OCT

Based on qualitative evaluation of SS-OCT and SD-OCT images, the SS-OCT en face images demonstrated more topographic detail of the vitreoretinal interface, more clearly identifying the plaques and folds of ERMs and underlying defects in the RNFL when compared to SD-OCT. Clear en face images of the RNFL could also be acquired in seven of nine eyes (78%) for the SS-OCT images. The RNFL could not be imaged in two eyes when the ERM was too diffuse or thick, such that that the characteristic arcades of fibers could not be reliably identified. No images of the RNFL could be acquired with the SD-OCT. Figure 1 demonstrates the en face images of the ERMs obtained from Patients 1 to 3 in the Table using both modalities, as well as RNFL imaging when it was able to be performed. Figure 2 shows standard cross-sectional SD-OCT from the same patients.


Swept-source optical coherence tomography (SS-OCT) en face image of an epiretinal membrane (ERM) (left column), the underlying retinal nerve fiber layer (RNFL) (middle column), and the spectral-domain OCT (SD-OCT) en face ERM image (right column) are shown for three eyes (A, B, and C). The SS-OCT en face images demonstrated more topographic detail of the vitreoretinal interface, better identifying the plaques and folds of ERMs and underlying defects in the RNFL when compared to SD-OCT. (Note: en face imaging of the RNFL could not be obtained with the SD-OCT device.)

Figure 1.

Swept-source optical coherence tomography (SS-OCT) en face image of an epiretinal membrane (ERM) (left column), the underlying retinal nerve fiber layer (RNFL) (middle column), and the spectral-domain OCT (SD-OCT) en face ERM image (right column) are shown for three eyes (A, B, and C). The SS-OCT en face images demonstrated more topographic detail of the vitreoretinal interface, better identifying the plaques and folds of ERMs and underlying defects in the RNFL when compared to SD-OCT. (Note: en face imaging of the RNFL could not be obtained with the SD-OCT device.)


(A, B, C) Standard spectral-domain optical coherence tomography cross-sectional images the same patients pictured in 1A to 1C.

Figure 2.

(A, B, C) Standard spectral-domain optical coherence tomography cross-sectional images the same patients pictured in 1A to 1C.

Discussion

SS-OCT is a novel method for generating en face images of ERMs. Compared with SD-OCT en face images, SS-OCT could more clearly identify the plaques and folds of ERMs and underlying defects in the RNFL. One factor that may contribute to superior imaging of ERMs with SS-OCT compared to SD-OCT is a different software algorithm. The SS-OCT algorithm may reduce motion artifact from microfixation errors during scanning better than the algorithm employed by SD-OCT. In any case, this enhanced en face imaging with SS-OCT could prove to be a useful compliment to standard cross-sectional imaging, especially for operative planning for ERMs. The higher resolution en face images of SS-OCT better demonstrated the attachment points of the ERM to the underlying retina and could help guide surgical approach for membrane peeling surgery.

The significance of RNFL integrity has not yet been established. Although multiple studies have demonstrated dimples in the underlying RNFL following internal limiting membrane peeling that can enlarge up to 6 months after the peel, these changes have not been correlated to postoperative visual acuity.5,14 However, recent studies have noted correlation between a number of SD-OCT characteristics with postoperative visual outcomes. For example, previous studies have shown correlation between preoperative SD-OCT characteristics with postoperative best-corrected visual acuity. Integrity of the cone outer segment tips and the photoreceptor inner segments — outer segments have both shown statistical correlations with final visual acuity in patients with ERM.12,13 Further studies are required to elucidate the role of RNFL integrity in postoperative visual outcomes. If RNFL features are shown to be clinically significant, SS-OCT en face imaging would be a useful tool to assess the health of the RNFL.

Further studies, including pre- and postoperative imaging, are necessary to identify the utility of this imaging modality to surgeons, and to correlate preoperative ERM and RNFL characteristics with postoperative visual outcomes.

References

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Characteristics of Patients Whose Eyes Were Imaged Using SS-OCT

PatientAge (Years)GenderSnellen Visual AcuityAdditional Macular Pathology
186F20/40Drusen and geographic atrophy
270F20/125Microcystic macular edema
369F20/25
449M20/40
568M20/20
688F20/200White fibrotic bands
767F20/20Lamellar macular hole
847M20/200
847M20/150
Authors

From Byers Eye Institute at Stanford, Stanford University School of Medicine, Palo Alto, CA.

Presented at the Association for Research in Vision and Ophthalmology Meeting in Denver on May 2, 2015.

Dr. Leng is a consultant to Zeiss. The remaining authors report no relevant financial disclosures.

Address correspondence to Theodore Leng, MD, MS, Byers Eye Institute at Stanford, Stanford University School of Medicine, 2452 Watson Court, Palo Alto, CA 94303; email: tedleng@stanford.edu.

Received: March 10, 2016
Accepted: June 08, 2016

10.3928/23258160-20160808-06

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