Can we measure the intraocular pressure when the eyeball is against the pillow in the lateral decubitus position?

Purpose: To evaluate the amount of intraocular pressure (IOP) change in the eye against the pillow in the lateral decubitus position (LDP). Methods: Thirty eyes from 15 healthy volunteers (12 men and three women) aged 29 ± 3 (range 25–37) years participated in this study. Using the rebound tonometer (Icare PRO, Icare Finland Oy, Helsinki, Finland), the IOP of both eyes was checked in sitting, supine, right and left LDPs. In the LDP, the additional IOP measurements were taken with the lower eyeball against the latex pillow. Results: Baseline IOP in the sitting position was 12.7 ± 1.9 mmHg in the right eye and 12.8 ± 2.2 mmHg in the left eye. Ten minutes after shifting from the sitting to the supine position, IOP increased significantly (right eye: +1.4 ± 1.4 mmHg, p = 0.006; left eye: +1.8 ± 1.5 mmHg, p = 0.001). Changing from the supine to the right and left LDP increased significantly the IOP of dependent eye (right eye: +2.3 ± 1.8 mmHg, p = 0.001; left eye: +1.5 ± 1.8 mmHg, p = 0.011). When the dependent eye was compressed against the pillow in the LDP, the IOP of the dependent eyes increased significantly after 10 min (right eye in the right LDP: +4.1 ± 4.9 mmHg, p = 0.011; left eye in the left LDP: +3.4 ± 3.7 mmHg, p = 0.006). Conclusion: The IOP was significantly elevated when the eyeball was against the pillow in the LDP.     

Epithelial phenotype and the RPE: is the answer blowing in the Wnt?

Cells of the human retinal pigment epithelium (RPE) have a regular epithelial cell shape within the tissue in situ, but for reasons that remain elusive the RPE shows an incomplete and variable ability to re-develop an epithelial phenotype after propagation in vitro. In other epithelial cell cultures, formation of an adherens junction (AJ) composed of E-cadherin plays an important early inductive role in epithelial morphogenesis, but E-cadherin is largely absent from the RPE. In this review, the contribution of cadherins, both minor (E-cadherin) and major (N-cadherin), to RPE phenotype development is discussed. Emphasis is placed on the importance for future studies of actin cytoskeletal remodeling during assembly of the AJ, which in epithelial cells results in an actin organization that is characteristically zonular. Other markers of RPE phenotype that are used to gauge the maturation state of RPE cultures including tissue-specific protein expression, protein polarity, and pigmentation are described. An argument is made that RPE epithelial phenotype, cadherin-based cell–cell adhesion and melanization are linked by a common signaling pathway: the Wnt/β-catenin pathway. Analyzing this pathway and its intersecting signaling networks is suggested as a useful framework for dissecting the steps in RPE morphogenesis.Also discussed is the effect of aging on RPE phenotype. Preliminary evidence is provided to suggest that light-induced sub-lethal oxidative stress to cultured ARPE-19 cells impairs organelle motility. Organelle translocation, which is mediated by stress-susceptible cytoskeletal scaffolds, is an essential process in cell phenotype development and retention. The observation of impaired organelle motility therefore raises the possibility that low levels of stress, which are believed to accompany RPE aging, may produce subtle disruptions of cell phenotype. Over time these would be expected to diminish the support functions performed by the RPE on behalf of photoreceptors, theoretically contributing to aging retinal disease such as age-related macular degeneration (AMD). Analyzing sub-lethal stress that produces declines in RPE functional efficiency rather than overt cell death is suggested as a useful future direction for understanding the effects of age on RPE organization and physiology. As for phenotype and pigmentation, a role for the Wnt/β-catenin pathway is also suggested in regulating the RPE response to oxidative stress. Exploration of this pathway in the RPE therefore may provide a unifying strategy for advancing our understanding of both RPE phenotype and the consequences of mild oxidative stress on RPE structure and function.     

How good is the match between the plane of the text and the plane of focus during reading?1

Because results from animal models demonstrate that retinal image defocus is a crucial factor in the visual control of eye growth, we have measured the precision of accommodation during reading at 1 m and at 30 cm distance. A newly developed photorefractor was used to sample both the refraction in the vertical meridian and direction of gaze at 25 Hz. Using these two parameters, a three-dimensional "refraction map" of the visual field was plotted. It showed the optic disc as an area with more myopic refractions and the course of refractions across a visual field of about +/- 25 deg. A special calibration scheme was employed to ensure that the precision of the refractions was 0.2 dpt or better (as estimated from the standard deviations of repeated measurements and the noise in the calibration curve). Twelve young adults (students from the lab) served as subjects. We found considerable inter-individual variability in the off-axis refractions but little variability among repeated measurements in the same subjects. Inter-individual variability reached a minimum in the foveal region. Both myopes wearing their spectacle corrections (n = 6) and emmetropes (n = 6) under-accommodated by about 0.3 D during reading at 30 cm distance but, at 1 m distance, only the emmetropes under-accommodated. Since both refraction groups under-accommodated similarly during reading at close distance, it remains unclear whether the small amount of defocus is critical for their future myopia development. Either accommodation errors differ at earlier times when myopia first appears (as suggested by the literature), or the subjects' eye growth was differently sensitive to defocus, or our simple protocol did not pick up existent differences in accommodation among the two groups.