R. T. Smith

A method of drusen measurement based on reconstruction of fundus background reflectance.

Background: The hallmarks of age related macular degeneration (AMD) are the subretinal deposits known as drusen. Current manual methods of drusen segmentation and quantification are laborious and subjective. The authors introduced a digital method and tested it for accuracy and reliability. Methods: Fourteen eyes with drusen were selected. The authors digitally reconstructed the macular background using normal background areas (“dots”) fitted to quadratic polynomials in two zones. The model was used to level the reflectance for the purpose of segmenting drusen by a global threshold. Measurements of drusen areas were compared with those of a semi-automated background levelling technique and manual drawings from stereo pairs. Results: Intraobserver reproducibility had standard deviations from 0.1% to 4.1%. Interobserver reproducibility yielded 95% limits of agreement of −2.7% to 6.3%. The dots method compared with manual drawings and with the semi-automated method had 95% limits of agreement of −8.3% to 2.8% and −7.1% to 4.8%, respectively. Conclusions: The dots method was reproducible and accurate with respect to validated methods. It provided less total operating time and greater precision than that of standard fundus photo grading. With implementation of commercial software, this technique for macular image analysis has potential for use in clinical research.

Evaluation of the ARMD1 locus on 1q25-31 in patients with age-related maculopathy: genetic variation in laminin genes and in exon 104 of HEMICENTIN-1.

The age-related maculopathy (ARM) genetics program at Columbia University utilizes comprehensive genetic analysis of candidate genes in large case-control studies to determine genotypes associated with the ARM complex trait. Genes encoding laminins, a class of extracellular matrix proteins, represent attractive candidates for two reasons. First, the presence of laminins in the basal lamina of the retinal pigment epithelium (RPE), Bruchs membrane, and choriocapillaris suggests a possible role in the pathophysiology of ARM. Second, three laminin genes, LAMC1, LAMC2, and LAMB3, are located in the 1q25–31 region, within the previously mapped ARMD1 locus. The entire open reading frame of the three laminin genes was screened for variants by denaturing high-performance liquid chromatography (DHPLC) and direct sequencing in at least 92, and up to 368 ARM patients and matched unaffected controls. Sixty-nine sequence variants were detected in the 69 exons of the LAMC1, LAMC2, and LAMB3 genes. Screening of exon 104 of the recently proposed ARMD1 gene, HEMICENTIN-1, residing in the 1q25–31 locus, did not detect the suggested causal variant, Q5345R, in 632 study subjects. Overall, we did not find statistically significant differences in the frequency of variants between ARM-affected individuals and age-matched controls. Four rare, non-synonymous, variants were detected in single cases of ARM patients. Our data on relatively limited numbers of study subjects do not suggest a significant role for genetic variation in the three laminin genes and in exon 104 of HEMICENTIN-1 in predisposing individuals to ARM. However, as in many instances in similar studies, involvement of rare amino acid-changing variants in a fraction of ARM cannot be ruled out.

Lipofuscin and autofluorescence metrics in progressive STGD.

PURPOSE To evaluate Stargardt disease (STGD) progression and relative lipofuscin levels via autofluorescence image analysis. METHODS The relationship between focally increased autofluorescence (FIAF), geographic atrophy (GA) and focally decreased autofluorescence (FDAF) was analyzed in serial, registered autofluorescence (AF) scans of 10 patients with STGD (20 eyes, 40 scans; mean follow-up, 2.0 years) using automated techniques. RESULTS GA progressed uniformly in a transition zone with minimal FIAF. Only 4.3% of FIAF progressed to GA or FDAF, despite significant progression of GA (median 30%/year) and FDAF (mean, 29%/year). As a spatial predictor, the mean chance of FIAF for progression to FDAF was 4.3% +/- 4.4%, significantly less than that of random areas (6.7% +/- 4.0%, P = 0.029, Mann-Whitney test). In the seven eyes with GA, the mean chance of FIAF in the transition zone for transition to GA was 12% +/- 8.9%, significantly less than that of random areas (33% +/- 3.6%, P = 0.026, Mann-Whitney test). CONCLUSIONS Autofluorescent flecks and FIAF deposits with AF levels elevated above the initial macular background were less likely in the short term (2 years) to transform to GA and FDAF (AF levels below the final background) than random areas, suggesting additional mechanisms beyond direct lipofuscin toxicity. FIAF/FDAF levels were observed to fluctuate, with focal remodeling of FIAF and FDAF, or rarely, even transition of FDAF to FIAF. FDAF tended to develop, not coincident with, but adjacent to initial FIAF. Because AF identifies these characteristic biological markers so specifically, autofluorescence metrics merit consideration in the study of STGD.

