Phenome- and genome-wide analyses of retinal optical coherence tomography images identify links between ocular and systemic health.

The human retina is a multilayered tissue that offers a unique window into systemic health. Optical coherence tomography (OCT) is widely used in eye care and allows the noninvasive, rapid capture of retinal anatomy in exquisite detail. We conducted genotypic and phenotypic analyses of retinal layer thicknesses using macular OCT images from 44,823 UK Biobank participants. We performed OCT layer cross-phenotype association analyses (OCT-XWAS), associating retinal thicknesses with 1866 incident conditions (median 10-year follow-up) and 88 quantitative traits and blood biomarkers. We performed genome-wide association studies (GWASs), identifying inherited genetic markers that influence retinal layer thicknesses and replicated our associations among the LIFE-Adult Study (N = 6313). Last, we performed a comparative analysis of phenome- and genome-wide associations to identify putative causal links between retinal layer thicknesses and both ocular and systemic conditions. Independent associations with incident mortality were detected for thinner photoreceptor segments (PSs) and, separately, ganglion cell complex layers. Phenotypic associations were detected between thinner retinal layers and ocular, neuropsychiatric, cardiometabolic, and pulmonary conditions. A GWAS of retinal layer thicknesses yielded 259 unique loci. Consistency between epidemiologic and genetic associations suggested links between a thinner retinal nerve fiber layer with glaucoma, thinner PS with age-related macular degeneration, and poor cardiometabolic and pulmonary function with a thinner PS. In conclusion, we identified multiple inherited genetic loci and acquired systemic cardio-metabolic-pulmonary conditions associated with thinner retinal layers and identify retinal layers wherein thinning is predictive of future ocular and systemic conditions.

Associations of systemic health and medication use with the enlargement rate of geographic atrophy in age-related macular degeneration.

BACKGROUND: The associations of geographic atrophy (GA) progression with systemic health status and medication use are unclear. METHODS: We manually delineated GA in 318 eyes in the Age-Related Eye Disease Study. We calculated GA perimeter-adjusted growth rate as the ratio between GA area growth rate and mean GA perimeter between the first and last visit for each eye (mean follow-up=5.3 years). Patients' history of systemic health and medications was collected through questionnaires administered at study enrolment. We evaluated the associations between GA perimeter-adjusted growth rate and 27 systemic health factors using univariable and multivariable linear mixed-effects regression models. RESULTS: In the univariable model, GA perimeter-adjusted growth rate was associated with GA in the fellow eye at any visit (p=0.002), hypertension history (p=0.03), cholesterol-lowering medication use (p<0.001), beta-blocker use (p=0.02), diuretic use (p<0.001) and thyroid hormone use (p=0.03). Among the six factors, GA in the fellow eye at any visit (p=0.008), cholesterol-lowering medication use (p=0.002), and diuretic use (p<0.001) were independently associated with higher GA perimeter-adjusted growth rate in the multivariable model. GA perimeter-adjusted growth rate was 51.1% higher in patients with versus without cholesterol-lowering medication use history and was 37.8% higher in patients with versus without diuretic use history. CONCLUSIONS: GA growth rate may be associated with the fellow eye status, cholesterol-lowering medication use, and diuretic use. These possible associations do not infer causal relationships, and future prospective studies are required to investigate the relationships further.

The influence of the topographic location of geographic atrophy on vision-related quality of life in nonexudative age-related macular degeneration.

