Effect of image compression and resolution on retinal vascular caliber.

PURPOSE: Changes in retinal vascular caliber measured from digital color fundus photographs have been independently associated with systemic outcomes in epidemiologic studies, but the effect of image resolution and compression on vascular measurements has not been previously evaluated. METHODS: To explore image compression, 40 natively digital fundus images were selected with good photo quality, high spatial resolution, and no previous image compression. Using Adobe Photoshop, these images were compressed at progressively higher levels up to 147:1, and then retinal vascular caliber was measured at each level using semiautomated software. To examine resolution, 40 fundus photographs acquired on high-resolution film were scanned with settings corresponding to 10, 7, 5, 3, and 1 megapixel fundus cameras. After adjusting for scale factor, vascular caliber was measured at each level of resolution. Data were analyzed by comparing the calculated central retinal arteriole equivalent (CRAE) and the central retinal venular equivalent (CRVE) of the original and altered images, using repeated measures ANOVA. RESULTS: CRAE became significantly wider with increasing levels of compression at the 25:1 threshold (~1 µm wider, P < 0.001) and was ~5 µm wider with 147:1 compression. CRVE also increased, but less than CRAE. Using 7 (megapixel)-MP resolution as the standard, CRVE was significantly narrower at the 5-MP simulation (~2 µm, P < 0.001) and was ~12 µm narrower at the 1-MP simulation. CRAE also decreased, but less than CRVE. CONCLUSIONS: Increasing digital image file compression and decreasing fundus image spatial resolution led to skewed measurements of the retinal vascular caliber.

Transition from film to digital fundus photography in the Longitudinal Studies of the Ocular Complications of AIDS.

PURPOSE: To describe the transition to digital imaging and assess any impact on ocular disease classification. METHODS: Film and digital images, acquired by certified photographers, were evaluated independently according to standard procedures for the following: image quality, presence of cytomegalovirus retinitis lesions, and their extent and proximity from disk and macula. Intergrader agreement within the digital medium was also assessed. RESULTS: Among the 15 eyes with cytomegalovirus retinitis, the mean difference between film and digital images for linear distance of lesion edge to disk was 0.02 disk diameters, for distance to center of macula was -0.04 disk diameters, and area covered by cytomegalovirus retinitis was 0.95 disk area. There was no statistically significant difference in distance and area measurements between media. Intergrader agreement in measurements of digital images was excellent for distance and area estimated. CONCLUSION: Our results suggest that digital grading of cytomegalovirus retinitis in Longitudinal Studies of the Ocular Complications of AIDS is comparable with that from film regarding disease classification, measurements, and reproducibility. These findings provide support for continuity of grading data, despite the necessary transition in imaging media.

Retinal vessel caliber among people with acquired immunodeficiency syndrome: relationships with visual function.

PURPOSE: To evaluate relationships between retinal vessel caliber and tests of visual function among people with AIDS. DESIGN: Longitudinal, observational cohort study. METHODS: We evaluated data for participants without ocular opportunistic infections at initial examination (baseline) in the Longitudinal Studies of the Ocular Complications of AIDS (1998-2008). Visual function was evaluated with best-corrected visual acuity, Goldmann perimetry, automated perimetry (Humphrey Field Analyzer), and contrast sensitivity (CS) testing. Semi-automated grading of fundus photographs (1 eye/participant) determined central retinal artery equivalent (CRAE), central retinal vein equivalent (CRVE), and arteriole-to-venule ratio (AVR) at baseline. Multiple linear regression models, using forward selection, sought independent relationships between indices and visual function variables. RESULTS: Included were 1250 participants. Smaller AVR was associated with reduced visual field by Goldmann perimetry (P = .003) and worse mean deviation (P = .02) on automated perimetry and possibly with worse pattern standard deviation (PSD) on automated perimetry (P = .06). There was a weak association between smaller AVR and worse CS (P = .07). Relationships were independent of antiretroviral therapy and level of immunodeficiency (CD4+ T lymphocyte count, human immunodeficiency virus [HIV] RNA blood level). On longitudinal analysis, retinal vascular indices at baseline did not predict changes in visual function. CONCLUSIONS: Variation in retinal vascular indices is associated with abnormal visual function in people with AIDS, manifested by visual field loss and possibly by reduced CS. Relationships are consistent with the hypothesis that HIV-related retinal vasculopathy is a contributing factor to vision dysfunction among HIV-infected individuals. Longitudinal studies are needed to determine whether changes in indices predict change in visual function.

