Retinal hemodynamics in early diabetic macular edema.

The objective of this study was to establish the baseline retinal hemodynamic characteristics of stratified groups of diabetic patients at increasing risk for the development of diabetic macular edema (DME). Group 1 had 50 control subjects, group 2 had 56 diabetic patients without clinically visible retinopathy, group 3 had 54 diabetic patients with microaneurysms and/or hard exudates within two disc diameters of the fovea in the absence of clinically manifest DME, and group 4 had 40 patients with clinically manifest DME. Retinal hemodynamics (diameter, velocity, maximum-to-minimum velocity ratio, and flow) were assessed. Intraocular pressure, blood pressure, and relevant systemic markers of diabetes control and complications were also undertaken. The maximum-to-minimum velocity ratio was elevated with increasing risk of clinically significant DME (P < 0.0001). No significant differences were found between the groups with respect to diameter, velocity, or flow. The maximum-to-minimum velocity ratio was correlated to age, duration of diabetes, blood pressure, pulse rate, intraocular pressure, and serum potassium levels. In conclusion, the maximum-to-minimum velocity ratio was significantly increased with increasing risk of development of DME. Retinal arteriolar hemodynamics were positively correlated to age, duration of diabetes, and blood pressure. These findings suggest a reduction in the compliance (i.e., an increase of vascular rigidity) of the arteriolar circulation with increasing risk of DME.

Surgical macular decompression for macular edema in retinal vein occlusion.

BACKGROUND: Recently, a number of surgical and laser approaches have been used to improve visual outcome in cases of central retinal vein occlusion (CRVO) and branch retinal vein occlusion (BRVO). Intravitreal steroid injection alone appears to offer only temporary improvement at best. Radial optic neurotomy for CRVO and arteriovenous adventitial sheathotomy for BRVO are the most frequently utilized surgical procedures for these conditions, but evidence regarding efficacy is still lacking. We have suggested that macular decompression by internal limiting membrane (ILM) peeling may reduce macular edema and hemorrhage and improve visual acuity by relieving elevated intraretinal tissue pressure and facilitating egress of blood and extracellular fluid out of inner retinal layers into the vitrectomized vitreous cavity. METHODS: 50 cases of severe visual loss due to macular edema caused by CRVO or BRVO, not eligible for laser photocoagulation, underwent pars plana vitrectomy with removal of preretinal hyaloid, peeling of the ILM stained with indocyanine green dye, air-fluid exchange, and postoperative prone positioning. RESULTS: In all cases, intraretinal blood and retinal thickening diminished within 6 weeks of surgery. Visual acuity improved in 87% of CRVO cases and 68% of BRVO cases. Vision improved and stabilized at 39 days after surgery. Average improvement was 2.6 lines with a 6-line improvement in 1 case. There was no difference in outcome between cases with ischemic or nonischemic features on fluorescein angiography. INTERPRETATION: Macular decompression using vitrectomy and ILM peeling is effective in the treatment of severe visual loss due to macular edema in CRVO and in those BRVO cases that do not qualify for laser photocoagulation.

Agreement of the Heidelberg Retina Tomograph II macula edema module with fundus biomicroscopy in diabetic maculopathy.

OBJECTIVES: To estimate the agreement between the macular edema maps (MEMs) of the Retina Module of the Heidelberg Retina Tomograph II (Heidelberg Engineering, Heidelberg, Germany) and contact lens fundus biomicroscopy (FB) and to assess the influence of combining MEM data with the results of short-wavelength automated perimetry (SWAP) and fluorescein angiography (FA) on diagnostic test performance. DESIGN: Prospective, observational case series. METHODS: Twenty patients (20 eyes) with diabetic retinopathy with or without clinically manifest macular edema (11 and 9 eyes, respectively) were enrolled. All patients underwent full ophthalmologic examination and also MEM assessment, SWAP, and FA. RESULTS: Using FB as the "gold standard," the agreement between the MEMs and FB was very good (Kendall coefficient of concordance, 0.80). Macular edema maps showed good agreement with FA and SWAP (Kendall coefficient, 0.64 and 0.65). Virtually all of the edematous areas detected with MEM but not seen clinically had decreased sensitivity on SWAP and/or fluorescein leakage. CONCLUSIONS: Macular edema maps demonstrated very good agreement with FB. Combining the results of FA and SWAP with those of the MEMs provided supporting evidence of concomitant blood-retinal barrier leakage and visual dysfunction, respectively, in areas of early retinal thickening. Prospective studies are ongoing to fully assess the diagnostic test performance of MEMs in the detection of early and progressive diabetic macular edema.

Comparison of Heidelberg Retina Tomograph II and Retinal Thickness Analyzer in the assessment of diabetic macular edema.

