Disc–foveal angle and its correlation with retinal layers in cyclovertical strabismic subjects using fundus photography and optical coherence tomography

One of the main indicators of dysfunctional extraocular muscles is cyclotorsion of the eye. Image tilting may result from cyclotorsion, especially in cases of developed cyclovertical muscular palsy.[1] Foveal dislocation due to ocular torsion may cause changes in the retinal layers, especially in retinal nerve fiber layer (RNFL) and macular thickness.[2] The angle between the foveola and the optic disc center is a major parameter of the posterior retina, which is characterized by the position of the foveola in relation to optic nerve head.[3] Cyclovertical deviations were categorized by Bielschowsky into (1) comitant vertical deviations, (2) paretic vertical deviations, (3) deviations with unilateral inferior oblique overaction, and (4) dissociated vertical deviations.[4] Any oblique malfunction can result in the appearance of ocular torsion since oblique muscles have a larger torsional activity than vertical recti. A crucial supplement to the diagnosis and management of cyclovertical strabismus is the clinical evaluation of anatomic and subjective torsion. The double Maddox rod test is used as subjective torsion method, whereas fundus photography is used objectively.[5] There is abnormal ocular torsion in case of paretic, overacting, or contracted cyclovertical muscle.[3] By observation through an ophthalmoscope, Locke[6] reported about the vertical ocular muscle imbalances and the relocation of the blind spot in the visual field of patients with A-V patterns. Through fundus photography, some studies explain that there is a disc–foveal relationship in vertical muscle paresis.[7] Studies demonstrated that in people with inferotemporal optic disc torsion, the temporal sector thickness of the RNFL scan increases.[8] Lee et al.[9] concluded in their study on variations of retinal layer changes due to ocular torsion that, the circumpapillary RNFL thickness is influenced by the direction of optic disc torsion, while the macular Ganglion cell- inner plexiform layer (GCIPL) thickness at all segments remains unaffected and also the temporal RNFL thickness varies greatly depending on the direction of disc torsion. The change in the foveal position due to ocular torsion may influence the changes in the thickness of the macula. Studies that deal with RNFL and macular thickness changes due to ocular torsion in the Indian subcontinent have not been done yet. We performed a prospective, cross-sectional study in which 53 cyclovertical strabismic eyes of 30 patients were included. This study was conducted after obtaining approval from the institutional human ethics committee of Little Flower Hospital and Research Centre, Angamaly. The mean age of patients was 20.51 ± 15.86 years during the study period from January 1, 2022 to December 31, 2022. We obtained informed consent from patients before enrolling them in the study through convenient sampling. Demographic details of all patients were recorded. They underwent complete ophthalmic examination and orthoptic evaluation according to the standard protocols. Patients having vertical muscle overaction, vertical muscle palsy, A-V pattern, and Dissociated vertical deviation (DVD) were selected. For measuring the disc–fovea angle, fundus photo was taken using a ZEISS retinal camera. Disc–fovea angle was measured using PowerPoint presentation and ImageJ software (Image-J 1.42q, developed by Wayne Rasband). Extorsion, intorsion, borderline intorsion, and borderline extorsion were all classified as present in the eyes. An eye was considered to have intorted and extorted if the fovea was located above and below the optic disc’s geometric center, respectively. In addition, eyes were considered borderline when the fovea lied halfway between the geometric center and the edge of the disc. The RNFL thickness and the macular thickness measurements were also taken. The data’s baseline properties were evaluated using descriptive statistics. Frequency and percentages were used to represent qualitative factors, whereas mean and standard deviation were used to convey quantitative variables. Karl Pearson correlation coefficient was used to evaluate the relationship between the thickness of the retinal layers and the degree of ocular torsion. Microsoft Excel and IBM Statistical Package for the Social Sciences version 20.0 were used for analysis. Age of our patients ranged from 6 to 66 years, with the mean age being 20.51 ± 15.86 years. Out of 53 cyclovertical strabismic eyes included in the study, 47% (25 eyes) were of males and 53% (28 eyes) were of females. Among them, 10 eyes (18.86%) had DVD, 12 eyes (22.64%) had palsies with seven superior oblique palsy and five inferior oblique palsy, 12 eyes (22.64%) had overacted muscles with 11 inferior oblique overaction and 1 superior oblique overaction, six eyes (11.32%) had hyper-deviations, and 13 eyes (24.52%) had an alphabetic pattern with 10 V-exotropias and three A-exotropias. Eleven patients showed borderline extorsion of the macula (20.75%), three (5.66%) had borderline intorsion, 33 (62.26%) had extorsion, and six had intorsion (11.32). On comparing the topographic changes in RNFL thickness, superior RNFL thickness was found to be normal in 64.1% eyes with a mean thickness of 128.97 ± 5.52 µm, and RNFL thinning was observed in 33.9% eyes (106.83 ± 13.96 µm) and RNFL thickening in 33.9% eyes (150 µm). Inferior RNFL thickness was normal in 67.92% eyes with a mean thickness of 134.65 ± 6.41 µm, and RNFL thinning was observed in 5.66% eyes (115.46 ± 6.60 µm) and RNFL thickening in 26.41% eyes (151.62 ± 3.96 µm). Nasal RNFL thickness was normal in 92.45% eyes with a mean thickness of 67.19 ± 6.22 µm, and RNFL thinning was observed in 7.55% eyes (58.25 ± 3.2 µm) and RNFL thickening in 26.41% eyes (82.5 ± 4.27 µm). Temporal RNFL thickness was normal in 67.81% eyes with a mean thickness of 67.19 ± 6.22 µm, and RNFL thinning was observed in 3.77% eyes (50.2 ± 0.7 µm) and RNFL thickening in 26.41% eyes (82.5 ± 4.27 µm). Average macular thickness was normal in 69.81% eyes with a mean thickness of 267.19 ± 6.92 µm, and RNFL thinning was observed in 3.77% eyes (189.9 ± 2.96 µm) and RNFL thickening in 26.41% eyes (283.55 ± 4.17 µm). Pearson correlation was used to examine the relationship between the degree of ocular torsion and changes in macula thickness and the association between ocular torsion and RNFL. With a correlation coefficient of -0.059, the relationship between changes in macula thickness and ocular torsion showed a weak negative correlation. The association between ocular torsion and RNFL showed little or weak positive correlation in the temporal quadrant (r = 0.024) and a weak negative correlation in the superior (r = -0.089), inferior (r = -0.048), and nasal (r = -0.027) quadrants. The clinical evaluation of anatomic and subjective torsion is an essential supplement to the diagnosis and treatment of cyclovertical strabismus. Our research showed a connection between the disc and the fovea, revealing that in some instances, the disc may be extorted, intorted, or borderline extorted. Depending on the condition, the angle formed by the disc and the foveal center varies from patient to patient. Most of the time, topographic changes in the retinal layers showed thinning in the superior RNFL and thickening in the inferior and temporal RNFL. However, in our study, significant correlation was not obtained to determine the relationship between the disc–foveal angle and retinal changes.