Comparison of stereoscopic digital imaging and slide film photography in the identification of macular degeneration

Automated Brightness and Contrast Adjustment of Color Fundus Photographs for the Grading of Age-Related Macular Degeneration

Purpose

The purpose of this study was to develop an algorithm to automatically standardize the brightness, contrast, and color balance of digital color fundus photographs used to grade AMD and to validate this algorithm by determining the effects of the standardization on image quality and disease grading.

Methods

Seven-field color photographs of patients (>50 years) with any stage of AMD and a control group were acquired at two study sites, with either the Topcon TRC-50DX or Zeiss FF-450 Plus cameras. Field 2 photographs were analyzed. Pixel brightness values in the red, green, and blue (RGB) color channels were adjusted in custom-built software to make the mean brightness and contrast of the images equal to optimal values determined by the Age-Related Eye Disease Study (AREDS) 2 group.

Results

Color photographs of 370 eyes were analyzed. We found a wide range of brightness and contrast values in the images at baseline, even for those taken with the same camera. After processing, image brightness variability (brightest image–dimmest image in a color channel) was reduced 69-fold, 62-fold, and 96-fold for the RGB channels. Contrast variability was reduced 6-fold, 8-fold, and 13-fold, respectively, after adjustment. Of the 23% images considered nongradable before adjustment, only 5.7% remained nongradable.

Conclusions

This automated software enables rapid and accurate standardization of color photographs for AMD grading.

Translational Relevance

This work offers the potential to be the future of assessing and grading AMD from photos for clinical research and teleimaging.

The Tromsø Eye Study: study design, methodology and results on visual acuity and refractive errors

PURPOSE

To describe the study design and methodology of the Tromsø Eye Study (TES), and to describe visual acuity and refractive error in the study population.

METHODS

The Tromsø Eye Study is a sub-study of the Tromsø Study, a population-based multipurpose longitudinal study in the municipality of Tromsø, Norway. The Tromsø Eye Study was a part of the sixth survey of the Tromsø Study, conducted from October 2007 through December 2008. The eye examination included information on self-reported eye diseases, assessment of visual acuity and refractive errors, retinal photography and optical coherence tomography. Retinal images were graded for diabetic retinopathy and age-related macular degeneration, and with computer-assisted measurements of arteriolar and venular diameters. In addition, TES researchers have access to the large comprehensive Tromsø Study database including physical examination results, carotid artery ultrasound, electrocardiogram, bone densitometry, cognitive tests, questionnaires, DNA, blood and urine samples and more from the present and the five previous surveys.

RESULTS

Visual acuity was assessed in 6459 subjects and refraction in 6566 subjects aged 38-87 years. Snellen visual acuity <20/60 was found in 1.2% (95% CI 0.95-1.5) of the participants and there was no gender difference. Visual impairment increased with age, and in the age group 80-87 years, the overall visual acuity <20/60 was 7.3% (95% CI 3.3-11.2). Spherical equivalent showed an increasing trend with age and there was no clinically relevant difference between men and women. Retinal photography was performed in 6540 subjects.

CONCLUSION

Prevalence of visual impairment was low but increased with age. There was a trend towards hyperopia with age and no clinically relevant difference in refraction between the sexes. TES aims to provide epidemiological research on several eye and eye-related diseases. Owing to a comprehensive data collection, it has the opportunity to explore issues related to environmental factors, cognition and their interaction with diseases in this community.

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.

Digital ocular fundus imaging: a review

Ocular fundus imaging plays a key role in monitoring the health status of the human eye. Currently, a large number of imaging modalities allow the assessment and/or quantification of ocular changes from a healthy status. This review focuses on the main digital fundus imaging modality, color fundus photography, with a brief overview of complementary techniques, such as fluorescein angiography. While focusing on two-dimensional color fundus photography, the authors address the evolution from nondigital to digital imaging and its impact on diagnosis. They also compare several studies performed along the transitional path of this technology. Retinal image processing and analysis, automated disease detection and identification of the stage of diabetic retinopathy (DR) are addressed as well. The authors emphasize the problems of image segmentation, focusing on the major landmark structures of the ocular fundus: the vascular network, optic disk and the fovea. Several proposed approaches for the automatic detection of signs of disease onset and progression, such as microaneurysms, are surveyed. A thorough comparison is conducted among different studies with regard to the number of eyes/subjects, imaging modality, fundus camera used, field of view and image resolution to identify the large variation in characteristics from one study to another. Similarly, the main features of the proposed classifications and algorithms for the automatic detection of DR are compared, thereby addressing computer-aided diagnosis and computer-aided detection for use in screening programs.