Retinal vessel caliber among people with acquired immunodeficiency syndrome: relationships with disease-associated factors and mortality.

PURPOSE: To evaluate relationships between retinal vessel caliber, AIDS-related factors, and mortality. DESIGN: Longitudinal, observational cohort study. METHODS: We evaluated data for participants without ocular opportunistic infections at initial examination (baseline) in the Longitudinal Studies of the Ocular Complications of AIDS (1998-2008). Semi-automated evaluation of fundus photographs (1 eye/participant) determined central retinal artery equivalent (CRAE), central retinal vein equivalent (CRVE), and arteriole-to-venule ratio (AVR) at baseline. Multiple linear regression models, using forward selection, identified independent relationships between indices and various host- and disease-related variables. RESULTS: Included were 1250 participants. Mean follow-up for determination of mortality was 6.1 years. Smaller CRAE was related to increased age (P < .001) and hypertension (P < .001); larger CRAE was related to lower hematocrit (P = .002). Larger CRAE and CRVE were associated with black race (P < .001). Larger CRVE was related to smoking (P = .004); smaller CRVE was related to age (P < .001) and higher mean corpuscular volume (P = .001). We observed the following relationships with AIDS-associated factors: smaller CRAE and larger CRVE with history of highly active antiretroviral therapy (HAART; P < .001); and larger CRAE with lower CD4+ T lymphocyte count (P = .04). We did not identify independent relationships with human immunodeficiency virus RNA blood levels. There was a 12% (95% CI, 2%-21%) increase in mortality risk per quartile of decreasing AVR (P = .02). CONCLUSIONS: Variations in retinal vascular caliber are associated with AIDS-specific factors and are markers for increased mortality risk. Relationships are consistent with the hypothesis that the vasculature is altered by known atherogenic effects of chronic HAART or the prolonged inflammatory state associated with AIDS.

Suboptimal image focus broadens retinal vessel caliber measurement.

PURPOSE: Studies have used central retinal arteriolar (CRAE) and central retinal venular (CRVE) calibers, measured from images produced with computerized image analysis, to detect risk factors for systemic diseases. The authors explored suboptimal image focus as a possible contributing factor to artificially larger vascular caliber measurements. METHODS: From the reading center image collections, 30 digital retinal images were selected for optimum quality. Image analysis software was used to derive nine progressively blurred versions of the originals. IVAN measurement software was used to measure CRAE and CRVE in the original and the blurred series derived from them. To check the adequacy of the simulation, progressively defocused series of images were taken of several volunteers. RESULTS: For CRAE, each level of simulated blurring produced a statically significant increase in apparent vessel caliber from the original (P<0.01, Wilcoxon signed rank test). For an average CRAE of 160 µm, mean broadening with minimal/moderate/severe blurring was 3 µm/12 µm/33 µm. For CRVE, every blurring level beyond the first was found to be significant (P<0.01). From an average CRVE of 200 µm, mean broadening ranged from 0 to 11 µm with minimal to severe blurring. Analysis of the progressively defocused series taken of volunteers yielded similar results overall. CONCLUSIONS: Suboptimal focus can result in erroneously larger vessel caliber measurements. Slight blurring has a minimal effect, but more severe blurring has a progressively greater effect.

Comparison of digital and film grading of diabetic retinopathy severity in the diabetes control and complications trial/epidemiology of diabetes interventions and complications study.

OBJECTIVE: To compare diabetic retinopathy (DR) severity as evaluated by digital and film images in a long-term multicenter study, as the obsolescence of film forced the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications Study (DCCT/EDIC) to transition to digital after 25 years. METHODS: At 20 clinics from 2007 through 2009, 310 participants with type 1 diabetes with a broad range of DR were imaged, per the Early Treatment Diabetic Retinopathy Study (ETDRS) protocol, with both film and digital cameras. Severity of DR was assessed centrally from film and tonally standardized digital cameras. For retinopathy outcomes with greater than 10% prevalence, we had 85% or greater power to detect an agreement κ of 0.7 or lower from our target of 0.9. RESULTS: Comparing DR severity, digital vs film yielded a weighted κ of 0.74 for eye level and 0.73 for patient level ("substantial"). Overall, digital grading did not systematically underestimate or overestimate severity (McNemar bias test, P = .14). For major DR outcomes (≥3-step progression on the ETDRS scale and disease presence at ascending thresholds), digital vs film κ values ranged from 0.69 to 0.96 ("substantial" to "nearly perfect"). Agreement was 86% to 99%; sensitivity, 75% to 98%; and specificity, 72% to 99%. Major conclusions were similar with digital vs film gradings (odds reductions with intensive diabetes therapy for proliferative DR at EDIC years 14 to 16: 65.5% digital vs 64.3% film). CONCLUSION: Digital and film evaluations of DR were comparable for ETDRS severity levels, DCCT/EDIC design outcomes, and major study conclusions, indicating that switching media should not adversely affect ongoing studies.