PURPOSE: To examine associations between the topographic distribution of geographic atrophy (GA) and vision-related quality of life (VRQoL). METHODS: This study included 237 eyes from 161 participants in the Age-Related Eye Disease Study (AREDS). GA lesions were manually delineated with color fundus photographs obtained by the AREDS Research Group and atrophic area was measured in an Early Treatment Diabetic Retinopathy Study (ETDRS) grid. VRQoL was measured using the National Eye Institute Visual Function Questionnaire (NEI-VFQ). Area of atrophy in the ETDRS grid subfields was correlated with VRQoL by linear regression modeling. RESULTS: The average area of atrophy in the better and worse eye was 3.43mm2 and 7.15mm2 respectively. In multivariable analysis, VRQoL was not associated with total area of atrophy in the better eye (ß, - 0.53; 95% confidence interval [CI], - 1.11 to 0.05; P = 0.07) or worse eye (ß, 0.12; 95% CI, - 0.32 to 0.55; P = 0.59). However, area of atrophy in the central 1-mm-diameter zone of the better eye was significantly associated with VRQoL when the ETDRS subfields were examined individually (ß, - 14.57; 95% CI, - 27.12 to - 2.02; P = 0.023), grouped into quadrants (ß, - 18.35; 95% CI, - 30.03 to - 6.67; P = 0.002), inner and outer zones (ß, - 17.26; 95% CI, - 29.38 to - 5.14; P = 0.006), or vertical and horizontal zones (ß, - 18.97; 95% CI, - 30.18 to - 7.77; P = 0.001). CONCLUSION: In patients with GA, greater area of atrophy in the central 1-mm-diameter zone of the better eye was independently associated with lower VRQoL, while total area of atrophy in the better or worse eye was not.

Association of the Affordable Care Act with Eye-Related Emergency Department Utilization in the United States.

PURPOSE: To investigate the association of the Affordable Care Act (ACA) with nationwide eye-related emergency department (ED) use. DESIGN: Retrospective, cross-sectional study. PARTICIPANTS: All patients who presented to the ED with an eye-related primary diagnosis were eligible for inclusion. METHODS: Nationally representative data from the US Nationwide Emergency Department Sample were used to analyze eye-related ED visits before (2010-2013) and after (2014-2017) the ACA was mandated. All ED visits were categorized as emergent or nonemergent or could not be determined. MAIN OUTCOME MEASURES: The primary outcome was to compare the nationwide and regional incidence of eye-related ED visits per 100 000 US population before (2010-2013) and after (2014-2017) the ACA was mandated. Secondary outcome measures included change in payor status, proportion of urgent versus nonurgent visits, proportion of visits at teaching versus nonteaching hospitals, associated charges, and discharge disposition. RESULTS: A total of 16 808 343 eye-related ED visits occurred in the United States during the study period from 2010 to 2017. Of these, 8 088 203 ED visits occurred before the ACA was mandated (2010-2013), and 8 720 766 ED visits occurred after the ACA was mandated (2014-2017). After the ACA was mandated in 2014, there was an initial decline in incidence of eye-related ED visits from 652.4 per 100 000 population in 2013 to 593.0 per 100 000 population in 2014, followed by a rapid increase in incidence to 658.5 per 100 000 population in 2015, with a further increase to 746.6 per 100 000 population in 2016. The percentage of uninsured patients decreased from 19.0% to 14.3%. The increase in ED use was greatest for individuals in the lowest income quartile (895.1 per 100 000 population in 2013 to 964.0 per 100 000 in 2017). Overall, 44.8% of ED visits were due to nonemergent eye conditions. CONCLUSIONS: Although the ACA increased insurance coverage for Americans, theoretically increasing access to outpatient ophthalmic care, this did not decrease ED reliance for management of ophthalmic conditions. Additional measures beyond expanding insurance coverage may be necessary to provide high-quality, efficient, and equitable outpatient ophthalmic care to all Americans.

Subretinal Drusenoid Deposit Formation: Insights From Turing Patterns.

PURPOSE: The purpose of this study was to demonstrate that the organized formation of subretinal drusenoid deposits (SDDs) may be a Turing pattern. METHODS: A Java-based computational model of an inferred reaction-diffusion system using paired partial differential equations was used to create topographic images. Reaction kinetics were varied to illustrate a spectrum of pattern development, which were then compared to dot-like, reticular, and confluent SDD patterns observed clinically. RESULTS: A reaction-diffusion system using two agents, one an "activator" that increases its own production, and the other an "inhibitor" that decreases the activator's production, can create patterns that match the spectrum of topographic appearance of organized SDD. By varying a single parameter, the strength of the activator, the full spectrum of clinically observed SDD patterns can be generated. A new pattern, confluence with holes, is predicted and identified in one case example. CONCLUSIONS: The formation of clinically significant SDD and its different patterns can be explained using Turing patterns obtained by simulating a two-component reaction-diffusion system. TRANSLATIONAL RELEVANCE: This model may be able to guide future risk stratification for patients with SDD, and provide mechanistic insights into the cause of the disease.

