Intraobserver Repeatability and Interobserver Reproducibility of Ellipsoid Zone Measurements in Retinitis Pigmentosa

Long-term natural history of ellipsoid zone width in USH2A-retinopathy

AIMS

To investigate the long-term natural history of ellipsoid zone (EZ) width in USH2A-retinopathy.

METHODS

EZ width measurements from optical coherence tomography were retrospectively obtained from 110 eyes of 55 participants with molecularly confirmed biallelic USH2A-retinopathy. We used a hierarchical Bayesian method to construct and compare different mathematical models describing the long-term decline of EZ width.

RESULTS

Compared with linear and quadratic models, exponential decline best represented the long-term loss of EZ width based on the deviance information criterion score. Log-transformed EZ width declined linearly over 30 years of inferred disease duration (median: 0.063 (IQR: 0.040-0.086) log (µm)/year). Compared with the raw EZ width decline rate, the log-transformed EZ width decline rate required 48% fewer patients to achieve an identically powered 1-year trial (38 vs 73 participants). Log EZ width decline rate was uncoupled from baseline EZ width (Spearman ρ=-0.18, p=0.06) and age (ρ=-0.10, p=0.31). Eyes with Usher syndrome exhibited earlier median onset ages of macular EZ width loss (18.8 (IQR: 13.1-24.7) vs 28.1 (IQR: 18.5-35.8) years, p<0.001) but comparable log EZ width decline rates (0.060 (IQR: 0.035-0.100) vs 0.065 (IQR: 0.050-0.079) log (µm)/year; p=0.42).

CONCLUSIONS

EZ width follows an exponential decline in USH2A-retinopathy. Compared with raw EZ width decline rate, log-transformed EZ width decline rate may be a superior endpoint for clinical trials. Syndromic eyes exhibit an earlier onset of macular EZ width loss but progress at comparable rates to non-syndromic eyes.

Use of ellipsoid zone width for predicting visual prognosis after cataract surgery in patients with retinitis pigmentosa

OBJECTIVE

To predict the visual prognosis of cataract surgery in patients with retinitis pigmentosa by measuring ellipsoid zone (EZ) width using spectral-domain optical coherence tomography.

METHODS

This retrospective study included patients with retinitis pigmentosa who underwent uncomplicated cataract surgery between December 2017 and June 2020. Preoperative best-corrected visual acuity (BCVA) and the best postoperative BCVA during follow-up were collected. EZ width was measured on preoperative cross-sectional optical coherence tomography images along the horizontal/vertical meridian through the fovea.

RESULTS

Thirty-eight eyes of 38 patients (22 female; mean [±standard deviation] age, 62.1 ± 11.8 years) were included. The median preoperative logarithm of the minimum angle of resolution BCVA of 0.52 (range, 0.00-3.00) significantly improved to 0.07 (range, -0.18-3.00) after surgery (P < 0.001). On preoperative spectral-domain optical coherence tomography images, the median horizontal, vertical, and average EZ widths were 783 (range, 0-9837), 761 (range, 0-10 250), and 769 (range, 0-10 043) μm, respectively. Postoperative BCVA significantly correlated with the horizontal (r = -0.784, P < 0.001), vertical (r = -0.777, P < 0.001), and average EZ widths (r = -0.777, P < 0.001). The area under the receiver operating characteristic curve for the ability of the horizontal, vertical, and average EZ widths to discriminate eyes with and without postoperative BCVA ≤ 0.3 was 0.971, 0.960, and 0.963, respectively, with best cut-off values of 513, 608, and 515 μm, respectively.

CONCLUSIONS

EZ width measurement can help predict the visual prognosis of cataract surgery in patients with retinitis pigmentosa. A preferable visual acuity prognosis can be expected in patients with an EZ width of approximately 600 μm.

The Natural History of CNGB1-Related Retinopathy: A Longitudinal Phenotypic Analysis

Cyclic nucleotide-gated channel β 1 (CNGB1) encodes a subunit of the rod cyclic nucleotide-gated channel. Pathogenic variants in CNGB1 are responsible for 4% of autosomal recessive retinitis pigmentosa (RP). Several treatment strategies show promise for treating inherited retinal degenerations, however relevant metrics of progression and sensitive clinical trial endpoints are needed to assess therapeutic efficacy. This study reports the natural history of CNGB1-related RP with a longitudinal phenotypic analysis of 33 molecularly-confirmed patients with a mean follow-up period of 4.5 ± 3.9 years (range 0-17). The mean best corrected visual acuity (BCVA) of the right eye was 0.31 ± 0.43 logMAR at baseline and 0.47 ± 0.63 logMAR at the final visit over the study period. The ellipsoid zone (EZ) length was measurable in at least one eye of 23 patients and had a mean rate of constriction of 178 ± 161 µm per year (range 1.0-661 µm), with 57% of patients having a decrease in EZ length of greater than 250 µm in a simulated two-year trial period. Hyperautofluorescent outer ring (hyperAF) area was measurable in 17 patients, with 10 patients not displaying a ring phenotype. The results support previous findings of CNGB1-related RP being a slowly progressive disease with patients maintaining visual acuity. Prospective deep phenotyping studies assessing multimodal retinal imaging and functional measures are now required to determine clinical endpoints to be used in a trial.