Imaging of diabetic retinopathy and diabetic macular edema.

Imaging of the retinal complications of diabetes mellitus is rapidly changing from the emergence of new technology such as optical coherence tomography. In particular, the characterization of diabetic macular edema is much easier for the clinician and there are new, more sensitive clinical research end points. However, our understanding of structure-functional relationships remains suboptimal and the classification of macular edema by optical coherence tomography continues to evolve. The classification of diabetic retinopathy severity continues to rely upon fundus photography, although the transition from film to digital photography presents both challenges and advantages.

Mosaics versus Early Treatment Diabetic Retinopathy seven standard fields for evaluation of diabetic retinopathy severity.

PURPOSE: To compare agreement between mosaicked and seven field photographs for classification of the diabetic retinopathy (DR) severity. METHODS: Mosaic digital (MosD) images were compared with seven field stereo film (7FF) and stereo digital (7FD) photographs from a 152-eye cohort with full-spectrum Early Treatment of Diabetic Retinopathy severity levels for agreement on severity level, DR presence with ascending severity thresholds, DR index lesion presence, and classification repeatability. RESULTS: There was a substantial agreement classifying the Early Treatment Diabetic Retinopathy Study DR severity level between MosD and 7FF (kunweighted = 0.59, klinear weighted = 0.83), MosD and 7FD (κ = 0.62, κ weighted = 0.86), and 7FD and 7FF (κ = 0.62, κ weighted = 0.86) images. Marginal homogeneity analyses found no significant difference between MosD and 7FF (P = 0.44, Bhapkar's test). Kappa between MosD and 7FF ranged from 0.75 to 0.91 for the presence or absence of DR at 8 ascending severity thresholds. Repeatability among readers using MosD images was similar to repeatability among those using 7FF or 7FD. Repeatability among readers using MosD and 7FF images at various severity thresholds was similar. Kappa between MosD and 7FF grading for identifying DR lesions ranged from 0.61 to 1.00. CONCLUSION: Mosaic images are generally comparable with standard seven-field photographs for classifying DR severity.

Long-term renal outcomes of patients with type 1 diabetes mellitus and microalbuminuria: an analysis of the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications cohort.

BACKGROUND: Microalbuminuria is a common diagnosis in the clinical care of patients with type 1 diabetes mellitus. Long-term outcomes after the development of microalbuminuria are variable. METHODS: We quantified the incidence of and risk factors for long-term renal outcomes after the development of microalbuminuria in the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications (DCCT/EDIC) study. The DCCT randomly assigned 1441 persons with type 1 diabetes to intensive or conventional diabetes therapy, and participants were subsequently followed up during the observational EDIC study. During the DCCT/EDIC study, 325 participants developed incident persistent microalbuminuria (albumin excretion rate, ≥30 mg/24 h at 2 consecutive study visits). We assessed their subsequent renal outcomes, including progression to macroalbuminuria (albumin excretion rate, ≥300 mg/24 h at 2 consecutive visits), impaired glomerular filtration rate (estimated glomerular filtration rate, <60 mL/min/1.73 m(2) at 2 consecutive study visits), end-stage renal disease, and regression to normoalbuminuria (albumin excretion rate, <30 mg/24 h at 2 consecutive visits). RESULTS: The median follow-up period after persistent microalbuminuria diagnosis was 13 years (maximum, 23 years). Ten-year cumulative incidences of progression to macroalbuminuria, impaired glomerular filtration rate, end-stage renal disease, and regression to normoalbuminuria were 28%, 15%, 4%, and 40%, respectively. Albuminuria outcomes were more favorable with intensive diabetes therapy, lower glycated hemoglobin level, absence of retinopathy, female sex, lower blood pressure, and lower concentrations of low-density lipoprotein cholesterol and triglycerides. Lower glycated hemoglobin level, absence of retinopathy, and lower blood pressure were also associated with decreased risk of impaired glomerular filtration rate. CONCLUSIONS: After the development of persistent microalbuminuria, progression and regression of kidney disease each commonly occur. Intensive glycemic control, lower blood pressure, and a more favorable lipid profile are associated with improved outcomes.