A hierarchical Bayesian entry time realignment method to study the long-term natural history of diseases.

A major question in clinical science is how to study the natural course of a chronic disease from inception to end, which is challenging because it is impractical to follow patients over decades. Here, we developed BETR (Bayesian entry time realignment), a hierarchical Bayesian method for investigating the long-term natural history of diseases using data from patients followed over short durations. A simulation study shows that BETR outperforms an existing method that ignores patient-level variation in progression rates. BETR, when combined with a common Bayesian model comparison tool, can identify the correct disease progression function nearly 100% of the time, with high accuracy in estimating the individual disease durations and progression rates. Application of BETR in patients with geographic atrophy, a disease with a known natural history model, shows that it can identify the correct disease progression model. Applying BETR in patients with Huntington's disease demonstrates that the progression of motor symptoms follows a second order function over approximately 20 years.

Photoreceptor Layer Thinning Is an Early Biomarker for Age-Related Macular Degeneration: Epidemiologic and Genetic Evidence from UK Biobank OCT Data.

PURPOSE: Despite widespread use of OCT, an early-stage imaging biomarker for age-related macular degeneration (AMD) has not been identified. Pathophysiologically, the timing of drusen accumulation in relationship to photoreceptor degeneration in AMD remains unclear, as are the inherited genetic variants contributing to these processes. Herein, we jointly analyzed OCT, electronic health record data, and genomic data to characterize the time sequence of changes in retinal layer thicknesses in AMD, as well as epidemiologic and genetic associations between retinal layer thicknesses and AMD. DESIGN: Cohort study. PARTICIPANTS: Forty-four thousand eight hundred twenty-three individuals from the UK Biobank (enrollment age range, 40-70 years; 54% women; median follow-up, 10 years). METHODS: The Topcon Advanced Boundary Segmentation algorithm was used for retinal layer segmentation. We associated 9 retinal layer thicknesses with prevalent AMD (present at enrollment) in a logistic regression model and with incident AMD (diagnosed after enrollment) in a Cox proportional hazards model. Next, we associated AMD-associated genetic alleles, individually and as a polygenic risk score (PRS), with retinal layer thicknesses. All analyses were adjusted for age, age-squared (age2), sex, smoking status, and principal components of ancestry. MAIN OUTCOME MEASURES: Prevalent and incident AMD. RESULTS: Photoreceptor segment (PS) thinning was observed throughout the lifespan of individuals analyzed, whereas retinal pigment epithelium (RPE) and Bruch's membrane (BM) complex thickening started after 57 years of age. Each standard deviation (SD) of PS thinning and RPE-BM complex thickening was associated with incident AMD (PS: hazard ratio [HR], 1.35; 95% confidence interval [CI], 1.23-1.47; P = 3.7 × 10-11; RPE-BM complex: HR, 1.14; 95% CI, 1.06-1.22; P = 0.00024). The AMD PRS was associated with PS thinning (ß, -0.21 SD per twofold genetically increased risk of AMD; 95% CI, -0.23 to -0.19; P = 2.8 × 10-74), and its association with RPE-BM complex was U-shaped (thinning with AMD PRS less than the 92nd percentile and thickening with AMD PRS more than the 92nd percentile). The loci with strongest support for genetic correlation were AMD risk-raising variants Complement Factor H (CFH):rs570618-T, CFH:rs10922109-C, and Age-Related Maculopathy Susceptibility 2 (ARMS2)/High-Temperature Requirement Serine Protease 1 (HTRA1):rs3750846-C on PS thinning and SYN3/Tissue Inhibitor of Metalloprotease 3 (TIMP3):rs5754227-T on RPE-BM complex thickening. CONCLUSIONS: Epidemiologically, PS thinning precedes RPE-BM complex thickening by decades and is the retinal layer most strongly predictive of future AMD risk. Genetically, AMD risk variants are associated with decreased PS thickness. Overall, these findings support PS thinning as an early-stage biomarker for future AMD development.

