Abstract
Purpose :
To evaluate the feasibility of a non-contact method to temporarily elevate intraocular pressure (IOP) and to investigate the influence of an induced IOP on ocular aberrations.
Methods :
Healthy volunteers (n=5) without a previous history of intraocular disease, trauma, or surgery were recruited for the study. An inversion table (Teeter Hang Ups, Puyallup, WA) was utilized to elevate IOP. Tono-Pen XL (Reichert, Buffalo, NY) was used to monitor the IOP of each subject’s right eye under three conditions: baseline (sitting upright) and two inversion angles of 135 degrees (D1) and 165 degrees (D2). A custom developed Shack-Hartmann wavefront sensor was then used to concurrently measure ocular aberrations under each condition. 0.5% tropicamide was used to dilate the pupil and paralyze accommodation prior to obtaining baseline measurements. Repeat measurements of ocular aberrations and IOP were taken at baseline and each inversion angle.
Results :
A significant (P<0.01) increase in IOP was observed within 1 minute after subjects achieved each inversion position. Repeat measurement confirmed a stable IOP elevation. From baseline to D1, IOP increased from 14.8 ± 1.9 mmHg to 23.7 ± 2.6 mmHg. A smaller increase was found from D1 to D2, with a highest IOP of 29.7 ± 3 mmHg. When subjects returned to the baseline position, IOP returned to normal values within 1 minute. Changes in ocular aberrations induced by the elevated IOP were observed in radially symmetric term, defocus (Z20) and asymmetric terms including astigmatism (Z2-2, Z22 ), trefoil (Z3-3, Z33), coma (Z3-1, Z31) and quadrafoil (Z4-4) of the eye. For pupil sizes ranging from 6 to 8 mm, the total wavefront root mean squared (RMS) value was 0.96 ± 0.69μm from baseline to D1 and 0.6 ± 0.24μm from baseline to D2. The difference in RMS between D1 and D2 was not statistically significant (P=0.80). In addition, a large inter-patient variability was observed in the magnitudes of changes in ocular aberrations among subjects.
Conclusions :
In vivo IOP can be temporarily elevated in a safe, efficient, non-contact manner using an inversion table. IOP elevation caused significant changes in ocular aberrations in healthy eyes. Despite inter-subject variability, the statistically significant changes in the asymmetric wavefront aberrations might suggest spatially-varying collagen fibril distribution across normal human corneas.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.