Comparability of digital photography with the ETDRS film protocol for evaluation of diabetic retinopathy severity.

PURPOSE: To evaluate digital photography parameters affecting comparability with the Early Treatment Diabetic Retinopathy Study (ETDRS) film protocol for diabetic retinopathy (DR) severity grading. METHODS: ETDRS protocol photographs and four variations of digital images (uncompressed stereoscopic, compressed stereoscopic, uncompressed monoscopic, and uncompressed monoscopic wide-angle mosaic) of 152 eyes were independently evaluated by using ETDRS classifications. Digital formats were compared to film and each other for agreement on severity level, DR presence at ascending threshold, presence of the DR index lesion, and repeatability of grading. Study parameters included image resolution sufficient to distinguish small lesions, color balancing of digital images to film, documenting essential ETDRS classification retinal regions, similar magnification, and supplementary green-channel viewing. RESULTS: The κ statistic was substantial or near substantial between all digital formats and film for classifying severity levels (κ = 0.59-0.62; κ(w) [linear weighted] = 0.83-0.87). The distribution of DR levels in all digital formats was not significantly different from that of the film (Bhapkar test, P = 0.09-0.44). The κ among digital formats for severity level was also substantial or near substantial (κ = 0.58-0.76, κ(w) = 0.82-0.92). Differences between digital formats and film for grading severity level, severity threshold, or index lesions were not significant. The repeatability of grading between readers using film and all digital formats was also similar. CONCLUSIONS: Digital format variations compared favorably with film for DR classification. Translating film characteristics (resolution, color/contrast) and protocol (magnification, retinal regions) to digital equivalents and augmentation of full color with green-channel viewing most likely contributed to the results.

Grading diabetic retinopathy severity from compressed digital retinal images compared with uncompressed images and film.

PURPOSE: To compare research grading of diabetic retinopathy (DR) severity level from compressed digital images versus uncompressed images and film. METHODS: Compressed (JPEG2000, 37:1) digital images (C) were compared with uncompressed digital (U) and film (F) stereoscopic photographs from a 152-eye cohort with full-spectrum Early Treatment Diabetic Retinopathy Study severity levels for agreement on severity level, DR presence with ascending severity threshold, presence of DR index lesions, and repeatability of grading. RESULTS: Classification of Early Treatment Diabetic Retinopathy Study severity levels from C images agreed substantially with results from F images (κ = 0.60, κ(w) [linear weighted] = 0.86) and uncompressed digital images (κ = 0.76, κ(w) = 0.92). For agreement of uncompressed digital versus F images, κ = 0.62 and κ(w) = 0.86. Distribution of Early Treatment Diabetic Retinopathy Study levels was not significantly different between C and F images (P = 0.09, Bhapkar's test for marginal homogeneity). For presence/absence of DR at 8 ascending severity thresholds, agreement between C and F was "almost perfect" (κ ≥ 0.8). Agreement on severity level between readers with C images was at least as good as that with uncompressed digital image or F. Repeatability of severity threshold grading between readers was similar using C or F images. For identifying individual DR lesions, agreement between C and F ranged from "moderate" to "perfect." Agreement of grading venous beading from C was slightly lower than from F. CONCLUSION: Full Early Treatment Diabetic Retinopathy Study scale DR severity level grading using C images is comparable to that using U images or film.

Comparison of multiple stereoscopic and monoscopic digital image formats to film for diabetic macular edema evaluation.

