Kimberly E. Stepien

Arrested Development: High-Resolution Imaging of Foveal Morphology in Albinism

Albinism, an inherited disorder of melanin biosynthesis, disrupts normal retinal development, with foveal hypoplasia as one of the more commonly associated ocular phenotypes. However the cellular integrity of the fovea in albinism is not well understood - there likely exist important anatomical differences that underlie phenotypic variability within the disease and that also may affect responsiveness to therapeutic intervention. Here, using spectral-domain optical coherence tomography (SD-OCT) and adaptive optics (AO) retinal imaging, we obtained high-resolution images of the foveal region in six individuals with albinism. We provide a quantitative analysis of cone density and outer segment elongation demonstrating that foveal cone specialization is variable in albinism. In addition, our data reveal a continuum of foveal pit morphology, roughly aligning with schematics of normal foveal development based on post-mortem analyses. Different albinism subtypes, genetic mutations, and constitutional pigment background likely play a role in determining the degree of foveal maturation.

Prophylactic antibiotic use after intravitreal injection: effect on endophthalmitis rate.

Purpose: Endophthalmitis after intravitreal injection is a serious complication. There are limited data to support the use of postinjection antibiotics to prevent endophthalmitis. Current endophthalmitis rates after intravitreal injection in the literature are based on studies where patients routinely received postinjection antibiotics. This study retrospectively compares the rate of endophthalmitis in a cohort of patients receiving postinjection antibiotics with that in a group that does not. Methods: A retrospective chart review was performed comparing a 12-month period where patients received postinjection topical antibiotics for several days after intravitreal injection with the next 12-month period where no postinjection topical antibiotics were used. Cases of suspected endophthalmitis after intravitreal injection during this period were identified and reviewed. Results: The rate of clinically suspected endophthalmitis in the cohort of patients receiving postinjection antibiotics after intravitreal injection and that in the cohort that did not was 0.22% and 0.20%, respectively. One culture-positive case was found overall. The difference between the 2 groups is not statistically significant (P = 0.75). Conclusion: The rate of endophthalmitis after intravitreal injections administered in a clinical practice setting when aseptic technique is used is similar with or without the use of postinjection antibiotics.

Retinal Imaging Using Commercial Broadband Optical Coherence Tomography

Aims To examine the practical improvement in image quality afforded by a broadband light source in a clinical setting and to define image quality metrics for future use in evaluating spectral domain optical coherence tomography (SD-OCT) images. Methods A commercially available SD-OCT system, configured with a standard source as well as an external broadband light source, was used to acquire 4 mm horizontal line scans of the right eye of 10 normal subjects. Scans were averaged to reduce speckling and multiple retinal layers were analysed in the resulting images. Results For all layers there was a significant improvement in the mean local contrast (average improvement by a factor of 1.66) when using the broadband light source. Intersession variability was shown not to be a major contributing factor to the observed improvement in image quality obtained with the broadband light source. We report the first observation of sublamination within the inner plexiform layer visible with SD-OCT. Conclusion The practical improvement with the broadband light source was significant, although it remains to be seen what the utility will be for diagnostic pathology. The approach presented here serves as a model for a more quantitative analysis of SD-OCT images, allowing for more meaningful comparisons between subjects, clinics and SD-OCT systems.

Comparison of intravitreal bevacizumab followed by ranibizumab for the treatment of neovascular age-related macular degeneration

Purpose: To compare outcomes after switching from intravitreal bevacizumab (Avastin) to ranibizumab (Lucentis) in patients with neovascular age-related macular degeneration (AMD). Methods: A retrospective review was performed of patients with neovascular AMD who were switched from treatment with intravitreal bevacizumab to intravitreal ranibizumab once ranibizumab became commercially available. All reviewed patients had at least three bevacizumab injections before being switched to ranibizumab. The treatment outcomes included comparisons of visual acuity and dosing frequency while receiving both drugs. Results: Eighty-four eyes met the inclusion criteria. Mean baseline visual acuity was 20/100+1. Mean duration of bevacizumab treatment was 7.1 months followed by 7.3 months with ranibizumab (P = 0.68). Best-obtained visual acuity during treatment was 20/63+1 with bevacizumab and 20/63+2 with ranibizumab (P = 0.5). Last mean visual acuity after receiving bevacizumab at the time of the first ranibizumab injection was 20/80. Mean visual acuity at the last ranibizumab follow-up visit was 20/80+1 (P = 0.49). Mean injection rates per month while receiving bevacizumab and ranibizumab were 0.66 (P = 0.98). Conclusion: In this subset of patients with neovascular AMD switched from bevacizumab to ranibizumab therapy, there were no apparent differences in visual acuity outcomes or injection rates. Larger prospective studies are under way to directly compare these drugs for the treatment of neovascular AMD.

