Optical coherence tomography imaging in the management of the Argus II retinal prosthesis system

Clinical significance of signal shadowing during intraoperative optical coherence tomography-assisted vitreoretinal surgery

This study aimed to analyze the clinical significance of signal shadowing during intraoperative optical coherence tomography (iOCT)-assisted vitreoretinal surgery caused by vitreoretinal instruments, tissue dyes, and vitreous substitutes, and to objectively quantify its impact on iOCT imaging. This is a retrospective observational study of postoperative image analysis from one hundred seventeen (117) patients who underwent iOCT-assisted vitrectomy. The image data were divided into three groups: vitreoretinal instruments, tissue dyes, and vitreous substitutes. The data was then processed using graphic software to measure the grade of picture quality distortion and compared to paired image controls without clinically perceptive interference, then analyzed statistically. The intraocular portion of all studied vitreoretinal instruments caused a high average gray level interference compared to controls ranging from 32 to 68% reduction, obscuring the area of interest significantly. The tips of the instruments produced low-grade shadowing, allowing the underlying tissue to be distinguished. The analyzed dyes demonstrated a wide interference range: ICG (- 75.12%), and triamcinolone (- 26.13%) showed dose-dependent high shadowing, while VITREODYNE™ (49.3%) and brilliant blue G (14.06%) exhibited no perceived distortions whilst increasing average gray levels. All analyzed vitreous substitutes (air, SF6, C3F8, PFCL, and silicone oil) showed an insignificant shadowing effect on iOCT. Certain dyes and vitreous substitutes produce a negligible shadowing effect compared to controls and other dyes, providing an advantage during real-time iOCT imaging. All analyzed vitreoretinal instruments showed a significant interference that should prompt the development of new imaging techniques or the implementation of materials with low-grade interference to overcome a clinically relevant shadowing effect on iOCT, maximizing the technology's visual accuracy and surgical diagnostic aid proficiency.

Interobserver Agreement of Electrode to Retina Distance Measurements in a Second-Generation (44-Channel) Suprachoroidal Retinal Prosthesis

Purpose

The electrode to retina (ER) distance is an important contributory factor to the safety and efficacy of a suprachoroidal retinal prosthesis. Measuring ER distance may be performed by different observers during multisite studies. The aim of this study was to assess the interobserver agreement in measuring ER distance.

Methods

Three independent, trained observers measured ER distance from the center of each suprachoroidal electrode to the inner retinal pigment epithelium in spectral-domain optical coherence tomography (SD-OCT) B-scans. A total of 121 ER distance measurements from 77 B-scans collected over 5 months from one subject implanted with a second-generation 44-channel suprachoroidal retinal prosthesis (NCT03406416) were made by each observer.

Results

ER distance ranged from 208 to 509 µm. Pearson's correlation coefficient (ρ) showed agreement of 0.99 (95% confidence interval [CI] = 0.98–0.99) in measuring ER for each pairwise comparison. The mean difference in ER distance between observers ranged from 2.4 to 6.4 µm with pairwise limits of agreement (95% CI) of ±20 µm (5.5% of mean). Intraclass correlation coefficient (ICC) showed agreement of 0.98 (95% CI = 0.97–0.99) between observers.

Conclusions

There is high agreement in measuring ER distances for suprachoroidal retinal prostheses using our systematic approach between multiple, trained observers, supporting the use of a single observer for each image.

Translational Relevance

High interobserver agreement outcomes indicate that multiple, trained observers can be used to take ER measurements across different images in suprachoroidal retinal prosthesis studies. This improves multisite study efficiency and gives confidence in interpreting results relating to the safety and efficacy of suprachoroidal retinal prostheses.

Simulating the perceptual effects of electrode-retina distance in prosthetic vision

OBJECTIVE

Retinal prostheses aim to restore some vision in retinitis pigmentosa and age-related macular degeneration blind patients. Many spatial and temporal aspects have been found to affect prosthetic vision. Our objective is to study the impact of the space-variant distance between the stimulating electrodes and the surface of the retina on prosthetic vision and how to mitigate this impact.

