Brian P. Higgins

Microscopic Inner Retinal Hyper-Reflective Phenotypes in Retinal and Neurologic Disease

PURPOSE We surveyed inner retinal microscopic features in retinal and neurologic disease using a reflectance confocal adaptive optics scanning light ophthalmoscope (AOSLO). METHODS Inner retinal images from 101 subjects affected by one of 38 retinal or neurologic conditions and 11 subjects with no known eye disease were examined for the presence of hyper-reflective features other than vasculature, retinal nerve fiber layer, and foveal pit reflex. The hyper-reflective features in the AOSLO images were grouped based on size, location, and subjective texture. Clinical imaging, including optical coherence tomography (OCT), scanning laser ophthalmoscopy, and fundus photography was analyzed for comparison. RESULTS Seven categories of hyper-reflective inner retinal structures were identified, namely punctate reflectivity, nummular (disc-shaped) reflectivity, granular membrane, waxy membrane, vessel-associated membrane, microcysts, and striate reflectivity. Punctate and nummular reflectivity also was found commonly in normal volunteers, but the features in the remaining five categories were found only in subjects with retinal or neurologic disease. Some of the features were found to change substantially between follow up imaging months apart. CONCLUSIONS Confocal reflectance AOSLO imaging revealed a diverse spectrum of normal and pathologic hyper-reflective inner and epiretinal features, some of which were previously unreported. Notably, these features were not disease-specific, suggesting that they might correspond to common mechanisms of degeneration or repair in pathologic states. Although prospective studies with larger and better characterized populations, along with imaging of more extensive retinal areas are needed, the hyper-reflective structures reported here could be used as disease biomarkers, provided their specificity is studied further.

Automatic Detection of Cone Photoreceptors In Split Detector Adaptive Optics Scanning Light Ophthalmoscope Images

Quantitative analysis of the cone photoreceptor mosaic in the living retina is potentially useful for early diagnosis and prognosis of many ocular diseases. Non-confocal split detector based adaptive optics scanning light ophthalmoscope (AOSLO) imaging reveals the cone photoreceptor inner segment mosaics often not visualized on confocal AOSLO imaging. Despite recent advances in automated cone segmentation algorithms for confocal AOSLO imagery, quantitative analysis of split detector AOSLO images is currently a time-consuming manual process. In this paper, we present the fully automatic adaptive filtering and local detection (AFLD) method for detecting cones in split detector AOSLO images. We validated our algorithm on 80 images from 10 subjects, showing an overall mean Dice’s coefficient of 0.95 (standard deviation 0.03), when comparing our AFLD algorithm to an expert grader. This is comparable to the inter-observer Dice’s coefficient of 0.94 (standard deviation 0.04). To the best of our knowledge, this is the first validated, fully-automated segmentation method which has been applied to split detector AOSLO images.

REPEATABILITY AND LONGITUDINAL ASSESSMENT OF FOVEAL CONE STRUCTURE IN CNGB3-ASSOCIATED ACHROMATOPSIA.

Purpose: Congenital achromatopsia is an autosomal recessive disease causing substantial reduction or complete absence of cone function. Although believed to be a relatively stationary disorder, questions remain regarding the stability of cone structure over time. In this study, the authors sought to assess the repeatability of and examine longitudinal changes in measurements of central cone structure in patients with achromatopsia. Methods: Forty-one subjects with CNGB3-associated achromatopsia were imaged over a period of between 6 and 26 months using optical coherence tomography and adaptive optics scanning light ophthalmoscopy. Outer nuclear layer (ONL) thickness, ellipsoid zone (EZ) disruption, and peak foveal cone density were assessed. Results: ONL thickness increased slightly compared with baseline (0.184 &mgr;m/month, P = 0.02). The EZ grade remained unchanged for 34/41 subjects. Peak foveal cone density did not significantly change over time (mean change 1% per 6 months, P = 0.126). Conclusion: Foveal cone structure showed little or no change in this group of subjects with CNGB3-associated achromatopsia. Over the time scales investigated (6–26 months), achromatopsia seems to be a structurally stable condition, although longer-term follow-up is needed. These data will be useful in assessing foveal cone structure after therapeutic intervention.

PHOTORECEPTOR INNER SEGMENT MORPHOLOGY IN BEST VITELLIFORM MACULAR DYSTROPHY.

Purpose: To characterize outer retina structure in best vitelliform macular dystrophy (BVMD) and to determine the effect of macular lesions on overlying and adjacent photoreceptors. Methods: Five individuals with BVMD were followed prospectively with spectral domain optical coherence tomography and confocal and nonconfocal split-detector adaptive optics scanning light ophthalmoscopy (AOSLO). The AOSLO cone photoreceptor mosaic images were obtained within and around retinal lesions. Cone density was measured inside and outside lesions. In 2 subjects, densities were compared with published measurements acquired ∼2.5 years before. One subject was imaged 3 times over a 5-month period. Results: The AOSLO imaging demonstrated that photoreceptor morphology within BVMD retinal lesions was highly variable depending on the disease stage, with photoreceptor structure present even in advanced disease. The AOSLO imaging was repeatable even in severe disease over short-time and long-time intervals. Photoreceptor density was normal in retinal areas immediately adjacent to lesions and stable over ∼2.5 years. Mobile disk-like structures possibly representing subretinal macrophages were also observed. Conclusion: Combined confocal and nonconfocal split-detector AOSLO imaging reveals substantial variability within clinical lesions in all stages of BVMD. Longitudinal cellular photoreceptor imaging could prove a powerful tool for understanding disease progression and monitoring emerging therapeutic treatment response in inherited degenerations such as BVMD.

