Stephen H. Tsang

A study of factors affecting the human cone photoreceptor density measured by adaptive optics scanning laser ophthalmoscope

To investigate the variation in human cone photoreceptor packing density with various demographic or clinical factors, cone packing density was measured using a Canon prototype adaptive optics scanning laser ophthalmoscope and compared as a function of retinal eccentricity, refractive error, axial length, age, gender, race/ethnicity and ocular dominance. We enrolled 192 eyes of 192 subjects with no ocular pathology. Cone packing density was measured at three different retinal eccentricities (0.5xa0mm, 1.0xa0mm, and 1.5xa0mm from the foveal center) along four meridians. Cone density decreased from 32,200 to 11,600xa0cells/mm(2) with retinal eccentricity (0.5xa0mm to 1.5xa0mm from the fovea, Pxa0<xa00.001). A trend towards a slightly negative correlation was observed between age and density (rxa0=xa0-0.117, Pxa0=xa00.14). There was, however, a statistically significant negative correlation (rxa0=xa0-0.367, Pxa0=xa00.003) between axial length and cone density. Gender, ocular dominance, and race/ethnicity were not important determinants of cone density (all, Pxa0>xa00.05). In addition, to assess the spatial arrangement of the cone mosaics, the nearest-neighbor distances (NNDs) and the Voronoi domains were analyzed. The results of NND and Voronoi analysis were significantly correlated with the variation of the cone density. Average NND and Voronoi area were gradually increased (all, Pxa0≤xa00.001) and the degree of regularity of the cone mosaics was decreased (Pxa0≤xa00.001) with increasing retinal eccentricity. In conclusion, we demonstrated cone packing density decreases as a function of retinal eccentricity and axial length and the results of NND and Voronoi analysis is a useful index for cone mosaics arrangements. The results also serve as a reference for further studies designed to detect or monitor cone photoreceptors in patients with retinal diseases.

Retinal damage in chloroquine maculopathy, revealed by high resolution imaging: a case report utilizing adaptive optics scanning laser ophthalmoscopy.

A 53-year-old Asian woman was treated with hydroxychloroquine and chloroquine for lupus erythematosus. Within a few years, she noticed circle-shaped shadows in her central vision. Upon examination, the patients visual acuity was 20 / 25 in both eyes. Humphrey visual field (HVF) testing revealed a central visual defect, and fundoscopy showed a ring-shaped area of parafoveal retinal pigment epithelium depigmentation. Fundus autofluorescence imaging showed a hypofluorescent lesion consistent with bulls eye retinopathy. Adaptive optics scanning laser ophthalmoscope (AO-SLO) revealed patch cone mosaic lesions, in which cones were missing or lost. In addition, the remaining cones consisted of asymmetrical shapes and sizes that varied in brightness. Unlike previous studies employing deformable mirrors for wavefront aberration correction, our AO-SLO approach utilized dual liquid crystal on silicon spatial light modulators. Thus, by using AO-SLO, we were able to create a photographic montage consisting of high quality images. Disrupted cone AO-SLO images were matched with visual field test results and functional deficits were associated with a precise location on the montage, which allowed correlation of histological findings with functional changes determined by HVF. We also investigated whether adaptive optics imaging was more sensitive to anatomical changes compared with spectral-domain optical coherence tomography.

Next-generation sequencing revealed a novel mutation in the gene encoding the beta subunit of rod phosphodiesterase.

Abstract Purpose: To report the phenotypes caused by a novel mutation in the PDE6B gene in a family with two affected siblings and one affected cousin with a 2-year follow-up. Design: Three patients from a family with a history of retinitis pigmentosa underwent clinical evaluations. The affected patients’ DNA was analyzed using next-generation sequencing and segregation analyses were performed for the family. Setting: Edward S. Harkness Eye Institute, New York Presbyterian Hospital. Participants: Two siblings, one cousin, and five unaffected family members. Main outcome measures: Macular appearance assessed by funduscopy, autofluorescence imaging, spectral-domain optical coherence tomography and visual function assessed by electroretinography. Results: The proband, brother, and cousin had rod-cone degeneration with cystoid macular edema. Fundus autofluorescence showed hyperautofluorescent ring constriction over time. Spectral-domain optical coherence tomography revealed retinal pigment epithelium atrophy, loss of external limiting membrane, retinal layer thinning, and reduction in ellipsoid zone length over time. Next-generation whole exome sequencing revealed a homozygous c.1923_1969ins6del47 nonsense PDE6B mutation, which has not been previously described, that segregated with the disease in the family. Conclusions: The homozygous PDE6B mutation causes retinitis pigmentosa. Acetazolamide treatment improved visual acuity but rod degeneration continued. Despite having the same mutation and living in the same environment, the proband’s brother progressed at a faster rate starting at a younger age, suggesting that gene modifiers may influence the expressivity of the phenotype. Next-generation sequencing, used to discover this mutation, is a practical new technology that can detect novel disease-causing alleles, where previous arrayed primer extension (APEX) technology could not.