Management of noninfectious scleritis.

Scleritis is a manifestation of inflammatory eye disease that involves the sclera. It can be divided into multiple subtypes, including diffuse anterior, nodular anterior, necrotizing, and posterior scleritis. In many cases, scleritis is restricted to the eye; however, it can occur in the context of systemic illness, particularly autoimmune and infectious conditions. Patients with autoimmune conditions, such as rheumatoid arthritis, inflammatory bowel disease, systemic lupus erythematosus, and polyangiitis with granulomatosis, may develop scleritis flares that may require topical and systemic therapy. Initial therapy typically involves oral nonsteroidal anti-inflammatory drugs (NSAIDs); however, it is important to address the underlying condition, particularly if systemic. Other treatment regimens typically involve either local or systemic steroids or the use of immunomodulatory agents, which have a wide range of efficacy and documented use in the literature. There is a myriad of immunomodulatory agents used in the treatment of scleritis including antimetabolites, calcineurin inhibitors, biologics, and alkylating agents. In this review, we highlight the various subtypes of noninfectious scleritis and explore each of the mainstay agents used in the management of this entity. We explore the use of steroids and NSAIDs in detail and discuss evidence for various immunomodulatory agents.

Natural history of central sparing in geographic atrophy secondary to non-exudative age-related macular degeneration.

BACKGROUND: The macular central 1 mm diameter zone is crucial to patients' visual acuity, but the long-term natural history of central sparing in eyes with geographic atrophy (GA) is unknown. METHODS: We manually segmented GA in 210 eyes with GA involving central 1 mm diameter zone (mean follow-up=3.8 years) in the Age-Related Eye Disease Study. We measured the residual area in central 1 mm diameter zone and calculated central residual effective radius (CRER) as square root of (residual area/π). A linear mixed-effects model was used to model residual size over time. We added a horizontal translation factor to each data set to account for different durations of GA involving the central zone. RESULTS: The decline rate of central residual area was associated with baseline residual area (p=0.008), but a transformation from central residual area to CRER eliminated this relationship (p=0.51). After the introduction of horizontal translation factors to each data set, CRER declined linearly over approximately 13 years (r2=0.80). The growth rate of total GA effective radius was 0.14 mm/year (95% CI 0.12 to 0.15), 3.7-fold higher than the decline rate of CRER (0.038 mm/year, 95% CI 0.034 to 0.042). The decline rate of CRER was 53.3% higher in eyes with than without advanced age-related macular degeneration in the fellow eyes at any visit (p=0.007). CONCLUSIONS: CRER in eyes with GA declined linearly over approximately 13 years and may serve as an anatomic endpoint in future clinical trials aiming to preserve the central zone.

Deep Learning of the Retina Enables Phenome- and Genome-Wide Analyses of the Microvasculature.

