Foveal phase retardation changes associated with normal aging

Abstract

This study quantified normal age-related changes to the photoreceptor axons in the central macula using the birefringent properties of the Henle fiber layer. A scanning laser polarimeter was used to acquire 15 × 15 deg macular images in 120 clinically normal subjects, ranging in age from the third decade to the eighth. Raw image data of the macular cross were used to compute phase retardation maps associated with Henle fiber layer. Annular regions of interest ranging from 0.25 to 3 deg eccentricity and centered on the fovea were used to generate intensity profiles from the phase retardation data, which were then analyzed using sine curve fitting and Fast Fourier Transform (FFT). The amplitude of a 2f sine curve was used as a measure of macular phase retardation magnitude. For FFT analysis, the 2f amplitude, as well as the 4f, were normalized by the remaining FFT components. The amplitude component of the 2f curve fit and the normalized 2f FFT component decreased as a function of age, while the eccentricity of the maximum value for the normalized 2f FFT component increased. The phase retardation changes in the central macula indicate structural alterations in the cone photoreceptor axons near the fovea as a function of age. These changes result in either fewer cone photoreceptors in the central macula, or a change in the orientation of their axons. This large sample size demonstrates systematic changes to the central cone photoreceptor morphology using scanning laser polarimetry.

Henle fiber layer phase retardation measured with polarization-sensitive optical coherence tomography

“…The retinal eccentricity at which maximum DPPR occurs in our study roughly approximates that in an earlier study of 120 clinically normal eyes (1.27° ± 0.29°; age: 50-60 years) [3]. In that study, normalized, but not absolute DPPR was measured with a confocal scanning laser polarimeter (GDx, Carl Zeiss Meditec) in conjunction with Fourier analysis to separate the contribution of HFL from that of the retinal nerve fiber layer.…”

“…Aging and macular diseases such as age-related macular degeneration and diabetic retinopathy are known to disrupt the organization of these fibers and reduce layer birefringence [2,3]. Since disruption indicates structural changes to otherwise well-ordered neural tissues, birefringence measurements may serve as a sensitive indicator of disease onset.…”

Concentric Macular Rings Sign in Patients With Foveal Hypoplasia

“…Foveal hypoplasia has been graded into 4 groups based on structure, 7 and although there was an association between VA with the different OCT-based grades of foveal hypoplasia in our study, The Henle layer exhibits form birefringence, 9 the characteristic that is responsible for producing the bowtie or macular cross on GDx VCC and IRR images ( Figure 1L and F). Birefringence in the eye is also exhibited by the RNFL and cornea but is dependent on thickness, so the bowtie reflex is believed to be formed by the Henle layer centrally with increasing influence of the RNFL more eccentrically 10 and is dependent on the normal foveal architecture. This theory would explain the presence of the macular cross pattern in normal eyes on IRR and GDx VCC images.…”

Distribution differences of macular cones measured by AOSLO: Variation in slope from fovea to periphery more pronounced than differences in total cones

“…The marked central decrease with aging in foveal cone density is predicted from previous imaging studies of cone photopigment density, in which the central fovea has both decreased cone photopigment and decreased macular pigment (Elsner, Burns, & Beausencourt et al, 1998). Similarly, there is a decrease with increasing age in foveal phase retardation, well-modelled by the near radial symmetry in the fovea of the birefringent Henle fiber layer (VanNasdale, Elsner, & Hobbs et al, 2011). …”