Ramsudha Narala

Comparison of manually corrected retinal thickness measurements from multiple spectral-domain optical coherence tomography instruments

Background/aims To compare retinal thickness measurements from three different spectral domain optical coherence instruments when manual segmentation is employed to standardise retinal boundary locations. Methods 40 eyes of 21 healthy subjects were scanned on the Cirrus HD-OCT, Topcon 3D-OCT-2000 and Heidelberg Spectralis-OCT. Raw data were imported into custom grading software (3D-OCTOR). Manual segmentation was performed on every data set, and retinal thickness values in the foveal central subfield were computed. Results 37 eyes of 20 subjects were gradable on every machine. The average retinal thicknesses for these eyes were 236.7 μm (SD 20.1), 235.7 μm (SD 20.4) and 236.5 μm (SD 18.0) for the Cirrus, 3D-OCT-2000 and Spectralis, respectively. Comparing manual retinal thickness measurements between any two machines, the maximum difference was 18.2 μm. The mean absolute differences per eye between two machines were: 4.9 μm for Cirrus versus 3D-OCT-2000, 3.7 μm for Cirrus versus Spectralis and 4.4 μm for 3D-OCT-2000 versus Spectralis. Conclusions When a uniform position is used to locate the outer retinal boundary, the retinal thickness measurements derived from three different spectral domain optical coherence instruments devices are virtually identical. Manual correction may allow OCT-derived thickness measurements to be compared between devices in clinical trials and clinical research.

Effect of anti-VEGF treatment on choroidal thickness over time in patients with neovascular age-related macular degeneration.

Purpose To evaluate change in subfoveal choroidal thickness (SCT) as measured by spectral-domain optical coherence tomography (SD-OCT) in patients with neovascular age-related macular degeneration (NVAMD) undergoing anti–vascular endothelial growth factor (VEGF) therapy. Methods Patients with a diagnosis of NVAMD were retrospectively reviewed to identify those who had at least 12 months of follow-up. The SCT was manually measured from Bruch membrane to the choroid–sclera junction at baseline and last follow-up. Only cases in which the choroid was fully visible were included in quantitative analyses. The SCT measurements were correlated with other characteristics including number and duration of treatments. Results Sixty eyes of 47 patients with a follow-up of 23.8 months (SD 7.3) met study inclusion criteria, and 49 eyes of 40 patients received anti-VEGF treatment. Mean age was 83.7 years, and 52% were female. Treated eyes received a mean of 7.8 (SD 7.3) intravitreal anti-VEGF injections. The SCT at baseline was 126.7 μm (SD 50.6) for untreated and 136.2 μm (SD 57.6) for treated eyes. The SCT showed a decrease over time in both groups, with a mean rate of reduction of 6.0 μm (p<0.0002) in treated eyes and 3.6 μm (p = 0.3741) in untreated eyes. However, the change in SCT did not differ between the groups (p = 0.5113), and did not correlate with the number of re-treatments (p = 0.552), visual acuity at baseline (p = 0.618), or change in visual acuity over time (p = 0.429). Conclusions Although choroidal thickness decreased over time in eyes with NVAMD, anti-VEGF therapy did not appear to accelerate or otherwise alter this decline.

Structural And Functional Implications Of Severe Foveal Dystopia In Epiretinal Membranes

Purpose The purpose of this study was to examine the functional and structural correlates of severe foveal dystopia in patients with epiretinal membranes. Methods For this retrospective study of 29 eyes with epiretinal membrane, we identified 7 eyes that had severe foveal dystopia (defined as fovea located >200 &mgr;m from its expected location) and followed the direction and rate of foveal movement pre- and postoperatively. Results Epiretinal membrane traction caused the fovea to move preoperatively at a rate of 275 &mgr;m/month from its anatomical location in 2 patients. The final preoperative foveal location was, on average, 1,217 ± 683 &mgr;m away from its expected location. Postoperatively, foveal movement toward its expected location was largest during the first month after surgery (mean = 547 ± 340 &mgr;m) and slowed down until the final follow-up position was achieved (mean = 301 ± 131 &mgr;m). Overall, the fovea moved a total of 848 ± 445 &mgr;m, allowing the fovea to correct only 32.8 ± 22.1% of the total displacement from its expected location. A univariate regression model confirmed a linear relationship between preoperative visual acuity and preoperative foveal distance from its expected anatomical location with an R2 of 0.759 (P = 0.0107). Conclusion The extent of tractional foveal dystopia correlates with decreased visual acuity. Although all patients experienced functional and anatomical improvements with surgery, long-standing or severe foveal dystopia may be associated with permanent structural changes that limit functional outcome. Cases with extreme degrees of foveal dystopia may benefit from early intervention to prevent irreversible structural and functional changes.