Disruption in Bruch membrane in patients with Stargardt disease

Purpose: To describe the spectral domain-optical coherence tomography (SD-OCT) findings of two patients with complete defects in the retinal pigment epithelium (RPE) with disruptions in Bruch membrane in Stargardt disease (STGD1). Methods: Two patients with STGD1 were referred to our clinic for further evaluation. Fundus autofluorescence (FAF), spectral domain optical coherence tomography (SD-OCT), electroretinography (ERG) and Microperimetry (MP-1) were performed to assess the retinal anatomy and function. Screening for mutations in the ABCA4 gene was carried out and detected mutations were confirmed by direct sequencing. Results: Both patients had bilateral macular geographic atrophy (GA) and yellowish subretinal pisciform flecks and mutations were detected in the ABCA4 gene by chip screening. SD-OCT revealed marked atrophy of the retina in the central macula, with focal defects in the RPE with disruptions in Bruch membrane and herniation of the retina through the defect in three of four eyes. Conclusion: This case report highlights the necessity for a detailed ophthalmic examination including SD-OCT of patients with STGD1.

Intraretinal Correlates of Reticular Pseudodrusen Revealed by Autofluorescence and En Face OCT

Purpose We sought to determine whether information revealed from the reflectance, autofluorescence, and absorption properties of RPE cells situated posterior to reticular pseudodrusen (RPD) could provide insight into the origins and structure of RPD. Methods RPD were studied qualitatively by near-infrared fundus autofluorescence (NIR-AF), short-wavelength fundus autofluorescence (SW-AF), and infrared reflectance (IR-R) images, and the presentation was compared to horizontal and en face spectral domain optical coherence tomographic (SD-OCT) images. Images were acquired from 23 patients (39 eyes) diagnosed with RPD (mean age 80.7 ± 7.1 [SD]; 16 female; 4 Hispanics, 19 non-Hispanic whites). Results In SW-AF, NIR-AF, and IR-R images, fundus RPD were recognized as interlacing networks of small scale variations in IR-R and fluorescence (SW-AF, NIR-AF) intensities. Darkened foci of RPD colocalized in SW-AF and NIR-AF images, and in SD-OCT images corresponded to disturbances of the interdigitation (IZ) and ellipsoid (EZ) zones and to more pronounced hyperreflective lesions traversing photoreceptor-attributable bands in SD-OCT images. Qualitative assessment of the outer nuclear layer (ONL) revealed thinning as RPD extended radially from the outer to inner retina. In en face OCT, hyperreflective areas in the EZ band correlated topographically with hyporeflective foci at the level of the RPE. Conclusions The hyperreflective lesions corresponding to RPD in SD-OCT scans are likely indicative of degenerating photoreceptor cells. The darkened foci at positions of RPD in NIR-AF and en face OCT images indicate changes in the RPE monolayer with the reduced NIR-AF and en face OCT signal suggesting a reduction in melanin that could be accounted for by RPE thinning.

The Role of Fundus Autofluorescence in Late-Onset Retinitis Pigmentosa (LORP) Diagnosis

Abstract Purpose: To demonstrate the utility and characteristics of fundus autofluorescence in late-onset retinitis pigmentosa. Methods: Observational case series. Patients diagnosed with late-onset retinitis pigmentosa were identified retrospectively in an institutional setting. Twelve eyes of six patients were identified and medical records were reviewed. Results: All patients presented with slowly progressive peripheral field loss and initial clinical examination revealed only subtle retinal changes. There was a notable lack of intraretinal pigment migration in all patients. Five out of six patients underwent magnetic resonance imaging of the brain to rule out intracranial processes and all were referred from another ophthalmologist for further evaluation. Fundus autofluorescence was ultimately employed in all patients and revealed more extensive retinal pathology than initially appreciated on clinical examination. Fundus autofluorescence directed the workup toward a retinal etiology in all cases and led to the eventual diagnosis of late-onset retinitis pigmentosa through electroretinogram testing. Conclusion: Fundus autofluorescence may be a more sensitive marker for retinal pathology than stereo fundus biomicroscopy alone in late-onset retinitis pigmentosa. Early use of fundus autofluorescence imaging in the evaluation of patients with subtle retinal lesions and complaints of peripheral field loss may be an effective strategy for timely and cost-efficient diagnosis.

Photoreceptor cells as a source of fundus autofluorescence in recessive Stargardt disease

