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Genetic eye disease
Longitudinal assessment of female carriers of choroideremia using multimodal retinal imaging
  1. Sena A Gocuk1,2,3,
  2. Lauren N Ayton1,2,3,
  3. Thomas L Edwards2,3,
  4. Myra B McGuinness2,3,4,
  5. Robert E Maclaren5,6,
  6. Laura J Taylor5,6,
  7. Jasleen K Jolly1,5,6,7
  1. 1Department of Optometry and Vision Sciences, The University of Melbourne, Melbourne, Victoria, Australia
  2. 2Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, East Melbourne, Victoria, Australia
  3. 3Ophthalmology, Department of Surgery, The University of Melbourne, Melbourne, Victoria, Australia
  4. 4Centre for Epidemiology and Biostatistics, The University of Melbourne, Melbourne, Victoria, Australia
  5. 5Oxford Eye Hospital, Oxford University Hospital NHS Foundation Trust, Oxford, UK
  6. 6Nuffield Laboratory of Ophthalmology, Department of Clinical Neurosciences, The University of Oxford, Oxford, UK
  7. 7Vision and Eye Research Institute, Anglia Ruskin University, Cambridge, UK
  1. Correspondence to A/Prof Jasleen K Jolly; info{at}jvisionsci.com

Abstract

Background/aims Female choroideremia carriers present with a spectrum of disease severity. Unlike in men, the rate of disease progression has not been well characterised in carriers. This longitudinal study aimed to determine the rate of retinal degeneration in choroideremia carriers, using multimodal imaging and microperimetry.

Methods Choroideremia carriers previously seen at Oxford Eye Hospital (United Kingdom) between 2012 and 2017 returned for testing between 2015 and 2023, providing up to 11 years’ follow-up data. Participants had optical coherence tomography, fundus-tracked microperimetry and fundus autofluorescence (FAF) imaging performed.

Results Thirty-four eyes of 17 choroideremia carriers were examined using multimodal imaging. Median age was 44 (range: 15–73) years at baseline and median follow-up duration was 7 (range: 1–11) years. At baseline, phenotype was classified as fine (n=5 eyes), coarse (n=13 eyes), geographic (n=12 eyes) or male pattern (n=4 eyes). Thirteen patients showed no change in phenotype classification, four showed slight changes associated with choroideremia-related retinal degeneration. Despite this, carriers with severe retinal phenotypes had a statistically significant decline in average retinal sensitivity (−0.7 dB and −0.8 dB per year, respectively, p<0.001), area of geographic loss defined by FAF (+2.5 mm2 and +3.7 mm2 per year, respectively, p<0.001) and thinning of the photoreceptor complex (up to −2.8 microns and −10.3 microns per year, p<0.001).

Conclusion Choroideremia carriers, particularly those with severe retinal phenotypes, exhibit progressive retinal degeneration, as evident by multimodal imaging biomarkers and functional testing. Clinicians should not rely on retinal severity classification alone to assess disease progression.

  • Degeneration
  • Diagnostic tests/Investigation
  • Imaging
  • Prospective Studies
  • Retina

Data availability statement

No data are available.

http://creativecommons.org/licenses/by-nc/4.0/

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.

https://doi.org/10.1136/bjo-2024-325578

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    WHAT IS ALREADY KNOWN ON THIS TOPIC

    • Choroideremia carriers present with a spectrum of retinal disease severities, ranging from near-normal retinae to severe retinal degeneration, the latter known as ‘male pattern’ degeneration. Previously, it was unknown whether retinal disease in choroideremia carriers was progressive, and if so, the rate of progression.

    WHAT THIS STUDY ADDS

    • In this longitudinal study, choroideremia carriers with moderate–severe retinal disease (ie, geographic or male pattern phenotypes) progress over time.

    HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY

    • This may provide proof that choroideremia carriers with severe retinal disease should be considered for retinal gene therapy clinical trials, aimed at reducing disease progression.