Utility of digital stereo images for optic disc evaluation

PURPOSE

To assess the suitability of digital stereo images for optic disc evaluations in glaucoma.

METHODS

Stereo color optic disc images in both digital and 35-mm slide film formats were acquired contemporaneously from 29 subjects with various cup-to-disc ratios (range, 0.26-0.76; median, 0.475). Using a grading scale designed to assess image quality, the ease of visualizing optic disc features important for glaucoma diagnosis, and the comparative diameters of the optic disc cup, experienced observers separately compared the primary digital stereo images to each subject's 35-mm slides, to scanned images of the same 35-mm slides, and to grayscale conversions of the digital images. Statistical analysis accounted for multiple gradings and comparisons and also assessed image formats under monoscopic viewing.

RESULTS

Overall, the quality of primary digital color images was judged superior to that of 35-mm slides (P < 0.001), including improved stereo (P < 0.001), but the primary digital color images were mostly equivalent to the scanned digitized images of the same slides. Color seemingly added little to grayscale optic disc images, except that peripapillary atrophy was best seen in color (P < 0.0001); both the nerve fiber layer (P < 0.0001) and the paths of blood vessels on the optic disc (P < 0.0001) were best seen in grayscale. The preference for digital over film images was maintained under monoscopic viewing conditions.

CONCLUSIONS

Digital stereo optic disc images are useful for evaluating the optic disc in glaucoma and allow the application of advanced image processing applications. Grayscale images, by providing luminance distinct from color, may be informative for assessing certain features.

The prevalence of diabetic retinopathy as identified by teleophthalmology in rural Alberta

OBJECTIVE

The purpose of this study was to assess the prevalence of diabetic retinopathy (DR) as identified by teleophthalmology in a sample population of people with diabetes living in rural Alberta and to identify the risks and benefits of a teleophthalmology program for these patients.

DESIGN

Retrospective consecutive case series.

PARTICIPANTS

Three hundred ninety-four diabetic patients (788 eyes).

METHODS

Medical histories were obtained, following which patients underwent visual acuity and intraocular pressure measurements and stereoscopic, 7-field, digital retinal photography. Images were graded by ophthalmologists in Edmonton, Alta., according to a modified Early Treatment Diabetic Retinopathy Study scoring template. Diagnosis, treatment, and follow-up recommendations were communicated to local health care providers and data were collected for review.

RESULTS

Three hundred ninety-four patients (788 eyes) were assessed via 593 teleophthalmology visits over the 3-year period. DR was identified in 27.2% of patients (2.3% with proliferative DR and 24.9% with nonproliferative DR). A variety of other diagnoses, independent of DR, were also made. Recommendations for follow-up teleophthalmology and in-person referral were completed in 76.8% and 87.3% of patients, respectively, although many were completed later than was recommended. Teleophthalmology saved approximately 450 round trips from Edson to the nearest urban centre (Edmonton) over the 2-year period, equating to approximately 1900 hours and 180 000 km of driving.

CONCLUSIONS

Teleophthalmology can effectively identify DR while reducing travel time and distance for patients with diabetes living in a rural community. However, many patients did not follow up or attend referral appointments in a timely fashion, underscoring the need for ongoing quality assessment.

Automated quality evaluation of digital fundus photographs

PURPOSE

Retinal images acquired by means of digital photography are often used for evaluation and documentation of the ocular fundus, especially in patients with diabetes, glaucoma or age-related macular degeneration. The clinical usefulness of an image is highly dependent on its quality. We set out to develop and evaluate an automatic method of evaluating the quality of digital fundus photographs.

METHODS

A method for making a numerical quantification of image sharpness and illumination was developed using Matlab image analysis functions. Based on their sharpness and illumination measures, 1000 fundus photographs, randomly selected from a clinical database, were assigned to four predefined quality groups (not acceptable, acceptable, good, very good). Six independent observers, comprising three experienced ophthalmologists and three ophthalmic nurses with extensive experience in fundus image acquisition, classified a selection of 100 of these images into the corresponding quality groups.

RESULTS

Automatic quality evaluation was more sensitive than evaluation by human observers in terms of ability to discriminate between good and very good images. The median concordance between the six human observers and the automatic evaluation was substantial (kappa = 0.64).

CONCLUSIONS

The proposed method provides an objective quality assessment of digital fundus photographs which agrees well with evaluations made by qualified human observers and which may be useful in clinical practice.