PURPOSE: To compare the within-session variability of the Macular Edema Module of the Heidelberg Retinal Tomograph II (HRT II; Heidelberg Engineering, Heidelberg, Germany) and the Retinal Thickness Analyzer (RTA, Talia Technology Ltd., Neve-Ilan, Israel) in patients with diabetes and nondiabetic subjects and to determine the agreement of both instruments to clinical observation. METHODS: Seventeen patients with diabetic macular edema (DME) and 17 nondiabetic subjects were examined. Three scans of the posterior pole were acquired for each volunteer with both the HRT II and the RTA. The edema index and foveal average thickness were derived for a 600- micro m radius circle centered on the fovea for the HRT II and RTA scans. The coefficient of variation (COV) was calculated. Clinical examination of detectable edema was performed using stereo fundus biomicroscopy and the level of agreement between each instrument and clinical observation was determined using a zonal analysis. RESULTS: Individual COVs for the HRT II and RTA ranged from 2.3% to 24.6% (median 8.3%) and 2.1% to 46.7% (median 6.4%), respectively, in diabetic subjects and 2.0% to 37.5% (median 6.0%) and 2.3% to 14.7% (median 8.5%), respectively, in nondiabetic subjects. Clinical assessment identified edema in a total of 47 sectors in patients with DME. In comparison to clinical assessment, the HRT II gave a sensitivity of 92% and a specificity of 68% and the RTA gave a sensitivity of 57% and a specificity of 71%. CONCLUSIONS: Both instruments have good within-session repeatability. The HRT II showed better agreement with clinical assessment than the RTA. The agreement between instruments was poor.

Assessment of retinal hemodynamics with the Canon laser blood flowmeter after a single dose of 2% dorzolamide hydrochloride eyedrops.

BACKGROUND: Dorzolamide hydrochloride is a carbonic anhydrase inhibitor that reduces intraocular pressure (IOP) by decreasing the production of aqueous humour in the ciliary body. Theoretically, topical use of this agent has the potential to directly affect retinal vasculature through local induced acidosis. We performed a study to determine whether there are changes in retinal arteriole hemodynamics, as assessed with the Canon laser blood flowmeter, in healthy subjects following topical administration of dorzolamide. METHODS: We recruited 17 healthy volunteers, nine men and eight women aged 25 to 55 years (mean 31.4 [standard deviation (SD) 9.88] years). The inclusion criteria were Snellen visual acuity of 20/30 or better, normal anterior eye examination, IOP of 21 mm Hg or less, and a normal fundus appearance. One eye of each subject was randomly assigned to receive a drop of 2% dorzolamide. The contralateral eye of 10 of the subjects received a placebo drop (artificial tears). Before and 1 hour after drop administration, we obtained blood flow measurements from an inferotemporal arteriole approximately 1 disc diameter from the optic nerve head rim using the Canon laser blood flowmeter, model 100. The IOP was measured by means of Goldmann applanation tonometry before and 1 hour after drop administration. RESULTS: The mean IOP was significantly reduced in the dorzolamide-treated eyes, from 14.4 mm Hg (SD 2.94 mm Hg) to 11.7 mm Hg (SD 2.50 mm Hg) (p < 0.001). The IOP was also reduced in the placebo group (15.6 mm Hg [SD 3.41 mm Hg] vs. 14.6 mm Hg [SD 3.28 mm Hg]), but the difference was not significant. There was no significant difference in mean arteriole diameter, mean blood velocity or mean blood flow after drug administration in the dorzolamide-treated eyes. INTERPRETATION: Our results indicate that a single topical application of dorzolamide in healthy subjects has no effect on retinal arteriole diameter, blood velocity or blood flow, as measured with the Canon laser blood flowmeter. Longer-term studies of retinal hemodynamics in patients with glaucoma are warranted as evolving treatments aim to improve ocular blood flow as well as reduce IOP.

Variability and repeatability of retinal blood flow measurements using the Canon Laser Blood Flowmeter.

The purpose of this work was to determine the within-session variability and between-session repeatability of the Canon Laser Blood Flowmeter (CLBF), Model 100, an instrument that permits the noninvasive measurement of retinal blood flow. The CLBF calculates flow in microl/min based on the Poiseuille principle. One eye of 20 normal subjects (mean age 36.5; SD 9.7 years) was randomly chosen. A minimum of five measurements was acquired of a temporal arteriole approximately 1 disc diameter from the optic nerve. Measurements were repeated within a 1-month period. Blood pressure and intraocular pressure were measured. The coefficient of variation (COV) and the coefficient of repeatability (COR) were calculated for each individual. The individual COVs for diameter, velocity, and flow ranged from 0.5 to 6.5% (median 2.0%), 4.8 to 39.7% (median 19.9%), and 4.8 to 37.3% (median 19.3%), respectively. The group mean CORs for diameter, velocity, and flow were 5.2 microm (relative to a mean effect of 104.6 microm), 8.8 mm/s (relative to a mean effect of 33.9 mm/s), and 2.6 microl/min (relative to a mean effect of 8.8 microl/min), respectively. The CLBF gave consistent and repeatable measurements of blood flow within retinal arterioles in normal subjects. Given the range of individual variation in the velocity measurement, and thus flow, confidence limits for retinal hemodynamics need to be determined on an individual basis.