Intraobserver Repeatability and Interobserver Reproducibility of Ellipsoid Zone Measurements in Retinitis Pigmentosa

Purpose To examine repeatability and reproducibility of ellipsoid zone (EZ) width measurements in patients with retinitis pigmentosa (RP) using a longitudinal reflectivity profile (LRP) analysis. Methods We examined Bioptigen optical coherence tomography (OCT) scans from 48 subjects with RP or Usher syndrome. Nominal scan lengths were 6, 7, or 10 mm, and the lateral scale of each scan was calculated using axial length measurements. LRPs were generated from OCT line scans, and the peak corresponding to EZ was manually identified using ImageJ. The locations at which the EZ peak disappeared were used to calculate EZ width. Each scan was analyzed twice by each of two observers, who were masked to their previous measurements and those of the other observer. Results On average, horizontal width (HW) was significantly greater than vertical width (VW), and there was high interocular symmetry for both HW and VW. We observed excellent intraobserver repeatability with intraclass correlation coefficients (ICCs) ranging from 0.996 to 0.998 for HW and VW measurements. Interobserver reproducibility was also excellent for both HW (ICC = 0.989; 95% confidence interval [CI] = 0.983–0.995) and VW (ICC = 0.991; 95% CI = 0.985–0.996), with no significant bias observed between observers. Conclusions EZ width can be measured using LRPs with excellent repeatability and reproducibility. Our observation of greater HW than VW is consistent with previous observations in RP, though the reason for this anisotropy remains unclear. Translational Relevance We describe repeatability and reproducibility of a method for measuring EZ width in patients with RP or Usher syndrome. This approach could facilitate measurement of retinal band thickness and/or intensity.

Assessing Photoreceptor Structure in Macular Hole using Split-detector Adaptive Optics Scanning Light Ophthalmoscopy

Introduction: Macular hole (MH) and vitreomacular traction (VMT) can involve disruption at the level of the photoreceptor interdigitation zone (IZ) and ellipsoid zone (EZ) with optical coherence tomography (OCT). Confocal adaptive optics scanning light ophthalmoscopy (AOSLO) has been used to examine the photoreceptor mosaic following surgical intervention in patients with MH and VMT, showing large ‘dark areas’ devoid of normal waveguiding cones. Using split-detector AOSLO, which allows visualisation of cone photoreceptor inner segments, we examined the macular cone structure in these disruptions. Methods: Seven eyes from six subjects with MH or VMT were imaged with spectral domain OCT (SD-OCT), confocal AOSLO and non-confocal split-detection AOSLO following pars plana vitrectomy (PPV) for MH or intravitreal injection with ocriplasmin for VMT. Results: Split-detector AOSLO imagery revealed remnant inner segment structure within dark areas observed with confocal AOSLO. In addition, split-detector images demonstrated that not all hyperreflective dots in confocal AOSLO images were derived from cones. Conclusion: Split-detector AOSLO provides additional information for these retinal conditions, and is likely to become an invaluable tool for assessing residual cone structure in conditions where disrupted cone structure interferes with the ability to visualise cells with confocal AOSLO.

Biocompatibility of Pooled Human Immunoglobulin (Gamunex 10%™) with Ocular Infusion Solutions (BSS™ and BSS Plus™): An In Vitro Evaluation of a Potential Antitoxin Treatment for Infectious Endophthalmitis

PURPOSE Gamunex 10% (Talecris Biotherapeutics, Research Triangle Park, NC), a commercially available preparation of pooled human immunoglobulin G, has been proposed as an antitoxin therapy against bacterial toxins released in infectious endophthalmitis. Its biocompatibility with two commonly used intraocular infusion fluids was evaluated to determine feasibility of its clinical application in endophthalmitis treatment. METHODS Gamunex 10% was mixed with BSS or BSS Plus (Alcon Laboratories, Fort Worth, TX) such that it constituted a range of 1.25%-50% by volume. Osmolality, pH, optical density, and ionic strength were measured across this range of concentrations. RESULTS The amount of pH reduction with increasing concentrations of Gamunex 10% was similar for both BSS and BSS Plus. In BSS Plus, solutions containing up to 20% by volume of Gamunex 10% remained at near-physiologic pH (∼7.0 or above). No physiologically significant changes in osmolality or optical density measurements that would be anticipated to have profound physiological effects were observed at any of the measured concentrations, nor was there visual evidence of tubidity/precipitation. A gradual increase in ionic strength was observed with increasing concentrations of Gamunex 10%. CONCLUSIONS Potentially therapeutic mixtures of Gamunex 10% in 2 commonly used intraocular infusion fluids, BSS and BSS Plus, showed no evidence of bioincompatibility when the solutions were evaluated for changes in osmolality, pH, ionic strength, aggregation, or precipitation.