Comparison of retinal and choriocapillaris thicknesses following sitting to supine transition in normal and age-related macular degeneration subjects

Abstract

Purpose: Effects of position on retinal and choroidal structure are absent from the literature yet may provide insights into disease states like age-related macular degeneration (AMD). We set out to evaluate the effect of postural change on retinal and choroidal structures in normal volunteers and subjects with non-neovascular AMD.

Methods: Prospective observational case series. Four unaffected volunteers (8 eyes) and 7 subjects (8 eyes) with intermediate AMD. Normal volunteers were selected that had no evidence of ocular disease. Subjects with AMD were required to have at least 10 intermediate sized drusen. Spectral domain optical coherence tomography (OCT) with enhanced depth imaging in upright (sitting) and supine positions. Stable imaging was achieved using a rotating adjustable mechanical arm that we constructed to allow the OCT transducer to rotate 90 degrees. The Iowa Reference Algorithms were used to quantify choroid and choriocapillaris thickness. Main outcome measures included changes in sitting and supine position central macular thickness (CMT, μm), total macular volume (TMV, mm³), choroidal thickness (CT, μm), and choriocapillaris equivalent thickness (CCET, μm).

Results: CCET was thinner in normal subjects (9.89 mm) compared to patients with intermediate AMD (16.73 mm) (p = 0.02); there was no difference in overall CT between the two groups (p = 0.38). There was a 15% CCET reduction among normal subjects when transitioning from sitting (9.89 mm) to supine position (8.40 μm) (p = 0.02) versus a CCET reduction of 11.1% from sitting (16.73 μm) to supine (14.88 μm) (p = 0.10) in patients with intermediate AMD.

Conclusions: Intermediate AMD appears to be associated with an increase in CCET and with a lack of positional responses that are observed in the CCET of normal eyes. Our results suggest that although outer portions of the choroid do not appear to be responsive to modest positional or hydrostatic pressure, the choriocapillaris capacity is, and this is measurable in vivo. Whether this physiologic deviation that occurs in AMD is related to atrophy, inflammation, or changes in autoregulatory factors or growth factors, remains to be determined.