APPROACH

A prosthetic vision simulation was built to demonstrate the perceptual effects of the electrode-retina distance (ERD) with different random spatial variations, such as size, brightness, shape, dropout, and spatial shifts. Three approaches for reducing the ERD effects are demonstrated: electrode grouping (quads), ERD-based input-image enhancement, and object scanning with and without phosphene persistence. A quantitative assessment for the first two approaches was done based on experiments with 20 subjects and three vision-based computational image similarity metrics.

MAIN RESULTS

The effects of various ERDs on phosphenes' size, brightness, and shape were simulated. Quads, chosen according to the ERDs, effectively elicit phosphenes without exceeding the safe charge density limit, whereas single electrodes with large ERD cannot do so. Input-image enhancement reduced the ERD effects effectively. These two approaches significantly improved ERD-affected prosthetic vision according to the experiment and image similarity metrics. A further reduction of the ERD effects was achieved by scanning an object while moving the head.

SIGNIFICANCE

ERD has multiple effects on perception with retinal prostheses. One of them is vision loss caused by the incapability of electrodes with large ERD to evoke phosphenes. The three approaches presented in this study can be used separately or together to mitigate the impact of ERD. A consideration of our approaches in reducing the perceptual effects of the ERD may help improve the perception with current prosthetic technology and influence the design of future prostheses.

Retinal Implantation of Electronic Vision Prostheses to Treat Retinitis Pigmentosa: A Systematic Review

Purpose

Retinitis pigmentosa (RP) is a hereditary disease causing photoreceptor degeneration and permanent vision loss. Retinal implantation of a stimulating electrode array is a new treatment for RP, but quantification of its efficacy is the subject of ongoing work. This review evaluates vision-related outcomes resulting from retinal implantation in participants with RP.

Methods

We searched MEDLINE and Embase for journal articles published since January 1, 2015. We selected articles describing studies of implanted participants that reported the postimplantation measurement of vision. We extracted study information including design, participants’ residual vision, comparators, and assessed outcomes. To assess the risk of bias, we used signaling questions and a target trial.

Results

Our search returned 425 abstracts. We reviewed the full text of 34 articles. We judged all studies to be at high risk of bias owing to the study design or experimental conduct. Regarding design, studies lacked the measures that typical clinical trials take to protect against bias (e.g., control groups and masking). Regarding experimental conduct, outcome measures were rarely comparable before and after implantation, and psychophysical methods were prone to bias (subjective, not forced choice, methods). The most common comparison found was between postimplantation visual function with the device powered off versus on. This comparison is at high risk of bias.

Conclusions

There is a need for high-quality evidence of efficacy of retinal implantation to treat RP.

Translational Relevance

For patients and clinicians to make informed choices about RP treatment, visual function restored by retinal implantation must be properly quantified and reported.

Monitoring Cortical Response and Electrode-Retina Impedance Under Epiretinal Stimulation in Rats

Retinal prosthesis can restore partial vision in patients with retinal degenerative diseases such as retinitis pigmentosa and age-related macular degeneration. Epiretinal prosthesis is one of three therapeutic approaches, which received regulatory approval several years ago. The thresholds of an epiretinal stimulation is partly determined by the size of the physical gap between the electrode and the retina after implantation. Precise positioning of epiretinal stimulating electrode array is still a challenging task. In this study, we demonstrate an approach to positioning epiretinal prostheses for an optimal response at the cortical output by monitoring both the impedance at the electrode-retina interface and the evoked-potential at the cortical level. We implanted a single-channel electrode on the epiretinal surface in adult rats, acutely, guided by both the impedance at the electrode-retina interface and by electrically evoked potentials (EEPs) in the visual cortex during retinal stimulation. We observe that impedance monotonously increases with decreasing electrode-retina distance, but that the strongest cortical responses were achieved at intermediate impedance levels. When the electrode penetrates the retina, the impedance keeps increasing. The effect of stimulation on the retina changes from epiretinal paradigm to intra-retinal paradigm and a decrease in cortical activation is observed. It is found that high impedance is not always favorable to elicit best cortical responses. Histopathological results showed that the electrode was placed at the intra-retinal space at high impedance value. These results show that monitoring impedance at the electrode-retina interface is necessary but not sufficient in obtaining strong evoked-potentials at the cortical level. Monitoring the cortical EEPs together with the impedance can improve the safety of implantation as well as efficacy of stimulation in the next generation of retinal implants.