BACKGROUND: The microvasculature, the smallest blood vessels in the body, has key roles in maintenance of organ health and tumorigenesis. The retinal fundus is a window for human in vivo noninvasive assessment of the microvasculature. Large-scale complementary machine learning-based assessment of the retinal vasculature with phenome-wide and genome-wide analyses may yield new insights into human health and disease. METHODS: We used 97 895 retinal fundus images from 54 813 UK Biobank participants. Using convolutional neural networks to segment the retinal microvasculature, we calculated vascular density and fractal dimension as a measure of vascular branching complexity. We associated these indices with 1866 incident International Classification of Diseases-based conditions (median 10-year follow-up) and 88 quantitative traits, adjusting for age, sex, smoking status, and ethnicity. RESULTS: Low retinal vascular fractal dimension and density were significantly associated with higher risks for incident mortality, hypertension, congestive heart failure, renal failure, type 2 diabetes, sleep apnea, anemia, and multiple ocular conditions, as well as corresponding quantitative traits. Genome-wide association of vascular fractal dimension and density identified 7 and 13 novel loci, respectively, that were enriched for pathways linked to angiogenesis (eg, vascular endothelial growth factor, platelet-derived growth factor receptor, angiopoietin, and WNT signaling pathways) and inflammation (eg, interleukin, cytokine signaling). CONCLUSIONS: Our results indicate that the retinal vasculature may serve as a biomarker for future cardiometabolic and ocular disease and provide insights into genes and biological pathways influencing microvascular indices. Moreover, such a framework highlights how deep learning of images can quantify an interpretable phenotype for integration with electronic health record, biomarker, and genetic data to inform risk prediction and risk modification.

An In Silica Model for RPE Loss Patterns in Choroideremia.

Purpose: To use empirical data to develop a model of cell loss in choroideremia that predicts the known exponential rate of RPE loss and central, scalloped preservation pattern seen in this disease. Methods: A computational model of RPE loss was created in Python 3.7, which constructed an array of RPE cells clusters, binarized as either live or atrophic. Two rules were applied to this model: the background effect gave each cell a chance of dying defined by a background function, and the neighbor effect increased the chance of RPE cell death if a neighbor were dead. The known anatomic distribution of rods, RPE, choriocapillaris density, amacrine, ganglion, and cone cells were derived from the literature and applied to this model. Atrophy growth rates were measured over arbitrary time units and fit to the known exponential decay model. The main outcome measures: included topography of atrophy over time and fit of simulated residual RPE area to exponential decay. Results: A background effect alone can simulate exponential decay, but does not simulate the central island preservation seen in choroideremia. An additive neighbor effect alone does not simulate exponential decay. When the neighbor effect multiplies the background effect using the rod density function, our model follows an exponential decay, similar to previous observations. Also, our model predicts a residual island of RPE that resembles the topographic distribution of residual RPE seen in choroideremia. Conclusions: The pattern of RPE loss in choroideremia can be predicted by applying simple rules. The RPE preservation pattern typically seen in choroideremia may be related to the underlying pattern of rod density. Further studies are needed to validate these findings.

Topographic Variation of Retinal Vascular Density in Normal Eyes Using Optical Coherence Tomography Angiography.

Purpose: To establish a continuous topography of retinal vessel density in normal eyes using optical coherence tomography angiography (OCTA). Methods: A retrospective chart review was performed, and 8-mm × 8-mm OCTA images from 22 normal eyes were analyzed. Vessel density was plotted as a continuous function of distance from the foveal center (radial vessel density) and directional meridians (directional vessel density) for the superficial capillary plexus and deep capillary plexus. Results: Continuous radial and directional vessel density plots for the superficial and deep capillary plexus were generated. Radial vessel density analysis revealed transition points at 657 microns (95% confidence interval [CI], 619-696) and 950 microns (95% CI, 903-997) from the foveal center for the superficial plexus and deep plexus, respectively. Directional vessel density analysis demonstrated significant vessel density variations in these vascular layers and provided greater detail compared to traditional quadrant analysis. Conclusions: There are significant topographic variations of retinal vessel density in normal eyes. Continuous vessel density analysis offers greater sensitivity in detecting topographic vessel density changes compared to traditional methods of analysis. Translational Relevance: This study establishes a normative continuous vessel density topography that may help elucidate the role of the vascular bed in different chorioretinal diseases.

Local Progression Kinetics of Geographic Atrophy Depends Upon the Border Location.