Bisretinoid fluorophores form in photoreceptor outer segments from nonenzymatic reactions of vitamin A aldehyde. The short‐wavelength autofluorescence (SW‐AF) of fundus flecks in recessive Stargardt disease (STGD1) suggests a connection to these fluorophores. Through multimodal imaging, we sought to elucidate this link. Flecks observed in SW‐AF images often colocalized with foci exhibiting reduced or absent near‐infrared autofluorescence signal, the source of which is melanin in retinal pigment epithelial (RPE) cells. With serial imaging, changes in near‐infrared autofluorescence (NIR‐AF) preceded the onset of fleck hyperautofluorescence in SW‐AF images and fleck profiles in NIR‐AF images tended to be larger. Flecks in SW‐AF and NIR‐AF images also corresponded to hyperreflective lesions traversing photoreceptor‐attributable bands in horizontal SD‐OCT scans. The hyperreflective lesions interrupted adjacent OCT reflectivity bands and were associated with thinning of the outer nuclear layer. These SD‐OCT findings are attributable to photoreceptor cell degeneration. Progressive increases and decreases in the SW‐AF intensity of flecks were evident in color‐coded quantitative fundus autofluorescence maps. In some cases, flecks appeared to spread radially from the fovea to approximately 8° of eccentricity, beyond which a circumferential spread characterized the distribution. Since the NIR‐AF signal is derived from melanin and loss of this autofluorescence is indicative of RPE atrophy, the SW‐AF of flecks cannot be accounted for by bisretinoid lipofuscin in RPE. Instead, we suggest that the bisretinoid serving as the source of the SW‐AF signal, resides in photoreceptors, the cell that is also the site of bisretinoid synthesis.

Mitochondrial A3243G mutation results in corneal endothelial polymegathism

Purpose nThe mitochondrial DNA point mutation A3243G leads to a spectrum of syndromes ranging from MIDD to MELAS. Ocular manifestations include pattern macular dystrophy and concentric perifoveal atrophy. Given the high metabolic demand of corneal endothelial cells, we performed specular biomicroscopy analysis in patients harboring the mitochondrial DNA point mutation A3243G to assess for the associated presence of corneal endothelial abnormalities.

Evaluating structural progression of retinitis pigmentosa after cataract surgery

PURPOSEnTo determine whether cataract surgery accelerates disease progression in retinitis pigmentosa (RP).nnnDESIGNnRetrospective cohort study.nnnMETHODSnSeventy eyes of 40 patients with RP were categorized as having had phacoemulsification with intraocular lens implantation vs no cataract surgery at a single tertiary-level institution. Spectral-domain optical coherence tomography (SDOCT) was used to measure the ellipsoid zone (EZ) width, which has been demonstrated to be a reliable marker of RP severity, at baseline and throughout follow-up (median 768xa0days). RP progression was calculated as the loss of EZ width over time for all patients. Additional postoperative data were collected for the cataract surgery group, including preoperative and postoperative best-corrected visual acuity, incidence of macular edema, posterior capsular opacification, epiretinal membrane, and intraocular lens subluxation.nnnRESULTSnMultivariable analysis including age, baseline EZ width, mode of inheritance, and cataract surgery status showed that there was no significant difference in RP progression between the cataract surgery and control groups (Pxa0= .23). Mode of inheritance was associated with RP progression, with autosomal recessive RP progressing at 148xa0μm/year and autosomal dominant RP progressing at 91xa0μm/year (Pxa0= .003). Visual acuity improved in almost all eyes that underwent surgery (17/19, 89%) and remained stable in remaining eyes (2/19, 11%). There was a high incidence of postsurgical posterior capsular opacification (18/19, 95%). There were no serious complications, such as lens subluxation or endophthalmitis.nnnCONCLUSIONSnOur findings suggest that cataract surgery is a safe and effective means of improving visual acuity in RP patients and that it does not seem to be associated with faster disease progression as measured using SDOCT.

Mutations in GPR143/OA1 and ABCA4 Inform Interpretations of Short-Wavelength and Near-Infrared Fundus Autofluorescence.

Purpose We sought to advance interpretations and quantification of short-wavelength fundus autofluorescence (SW-AF) emitted from bisretinoid lipofuscin and near-infrared autofluoresence (NIR-AF) originating from melanin. Methods Carriers of mutations in X-linked GPR143/OA1, a common form of ocular albinism; patients with confirmed mutations in ABCA4 conferring increased SW-AF; and subjects with healthy eyes were studied. SW-AF (488 nm excitation, 500–680 nm emission) and NIR-AF (excitation 787 nm, emission >830 nm) images were acquired with a confocal scanning laser ophthalmoscope. SW-AF images were analyzed for quantitative autofluoresence (qAF). Analogous methods of image acquisition and analysis were performed in albino and pigmented Abca4−/− mice and wild-type mice. Results Quantitation of SW-AF (qAF), construction of qAF color-coded maps, and examination of NIR-AF images from GPR143/OA1 carriers revealed mosaics in which patches of fundus exhibiting NIR-AF signal had qAF levels within normal limits whereas the hypopigmented areas in the NIR-AF image corresponded to foci of elevated qAF. qAF also was increased in albino versus pigmented mice. Although melanin contributes to fundus infrared reflectance, the latter appeared to be uniform in en face reflectance images of GPR143/OA1-carriers. In patients diagnosed with ABCA4-associated disease, NIR-AF increased in tandem with increased qAF originating in bisretinoid lipofuscin. Similarly in Abca4−/− mice having increased SW-AF, NIR-AF was more pronounced than in wild-type mice. Conclusions These studies corroborate RPE melanin as the major source of NIR-AF but also indicate that bisretinoid lipofuscin, when present at sufficient concentrations, contributes to the NIR-AF signal. Ocular melanin attenuates the SW-AF signal.