Correlation between Argus II array-retina distance and electrical thresholds of stimulation is improved by measuring the entire array

PURPOSE

To describe two methods of measuring Argus II array-retina distance and to correlate array-retina distance to electrode stimulation thresholds.

METHODS

This was a case series of eight patients implanted with the Argus II. Spectral domain-optical coherence tomography array-retina distance was measured by two methods and correlated to corresponding electrode thresholds: (1) array-retina distance at each array corner and the largest array-retina distance and (2) using manual optical coherence tomography segmentation, the average array-retina distance was determined for each group of four electrodes. Patients 1-5 and 6-8 were analyzed separately due to a different threshold programming software.

RESULTS

The Spearman's rank coefficient between array-retina distance and thresholds was -0.006 (p = 0.98) for patients 1-5, and 0.16 (p = 0.59) for patients 6-8 with the first method. The Spearman's rank coefficient was 0.25 (p < 0.001) for patients 1-5 and 0.36 (p < 0.001) for patients 6-8 with the second method.

CONCLUSION

There is a positive correlation between array-retina distance and threshold measurements when measuring the entire array but not when using a faster measurement method of four corners and largest array-retina distance.

Relationship Between Macular Curvature and Common Causative Genes of Retinitis Pigmentosa in Japanese Patients

Purpose

To determine the relationship between the macular curvature and the causative genes of retinitis pigmentosa (RP).

Methods

We examined the medical records of the right eyes of 65 cases with RP (31 men and 34 women; average age, 47.6 years). There were 31 cases with the EYS variants, 11 cases with the USH2A variants, six cases with the RPGR variants, 13 cases with the RP1 variants, and four cases with the RP1L1 variants. The mean curvature of Bruch's membrane was calculated within 6 mm of the fovea as the mean macular curvature index (MMCI, 1/µm). We used multiple linear regression analysis to determine the independence of the causative genes contributing to the MMCIs after adjustments for age, sex, axial length, and width of the ellipsoid zone.

Results

The median MMCI was −31.2 × 10⁻⁵/µm for the RPGR eyes, −16.5 × 10⁻⁵/µm for the RP1L1 eyes, −13.0 × 10⁻⁵/µm for the RP1 eyes, −9.8 × 10⁻⁵/µm for the EYS eyes, and −9.0 × 10⁻⁵/µm for the USH2A eyes. Compared with the EYS gene as the reference gene, the RPGR gene was significantly related to the MMCI values after adjusting for the other parameters (P = 5.30 × 10⁻⁶). In contrast, the effects of the other genes, USH2A, RP1, and RP1L1, were not significantly different from that of the EYS gene (P = 0.26, P = 0.49, and P = 0.92, respectively).

Conclusions

The RPGR gene had a stronger effect on the steep macular curvature than the other ciliopathy-related genes.

Longitudinal Changes of Macular Curvature in Patients with Retinitis Pigmentosa

Purpose

To investigate the longitudinal changes of the macular curvature in eyes with retinitis pigmentosa (RP) and to determine the factors associated with the changes.

Methods

We reviewed the medical charts of 107 RP patients, for whom the axial length of their right eyes ranged from 21.5 to 26.0 mm and who had had been followed by spectral-domain optical coherence tomography (OCT). The OCT images at the initial and the most recent examinations were compared. The mean curvature of Bruch's membrane within 6 mm of the central macula obtained from the OCT images was evaluated as the mean macular curvature index (MMCI). Changes in the MMCI and their relationships with other clinical factors, including the ellipsoid zone (EZ) width, were assessed.