PURPOSE: To assess agreement between evaluations of monoscopic and stereoscopic digital images versus stereo film photographs in diabetic macular edema (DME). METHODS: A 152-eye group of digital monoscopic macular images (seven-field sets and wide-angle mosaics) were compared with digital stereoscopic images (uncompressed and compressed seven-field sets) and stereo 35-mm film photos (Early Treatment Diabetic Retinopathy Study protocol) for the presence of hard exudates (HE), retinal thickening (RT), clinically significant macular edema (CSME), and RT at the center of the macular (RTCM). RESULTS: Agreement, according to the κ statistic, was almost perfect in identifying HE and RT between all digital formats and stereo film (HE, κ = 0.81-0.87; RT, κ = 0.87-0.92). Distribution in all digital formats was not significantly different from that in film (Bhapkar test: HE, P = 0.20-0.40; RT, P = 0.06-1.0). CSME and RTCM grading differences were either significant or trended toward significance. The readers detected CSME and RTCM in film images more often than in digital formats. In identifying DME features, agreement between evaluations of monoscopic digital formats and film was similar to that between stereo digital formats and film, and the performance of uncompressed images versus film was similar to that of compressed images versus film. Repeatability between readers was similar in evaluations of film and all digital formats. Repeatability in identifying RTCM was lower than that of other DME components in film and all digital formats. CONCLUSIONS: Stereoscopic digital formats are equivalent to monoscopic for DME evaluation, but digital photography is not as sensitive as film in detecting CSME and RTCM.

Evaluation of the age-related eye disease study clinical lens grading system AREDS report No. 31.

PURPOSE: To examine the grading (interrater) reliability of the Age-Related Eye Disease Study (AREDS) Clinical Lens Grading System (ARLNS). DESIGN: Evaluation of diagnostic test or technology. PARTICIPANTS: One hundred fifty volunteers (284 eyes). METHODS: Participants with lens opacities of varying severity were independently graded at the slit lamp for cataract severity by 2 examiners (retinal or anterior segment specialists) using the ARLNS, which employs 3 standard photographs of increasing severity for classifying each of the 3 major types of opacity. Lens photographs were taken and graded at a reading center using the more detailed AREDS System for Classifying Cataracts from photographs. MAIN OUTCOME MEASURES: The Pearson correlation, weighted-kappa, and limits-of-agreement statistics were used to assess the interrater agreement of the gradings. RESULTS: Examinations were performed on 284 lenses (150 participants). Tests of interrater reliability between pairs of clinicians showed substantial agreement between clinicians for cortical and posterior subcapsular opacities and moderate agreement for nuclear opacities. A similar pattern and strength of agreement was present when comparing scores of retinal versus anterior segment specialists. Interrater agreement between clinical and reading center gradings was not as great as inter-clinician agreement. CONCLUSIONS: Interrater agreements were in the moderate to substantial range for the clinical assessment of lens opacities. Inherent differences in cataract classification systems that rely on slit lamp vs photographic assessments of lens opacities may explain some of the disagreement noted between slit lamp and photographic gradings. Given the interrater reliability statistics for clinicians and the simplicity of the grading procedure, ARLNS is presented for use in studies requiring a simple, inexpensive method for detecting the presence and severity of the major types of lens opacities. FINANCIAL DISCLOSURE(S): The authors have no proprietary or commercial interest in any of the materials discussed in this article.

Digital versus film Fundus photography for research grading of diabetic retinopathy severity.

PURPOSE: To assess agreement between digital and film photography for research classification of diabetic retinopathy severity. METHODS: Digital and film photographs from a 152-eye cohort with a full spectrum of Early Treatment Diabetic Retinopathy Study (ETDRS) severity levels were assessed for repeatability of grading within each image medium and for agreement on ETDRS discrete severity levels, ascending severity thresholds, and presence or absence of diabetic retinopathy index lesions, between digital and 35-mm slides (film). Digital photographs were color balanced to match film. RESULTS: There was substantial agreement (κ = 0.61, κ(w) [linear weighted] = 0.87) in classification of ETDRS diabetic retinopathy severity levels between digital images and film. Marginal homogeneity analyses found no significant difference in frequency distributions on the severity scale (P = 0.21, Bhapkar test). The κ results ranged from 0.72 to 0.95 for presence or absence of eight ascending diabetic retinopathy severity thresholds. Repeatability of grading between readers viewing digital images was equal to or better than that obtained with film (pair-wise interreader κ for digital images ranged from 0.47 to 0.57 and for film from 0.43 to 0.57. The κ results for identifying diabetic retinopathy lesions ranged from moderate to almost perfect. Moderate agreement of intraretinal microvascular abnormalities and venous beading between digital images and film accounted for slightly lower concordance for severity thresholds ≥47 and for slightly lower interreader agreement within digital and film images at severity thresholds ≥43 and ≥47. CONCLUSIONS: Under controlled circumstances, digital photography can equal the reliability of 35-mm slides for research classification of ETDRS severity level.