Retinal Phenotypes in Patients Homozygous for the G1961E Mutation in the ABCA4 Gene

PURPOSE We evaluated the pathogenicity of the G1961E mutation in the ABCA4 gene, and present the range of retinal phenotypes associated with this mutation in homozygosity in a patient cohort with ABCA4-associated phenotypes. METHODS Patients were enrolled from the ABCA4 disease database at Columbia University or by inquiry from collaborating physicians. Only patients homozygous for the G1961E mutation were enrolled. The entire ABCA4 gene open reading frame, including all exons and flanking intronic sequences, was sequenced in all patients. Phenotype data were obtained from clinical history and examination, fundus photography, infrared imaging, fundus autofluorescence, fluorescein angiography, and spectral domain-optical coherence tomography. Additional functional data were obtained using the full-field electroretinogram, and static or kinetic perimetry. RESULTS We evaluated 12 patients homozygous for the G1961E mutation. All patients had evidence of retinal pathology consistent with the range of phenotypes observed in ABCA4 disease. The latest age of onset was recorded at 64 years, in a patient diagnosed initially with age-related macular degeneration (AMD). Of 6 patients in whom severe structural (with/without functional) fundus changes were detected, 5 had additional, heterozygous or homozygous, variants detected in the ABCA4 gene. CONCLUSIONS Homozygous G1961E mutation in ABCA4 results in a range of retinal pathology. The phenotype usually is at the milder end of the disease spectrum, with severe phenotypes linked to the presence of additional ABCA4 variants. Our report also highlights that milder, late-onset Stargardt disease may be confused with AMD.

In vivo snapshot hyperspectral image analysis of age-related macular degeneration

Drusen, the hallmark lesions of age related macular degeneration (AMD), are biochemically heterogeneous and the identification of their biochemical distribution is key to the understanding of AMD. Yet the challenges are to develop imaging technology and analytics, which respect the physical generation of the hyperspectral signal in the presence of noise, artifacts, and multiple mixed sources while maximally exploiting the full data dimensionality to uncover clinically relevant spectral signatures. This paper reports on the statistical analysis of hyperspectral signatures of drusen and anatomical regions of interest using snapshot hyperspectral imaging and non-negative matrix factorization (NMF). We propose physical meaningful priors as initialization schemes to NMF for finding low-rank decompositions that capture the underlying physiology of drusen and the macular pigment. Preliminary results show that snapshot hyperspectral imaging in combination with NMF is able to detect biochemically meaningful components of drusen and the macular pigment. To our knowledge, this is the first reported demonstration in vivo of the separate absorbance peaks for lutein and zeaxanthin in macular pigment.

An interinstitutional comparative study and validation of computer aided drusen quantification.

Aims: To assess the portability and clinical applicability of a software program based on Photoshop (Adobe Systems Inc, San Jose, CA, USA) for digital drusen quantification. Methods: Independent graders from the Digital Fundus Photo Reading Center of Columbia University and King’s College Hospital used macular background levelling software to quantify the percentage of drusen in the central and middle Wisconsin subfields. 100 images of consecutive patients with choroidal neovascularisation in one eye and significant drusen in the other eye were analysed to determine suitability, and 10 were chosen for assessment by this software. Results: Of the 10 images used in the interinstitutional validation, the random effects ANOVA for the central and middle subfields showed a high degree of interobserver agreement. The ICC for interobserver reliability was 0.83 (95% CI: 67 to 95) for the central subfield and 0.84 (95% CI: 69 to 99) for the middle subfield. Overall agreement with the manual grading results was good and the within patient coefficient of variation was about 20% for all the pairwise comparisons between observers and the manual stereo gradings. Of the 100 images used to assess practical applicability of the software, 79 were suitable for semiautomated analysis. 13 had extensive mixed retinal pigment epithelial (RPE) changes limiting drusen identification, five had a significant number of reticular drusen, which are poorly identified by the software, and three had multiple small areas of RPE atrophy, which are difficult to distinguish from drusen. Conclusions: The software was successfully used by two institutions demonstrating portability, with good correlation between graders and to the manual stereo grading. Digital drusen quantification was possible in 79% of the images analysed.

Decoding simulated neurodynamics predicts the perceptual consequences of age-related macular degeneration.

Age-related macular degeneration (AMD) is the major cause of blindness in the developed world. Though substantial work has been done to characterize the disease, it is difficult to predict how the state of an individuals retina will ultimately affect their high-level perceptual function. In this paper, we describe an approach that couples retinal imaging with computational neural modeling of early visual processing to generate quantitative predictions of an individuals visual perception. Using a patient population with mild to moderate AMD, we show that we are able to accurately predict subject-specific psychometric performance by decoding simulated neurodynamics that are a function of scotomas derived from an individuals fundus image. On the population level, we find that our approach maps the disease on the retina to a representation that is a substantially better predictor of high-level perceptual performance than traditional clinical metrics such as drusen density and coverage. In summary, our work identifies possible new metrics for evaluating the efficacy of treatments for AMD at the level of the expected changes in high-level visual perception and, in general, typifies how computational neural models can be used as a framework to characterize the perceptual consequences of early visual pathologies.