Investigating Biomarkers for USH2A Retinopathy Using Multimodal Retinal Imaging

Pathogenic mutations in USH2A are a leading cause of visual loss secondary to non-syndromic or Usher syndrome-associated retinitis pigmentosa (RP). With an increasing number of RP-targeted clinical trials in progress, we sought to evaluate the photoreceptor topography underlying patterns of loss observed on clinical retinal imaging to guide surrogate endpoint selection in USH2A retinopathy. In this prospective cross-sectional study, twenty-five patients with molecularly confirmed USH2A-RP underwent fundus autofluorescence (FAF), spectral-domain optical coherence tomography (SD-OCT) and adaptive optics scanning laser ophthalmoscopy (AOSLO) retinal imaging. Analysis comprised measurement of FAF horizontal inner (IR) and outer (OR) hyperautofluorescent ring diameter; SD-OCT ellipsoid zone (EZ) and external limiting membrane (ELM) width, normalised EZ reflectance; AOSLO foveal cone density and intact macular photoreceptor mosaic (IMPM) diameter. Thirty-two eyes from 16 patients (mean age ± SD, 36.0 ± 14.2 years) with USH2A-associated Usher syndrome type 2 (n = 14) or non-syndromic RP (n = 2) met the inclusion criteria. Spatial alignment was observed between IR-EZ and OR-ELM diameters/widths (p < 0.001). The IMPM border occurred just lateral to EZ loss (p < 0.001), although sparser intact photoreceptor inner segments were detected until ELM disruption. EZ width and IR diameter displayed a biphasic relationship with cone density whereby slow cone loss occurred until retinal degeneration reached ~1350 μm from the fovea, beyond which greater reduction in cone density followed. Normalised EZ reflectance and cone density were significantly associated (p < 0.001). As the strongest correlate of cone density (p < 0.001) and best-corrected visual acuity (p < 0.001), EZ width is the most sensitive biomarker of structural and functional decline in USH2A retinopathy, rendering it a promising trial endpoint.

Challenges Associated With Ellipsoid Zone Intensity Measurements Using Optical Coherence Tomography

Translational Relevance

Qualitative evaluation of the ellipsoid zone band on optical coherence tomography is a valuable clinical tool for assessing photoreceptor structure, though more quantitative metrics are emerging. Awareness of the challenges involved in interpreting quantitative metrics is important for their clinical translation.

Assessing the Use of Incorrectly Scaled Optical Coherence Tomography Angiography Images in Peer-Reviewed Studies: A Systematic Review

Importance

Individual differences in axial length affect the lateral magnification of in vivo retinal images and as a result can affect the accuracy of quantitative measurements made from these images. As measurements from optical coherence tomography angiography (OCTA) images are becoming increasingly used in the diagnosis and monitoring of a wide range of diseases, evaluating which studies use correctly scaled images is crucial to their interpretation.

Objective

To perform a systematic literature review to assess the percentage of articles that report correcting the scale of their OCTA images for individual differences in retinal magnification.

Evidence Review

A PubMed (MEDLINE) search was conducted for articles on OCTA retinal imaging published between June 1, 2015, and June 1, 2018. Initial results included 7552 articles. Initial exclusion criteria removed studies of animal models, as well as reviews, letters, replies, comments, and image-based or photographic essays. Articles not written in English and those that required purchase from non-English language websites were excluded. Articles that did not use OCTA for imaging the retina were also excluded. Remaining articles were reviewed in detail to assess whether the OCTA measurements required correct lateral scaling, and if so, whether axial length was reported or used to scale the images. We also determined the number of articles that mentioned the lack of correct lateral scaling as a limitation of the study.

Findings

A total of 989 articles were included in the detailed review. Of these, 509 were determined to require correct image scaling for their analyses, but only 41 (8.0%) report measuring and using axial length to correct the lateral scale of their OCTA images. Furthermore, of the 468 articles that did not correctly scale their images, only 18 (3.8%) mentioned this as a limitation to their study.

Conclusions and Relevance

These findings suggest that most peer-reviewed articles in PubMed that use quantitative OCTA measurements use incorrectly scaled images. This could call into question the conclusions of such studies and warrants consideration by OCTA manufacturers, physicians, authors, journal reviewers, and journal editors.