    Choroideremia is a progressive chorioretinal degeneration caused by mutations in the CHM gene (OMIM: 303100) encoding Rab escort protein-1. The condition affects 1 in 50 000 men, with known variations between geographic regions and ethnic groups.1 The condition follows an X-linked inheritance pattern characterised by severe retinal disease in men with the disease-causing variant, and variable disease severities in female carriers.2 Affected men typically present with night blindness during early adolescence, followed by progressive degeneration of peripheral vision, leading to eventual central vision loss beginning between 30 and 40 years of age.3 Female carriers of choroideremia present with a spectrum of retinal disease severity ranging from near-normal retina to severe degeneration, the latter known as ‘male pattern’ degeneration.4 This variability may be explained by X-chromosome inactivation occurring at random during early embryonic development and skewing of phenotypic expression between the two X-chromosomes.2

    There have been several studies reporting retinal structure and functional biomarkers using multimodal imaging in affected men to predict disease prognosis. Progression rates in affected men were found to be 7.7% of the residual fundus autofluorescence (FAF) area each year, following a logarithmic decline with age.5 Affected men were found to have strong intereye symmetry measured by average retinal sensitivity threshold.6 Similarly, affected men also had moderate intereye symmetry of best-corrected visual acuity until macular involvement in later stages of the condition.6

    Unlike in men, female choroideremia carriers have been historically overlooked, evident by the limited clinical data regarding progression of retinal disease. Extrapolating from male data will not necessarily be appropriate as has been seen in other areas of medicine.7 Disparities in women’s healthcare continue to exist and a key reason identified is the lack of evidence pertaining specifically to women.8 This necessitates the study of progression in female carriers specifically.

    A 2006 study by Renner et al reported retinal appearance in two choroideremia carriers and found fundus alterations (such as pigmentary changes and enlargement of peripapillary atrophy) primarily using retinal fundus photography.9 A more recent study by Jauregui et al found no change in the retinal classification of mild, moderate or severe disease, using FAF imaging, in four choroideremia carriers over a period of 2–4 years.10 Furthermore, a cross-sectional study of choroideremia carriers has previously found no significant differences in visual acuity when carriers were stratified by age; however, it is well known that visual acuity is a poor indicator of overall retinal sensitivity, particularly in conditions such as choroideremia.11–13 There is a need for longitudinal assessment in a larger group of choroideremia carriers to determine whether the condition is progressive, as seen in affected men, and if so, which retinal biomarkers accurately predict progression of retinal disease using multimodal imaging and microperimetry.

    The recent US Food and Drug Administration (FDA)-approval of the first retinal gene therapy, Luxturna, for RPE65-assiocated Leber congenital amaurosis, has sparked interest in developing gene therapy for other inherited retinal diseases (IRDs). There are currently 10 retinal gene therapy clinical trials for men with choroideremia registered on clinicaltrials.gov, eight of which have been completed.2 These early phase trials report benefit of gene therapy for halting disease progression.14 However, none of these clinical trials includes female carriers in their inclusion criteria, despite some women presenting with severe retinal degeneration. The lack of inclusion of choroideremia carriers in current clinical trials may also be potentially attributed to unknown interactions of the disease-causing gene with the X-chromosome containing the wildtype gene. Therefore, it is imperative to understand genotype–phenotype correlations and disease prognosis in female carriers to determine carriers with, or at risk of, vision impairment, and subsequently whether they should be included in therapeutic treatment clinical trials for choroideremia.

    The aim of this longitudinal cohort study was to investigate rates of progression of FAF, optical coherence tomography (OCT) and perimetric parameters among female choroideremia carriers and to compare rates of progression from the baseline retinal classifications (fine, coarse, geographic or male pattern FAF phenotypes), over a period of up to 11 years.

    Methods

    Female carriers of choroideremia (genetically confirmed or obligate carriers) previously seen at the Oxford Eye Hospital between 2012 and 2017, who had provided consent to be contacted for future research, were contacted to attend a single follow-up study visit. Baseline visits of most carriers (70.5%) had been previously reported elsewhere.4 Ethics approval by Anglia Ruskin University Human Research Ethics Committee (ID # ETH2223) was obtained to contact and review identified carriers, to prospectively obtain longitudinal data. Carriers were invited to attend this follow-up visit at the Vision and Eye Research Institute at Anglia Ruskin University, Cambridge, UK in 2023. Participants provided informed consent prior to commencement of the follow-up visits and all works were conducted in accordance with the Declaration of Helsinki and institutional ethics and governance requirements.

