Does Foveal Position Relative to the Optic Disc Affect Optical Coherence Tomography Measurements in Glaucoma?

Validity and Reliability of 2 Cirrus Optical Coherence Tomography Procedures for Measuring Objective Ocular Torsion

PURPOSE

Torsional eye position by the disc-fovea angle (DFA) is a relevant objective parameter in vertical strabismus. DFA measurement with optical coherence tomography (OCT) has proven to be a good alternative to the gold standard measurement in fundus photography. Our study aims to analyze the validity and reliability of 2 undescribed Cirrus high-definition OCT (HD-OCT; Carl Zeiss Meditec) methods that offer clinical advantages for measuring objective cycloposition in normal patients compared with Spectralis spectral-domain OCT (Heidelberg Engineering) and the reference method.

DESIGN

Prospective validity and reliability analysis.

METHODS

Objective cycloposition by means of the DFA was measured in the right eyes of 59 binocularly normal individuals attending the ophthalmology service of a medical institution. DFA was obtained by fundus photography (gold standard), FoDi software of Spectralis spectral-domain OCT, HD 1 line scan of Cirrus HD-OCT, and macular cube of Cirrus HD-OCT (fundus, FoDi, line, and cube methods, respectively). Measurements were performed 3 times for each method and the patient was repositioned and realigned between captures. Posterior manual quantification was made by 2 observers with external protractor software for the fundus and cube methods.

RESULTS

The 3 OCT methods showed and excellent agreement with fundus photography (ICC 0.83-0.84) with no significant differences comparing mean values (P = .36 for fundus-FoDi, P = .09 for fundus-line, and P = .09 for fundus-cube). Absolute differences between methods were 1.5°. All methods showed excellent reliability (ICC 0.92 for FoDi, 0.91 for line, 0.92 for cube, and 0.91 for fundus). The minimal detectable change was lower than 3° and the absolute difference between repeated measurements was 1° for all methods. Interrater reliability was excellent for methods requiring manual quantification (ICC 0.98 for cube, ICC 0.94 for fundus).

CONCLUSIONS

Measurement of the DFA by Cirrus HD-OCT methods in normal patients was a valid and reliable alternative for the cycloposition assessment. Among the methods, the Cirrus OCT HD 1 line improved clinical performance due to the simplicity and speed of measurement, with no need to export the image for quantification.

Evaluation of the Diagnostic Capability of Spectralis SD-OCT 8 × 8 Posterior Pole Software with the Grid Tilted at 7 Degrees and Horizontalized in Glaucoma

Background: The goal was to evaluate the diagnostic capability of different parameters obtained with the posterior pole (PP) software in Spectralis SD-OCT with the 8 × 8 grid tilted at 7° and horizontalized in glaucomatous eyes. Methods: A total of 299 eyes were included, comprising 136 healthy eyes and 163 with primary open-angle glaucoma (POAG). The following segmentations were evaluated: complete retina, retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), GCL and inner plexiform layer (GCLIPL), ganglion cell complex (GCC), outer plexiform layer and outer nuclear layer (OPLONL), inner retinal layer (IRL), and outer retinal layer (ORL). Different patterns of macular damage were represented using heatmaps for each studied layer, where the areas under the curve (AUROC) values and a retinal thickness cutoff point were defined to discriminate POAG patients. Results: There was not any difference in the diagnostic capability for detecting glaucoma between the grid tilted at 7° and horizontalized. The macular segmentations that offer the highest diagnostic ability in glaucoma discrimination were, in the following order, RNFL (AUROC = 0.796), GCC (AUROC = 0.785), GCL (AUROC = 0.784), GCLIPL (AUROC = 0.770), IRL (AUROC = 0.755), and the complete retina (AUROC = 0.752). In contrast, ORL and OPLONL do not appear to be helpful for discriminating POAG. Conclusions: Some results of PP software may be useful for discriminating POAG.

Optic disc tilt and rotation effects on positions of superotemporal and inferotemporal retinal nerve fibre layer peaks in myopic Caucasians

CLINICAL RELEVANCE

In myopic eyes, the optic disc may become tilted and rotated, making glaucoma diagnosis more difficult.

BACKGROUND

To determine the presence of tilted optic disc, the degree of optic disc rotation, and their effects on the angular location of superotemporal and inferotemporal retinal nerve fibre layer (RNFL) peaks in healthy myopic Caucasians.

METHODS

Non-glaucomatous healthy myopic Caucasian eyes with an axial length > 24 mm were evaluated. ImageJ was used to quantify optic disc tilt and torsion on red-free fundus photography. The RNFL was scanned using spectral-domain optical coherence tomography. The angle of the superotemporal and inferotemporal peaks with the vertical-horizontal meridian was measured.

RESULTS

Fifty-four eyes of 54 individuals were evaluated. The axial length was correlated with the angular location for both the superotemporal (r = -0.549, p < 0.001) and inferotemporal (r = -0.415, p = 0.002) RNFL peaks; they were placed more temporally in eyes with higher axial lengths. For each 1 mm increase in axial length, the angle between the superotemporal peak and the temporal horizontal meridian decreased by 3.976°, and the angle between the inferotemporal apex and the temporal horizontal meridian decreased by 3.028°. The angle between the inferotemporal peak and the temporal horizontal meridian decreased by 0.231° for each 1° increase in optical disc torsion (R2 = 0.09 Regression coefficient = -0.231, p = 0.027).

CONCLUSIONS

The temporal shift of superior and inferior peaks, the thickening of temporal and nasal RNFL, the presence of tilted optic disc, and optic disc rotation may cause misinterpretation of the RNFL in myopic Caucasians. When evaluating peripapillary RNFL thickness in myopic individuals, it would be better to consider these to avoid misinterpretation.

Minimal detectable change of the disc-fovea angle for ocular torsion assessment

PURPOSE

The disc-fovea angle (DFA) is used as a relevant indicator of ocular torsion change in cyclovertical strabismus. However, interpretation of the variation in time must differentiate whether a real change has occurred or if the disparity is due to random measurement error. The aim of the study was to obtain the minimal detectable change (MDC) of the DFA. It represents the minimal variation between two measurements that may be considered a real ocular torsion change.

METHODS

A prospective cross-sectional study was conducted in San Carlos Clinical Hospital of Madrid, Spain. Sixty healthy right eyes from 60 patients (31 men and 29 women) were recruited. Three digital fundus photographs were obtained, and between measurements, the patient moved their head away from the head support and then returned. Two observers quantified the DFA with software designed with MATLAB. Test-retest and interrater reliability were calculated.

RESULTS

Mean participant age was 56.1 years (SD 16.6, range 25-85). Mean DFA was 8.1° (SD 3.5, range 1.3-18.5). Test-retest reliability for Observer 1 (Ob1), Observer 2 (Ob2) and interrater reliability were excellent (ICC 0.80, 0.83 and 0.95, respectively). Precision was 2.9° (Ob1) and 3.0° (Ob2), and the MDC₉₅ was 4.1° (Ob1) and 4.2° (Ob2). Bland-Altman analysis revealed an absence of bias and a homoscedastic distribution of the differences.

CONCLUSIONS

The MDC of the DFA in fundus photography was 4°, which represents the minimal change that may be considered a real change in ocular torsion. This result may improve the interpretation of ocular torsion changes in surgery and clinical scenarios.