LONGITUDINAL QUANTITATIVE EVALUATION OF PHOTORECEPTOR VOLUME FOLLOWING REPAIR OF MACULA-OFF RETINAL DETACHMENT.

Purpose: To quantify photoreceptor volume changes after successful surgical repair of macula-off retinal detachment and to correlate these volumetric changes to postoperative best-corrected visual acuity (BCVA). Methods: Retrospective study of 15 eyes of 15 patients with macula-off retinal detachment who underwent successful surgical repair. A minimum of 4 optical coherence tomography scans that straddled the foveal center was used to quantify the central photoreceptor volume (central 1 mm). Results: Mean photoreceptor volume at the first postoperative visit was 0.451 mm3, increasing to 0.523 mm3 at the final postoperative visit (P = 0.004). Mean BCVA improved from 1.13 ± 0.59 logarithm of the minimum angle of resolution units (∼20/270) preoperatively to 0.52 ± 0.42 logarithm of the minimum angle of resolution units (∼20/66) at the final postoperative visit (P = 0.001). Mean photoreceptor volume at either the initial or final visit demonstrated significant correlations with final postoperative BCVA (r = −0.670, P = 0.017 and r = −0.753, P = 0.005, respectively). Shorter time interval from diagnosis to surgery was significantly associated with greater mean final postoperative photoreceptor volume (r = −0.588, P = 0.021) and better mean final postoperative BCVA (r = 0.709, P = 0.003). Conclusion: We observed a significant increase in photoreceptor volume after successful retinal detachment repair; photoreceptor volume was positively associated with BCVA and time to surgery. Our series emphasizes the importance of prompt surgical repair and shows that photoreceptor recovery and volumetric improvement correlate significantly with BCVA.

LOSS OF EXTERNAL LIMITING MEMBRANE INTEGRITY PREDICTS PROGRESSION OF HYDROXYCHLOROQUINE RETINAL TOXICITY AFTER DRUG DISCONTINUATION.

Purpose: To quantify external limiting membrane (ELM) disruption and photoreceptor volume over time, using spectral domain optical coherence tomography in eyes with hydroxychloroquine (HCQ) toxic effects after discontinuation. Methods: We performed a retrospective chart review of patients who were screened for toxic effects of HCQ between January 1, 2009 and August 31, 2014, and identified 10 patients diagnosed as having HCQ retinal toxic effects. Intact ELM and the Bruch membrane were manually traced using ImageJ software and their lengths from each scan of the spectral domain optical coherence tomography macular volume were summed. The ratio of intact ELM length/Bruch membrane length was calculated. We measured the two-dimensional photoreceptor area between the intact ELM and Bruch membrane in every cross-sectional B-scan. We calculated the total volume of photoreceptors in a volumetric OCT by multiplying photoreceptor area by the distance between B-scans. Results: Of the 10 patients (120 eyes), 1 eye was excluded because of the presence of vitreomacular traction. The mean cumulative dose of HCQ was 1,951 g (range, 584–3,650 g). The mean follow-up duration was 34.1 months (range, 11–64 months). Based on the extent of ELM integrity at diagnosis of HCQ toxicity, we classified eyes into 2 groups: 1) 12 eyes showed severe ELM disruption and 2) 7 eyes had intact ELM. All 19 eyes showed characteristic signs of HCQ toxicity on the visual field examination at the baseline. Seven of 12 eyes with ELM disruption showed progressive ELM changes, including 7 eyes that additionally developed progressive photoreceptor volume decline, whereas 5 eyes remained stable. All 7 eyes with intact ELM remained stable over time. Conclusion: Intact ELM status at the time of HCQ discontinuation is a good prognostic sign, and ELM status may allow clinicians to predict patients at risk for progression of retinopathy. Quantitative measurements of ELM disruption and photoreceptors volume may provide an objective tool to monitor outer retinal changes due to HCQ.