    Assessment of macular sensitivity was performed for both eyes under mesopic test conditions prior to pupil dilation using the Macular Integrity Assessment (S-MAIA) microperimeter (iCare Finland Oy, Vantaa, Finland) with fundus tracking using a 10–2 grid (68 points) centred on the fovea and without formal dark adaptation.15 The follow-up function of exported baseline imaging was used to ensure the tested area matched the baseline examination. Following pupil dilation, macular-centred FAS(FAF; Spectralis, Heidelberg Engineering, Heidelberg, Germany) images of posterior pole (30° and 55°) were captured in both eyes. Participants had OCT(OCT 30° x 20°, 37 B-scans, High speed, ART 9; Spectralis, Heidelberg Engineering, Heidelberg, Germany) performed using the follow-up function to match the baseline testing protocol and position. Retinal phenotype was classified into fine, coarse, geographic and male pattern using the scheme previously published by Edwards et al4 (figure 1). All FAF images were graded by an optometry-trained researcher with expertise in choroideremia (SAG), and any uncertainty in retinal phenotype was resolved by an ophthalmology-trained researcher (TLE).

    Figure 1
    Figure 1

    Retinal disease severity classification of female carriers of choroideremia. Retinal disease severity classification as defined by Edwards et al4, using fundus autofluorescence (FAF) imaging: (A) fine, (B) coarse, (C) geographic and (D) male-pattern degeneration.

    Retinal sensitivities, presented as average threshold in decibels (dB), were obtained from the MAIA output files. The raw output files were also used to calculate the volumetric measure of the hill of vision (HoV), using an online open-source programme (https://ocular.shinyapps.io/MAIA3D/).16 FAF images were analysed to determine change in grayscale intensity over the entire image as well as the defined areas of geographic loss (hypo-FAF), following normalisation of the FAF images based on the average optic nerve grayscale intensity. Baseline and follow-up FAF images were matched using histogram equalisation methods17 in Fiji ImageJ18 (V.2.14.0) based on the normalised grayscale intensity of the optic nerve intensity. The average grayscale intensity (an average value between 0 to 255, with lower values indicating darker pixels) was calculated for fovea-centred 10 degrees using the 55° FAF images from both study visits in carriers with milder disease (fine and coarse phenotypes). For carriers with geographic or male pattern degeneration, area of atrophy was manually traced using Heyex (Heidelberg Engineering, Heidelberg, Germany) at baseline and follow-up, based on hypo-FAF and OCT B-scans to determine edges of retinal pigment epithelium (RPE) loss, as previously described.19 OCT images were exported in XML format and retinal segmentation was performed using the Orion software (Voxeleron, LLC, Pleasanton, California) to calculate retinal thickness of all retinal layers for each B-scan and pixel along the horizontal plane. The exported comma-separated values (CSV) output files from Orion were analysed using Python (PyCharm CE 2023.2, JetBrains, Prague, Czech Republic). Retinal thickness was calculated as total retinal thickness (TRT; from inner limiting membrane to Bruch’s membrane), inner retinal thickness (IRT; from inner limiting membrane to the outer surface of the outer plexiform layer) and photoreceptor complex (PRC; from the inner border of the outer nuclear layer to the inner margin of the RPE) for 1°, 3°, 5° and 7° in the horizontal and vertical planes from the fovea as previously described20 (online supplemental figure S1). Any decentred OCT scans were analysed for 1, 3 and 5 degrees, and the incomplete 7-degree rings were excluded from the analysis.