Monoscopic versus stereoscopic retinal photography for grading diabetic retinopathy severity.

PURPOSE: To assess agreement between monoscopic and stereoscopic photography for research classification of the severity of diabetic retinopathy (DR). METHODS: Monoscopic digital (MD) images were compared with stereo digital (SD) and film (SF) photographs from a 152-eye cohort with full-spectrum Early Treatment Diabetic Retinopathy Study (ETDRS) severity levels for agreement on severity level, DR presence with ascending severity threshold, presence of DR index lesions, and repeatability of grading. RESULTS: There was substantial agreement classifying ETDRS DR severity levels between MD and SF (kappa = 0.65, kappa(w) [linear weighted] = 0.87), MD and SD (kappa = 0.66, kappa(w) = 0.87), and SD and SF (kappa = 0.62, kappa(w) = 0.86) images. Marginal homogeneity analyses found no significant difference between MD and SF images (P = 0.53, Bhapkar test). The kappa agreement between MD and SF ranged from 0.80 to 0.94 for the presence or absence of eight ascending DR severity thresholds. Repeatability between the readers of the MD images was equal to or better than that of the readers of SD or SF images. Severity threshold grading repeatability between readers was similar with the MD and SF images. The kappa agreement between MD and SF for identifying diabetic retinopathy lesions ranged from moderate to almost perfect. The kappa comparisons showed that performance of grading new vessels on the disc in MD images was slightly lower than that with the SF images. CONCLUSIONS: Monoscopic photography can equal the reliability of stereo photography for full ETDRS DR severity scale grading.

Prolonged effect of intensive therapy on the risk of retinopathy complications in patients with type 1 diabetes mellitus: 10 years after the Diabetes Control and Complications Trial.

OBJECTIVE: To examine the persistence of the original treatment effects 10 years after the Diabetes Control and Complications Trial (DCCT) in the follow-up Epidemiology of Diabetes Interventions and Complications (EDIC) study. In the DCCT, intensive therapy aimed at near-normal glycemia reduced the risk of microvascular complications of type 1 diabetes mellitus compared with conventional therapy. METHODS: Retinopathy was evaluated by fundus photography in 1211 subjects at EDIC year 10. Further 3-step progression on the Early Treatment Diabetic Retinopathy Study scale from DCCT closeout was the primary outcome. RESULTS: After 10 years of EDIC follow-up, there was no significant difference in mean glycated hemoglobin levels (8.07% vs 7.98%) between the original treatment groups. Nevertheless, compared with the former conventional treatment group, the former intensive group had significantly lower incidences from DCCT close of further retinopathy progression and proliferative retinopathy or worse (hazard reductions, 53%-56%; P < .001). The risk (hazard) reductions at 10 years of EDIC were attenuated compared with the 70% to 71% over the first 4 years of EDIC (P < .001). The persistent beneficial effects of former intensive therapy were largely explained by the difference in glycated hemoglobin levels during DCCT. CONCLUSION: The persistent difference in diabetic retinopathy between former intensive and conventional therapy ("metabolic memory") continues for at least 10 years but may be waning. TRIAL REGISTRATION: (clinicaltrials.gov) Identifiers: NCT00360815 and NCT00360893.

Calibration of fundus images using spectral domain optical coherence tomography.

BACKGROUND AND OBJECTIVE: Measurements performed on fundus images using current software are not accurate. Accurate measurements can be obtained only by calibrating a fundus camera using measurements between fixed retinal landmarks, such as the dimensions of the optic nerve, or by relying on a calibrated model eye provided by a reading center. However, calibrated spectral domain OCT (SD-OCT) could offer a convenient alternative method for the calibration of any fundus image. PATIENTS AND METHODS: The ability to measure exact distances on SD-OCT fundus images was tested by measuring the distance between the center of the fovea and the optic nerve. Calibrated SD-OCT scans measuring 6 X 6 X 2 mm centered on the fovea and the optic nerve were analyzed in 50 healthy right eyes. The foveal center was identified using cross-sectional SD-OCT images, and the center of the optic nerve was identified manually. The SD-OCT scans were registered to each other, and the distances between the center of the optic nerve and fovea were calculated. The overlay of these SD-OCT fundus images on photographic fundus images was performed. RESULTS: Any image of the fundus could be calibrated by overlaying the SD-OCT fundus image, and the measurements were consistent with previously defined calibration methods. The mean distance between the center of the fovea and the center of the optic nerve was 4.32 +/-0.32 mm. The line from the center of the optic nerve to the foveal center had a mean declination of 7.67 +/- 3.88 degrees. Mean horizontal displacement and vertical displacement were 4.27 +/- 0.29 mm and 0.58 +/- 0.29 mm, respectively. CONCLUSIONS: The overlay of the SD-OCT fundus image provides a convenient method for calibrating any image of the fundus. This approach should provide a uniform standard when comparing images from different devices and from different reading centers.

