Lens opacity and refractive influences on the measurement of retinal vascular fractal dimension

Abstract

ABSTRACT.Purpose: To examine the influence of lens opacity and refraction on the measurement of retinal vascular fractal dimension (Df). Methods: Optic disc photographs (right eyes) of 3654 baseline Blue Mountains Eye Study participants (aged 49-97 ) were digitized. Retinal vascular Df was quantified using a computer-based program. Summated severity scores for nuclear, cortical and posterior subcapsular (PSC) cataract were assessed from lens photographs. Refraction data were converted to spherical equivalent refraction (SER), as sum spherical plus 0.5 cylinder power. Axial length was measured at 10-year follow-up examinations using an IOL master. Results: Mean Df of the retinal vasculature was 1.444 ± 0.023 for 2859 eligible participants. Increasing lens opacity scores were associated with significant reduction in Df (b = )0.0030, p < 0.0001). Both cortical and PSC cataract involving central lens area were associated with reduced Df, after controlling for confounding factors (p trend £ 0.0105). Increasing myopia severity was associated with reduced Df after adjusting for lens opacity scores and other confounders (p trend < 0.0001). The slope of Df decrease per SER reduction was 0.0040 in eyes with SER £ )4D, compared to )0.0016 in eyes with SER > )4D. For axial length quintiles, there were no significant differences in mean Df in all groups except a reduction in the fifth quintile (axial length ‡24.15 mm) (all p < 0.05). Conclusion: Ocular media opacity independently influenced retinal vascular Df measurement, but we found no evidence supporting any refractive axial magnification effect on this measure. Myopic refraction £)4D was associated with a reduction in Df, suggesting rarefaction of retinal vasculature associated with high myopia.

Retinal Microvasculature Alteration in High Myopia

“…Based on fundus images, a reduction in the large retinal vessel density was associated with myopia. 6,19 However, Chueng et al 22 found no difference between myopic and normal eyes after correcting for field of view magnification. Hollo et al, 23 using the Heidelberg retina flowmeter, reported that capillary perfusion near the temporal edge of the optic disc was significantly decreased in healthy subjects and glaucoma patients with myopia.…”

“…6,19 Indeed, OCTA revealed alterations in both the superficial and deep retinal vascular plexuses, which indicates that alterations occur throughout the entire retina. Considering that the degree of decreased microvascular density correlated with axial elongation, the significantly altered microvascular network in highly myopic eyes may represent disease progression.…”

“…6,19 In the present study, the fractal analysis toolbox from Benoit (TruSoft Benoit fractal analysis toolbox; TruSoft International, Inc., St. Petersburg, FL, USA) was incorporated into our custom algorithm to analyze the fractal dimensions (representing vessel density) of the large retinal vessels and microvessels on the segmented vascular network images. The fractal dimension (D box ) was measured using the box-counting technique.…”

“…Fractal analysis is commonly used to investigate the vascular network in fundus images 6,19,20 or to quantitatively analyze large retinal vessel density in myopic eyes. 6,19 In the present study, the fractal analysis toolbox from Benoit (TruSoft Benoit fractal analysis toolbox; TruSoft International, Inc., St. Petersburg, FL, USA) was incorporated into our custom algorithm to analyze the fractal dimensions (representing vessel density) of the large retinal vessels and microvessels on the segmented vascular network images.…”

Retinal Microvasculature as a Model to Study the Manifestations of Hypertension

“…114 Other ocular factors, including retinal pigmentation, pupil dilation, presence of cataract, and other ocular media opacities, may vary image brightness, focus, and contrast, which significantly affect the measurement of retinal vascular changes. [115][116][117] Furthermore, photographic technique and camera type may also affect the image quality for retinal fundus photography. Such possible ocular factors and confounders should be controlled for (eg, factoring in magnification effect and iris color) in the further development of retinal vascular imaging technology.…”