Purpose: To assess the influence of lesion morphology and location on geographic atrophy (GA) growth rate. Methods: We manually delineated GA on color fundus photographs of 237 eyes in the Age-Related Eye Disease Study. We calculated local border expansion rate (BER) as the linear distance that a point on the GA border traveled over 1 year based on a Euclidean distance map. Eye-specific BER was defined as the mean local BER of all points on the GA border in an eye. The percentage area affected by GA was defined as the GA area divided by the total retinal area in the region. Results: GA enlarged 1.51 ± 1.96 mm2 in area and 0.13 ± 0.11 mm in distance over 1 year. The GA area growth rate (mm2/y) was associated with the baseline GA area (P < 0.001), perimeter (P < 0.001), lesion number (P < 0.001), and circularity index (P < 0.001); in contrast, eye-specific BER (mm/y) was not significantly associated with any of these factors. As the retinal eccentricity increased from 0 to 3.5 mm, the local BER increased from 0.10 to 0.24 mm/y (P < 0.001); in contrast, the percentage of area affected by GA decreased from 49.3% to 2.3%. Conclusions: Using distance-based measurements allows GA progression evaluation without significant confounding effects from baseline GA morphology. Local GA progression rates increased as a function of retinal eccentricity within the macula which is opposite of the trend for GA distribution, suggesting that GA initiation and enlargement may be mediated by different biological processes.

Altered transcriptome and disease-related phenotype emerge only after fibroblasts harvested from patients with age-related macular degeneration are differentiated into retinal pigment epithelium.

We have reported previously that retinal pigment epithelium (RPE) differentiated from induced pluripotent stem cells (iPSC) generated from fibroblasts of patients with age-related macular degeneration (AMD) exhibit a retinal degenerative disease phenotype and a distinct transcriptome compared to age-matched controls. Since the genetic composition of the iPSC and RPE are inherited from fibroblasts, we investigated whether differential behavior was present in the parental fibroblasts and iPSC prior to differentiation of the cell lines into RPE. Principal component analyses revealed significant overlap (essentially no differences) in the transcriptome of fibroblasts between AMD and controls. After reprogramming, there was no significant difference in the transcriptome of iPSC generated from AMD versus normal donors. In contrast, the transcriptome of RPE derived from iPSC segregated into two distinct clusters of AMD-derived cells versus controls. Interestingly, mitochondrial dysfunction in AMD-derived RPE was evident after approximately two months in culture. Moreover, these differences in mitochondrial dysfunction were not evident in the parental fibroblasts and iPSC. This study demonstrates an altered transcriptome and impaired mitochondrial function in RPE derived from AMD patients versus controls, and demonstrates these differences are not present in the original fibroblasts or iPSC. These results suggest that pathology in AMD is triggered upon differentiation of parent cells into RPE. More study of this phenomenon could advance the current understandings of the etiology of AMD and the development of novel therapeutic targets.

Geographic atrophy severity and mortality in age-related macular degeneration.

PURPOSE: To examine the association between geographic atrophy (GA) disease characteristics and mortality risk. METHODS: We manually delineated color fundus photographs of 209 Age-Related Eye Disease Study (AREDS) participants with GA secondary to age-related macular degeneration to identify total area of atrophy, GA effective radius growth rate, disease laterality, and the presence of foveal center involvement. Associations between GA characteristics and mortality were assessed with Cox proportional hazards models adjusted for health status indicators. RESULTS: During a median follow-up of 6.8 years, 48 (23.0%) participants with GA died. In adjusted models, accounting for age, sex, and health status, participants with total GA area in the highest quartile had a significantly increased risk of all-cause mortality compared to those with total GA area in the lowest quartile (hazard ratio [HR], 3.42; 95% confidence interval [CI], 1.32-8.86; P = 0.011). GA effective radius growth rate, bilateral disease, and the presence of foveal center involvement were not significantly associated with mortality. In a multivariable model, including health status indicators and all GA characteristics, total area of atrophy in the highest quartile remained significantly associated with mortality (HR, 4.65; 95% CI, 1.29-16.70; P = 0.019). CONCLUSIONS: More extensive GA, as indicated by a greater total area of atrophy, was associated with an increased risk of all-cause mortality in our cohort. The extent of GA may reflect the extent of underlying disease processes that contribute to greater mortality risk, further suggesting that GA may be part of a systemic rather than purely ocular disease process.

