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ORIGINAL ARTICLE
Year : 2023 | Volume
: 22
| Issue : 4 | Page : 451-455
Clinical presentation and macular morphology in retinitis pigmentosa patients
Ogugua Ndubuisi Okonkwo1, Adekunle Olubola Hassan1, Chineze Thelma Agweye2, Umeh Victor3, Toyin Akanbi3
1 Department of Ophthalmology, Eye Foundation Hospital and Eye Foundation Retina Institute, Lagos, Nigeria
2 Department of Ophthalmology, University of Calabar Teaching Hospital, Calabar, Nigeria
3 Department of Ophthalmology, Eye Foundation Hospital, Abuja, Nigeria
Correspondence Address:
Ogugua Ndubuisi Okonkwo
Eye Foundation Hospital and Eye Foundation Retina Institute, Lagos
Nigeria
Source of Support: None, Conflict of Interest: None
CheckDOI: 10.4103/aam.aam_181_22
Abstract
Background: Optical coherence tomography (OCT) is a noninvasive, frequently used imaging technology that enables detailed viewing of retina anatomy. It is used to monitor disease progression in retinitis pigmentosa (RP) eyes, including detecting changes in retinal thickness. Purpose: The purpose of the study is to determine the clinical presentation and macular morphology in RP eyes using OCT imaging. Methods: A retrospective review of case records and OCT scans in eyes diagnosed with RP in two ophthalmic clinics in Nigeria. Biodata, Snellen best-corrected visual acuity (BCVA), intraocular pressure (IOP), vertical cup-to-disc ratio (VCDR), and presence of maculopathy were determined. Data were analyzed using IBM SPSS version 22.0 (IBM Corp. Armonk, NY, USA). Results: Fifty-five eyes of 28 patients (18 males and 10 females), with a mean age of 47.16 ± 15.56 years (22–77 years), were studied. 40–49 years was the most frequent age group, 28.6%. Severe visual impairment occurred in 22% of eyes and myopia in 32%. Twenty-nine percent had undergone cataract surgery or had a significant cataract. The mean IOP was 11 mmHg, and the mean VCDR was 0.46. On OCT examination, macular atrophy was the most common finding in 74.5% of eyes, epiretinal membrane in 16.3%, cystoid macular edema in 7.3%, vitreomacular adhesion in 5.4%, and vitreomacular traction in 1.8%. There was no association between macular morphology, macular thickness, and BCVA (P = 0.155, P = 0.424). Conclusion: OCT provides information on macula structure in RP eyes. About 14.5% of eyes had a normal macula, while 85.5% had a maculopathy, confirming that RP eyes have a higher rate of maculopathy than non RP eyes. OCT evaluation of an RP eye should be a standard workup for the early detection of such maculopathy and monitoring for disease progression.
Résumé
Contexte: La tomographie par cohérence optique (OCT) est une technologie d'imagerie non invasive fréquemment utilisée qui permet une visualisation détaillée de l'anatomie de la rétine. Elle est utilisée pour surveiller la progression de la maladie dans les yeux de la rétinite pigmentaire (RP), y compris la détection des changements dans l'épaisseur de la rétine. Objectif: Le but de l'étude était de déterminer la présentation clinique et la morphologie maculaire des yeux présentant une RP à l'aide de l'imagerie OCT. Méthodes: Une revue rétrospective des dossiers de cas et des scans OCT dans les yeux diagnostiqués de RP a été réalisée dans deux cliniques ophtalmologiques au Nigeria. Les données biographiques, la meilleure acuité visuelle corrigée de Snellen (MAVC), la pression intraoculaire (PIO), le rapport cup-sur-disc vertical (RCDV) et la présence de maculopathie ont été déterminés. Les données ont été analysées à l'aide d'IBM SPSS version 22.0 (IBM Corp. Armonk, NY, USA). Résultats: Cinquante-cinq yeux de 28 patients (18 hommes et 10 femmes), âgés en moyenne de 47,16 ± 15,56 ans (22–77 ans) ont été étudiés. Les 40 à 49 ans étaient la tranche d'âge la plus fréquente à 28,6 %. Une déficience visuelle sévère est survenue dans 22 % des yeux et une myopie dans 32 %. Vingt-neuf pour cent avaient subi une chirurgie de la cataracte ou avaient une cataracte importante. La PIO moyenne était de 11 mmHg et le RCDV moyen était de 0,46. À l'examen OCT, on retrouvait l'atrophie maculaire prédominante dans 74,5 % des yeux, la membrane épirétinienne (16,3 %), l'œdème maculaire cystoïde (7,3 %), l'adhérence vitréomaculaire (5,4 %) et la traction vitréomaculaire (1,8 %). Il n'y avait aucune association entre la morphologie maculaire, l'épaisseur maculaire et la MAVC (P = 0,155, P = 0,424). Conclusion: l'OCT fournit des informations sur la structure de la macula dans la RP. Environ 14,5% des yeux avaient une macula normale contre 85,5% avec maculopathie, confirmant ainsi que les yeux avec RP ont un taux de maculopathie plus élevé que les yeux sans RP. L'évaluation OCT d'un œil avec RP devrait être un bilan standard pour la détection précoce de maculopathie et la surveillance de la progression de la maladie.