Interobserver and intraobserver reliability of detecting age-related macular degeneration using a nonmydriatic digital camera

PURPOSE

To evaluate the interobserver and intraobserver reliability of detecting early and late age-related macular degeneration (AMD) using a nonmydriatic digital camera in two distinct groups of older people.

DESIGN

Prospective study.

METHODS

The two groups consisted of a series of patients older than 70 years hospitalized in a geriatric unit and a younger series of people older than 55 years. In both groups, nonmydriatic color fundus photographs were obtained and graded independently by two ophthalmologists (V.L. and M.S.). No ophthalmic examination was performed. Main outcome measures were frequencies of early and late AMD and interobserver and intraobserver agreement.

RESULTS

Among 233 patients in group 1 (mean age, 84.6 years), only 119 patients (51%) could undergo photography because of associated multiple morbidities. Mean age of group 2 was 63.8 years. In group 1, 35 (14.5%) of 238 pictures were ungradable. In series 2, 65 (9.1%) of 716 pictures were ungradable. Frequencies of early and late AMD were 30.3% and 5.9% vs 12.6% and 2.6% in series 1 and 2, respectively. Interobserver and intraobserver agreement was good or excellent (kappa > 0.6) in both groups.

CONCLUSIONS

In the entire geriatric cohort, 43% of the patients had gradable pictures allowing a diagnosis. These patients would otherwise have had no access to any form of funduscopy. In the younger population, nonmydriatic pictures permitted a diagnosis in 90% of the individuals. Detection of AMD with a nonmydriatic digital camera may lead to large-scale screening and specific management.

Comparison of nonmydriatic digital retinal imaging versus dilated ophthalmic examination for nondiabetic eye disease in persons with diabetes

OBJECTIVE

To evaluate the ability of stereoscopic nonmydriatic digital retinal imaging to detect ocular pathologic features other than diabetic retinopathy (DR) in patients with diabetes mellitus (DM) compared with dilated retinal examination by retinal specialist ophthalmologists.

DESIGN

Clinic-based comparative instrument study and retrospective chart review.

PARTICIPANTS

Two hundred eighty Joslin Diabetes Center outpatients (560 eyes) with type 1 or type 2 DM.

METHODS

Nonsimultaneous stereoscopic nonmydriatic digital retinal images (640 x 480 pixels) of three 45 degrees retinal fields were acquired and graded for clinical level of DR and other ocular pathologic features by certified readers according to Joslin Vision Network (JVN) protocol. Retrospective chart review compared findings from JVN digital images with findings from dilated retinal examination by retinal specialists performed within an average of 39.6 days of digital imaging. An independent senior retinal specialist adjudicated disagreements by review of 7 standard field 35-mm Early Treatment Diabetic Retinopathy Study protocol fundus photographs and JVN images.

MAIN OUTCOME MEASURES

Detection of non-DR ocular pathologic features by digital imaging as compared with clinical examination.

RESULTS

Nonmydriatic digital evaluation identified at least 1 non-DR ocular finding in 40.7% of patients (114/280). Non-diabetes mellitus ocular pathologic features identified by digital images, clinical examination, or both included cataract (n = 100); age-related maculopathy (n = 52); suspicion of glaucoma (n = 18); choroidal lesions (n = 18); evidence of systemic disorder (e.g., hypertension or renal disease; n = 15); epiretinal membrane (n = 11); chorioretinal atrophy, scar, or both (n = 6); retinal emboli (n = 3); retinitis pigmentosa (n = 1); and asteroid hyalosis (n = 1). Agreement of nonmydriatic imaging with clinical examination for presence and absence of these findings was 95.4%, 91.3%, 98.2%, 98.6%, 98.2%, 99.6%, 100%, 100%, 100%, and 100%, respectively. Kappa values for all non-DR lesions demonstrated near perfect agreement (kappa> or =0.80) except for age-related maculopathy (kappa = 0.71) and choroidal lesions (kappa = 0.73), where agreement was substantial. Overall, only 55 eyes (9.8%) were ungradable for level of DR and 85 eyes (15.2%) were ungradable for macular edema.

CONCLUSIONS

Joslin Vision Network nonmydriatic digital imaging demonstrated excellent agreement with dilated ophthalmic examination by retinal specialists in the detection of ocular disease other than DR, suggesting a potential role for this technology in evaluating non-DR disorders and highlighting the extent of findings other than retinopathy in patients with diabetes.