Results

The MMCI decreased significantly in the vertical OCT images, from –15.47 × 10⁻⁵ µm⁻¹ to –16.36 × 10⁻⁵ µm⁻¹ (P = 0.008) during the mean observation period of 3.4 ± 1.4 years (mean ± SD). This indicated that the macular shape became more concave. The change to a steeper shape was more prominent in eyes with less photoreceptor degeneration and for which the EZ width was preserved at >2000 µm. In three eyes, the MMCI increased markedly by >5 × 10⁻⁵ µm⁻¹, and this was accompanied by absorption of the macular edema.

Conclusions

The macular curvature in RP eyes becomes more concave in eyes with preserved EZ width.

Translational Relevance

Longitudinal changes of the macular curvature in RP should be considered in future therapies, such as the implantation of the retinal prosthesis.

POSTERIOR STAPHYLOMAS IN EYES WITH RETINITIS PIGMENTOSA WITHOUT HIGH MYOPIA

PURPOSE

To describe features of posterior staphylomas in nonhighly myopic eyes with retinitis pigmentosa (RP).

METHODS

The retrospective observational case series study included patients with RP and an axial length of <26.5 mm and searched for eyes with posterior staphylomas. All study participants underwent fundus photography and optical coherence tomography.

RESULTS

The study identified 13 eyes of 7 patients with a narrow macular staphyloma. Mean age was 40.9 ± 17.9 years (range 9-62 years) and mean axial length was 24.90 ± 0.69 mm. The staphyloma edges corresponded to the margin between the retinal atrophic area in the fundus midperiphery and the relatively unaffected fundus center. On vertically orientated optical coherence tomography images, the staphyloma edges showed a slight inward protrusion of the sclera and a ring-like localized choroidal thinning with choroidal rethickening in direction toward the fovea and toward the periphery of the fundus. The upper and lower staphyloma edges did not differ in steepness. The thickness of the subfoveal choroid (138.6 m ± 50.1 µm) was thinner than the normal range after adjusting for age and axial length in all eyes. Two eyes with advanced RP in the macula showed a subfoveal choroidal thickness of 95 µm and 88 µm.

CONCLUSION

Narrow macular staphylomas can occur in nonhighly myopic eyes with RP and, in contrast to staphylomas in highly myopic eyes, show a less marked thinning of the subfoveal choroid. The occurrence of posterior staphylomas in nonhighly myopic eyes with RP may provide hints to unravel the etiology of posterior staphyloma formation.

Steeper Macular Curvature in Eyes With Non-Highly Myopic Retinitis Pigmentosa

Purpose

A posterior staphyloma has been reported to be present in some eyes with retinitis pigmentosa (RP), and the purpose of this study was to determine the macular curvature of non-highly myopic RP eyes.

Methods

This was a retrospective, observational study. The medical charts of the right eyes of 143 patients with RP and 60 controls whose axial length ranged from 21.5 mm to 26.0 mm were reviewed. The mean curvature of Bruch's membrane within 6 mm of the central macula obtained from the horizontal optical coherence tomographic images were evaluated as the mean macular curvature index (MMCI). The relationships between the MMCI and other clinical factors were assessed.

Results

The mean MMCI of RP patients (-13.73 ± 9.63 × 10-5 μm-1) was significantly lower than that of the controls (-6.63 ± 5.63 × 10-5 μm-1). This indicated a deeper concave shape of the macula in RP eyes (P < 0.001). The MMCI was significantly correlated with the age (r = 0.20; P = 0.016) and the axial length (r = -0.24; P = 0.004). Further analysis suggested a nonlinear effect of the ellipsoid zone width on the macular curvature in the RP eyes.

Conclusions

There is a high incidence of steeper macular curvatures even in non-highly myopic RP eyes, and the steepness was also affected by the degree of photoreceptor degeneration.