Mots-clés: Membrane épirétinienne, dystrophie rétinienne héréditaire, atrophie maculaire, œdème maculaire, tomographie par cohérence optique, rétinite pigmentaire
Keywords: Epiretinal membrane, inherited retinal dystrophy, macular atrophy, macular edema, optical coherence tomography, retinitis pigmentosa
Introduction 
Retinitis pigmentosa (RP) is an inherited retinal disease. It progresses slowly, typically affecting the rod photoreceptors earlier than the cones.[1],[2] A clinical diagnosis of RP can be made based on the following: a positive family history of RP, presence of night blindness, impaired peripheral and subsequent central vision leading to visual field constriction, characteristic intraretinal bone spicule pigmentation in the mid-periphery, waxy optic disc pallor, attenuation of the retinal arteries, and reduction in the standard full-field electroretinogram.[3],[4],[5] The worldwide prevalence of RP ranges from 1:1878 to 1:7000 across different racial groups.[6] Nkanga et al., in a multicenter study done in Nigeria, reported an RP prevalence of 3.6%.[7]
Optical coherence tomography (OCT) has been used for over two decades in ophthalmology to obtain in situ images of the retina in health and several diseases.[8] The macula, the central part of the retina, can be assessed objectively using OCT in a noncontact and noninvasive manner.[9],[10] OCT uses the principle of low coherence interferometer to form cross-sectional images of the retina with an axial resolution of 10 μm and lateral resolution of 20 μm.[10] With high-resolution cross-sectional images of retinal structure, measurement of retinal thickness, detection of macular disease, and monitoring for progressive disease on sequential examinations are possible.[10] The OCT provides a clinically relevant method of analyzing retinal architecture, thus giving qualitative and quantitative information regarding the macula and adjacent structures in several retinal diseases, including RP.[2],[3],[10] In the case of RP, OCT would reveal an initial involvement of photoreceptors and retinal pigment epithelial cells. Eventually, there is widespread atrophy of several more layers of the retina.[10] The study objective is to determine the clinical presentation and macular morphology in RP eyes using the spectral domain (SD) OCT.
Methods This study is a retrospective review of 55 eyes of 28 consecutive patients diagnosed with RP who attended the retina clinic in two ophthalmic hospitals in Nigeria. Ethical approval was obtained from the Eye Foundation Hospital Health Research Ethics Committee. A waiver was given on the basis that the study involved a review of medical records. This research was performed according to the principles of the Helsinki declaration, and the patient's information was anonymized.
RP was diagnosed based on a history of impaired nighttime vision or poor illumination, impairment in visual fields, and clinical examination, which revealed mid-peripheral intraretinal perivascular “bone-spicule” pigmentary changes, arteriolar narrowing, and waxy disc pallor. We excluded eyes with significant media opacities that prevented a detailed view of the posterior segment and obtained good quality retina OCT images. Eyes having a history of concomitant ocular disease or treatment (such as diabetic macula edema, intravitreal antivascular endothelial growth factor injection, and laser therapy) were excluded. Those eyes in which SD-OCT images were not available or were deemed not to be of good quality were also excluded.