High-Resolution Images of Retinal Structure in Patients with Choroideremia

PURPOSE To study retinal structure in choroideremia patients and carriers using high-resolution imaging techniques. METHODS Subjects from four families (six female carriers and five affected males) with choroideremia (CHM) were characterized with best-corrected visual acuity (BCVA), kinetic and static perimetry, full-field electroretinography, and fundus autofluorescence (FAF). High-resolution macular images were obtained with adaptive optics scanning laser ophthalmoscopy (AOSLO) and spectral domain optical coherence tomography (SD-OCT). Coding regions of the CHM gene were sequenced. RESULTS Molecular analysis of the CHM gene identified a deletion of exons 9 to 15 in family A, a splice site mutation at position 79+1 of exon 1 in family B, deletion of exons 6 to 8 in family C, and a substitution at position 106 causing a premature stop in family D. BCVA ranged from 20/16 to 20/63 in carriers and from 20/25 to 5/63 in affected males. FAF showed abnormalities in all subjects. SD-OCT showed outer retinal layer loss, outer retinal tubulations at the margin of outer retinal loss, and inner retinal microcysts. Patchy cone loss was present in two symptomatic carriers. In two affected males, cone mosaics were disrupted with increased cone spacing near the fovea but more normal cone spacing near the edge of atrophy. CONCLUSIONS High-resolution retinal images in CHM carriers and affected males demonstrated RPE and photoreceptor cell degeneration. As both RPE and photoreceptor cells were affected, these cell types may degenerate simultaneously in CHM. These findings provide insight into the effect of CHM mutations on macular retinal structure, with implications for the development of treatments for CHM. (ClinicalTrials.gov number, NCT00254605.).

Relationship Between Foveal Cone Specialization and Pit Morphology in Albinism

PURPOSE Albinism is associated with disrupted foveal development, though intersubject variability is becoming appreciated. We sought to quantify this variability, and examine the relationship between foveal cone specialization and pit morphology in patients with a clinical diagnosis of albinism. METHODS We recruited 32 subjects with a clinical diagnosis of albinism. DNA was obtained from 25 subjects, and known albinism genes were analyzed for mutations. Relative inner and outer segment (IS and OS) lengthening (fovea-to-perifovea ratio) was determined from manually segmented spectral domain-optical coherence tomography (SD-OCT) B-scans. Foveal pit morphology was quantified for eight subjects from macular SD-OCT volumes. Ten subjects underwent imaging with adaptive optics scanning light ophthalmoscopy (AOSLO), and cone density was measured. RESULTS We found mutations in 22 of 25 subjects, including five novel mutations. All subjects lacked complete excavation of inner retinal layers at the fovea, though four subjects had foveal pits with normal diameter and/or volume. Peak cone density and OS lengthening were variable and overlapped with that observed in normal controls. A fifth hyper-reflective band was observed in the outer retina on SD-OCT in the majority of the subjects with albinism. CONCLUSIONS Foveal cone specialization and pit morphology vary greatly in albinism. Normal cone packing was observed in the absence of a foveal pit, suggesting a pit is not required for packing to occur. The degree to which retinal anatomy correlates with genotype or visual function remains unclear, and future examination of larger patient groups will provide important insight on this issue.

Increased incidence of sterile endophthalmitis after intravitreal triamcinolone acetonide in spring 2006.

Purpose: To compare the incidence of sterile endophthalmitis after intravitreal triamcinolone acetonide injections during a 6 month period in 2006 to the same period in 2005 and determine the incidence after switching to intravitreal preservative-free triamcinolone acetonide. Methods: Retrospective multicenter interventional case series in which patients receiving intravitreal triamcinolone acetonide at three institutions from March 2005 to August 2005 and from March 2006 to August 2006 and intravitreal preservative-free triamcinolone acetonide from late summer 2006 through February 2007 were reviewed for the development of sterile endophthalmitis. Results: From March 2005 to August 2005, the rate of sterile endophthalmitis was 0% at all institutions. From March 2006 to August 2006, a statistically significant increase in sterile endophthalmitis was seen at all institutions with frequencies of 3.5% to 6.3% (P < 0.001). With transition to preservative-free triamcinolone acetonide, sterile endophthalmitis over the next 6 months decreased to 0% at two sites and to 2.5% (from 5.5%) at the third institution (P < 0.009). Conclusions: A statistically significant increase in the rate of sterile endophthalmitis after intravitreal triamcinolone acetonide was seen in a 6 month period in 2006 when compared with the same period in 2005. Transition to preservative-free triamcinolone acetonide produced a frequency of sterile endophthalmitis similar to 2005.