Molecular Therapies for Choroideremia

Advances in molecular research have culminated in the development of novel gene-based therapies for inherited retinal diseases. We have recently witnessed several groundbreaking clinical studies that ultimately led to approval of Luxturna, the first gene therapy for an inherited retinal disease. In parallel, international research community has been engaged in conducting gene therapy trials for another more common inherited retinal disease known as choroideremia and with phase III clinical trials now underway, approval of this therapy is poised to follow suit. This chapter discusses new insights into clinical phenotyping and molecular genetic testing in choroideremia with review of molecular mechanisms implicated in its pathogenesis. We provide an update on current gene therapy trials and discuss potential inclusion of female carries in future clinical studies. Alternative molecular therapies are discussed including suitability of CRISPR gene editing, small molecule nonsense suppression therapy and vision restoration strategies in late stage choroideremia.

One-Year Safety and Performance Assessment of the Argus II Retinal Prosthesis: A Postapproval Study

Importance

The Argus II Retinal Prosthesis System is indicated for patients with vision loss due to severe to profound outer retinal degeneration, a group with few treatment options.

Objectives

To collect postapproval safety and visual function data for the Argus II.

Design, Setting, and Participants

Multicenter, postapproval clinical trial conducted at 9 sites in Germany and Italy. Data were collected from December 2, 2011, to September 30, 2017, and patients were followed-up for 12 months or longer. Patients were 25 years or older with severe to profound outer retinal degeneration, some residual light perception or the ability of the retina to respond to electrical stimulation, and a history of useful form vision and were already planning to undergo Argus II implantation.

Main Outcomes and Measures

The primary end point of this study was the nature and rate of adverse events. Secondary end points included 3 visual function tests: square localization (SL), direction of motion, and grating visual acuity (GVA).

Results

Forty-seven patients were followed for 12 months or longer after implant. Mean (SD) age was 56 (12) years, 37 (79%) had retinitis pigmentosa, and 27 (57%) were male. Through the first 12 months postimplantation, 23 patients (49%) experienced 51 nonserious adverse events and 12 (26%) experienced 13 serious adverse events (SAEs), 9 of which were judged to be related to the Argus II, and 4 of which were judged to be related to the procedure. The most common SAE was conjunctival erosion, reported in 4 patients. No significance testing was done for group analysis for the SL or direction-of-motion tests. When averaged across the group, patients' accuracy on the SL test, but not on the direction-of-motion test, appeared better when the Argus II was on than when it was switched off. For GVA, more patients at each point in time achieved the 2.9 GVA cutoff in the implanted eye when the Argus II was on compared with it switched off.

Conclusions and Relevance

Safety and visual function outcomes in this clinical practice setting cohort of patients with Argus II implants were consistent with previously reported results. Longer follow-up of these patients and data from additional patients are required to better outline the risks and benefits of this approach to addressing blindness secondary to severe-to-profound outer retinal degeneration.

Trial Registration

ClinicalTrials.gov identifier: NCT01490827.

Assessment of Postoperative Morphologic Retinal Changes by Optical Coherence Tomography in Recipients of an Electronic Retinal Prosthesis Implant

Importance

The postoperative retinal changes at the interface between an implant electrode array and the retina and whether these anatomic changes have an association with the patient visual performance are unknown.

Objective

To report morphologic changes in recipients of an Argus II Retinal Prosthesis.

Design, Setting, and Participants

This consecutive, noncomparative case series study included a retrospective review of the preoperative and postoperative optical coherence tomography of 33 eyes among 33 individuals who underwent Argus II Retinal Prosthesis System implantation between October 28, 2011, and June 8, 2017, at 2 different centers, by the same surgeon (S.R.). Thirteen patients received an implant at Azienda Ospedaliero Universitaria Pisana, Pisa, Italy, between October 28, 2011, and October 27, 2014, and 20 patients underwent surgery at Azienda Ospedaliera Universitaria Careggi, Florence, Italy, between December 20, 2014, and June 8, 2017. Patients were excluded if they did not reach the 6-month follow-up.