Information derived from patients' case notes included biodata, Snellen best-corrected visual acuity (BCVA) and refraction, intraocular pressure (IOP), lens status, findings on the SD-OCT imaging of the macula, and OCT-derived vertical cup-to-disc ratio (VCDR). Monocular Snellen BCVA of each eye was categorized using the International Classification of Disease 11 World Health Organization categorization of visual impairment as indicated;[11]
Mild – Visual acuity worse than 6/12–6/18Moderate – Visual acuity worse than 6/18–6/60Severe – Visual acuity worse than 6/60–3/60Blindness – Visual acuity worse than 3/60.SD-OCT macula scans were acquired using the Optovue RTVue OCT machine (Optovue Inc., Fremont, CA). Repeat A-scans at 70,000 A-scans per second were used to obtain composite B-scan images. A 6 mm × 6 mm scan of the central macula for each eye was acquired, and horizontal and vertical cross line sections through the fovea. We evaluated all photograph's quality, and a scan quality index of ≥50 was acceptable for all the images (manufacturer's signal quality range 0–100). In each cross-sectional OCT scan, we examined the foveomacular area and the vitreomacular interface for the presence of vitreomacular traction (VMT), vitreomacular adhesion (VMA), or epiretinal membrane (ERM). Macula status was further categorized based on OCT-determined central macular thickness (CMT) as atrophic (0–249 μm), normal (250–299 μm), and macular edema or thickened (≥300 μm).[12],[13] In all the macular edema eyes, cystic spaces were also present within the OCT scan of the macula.
Statistical analysis of the data collected was performed using the Statistical Package for the Social Sciences (SPSS) for Windows (version 20, SPSS inc., Chicago, IL, USA). Descriptive statistics was done using frequencies and histograms. Pearson's Chi-square was used to correlate the visual acuity and CMT; a P < 0.05 was statistically significant.
Results Twenty-eight RP patients were diagnosed within the study period. Fifty-five eyes of the 28 patients (10 males, 18 females) diagnosed with RP served as the study sample. In a 57-year-old male patient, one eye was excluded due to a postsurgical cornea decompensation and opacity, preventing view of the posterior segment. [Table 1] shows the age distribution of study participants. The mean age of the study participants was 47.16 ± 15.56 years (22–77 years). Most patients (14, 50%) were within the 30–49-year age group, and the two extreme age groups had the lowest number of participants.
The distribution of visual acuity is represented in [Table 2]. Most eyes had normal or mild vision impairment. Moderate and severe vision impairment was present in 52.7% of eyes.
Myopia was the most common refractive error (17 eyes, 31.5%). In 16.6% and 9.3% of eyes, hyperopia and emmetropia were present, respectively. In 43% of eyes, the refractive error could not be determined because of the poor presenting vision.
Majority of eyes had a clear lens, and 29.2% of eyes had undergone cataract surgery or had a significant cataract at presentation. Lens categories are represented in [Table 3].
The distribution of IOP in the 55 eyes is represented using the histogram in [Figure 1]. The IOP range was between 7 and 19 mmHg (average 11 mmHg). The distribution of VCDR determined using the SD-OCT is represented in [Figure 2]. The VCDR ranges from 0.1 to 0.9, with a median of 0.5.
Figure 1: Bar chart illustrating the frequency of the different intraocular pressure readings of participating eyes in “mmHg”
Figure 2: Bar chart illustrating the frequency of the different vertical cup to disc ratio, measured using the optical coherence tomogramOCT examination of the macula revealed the following macular morphological features and maculopathy, represented in [Table 4].
Table 4: Optical coherence tomography characterization and distribution of macular morphology in 55 eyesMacular atrophy was the most common morphological feature in 41/55 eyes (74.5%), while a normal macula was present in 8/55 eyes (14.5%). Analysis of macular morphology and visual acuity showed no significant association (P = 0.155) and there was no association between CMT and BCVA (P = 0.424).
Discussion In this study, more than half of the eyes had moderate-to-severe visual impairment. Lens findings, including pseudophakia, aphakia, and significant cataracts, were identified in about a third of eyes. Most RP eyes presented with a VCDR of 0.4, and IOP was mostly within the normal range. Myopia was the most prevalent refractive error. The most common macula morphology was an atrophic macula. However, there was no statistically significant association between macula morphology, CMT and BVCA (P = 0.155 and P = 0.424, respectively).