Assessing Errors Inherent in OCT-Derived Macular Thickness Maps.

SD-OCT has become an essential tool for evaluating macular pathology; however several aspects of data collection and analysis affect the accuracy of retinal thickness measurements. Here we evaluated sampling density, scan centering, and axial length compensation as factors affecting the accuracy of macular thickness maps. Forty-three patients with various retinal pathologies and 113 normal subjects were imaged using Cirrus HD-OCT. Reduced B-scan density was associated with increased interpolation error in ETDRS macular thickness plots. Correcting for individual differences in axial length revealed modest errors in retinal thickness maps, while more pronounced errors were observed when the ETDRS plot was not positioned at the center of the fovea (which can occur as a result of errant fixation). Cumulative error can exceed hundreds of microns, even under “ideal observer” conditions. This preventable error is particularly relevant when attempting to compare macular thickness maps to normative databases or measuring the area or volume of retinal features.

Spectral Domain Optical Coherence Tomography and Adaptive Optics: Imaging Photoreceptor Layer Morphology to Interpret Preclinical Phenotypes

Recent years have seen the emergence of advances in imaging technology that enable in vivo evaluation of the living retina. Two of the more promising techniques, spectral domain optical coherence tomography (SD-OCT) and adaptive optics (AO) fundus imaging provide complementary views of the retinal tissue. SD-OCT devices have high axial resolution, allowing assessment of retinal lamination, while the high lateral resolution of AO allows visualization of individual cells. The potential exists to use one modality to interpret results from the other. As a proof of concept, we examined the retina of a 32 year-old male, previously diagnosed with a red-green color vision defect. Previous AO imaging revealed numerous gaps throughout his cone mosaic, indicating that the structure of a subset of cones had been compromised. Whether the affected cells had completely degenerated or were simply morphologically deviant was not clear. Here an AO fundus camera was used to re-examine the retina (~6 years after initial exam) and SD-OCT to examine retinal lamination. The static nature of the cone mosaic disruption combined with the normal lamination on SD-OCT suggests that the affected cones are likely still present.

Assessing photoreceptor structure in retinitis pigmentosa and usher syndrome

Purpose The purpose of this study was to examine cone photoreceptor structure in retinitis pigmentosa (RP) and Usher syndrome using confocal and nonconfocal split-detector adaptive optics scanning light ophthalmoscopy (AOSLO). Methods Nineteen subjects (11 RP, 8 Usher syndrome) underwent ophthalmic and genetic testing, spectral-domain optical coherence tomography (SD-OCT), and AOSLO imaging. Split-detector images obtained in 11 subjects (7 RP, 4 Usher syndrome) were used to assess remnant cone structure in areas of altered cone reflectivity on confocal AOSLO. Results Despite normal interdigitation zone and ellipsoid zone appearance on OCT, foveal and parafoveal cone densities derived from confocal AOSLO images were significantly lower in Usher syndrome compared with RP. This was due in large part to an increased prevalence of non-waveguiding cones in the Usher syndrome retina. Although significantly correlated to best-corrected visual acuity and foveal sensitivity, cone density can decrease by nearly 38% before visual acuity becomes abnormal. Aberrantly waveguiding cones were noted within the transition zone of all eyes and corresponded to intact inner segment structures. These remnant cones decreased in density and increased in diameter across the transition zone and disappeared with external limiting membrane collapse. Conclusions Foveal cone density can be decreased in RP and Usher syndrome before visible changes on OCT or a decline in visual function. Thus, AOSLO imaging may allow more sensitive monitoring of disease than current methods. However, confocal AOSLO is limited by dependence on cone waveguiding, whereas split-detector AOSLO offers unambiguous and quantifiable visualization of remnant cone inner segment structure. Confocal and split-detector thus offer complementary insights into retinal pathology.