Long-term natural history of visual acuity in eyes with choroideremia: a systematic review and meta-analysis of data from 1004 individual eyes.

BACKGROUND/AIMS: Best-corrected visual acuity (BCVA) is the most common primary endpoint in treatment trials for choroideremia (CHM) but the long-term natural history of BCVA is unclear. METHODS: We searched in seven databases to identify studies that reported BCVA of untreated eyes with CHM. We sought individual-level data and performed segmented regression between BCVA and age. For eyes followed longitudinally, we introduced a horizontal translation factor to each dataset to account for different ages at onset of a rapid BCVA decline. RESULTS: We included 1004 eyes from 23 studies. BCVA of the right and left eyes was moderately correlated (r=0.60). BCVA as a function of age followed a 2-phase decline (slow followed by rapid decline), with an estimated transition age of 39.1 years (95% CI 33.5 to 44.7). After the introduction of horizontal translation factors to longitudinal datasets, BCVA followed a 2-phase decline until it reached 0 letters (r2=0.90). The BCVA decline rate was 0.33 letters/year (95% CI -0.38 to 1.05) before 39 years, and 1.23 letters/year (95% CI 0.55 to 1.92) after 39 years (p=0.004). CONCLUSION: BCVA in eyes with CHM follows a 2-phase linear decline with a transition age of approximately 39 years. Future trials enrolling young patients may not be able to use BCVA as a primary or sole endpoint, but rather, may need to employ additional disease biomarkers that change before age 39. BCVA may still have utility as a primary endpoint for patients older than 39 years who have measurable BCVA decline rates.

Geographic Atrophy Growth Is Strongly Related to Lesion Perimeter: Unifying Effects of Lesion Area, Number, and Circularity on Growth.

PURPOSE: To investigate the underlying reason for the previously observed impact of baseline lesion size, number, and circularity on geographic atrophy (GA) growth rate. DESIGN: Retrospective analysis of a multicenter, prospective, randomized controlled trial. PARTICIPANTS: Age-Related Eye Disease Study participants with GA secondary to nonexudative age-related macular degeneration. METHODS: We manually delineated atrophic lesions on color fundus photographs of 318 eyes with GA followed up over at least 2 visits (mean follow-up duration, 5.1 ± 3.0 years). We calculated GA area growth rate for each eye based on the first and last visit. GA perimeter-adjusted growth rate was defined as the ratio between GA area growth rate and mean GA perimeter between the first and last visit for each eye. MAIN OUTCOME MEASURES: GA area growth rate, growth rate of the square root of GA area, and GA perimeter-adjusted growth rate. RESULTS: GA area growth rate was correlated strongly with mean GA perimeter (r2 = 0.66). GA area growth rate was associated with baseline GA area (r2 = 0.39; P < 0.001), lesion number (r2 = 0.10; P < 0.001), and circularity index (r2 = 0.28; P < 0.001). The use of the square root of GA area reduced the influence of baseline GA area (but not lesion number or circularity) on GA growth rate. In comparison, GA perimeter-adjusted growth rate (0.098 ± 0.062 mm/year) was not correlated with baseline GA area (r2 = 0.005; P = 0.20), lesion number (r2 = 0.00009; P = 0.86), or circularity index (r2 = 0.007; P = 0.14). GA perimeter-adjusted growth rate was 50.0% higher in eyes whose fellow eyes showed GA at any visit (0.102 ± 0.062 mm/year) than in eyes whose fellow eyes never demonstrated GA during follow-up (0.068 ± 0.049 mm/year). CONCLUSIONS: The growth rate of GA area is associated strongly with lesion perimeter. This relationship explains the previously observed influences of baseline GA size, lesion number, and circularity on GA growth rate. GA perimeter-adjusted growth rate is uncorrelated with the 3 morphologic factors and may serve as a surrogate outcome measure to monitor GA progression in future studies.