Impaired vision and impaired night time vision (52.7%) were the most common symptom that necessitated RP patients to seek ophthalmic consultation. This is similar to the previous hospital-based report from Cameroon, which reported a 57.5% rate of visual impairment, but lower than reports from hospitals in Pakistan (80.3%), Saudi Arabia (86.65%), and Nigeria (69.8%, 76.7%), respectively.[14],[15],[16],[17],[18]
Significant cataracts and previous cataract surgery were observed in 29.2% of eyes. This rate is higher than was previously reported in Cameroon and Nigeria.[14],[17] However, the rate is lower than those observed by Auffarth in Germany,[19] Pruett in the United States[20] and in Pakistan.[15] The prevalence of myopia noted in this study was lower than that observed in Pakistan[15] but higher than reported by Onakpoya et al.[17] The refractive state of 23 eyes could not be ascertained. This finding could partly reflect the reduced vision in RP eyes, making refraction difficult. Such patients would require low-vision rehabilitative services. Crystalline lens findings and the occurrence of cataract are a significant clinical presentation in an RP eye. Cataracts can be a reason for central vision loss. Cataract surgery in RP eyes is known to result in improved vision, and the prognosis for visual improvement is determined by the preoperative presence of the ellipsoid zone (EZ).[21],[22],[23],[24]
Macular lesions are observed to be more prevalent in RP eyes compared to the general population.[25] OCT has been used over the past two decades to assess RP eyes. In 1997, Jacobson et al. first described the OCT findings of retinal thinning and loss of the RPE and choriocapillaris in patients with X-linked RP.[26] This was one of the first reported uses of OCT.[27] These OCT findings agreed with previous histological findings in RP eyes, suggesting that OCT could be used as a reliable surrogate for monitoring retinal anatomy in RP.[27] Sandberg et al., in 2005, first reported on the correlation of retinal thickness with BCVA in RP eyes.[28] This pioneering work reported a positive correlation using time domain OCT of total retinal thickness and BCVA. They found that thinner retinas tend to have poor BCVA. Since this initial report, controversy has trailed this finding as several studies have not found a significant correlation between retina thickness and BCVA. Our study is one such study. It has been previously demonstrated that vision in RP eyes, as in other eyes, depends on the presence of biomarkers for vision, such as the EZ and external limiting membrane and not on the thickness of the macula.[13] Ibrahim and Eldaly, however, have reported a strong positive correlation between CMT and BCVA in their small series of 26 eyes.[29] Moreover, OCT parameters, including total retina thickness, outer retina thickness, and EZ width, are used to monitor the natural history of different forms of RP and as outcome measures in the treatment trials targeting RP eyes.[27]
Using the OCT for examination, we found that the most frequent macula abnormality was macular atrophy (53.2% of eyes), similar to the 53.8% of eyes reported in a prospective study in Egypt.[29] However, the prevalence of atrophy in our study was higher than in previous studies from Pakistan and Nigeria.[15],[17] These two studies, however, used clinical examination to detect macular atrophy, which could result in underreporting the macular atrophy rate, as OCT yields a higher detection rate than clinical examination.
ERM was the second-most common finding in our research. The prevalence of ERMs in RP eyes varies widely and has been reported to be between 1.4% and 20.3%.[30] Our study rate of 16.3% for ERM falls within this range. The majority of the ERM eyes had an atrophic macula. VMA occurred in 5.4% of study eyes and VMT in 1.8%. Ikeda et al. reported on the outcome of surgical after removal of ERM in RP eyes and only 27.3% of eyes had a postoperative improvement in vision.[30] Therefore, it is yet to be determined whether our patients could obtain significant visual benefits after ERM removal. Although the occurrence of macular holes in RP eyes has been reported in other studies,[29],[30] we did not find a macular hole as a presentation in our study.
In our research, cystoid macular edema (CME) was the fourth-most common macular finding, after atrophic macula, ERM, and normal macula. OCT is more sensitive than clinical examination in detecting macular edema in RP eyes.[31] Our study rate of 7.3% for macular edema in RP eyes is likely more accurate than reports using only clinical examination. Our rate is, however, significantly lower than some other reported rates, which varies between 10% and 40% from previous research.[30] CME is a significant cause of vision loss in RP eyes and can be managed with topical or oral carbonic anhydrase inhibitors.
Conclusion This study though weakened by being retrospective and having a small sample size; we found RP in Nigerians to be a bilateral disease, with moderate-to-severe visual impairment in over 50% of eyes. Most patients were males and within working age. On OCT evaluation, most eyes (85.5%) have a macula abnormality and macular atrophy is the most common finding. In varying proportions, ERM, macular edema, VMT, and VMA were also present in the study eyes. A macular hole was not encountered. For Nigerians, genetic testing for inherited retinal disease, including RP, should be a priority as more than half of RP eyes in this study suffer moderate-to-severe visual impairment.[32],[33] Genetic testing will enable the genetic characterization of diseases in Nigerians, improve our understanding of disease transmission, and prepare for the prospects of gene therapy for treating RP and other inherited retinal diseases.
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Conflicts of interest
There are no conflicts of interest.
References 
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