Clinical trial design for neuroprotection in RHO autosomal dominant retinitis pigmentosa; outcome measure considerations

Purpose: To identify structural and functional outcome measures among patients with Rho-positive autosomal dominant Retinitis Pigmentosa (adRP) to aid neuroprotection trial design.Methods: This was a retrospective cohort study of 52 patients with Rho-positive adRP. We measured Goldmann Visual Fields (GVF) constriction in four sectors (nasal, temporal, inferior, superior), and sectoral Ellipsoid Zone (EZ) width degeneration using Spectral Domain Optical Coherence Tomography (OCT) scans. Disease progression trajectories were projected using mixed effects modeling.Results: Superior GVF was most constricted at presentation and had the shallowest trajectory (less steep negative slope); Inferior GVF was less constricted (corrected p < .001) and had a steeper negative slope (corrected p = .019) than superior GVF. Temporal EZ was most stable on OCT with a relatively shallow negative trajectory (corrected p = .011).Conclusions: Patients' superior visual fields presented with more constriction and subsequently had a shallow negative slope suggesting the corresponding inferior retina may be "burned out" at presentation. Targeted therapies for adRP will likely show a greater efficacy signal if delivered to the superior and nasal retina, which may demonstrate more change on OCT and GVF over the course of a neuroprotection trial.Translational Relevance: Mixed effects analysis of sectoral visual field constriction and EZ degeneration in Rho-positive adRP can prove useful in monitoring therapeutic efficacy and identifying targets for local therapies.

Early Cone Photoreceptor Outer Segment Length Shortening in RPGR X-Linked Retinitis Pigmentosa

INTRODUCTION

Introduction of retinal gene therapy requires established outcome measures along with thorough understanding of the pathophysiology. Evidence of early, thinned outer segments in RPGR X-linked retinitis pigmentosa could help understand how the level of cone photoreceptor involvement translates to visual potential.

OBJECTIVE

Analysis of foveal photoreceptor outer segment length in a young cohort of RPGR patients to help clarify the reason for absent maximal visual acuity seen.

METHODS

Case-control study of RPGR patients. Quantitative measurement of photoreceptor outer segment by OCT.

RESULTS

Eighteen male RPGR patients and 30 normal subjects were included. Outer segment thickness differed significantly between the RPGR and normal eyes (p < 0.0005). Mean outer segment values were 35.6 ± 2.3 µm and 35.4 ± 2.6 µm for RPGR right and left eyes, respectively. In normal eyes, the mean outer segment thickness was 61.4 ± 0.7 µm for right eyes and 62.4 ± 0.7 µm for left eyes.

CONCLUSIONS

Patients with RPGR X-linked retinitis pigmentosa show thinning of the foveal photoreceptor outer segment thickness early in the disease course, which could be an explanation for the lower maximum visual acuity seen. These findings must be taken into consideration when assessing efficacy outcome measures in retinal gene therapy trials.

Reliability of Spectral-Domain OCT Ellipsoid Zone Area and Shape Measurements in Retinitis Pigmentosa

Purpose

We investigate the ellipsoid zone (EZ) area and EZ boundary shape measurement reliability and the operability characteristics of two methods of EZ boundary delineation in spectral-domain optical coherence tomography (SD-OCT).

Methods

EZ boundaries in SD-OCT scans of 122 eyes from 64 subjects with autosomal dominant retinitis pigmentosa were delineated by three raters using two methods, termed the profile and en face methods. For each method, we determined the measurement reliabilities for boundary area (EZ area) and boundary shape, percentage of eyes with measurable EZ (measurability), time required, and effect of rater experience.

Results

With expert raters, inter- and intrarater area intraclass correlation coefficients (ICCs) were 0.986 and 0.980 (profile) and 0.959 and 0.976 (en face), respectively. In comparison, the corresponding shape ICCs were 0.906 and 0.891 (profile) and 0.845 and 0.885 (en face), indicating lower reliability for the raw measurements (P ≤ 0.01). Only profile method interrater reliability depended on experience. Average measurement times per eye were 8.2 (profile) and 4.1 (en face) minutes. Measurability percentages were 99.2% (profile) and 73.0% (en face).

Conclusions

The slower profile method had better measurability, and with expert raters yielded the best area and shape reliabilities. The faster, but less sensitive, en face method still showed excellent reliability, and was less dependent on experience. Shape analysis reveals the boundary measurements underpinning EZ area have lower reliability than suggested by area analysis.

Translational Relevance

This study provides new reliability perspectives and logistical considerations for the manual measurement procedures that generate EZ area outcome measures.