Main Outcomes and Measures

All patients were evaluated before surgery, during the first postoperative day, and at 1, 3, 6, 12, and 24 months (subsequently once a year, except for patient-related adverse events), with a comprehensive ophthalmic examination, retinal fundus photography, spectral-domain optical coherence tomography, and visual function tests to evaluate the stability or improvement of their visual performance.

Results

Of the 20 patients included in the analysis, all were of white race/ethnicity, 12 (60%) were male, and the mean (SD) age was 57.4 (11.6) years. Optical coherence tomography revealed the development of a fibrosislike hyperreflective tissue limited at the interface between the array and retina in 10 eyes (50%). In 9 of 10 patients (90%), fibrosis evolved and progressed to retinal schisis. Despite the development of the fibrosis and schisis, there was no deterioration in the patient's visual performance evaluated prospectively with visual function tests (square localization and direction of motion).

Conclusions and Relevance

Optical coherence tomography may be used to observe the retinal anatomic changes in patients with an Argus II Prothesis. This analysis revealed the development of a fibrosislike hyperreflective tissue limited at the interface between array and retina that progressed to retinal schisis but with no deterioration in the patients' visual performance.

Retinal Anatomy and Electrode Array Position in Retinitis Pigmentosa Patients After Argus II Implantation: An International Study

PURPOSE

To assess the retinal anatomy and array position in Argus II retinal prosthesis recipients.

DESIGN

Prospective, noncomparative cohort study.

METHODS

Setting: International multicenter study.

PATIENTS

Argus II recipients enrolled in the Post-Market Surveillance Studies.

PROCEDURES

Spectral-domain optical coherence tomography images collected for the Surveillance Studies (NCT01860092 and NCT01490827) were reviewed. Baseline and postoperative macular thickness, electrode-retina distance (gap), optic disc-array overlap, and preretinal membrane presence were recorded at 1, 3, 6, and 12 months.

MAIN OUTCOME MEASURES

Axial retinal thickness and axial gap along the array's long axis (a line between the tack and handle); maximal retinal thickness and maximal gap along a B-scan near the tack, midline, and handle.

RESULTS

Thirty-three patients from 16 surgical sites in the United States and Germany were included. Mean axial retinal thickness increased from month 1 through month 12 at each location, but reached statistical significance only at the array midline (P = .007). The rate of maximal thickness increase was highest near the array midline (slope = 6.02, P = .004), compared to the tack (slope = 3.60, P < .001) or the handle (slope = 1.93, P = .368). The mean axial and maximal gaps decreased over the study period, and the mean maximal gap size decrease was significant at midline (P = .032). Optic disc-array overlap was seen in the minority of patients. Preretinal membranes were common before and after implantation.

CONCLUSIONS

Progressive macular thickening under the array was common and corresponded to decreased electrode-retina gap over time. By month 12, the array was completely apposed to the macula in approximately half of the eyes.

Multimodal Imaging Including Optical Coherence Tomography Angiography of a Patient With Argus II Retinal Prosthesis One Year After Implantation

A 58-year-old man with end-stage retinitis pigmentosa (RP) and visual acuity of light perception in both eyes received simultaneous phacoemulsification with intraocular lens implantation and implantation of the Argus II Retinal Prosthesis System (Second Sight Medical Products, Sylmar, CA) to his right eye 1 year ago. He accomplished the fitting and rehabilitation sessions, and no extraocular or intraocular complications were encountered perioperatively, postoperatively, or during the follow-up. The patient used the prosthesis actively for 2.5 to 3 hours per day. In this report, the authors compare the multimodal imaging findings including optical coherence tomography angiography of the chronic electrically stimulated retinal prosthesis implanted eye with the fellow eye. [Ophthalmic Surg Lasers Imaging Retina. 2018;49:55-59.].