A severity scale for diabetic macular edema developed from ETDRS data.

PURPOSE: To develop a severity scale for diabetic macular edema (DME) and to assess relationships between severity and duration of DME and visual acuity (VA). METHODS: From the Early Treatment Diabetic Retinopathy Study (ETDRS), mean baseline VA scores were tabulated for 7422 eyes cross-classified by (1) location of retinal thickening (RT) and its area within 1 disc diameter of the macular center, and (2) degree of RT at the center. Adjacent (row, column, and off-diagonal) cells with the greatest similarity in baseline VA (mean and SD) based on a Gaussian (normal) likelihood were merged. An initial eight-step scale was chosen using the Schwarz criterion (Bayesian information criterion; BIC) and was revised based on clinical judgment to nine steps. Relationships between baseline VA and other photographic and fluorescein angiographic characteristics were examined singly and in combination with the scale. RESULTS: Modeling baseline VA as a function of the nine-step scale yielded an R(2) of 38.0%, compared with 38.4% using the full cross-classification of these variables. Addition of each of the other baseline characteristics changed the adjusted R(2) for the combination very little. Between scale levels 1A and 5B mean (SD) VA decreased from 86.8 (5.8) letters to 59.8 (13.6) letters. In a model of change in VA as a function of time spent at each DME severity level, VA loss increased progressively from 1 letter per year at level 2 to 17 letters per year at level 5B. CONCLUSIONS: The scale facilitates documentation of the relationship of severity and duration of DME with VA.

Brightness, contrast, and color balance of digital versus film retinal images in the age-related eye disease study 2.

PURPOSE: To analyze brightness, contrast, and color balance of digital versus film retinal images in a multicenter clinical trial, to propose a model image from exemplars, and to optimize both image types for evaluation of age-related macular degeneration (AMD). METHODS: The Age-Related Eye Disease Study 2 (AREDS2) is enrolling subjects from 90 clinics, with three quarters of them using digital and one quarter using film cameras. Image brightness (B), contrast (C), and color balance (CB) were measured with three-color luminance histograms. First, the exemplars (film and digital) from expert groups were analyzed, and an AMD-oriented model was constructed. Second, the impact of B/C/CB on the appearance of typical AMD abnormalities was analyzed. Third, B/C/CB in AREDS2 images were compared between film (156 eyes) and digital (605 eyes), and against the model. Fourth, suboptimal images were enhanced by adjusting B/C/CB to bring them into accord with model parameters. RESULTS: Exemplar images had similar brightness, contrast, and color balance, supporting an image model. Varying a specimen image through a wide range of B/C/CB revealed greatest contrast of drusen and pigment abnormalities against normal retinal pigment epithelium with the model parameters. AREDS2 digital images were more variable than film, with lower correspondence to our model. Ten percent of digital were too dim and 19% too bright (oversaturated), versus 1% and 4% of film, respectively. On average, digital had lower green channel contrast (giving less retinal detail) than film. Overly red color balance (weaker green) was observed in 23% of digital versus 8% of film. About half of digital (but fewer film) images required enhancement before AMD grading. After optimization of both image types, AREDS2 image quality was judged as good as that in AREDS (all film). CONCLUSIONS: A histogram-based model, derived from exemplars, provides a pragmatic guide for image analysis and enhancement. In AREDS2, the best digital images matched the best film. Overall, however, digital provided lower contrast of retinal detail. Digital images taken with higher G-to-R ratio showed better brightness and contrast management. Optimization of images in the multicenter study helps standardize documentation of AMD (ClinicalTrials.gov NCT00345176).