    Supplemental material

    Statistical analysis

    Baseline characteristics were presented according to the baseline phenotypic classification (fine/coarse/geographic/male pattern) as; frequency and per cent for retinal phenotype; mean and SD for continuous variables, with an approximately normal distribution; and median and IQR for other continuous variables. Data from both eyes of each participant at the baseline and follow-up visit were used to estimate the average rate of change for retinal sensitivity (dB), grayscale intensity (pixels), geographic loss (mm2) and retinal thickness (microns).

    Mixed effects models were used to account for correlation between right and left eyes, with an interaction term between time from baseline and retinal classification. Age was considered a potential confounder of the classification-outcome relationship a priori, and, therefore, added as a covariate to each of the mixed-effects models. Simple linear regression was used to determine the effect of age on the logarithmic area of atrophic region in carriers with geographic or male pattern phenotypes. All statistical analyses were performed using Prism (GraphPad Software, San Diego, California) and Stata (StataBE 18, StataCorp, College Station, Texas). An alpha level of 0.05 was used to indicate statistical significance.

    Results

    A total of 23 potentially eligible participants were identified through review of previous research databases. Of those three were not able to be contacted, and three were unable to attend the study visit due to personal circumstances. Seventeen female choroideremia carriers were included in this study (table 1).

    View this table:
    Table 1

    Participant baseline demographics

    Median age at baseline was 44 years (IQR: 29–60.5) with older participants presenting with more severe disease on average (see online supplemental figure S2). Baseline visits were performed at the Oxford Eye Hospital between 2012 and 2017. Carriers had a median follow-up visit duration of 7 years (range: 1–11 years).

    At baseline, there were 5 eyes with fine, 13 eyes with coarse, 12 eyes with geographic, and 4 eyes with male pattern phenotypes. Thirteen patients showed no change in phenotype classification, four showed slight changes that we were associated with choroideremia retinal degeneration (three eyes from fine to coarse and one eye from geographic to male pattern phenotype, figure 2A). Baseline imaging and perimetric parameters are detailed in online supplemental table 1.

    Figure 2
    Figure 2

    Change in retinal severity classification and retinal sensitivity between baseline and follow-up visits. (A) Classification based on FAF imaging, as defined by Edwards et al.4: (1) fine; (2) coarse; (3) geographic and (4) male pattern degeneration. (B) Change in retinal sensitivity measured by the macular integrity assessment (MAIA) microperimeter. (C) Change in volumetric measure of hill of vision. Carriers with fine retinal phenotype (n=2) do not have follow-up MAIA performed, therefore, only baseline average threshold and hill of vision volume are displayed. FAF, fundus autofluorescence; HoV, hill of vision.

    Microperimetry

    Female carriers with fine phenotype in both eyes did not have microperimetry performed at follow-up, as their data were obtained retrospectively, and, therefore, were excluded from the analysis. Furthermore, three carriers with geographic phenotype did not have follow-up microperimetry performed.

    Of those who performed both microperimetry measures (n=11), the carriers with geographic and male pattern phenotypes had statistically significant decrease in average threshold over time (geographic: −0.7 dB/year; male pattern: −0.8 dB/year, p<0.001; figure 2B and online supplemental figures S3 and S4). Carriers with coarse phenotype at baseline did not significantly change in retinal sensitivity over time (−0.2 dB per year, p=0.16, see online supplemental table 2). There were no significant differences between average threshold and HoV volume in monitoring progression over time.

    Fundus autofluorescence

    The area of geographic loss visible in the 55-degree FAF scan was quantified for carriers with geographic and male pattern phenotypes (n=16 eyes). Both phenotypes had significant increase in atrophic region over time (geographic: +2.5 mm2 per year; male pattern: +3.7 mm2 per year, p<0.001). Age was not found to significantly affect the rate of progression of the atrophic region logarithmic area in carriers with geographic or male pattern phenotypes (p>0.05; figure 3), thereby proving geographic loss does not depend on age. We propose that the more important factor is the presentation at baseline and rate of progression is determined by factors that are yet to be determined, as is the case with male patients. Further measures from natural history studies would confirm whether the rate of degeneration remains constant. None of the carriers with fine or coarse retinal phenotypes at baseline progressed to geographic or male pattern phenotypes, therefore, was not included in the analysis (as there were no atrophic lesions to measure).

