The Relationship Between Macular Sensitivity and Retinal Thickness in Eyes With Diabetic Macular Edema

Abstract

Purpose: : To investigate relationship between macular sensitivity and retinal thickness in diabetic macular edema (DME) quantified with an automatic fundus perimetry/ tomography system [Scanning laser ophthalmoscope/ Spectral domain optical coherence tomography (SLO/OCT^TM), OPKO/OTI, Toronto, Canada].

Methods: : Fourteen eyes of 9 patients (mean age = 69 years; range 35 - 88 years) with DME (4 eyes with less than 1 year, 9 between 1-5 years, and 1 with more than 5 years in duration) were evaluated with SLO/OCT^TM device by same operator. Macular perimetry (fundus-related perimetry together with retinal thickness map) was used to quantify macular sensitivity, fixation pattern (location and stability), and relationship between macular sensitivity and thickness. Multiple linear regression model with generalized estimation equation (GEE) was used to evaluate relationship between macular sensitivity and thickness. GEE model counted for correlation within repeated measures of thickness and sensitivity for same macular area.

Results: : Fixation pattern revealed that 9 eyes (64.29%) had central (greater than 50% of fixation point within 0.5mm of foveal center); 3(21.43%) peri-central (between 25% - 50% within 0.5mm of foveal center); and 2 eyes (14.29%) eccentric (less than 25% of fixation point within 0.5mm of foveal center) fixation pattern. Fixation stability revealed that 12 eyes (85.71%) had stable (more than 75% within the central 2° of point of fixation); 2 (14.29%) relatively unstable (less than 75% of fixation points located within 2°, but more than 75% located within 4°, of point of fixation); none had unstable fixation (less than 75% of fixation points located within 4°). We measured macular sensitivity and corresponding thickness in 391 points of 14 study eyes. We regressed macular sensitivity against its thickness, distance from fovea (3 circles with radius of 0.5, 3, 6 mm from fovea center), duration of DME (< 1 year, 1 to 5, > 5 years), visual acuity in LOGMAR, age, and gender. Macular sensitivity decreased 0.01 dB (95% Confidence Interval (CI); -0.02, -0.00) with every 1µm increase in macular thickness. It decreased 0.13 dB (95% CI; -0.21, -0.05) with every one-year increase in age. There was an increase of 1.90 dB (95% CI; 1.09, 2.71) moving from foveal center to second and third circles.

Conclusions: : Perimetry quantification of macular sensitivity and retinal thickness, in association with other factors such as age, may offer novel information regarding impact of DME on retinal function.

Keywords: diabetic retinopathy • perimetry • microscopy: fixation processing