In this cross-sectional study, we enrolled 170 subjects older than 50 years of age. One eye per participant was randomly selected for inclusion. All subjects were examined at the outpatient clinic of the Senshokai Eye Institute in Kyoto, Japan. Of the 170 eyes, 45 were healthy (defined by intraocular pressure [IOP] <22 mm Hg, no history of diabetes or elevated IOP, a healthy optic disc, and no repeatable abnormal visual field results); 47 subjects were receiving medical treatment for POAG without diabetes mellitus, and 78 subjects (40 without POAG and 38 with POAG) had diabetes mellitus diagnosed on the basis of the diabetes diagnostic criteria of the World Health Organization and were under medical treatment by an experienced endocrinologist.
All GDx-VCC and StratusOCT scans were obtained between September 28, 2005, and March 26, 2007. Informed consent was obtained from all subjects in accordance with the tenets of the Declaration of Helsinki. The institutional ethics committee approved the methodology. All subjects underwent comprehensive ophthalmologic examination, including best-corrected visual acuity (BCVA), applanation tonometry, slit-lamp examination, dilated funduscopic examination, 45° high-quality fundus color photography (CF-PU2; Canon Inc., Tokyo, Japan) for evaluation of cup and disc size, and automated perimetry using the full-threshold G1 program (Octopus 301, version 2.04; Haag-Streit, Schlieren, Switzerland) within 3 months of the GDx-VCC and StratusOCT scans. IOP measurements were repeated on at least three consecutive visits with the use of Goldmann applanation tonometry. Two experienced graders measured each fundus color photograph independently and were masked to the test results of the other. Graders visually estimated the horizontal and vertical cup-to-disc ratios based on the contour of the cup. The mean value of the two graders was recorded as the final grade.
All subjects had a logMAR BCVA of 0.1 or better, spherical equivalent refractive error within ±5.00 diopters, astigmatism within ±3.00 diopters, and clear media without clinically relevant cataract.
We excluded eyes with coexisting neuro-ophthalmologic disease, uveitis, macular disease (including macular degeneration and macular edema), retinal artery or vein occlusion, retinal detachment, history of refractive or intraocular surgery, and degenerative myopia that could lead to less reliable assessment of RNFL thickness and poor quality of obtained images.
Glaucomatous optic disc changes were defined as undermining of the cup, notching, and focal or diffuse thinning of the rim area; splinter hemorrhages; nasal shifting of the retinal vessels; and asymmetric enlargement of the cup (cup-to-disc asymmetries >0.2). A glaucomatous visual field defect using the field program (Octopus G1; Haag-Streit) was defined as three consecutive point depressions exceeding 5 dB more than the age-matched controls and at least one of three consecutive points with a depression greater than 10 dB or two consecutive points depressed greater than 10 dB and two adjacent points across the nasal horizontal meridian with a difference of greater than 5 dB. Visual field defects had to be repeatable on at least two consecutive tests. Glaucomatous eyes with visual field defects on fundus photography caused by retinal hemorrhages or exudates were excluded from the study. Glaucomatous visual field defects were evaluated by the Hodapp-Parrish-Anderson grading scale of severity of visual field defects,
12 and each enrolled subject was classified as having defects of mild to moderate stage. Glaucomatous optic neuron damage in eyes with diabetic retinopathy might have been slightly underestimated because of the potential effects of intraretinal structural changes. Average mean deviations on the test nearest the imaging date were 7.58 dB (range, −0.2 to 15.0) and 6.56 dB (range, −0.5 to 12.3) in glaucomatous eyes with and without diabetes, respectively. Of 47 eyes with simple glaucoma, 28 were classified as having mild disease and 19 as having moderate disease. Of 38 eyes with glaucoma and coexisting diabetes, 23 were classified as having mild disease and 15 as having moderate disease.
Enrolled subjects with diabetes had mild to moderate NPDR based on the International Clinical Diabetic Retinopathy Disease Severity Scale.
13 Fluorescein angiography (TRC-50X; Topcon Instrument Corp., Tokyo, Japan) was performed in subjects with mild to moderate NPDR or maculopathy to classify the stages of retinopathy and to exclude subjects with macular edema. Two trained ophthalmologists determined, in a masked fashion, the classifications of diabetic retinopathy. Of 40 eyes with simple diabetes, 22 eyes were classified with mild NPDR and 18 with moderate NPDR. Of 38 eyes with glaucoma and coexisting diabetes, 13 eyes were classified with mild NPDR and 25 with moderate NPDR.