    Figure 3
    Figure 3

    Logarithmic atrophy plotted against age for CHM carriers with geographic or male pattern degeneration. Mean (solid line) and error bars (dotted lines) for baseline and follow-up logarithmic area of atrophic region plotted against age (in years). Individual values are depicted for baseline (circles) and follow-up (diamond).

    Postprocessing FAF quantification of image grayscale intensity decreased over time for all carriers, indicating increase in retinal mottling in milder phenotypes and/or geographic loss area in more severe phenotypes (fine: −2.3 pixels per year, p=0.005; coarse: −1.8 pixels per year, p<0.001; geographic: −2 pixels per year, p<0.001; male pattern: −1.7 pixel per year, p=0.007). While this decrease is statistically significant, these values do not indicate clinical significance.21

    Subanalysis: area of preserved retina in female carriers with male pattern degeneration

    A subanalysis of the change in area of preserved retina seen in the two carriers with male pattern phenotype revealed carrier #3 had an average −1.29 mm2 decline per year in the right eye and −3.58 mm2 decline per year in the left eye, while carrier #10 had an average −0.19 mm2 decline per year in the right eye and −2.26 mm2 decline per year in the left eye.

    Optical coherence tomography

    All carriers had OCT performed, however, due to the baseline OCT protocol (15 degrees vertically), some volume scans were decentred (n=5 carriers: 2 fine, 2 geographic and 1 male pattern phenotypes) and had incomplete 7-degree measurements, and, therefore, these scans were analysed for the central 1–5 degrees only. Female carriers with male pattern degeneration consistently had retinal thinning as defined by TRT and PRC thickness, throughout the central retina (ie, 1°, 3°, 5° and 7°; p<0.001; figure 4). Furthermore, although thinning was seen throughout the central retina, the estimated change over time was greater closer to the fovea (1°: −10.8 µm per year; 3°: −9.7 microns per year; 5°: −6.2 microns per year, 7°: −4.8 microns per year, p<0.001). IRT did not significantly change for any carriers, except those with coarse phenotype at baseline, had an estimated inner retina thickening at 3° from the fovea over time (+1.7 microns per year, p=0.033). Carriers with coarse phenotype also had thinning of the PRC between 4° and 5° from the fovea (−0.7 microns per year, p=0.031), which may have contributed to no significant changes to the overall TRT.

    Figure 4
    Figure 4

    Changes to retinal thickness as detected using optical coherence tomography over time, in female carriers of choroideremia. Measurements taken for total retinal thickness (A), inner retinal thickness (B) and photoreceptor complex thickness (C) at 1°, 3°, 5° and 7° from the fovea between baseline and follow-up.

    Female carriers with geographic retinal phenotype had significant thinning of retinal layers in the parafovea (TRT at 5°: −2.0 microns per year, p<0.001; and 7°: −2.4 microns per year, p<0.001). These changes are due to thinning of the PRC at the parafovea (3°: −1.5 microns per year, p=0.007; 5°: −2.1 microns per year, p<0.001 and 7°: −1.9 microns per year, p<0.001). There were no significant changes to the inner retina over time for carriers with geographic retinal disease. All estimates of progression of each retinal biomarker may be found in online supplemental table S1.

    Discussion

    This study is the first to describe longitudinal changes in retinal biomarkers using multimodal imaging and microperimetry in female carriers of choroideremia. The current study found carriers with mild phenotypes (ie, fine and coarse) did not progress significantly over the study period, however, carriers with severe phenotypes (ie, geographic and male pattern) had faster rates of retinal degeneration, measured by macula sensitivity, area of geographic loss and thinning of the retina. The retinal phenotype classifications given at baseline did not change during the study period for most participants; this is indicative of the broad range of disease state that each classification category covers.

    Choroideremia carriers with geographic or male pattern retinal phenotypes had a statistically significant reduction in microperimetry central retinal sensitivity over the years-long data period. These changes were greater than the expected test–retest variability reported with macular disease, choroideremia and RPGR-associated retinitis pigmentosa.6 22 23 Men with choroideremia have previously been found to have small and inconsistent changes to mean retinal sensitivity during 6-month and 12-month follow-up periods.24 However, estimate of retinal sensitivity change over time has not been previously reported in a longer term study of men with choroideremia and remains an area for future work. Although it may take years for choroideremia carriers to obtain the mean sensitivity change recommended by the US FDA for progression (ie, 7 dB),25 there is evidence to suggest lower changes may be clinically meaningful. A study by Schönbach et al assessed longitudinal microperimetry changes of macular sensitivity in people with Stargardt disease and reported −0.68 dB decrease in retinal sensitivity over 12 months,26 which the authors postulated are clinically meaningful changes. The study team further proposed that such functional deficits precede structural changes apparent on FAF imaging.26 Likewise, Wu et al reported that people with intermediate age-related macular degeneration at baseline that had worsened clinical features at follow-up had −0.42 dB decrease in retinal sensitivity over a 12-month period.27 Such reported estimates in other conditions had a clinically significant impact on affected individuals, which suggest the reduction in retinal sensitivity seen in these choroideremia carriers may also potentially be clinically significant.

    Another significant finding in carriers with geographic or male pattern retinal phenotypes was the rate of progression of atrophy over time. A previous systematic review of atrophy in men with choroideremia reported an exponential decline of 0.05 log (mm2) per year (approximately −1.3 mm2 per year) of the residual RPE area.28 Despite the variation in the rate of degeneration between the two carriers in the current cohort, these rates of decline are comparable to those reported in affected men, potentially explained by X-inactivation skewing. Such results potentially indicate that female carriers with male pattern degeneration progress at similar rates seen in their male counterparts.

    Female carriers with severe retinal disease (ie, geographic or male pattern) were found to have statistically significant retinal thinning over time. Changes observed in carriers with male pattern degeneration are comparable to foveal thickness changes reported in men with choroideremia.3 The thinning observed in choroideremia carriers was due to degeneration of the PRC, rather than the inner retina. Our results are supported through histological findings by Syed et al, who examined the eyes of an 88-year-old symptomatic choroideremia carrier and concluded that outer nuclear layer thinning or loss occurs even in areas of preserved RPE and choroid.29 Furthermore, a cross-sectional study by Jauregui et al reported intact retinal layers in carriers with mild disease compared with retinal thinning and outer retinal loss seen in carriers with severe disease.10 Findings in our current study support such findings and also help estimate the rate of degeneration over time to determine disease prognosis in female carriers. However, evidence of inner retinal thickening in the coarse phenotype group may alternatively be a marker of active disease inflammatory processes with secondary changes supporting the retinal remodeling theory as found in other IRDs,20 30 suggesting that women with the course phenotype may warrant active monitoring.

    Although retinal disease in choroideremia carriers was found to be progressive over time, there was certainly no evidence to suggest all carriers will eventually develop the male pattern phenotype. The amount of progression in our cohort correlated with the retinal phenotype presented at baseline; carriers with severe presentations at baseline progress faster than those with milder presentations. While future work is required to determine correlations between genotype and phenotypic expression, results from the current study suggest that age was not a predictive factor for disease progression when stratified by retinal phenotype. Although the two carriers with male pattern degeneration were relatively older (60–69 and 70–79 age group, respectively), age of carriers with other retinal phenotypes varies considerably (fine: 30–69 years; coarse: 10–59 years; geographic: 30–79 years of age), indicating no clear phenotypic correlations with age, also supporting findings from other studies.10 31 Rather, this variability may be explained by X-inactivation skewing, which involves random inactivation of one X-chromosome in women (XX individuals) occurring during early embryonic development.32 33

    This study is the first of its kind to report on a cohort of carriers with a rare disease. Given that carriers are not routinely investigated, our sample size is reasonable but limited. The primary aim was to determine disease prognosis based on retinal phenotype grading to identify carriers at risk of vision loss who might benefit from therapeutic intervention. However, this focus may have further reduced the power of our analyses, especially for microperimetry, which was only performed at both visits for 11 out of the 17 carriers in the study. Future studies should consider conducting similar longitudinal assessments on a larger number of carriers, with complete datasets that include clinical tests, multimodal imaging and microperimetry. Furthermore, having only a baseline and a single follow-up visit may obscure the true nature of the disease’s progression rate, preventing us from assuming linearity in progression. With our current estimates of the rate of progression, it is now evident that future studies should employ a longitudinal design with multiple visits to accurately determine the progression pattern. This approach will provide a clearer understanding of how the disease evolves over time and improve patient care strategies.

    Postprocessing of FAF images enabled measurement and comparison of autofluorescence mottling over time, this worked well as a biomarker for disease progression in female carriers with fine or coarse retinal phenotypes. However, quantification of absolute intensities remains a challenge of FAF imaging for comparisons between subjects and longitudinal assessments of the same individual.34 FAF imaging may result in variable background intensities and image contrast due to ocular media and image resolution, which limits interpretation of grayscale intensity quantification.35 Currently, there is no universally accepted method or software for FAF quantification,36 with several studies adopting different approaches to achieve this for various retinal conditions.37–39 The current study acknowledges the limitations involved in histogram equalisation, however adopted this method due to the least amount of modification of the original FAF image. Although a statistically significant change of grayscale intensities was found for all carriers, these values do not represent clinical significance considering the pixel range in a grayscale image (ie, 0–255 pixels). However, the results provide an objective measure of the increase in mottling seen in female carriers with mild disease over time.

    Conclusions

    Retinal disease in female carriers of choroideremia was found to be progressive using multimodal imaging and microperimetry. Average retinal sensitivity, area of geographic loss and PRC thickness were found to be sensitive retinal biomarkers to determine progression in choroideremia carriers.

    The rate of disease progression in female carriers was found to be affected by the initial presenting retinal phenotype, whereby carriers with severe retinal phenotypes (ie, geographic or male pattern) progress faster, compared with carriers with milder retinal phenotypes (ie, fine or coarse). Future research is required to understand whether retinal disease progression follows a linear or exponential trend. Furthermore, although further information is required to understand interactions of the wildtype gene and any potential issues with gene therapy treatment, the authors advocate for inclusion of choroideremia carriers with severe retinal phenotypes in therapeutic treatment trials, such as retinal gene therapy, to potentially slow disease progression in these individuals.

    Data availability statement

    No data are available.

    Ethics statements

    Patient consent for publication

    Ethics approval

    Ethics approval by Anglia Ruskin University Human Research Ethics Committee (ID # ETH2223). Participants gave informed consent to participate in the study before taking part.

    Acknowledgments

    We would like to extend our gratitude to all our participants for volunteering their time and providing valuable insights during the study.

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    Supplementary materials

    • Supplementary Data

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    Footnotes

    • X @@sgocuk, @@DrLaurenAyton, @@MyraMcguinness, @@eyeMacLaren, @@jkjolly4

    • Contributors SAG and JKJ accept full responsibility for the overall content as guarantors, ensuring the integrity of the research, access to the data, and control over the decision to publish. SAG and JKJ led the planning and design of the study, conducted the research, analysed the data, and wrote the manuscript. All other co-authors contributed to the study design, supervised data collection, assisted with interpretation of the results and provided critical revisions to the manuscript.

    • Funding This work was supported by the Australian Government Research Training Program Scholarship awarded to SAG; the Benelli Family Award by the Choroideremia Research Foundation to SAG; a University of Melbourne Driving Research Momentum Fellowship to LNA; and an NHMRC Investigator grant to LNA (GNT#1195713). JKJ was supported by a National Institute for Health and Social Care Fellowship (NIHR). The Centre for Eye Research Australia receives support from the Victorian State Government through its Operational Infrastructure Support Program. The sponsor and funding organisation had no role in the design or conduct of this research.

    • Competing interests None declared.

    • Provenance and peer review Not commissioned; externally peer-reviewed.

    • Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.