Purchase this article with an account.
Saeideh Ghahghaei, Jeremy B Badler, T Rowan Candy, Arvind Chandna; The calibration of the PlusOptix PowerRef 3 as a function of viewing distance. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2746.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
The PlusOptix PowerRef 3 is an infrared video-based eccentric photorefractor used to estimate accommodation. It measures the eye’s refractive state using the slope of a linear regression fit to the distribution of reflected light across the pupil, and a calibration function based on a population mean. Accurate measurements require calibration for an individual due to differences in eye anatomy. Calibration is typically performed for a single reference viewing distance. Eye alignment, pupil size and higher-order optical aberrations are likely to change when viewing distance changes, which may influence the calibration function. We performed calibrations at multiple viewing distances for adult subjects with varying accommodative ability, to assess the need for multiple calibration distances and range of inter-subject variability.
Adult participants fixated an accommodative target at 50 cm, 1 m and 6 m. A central letter ‘E’ was surrounded by two rings of letters. Each letter subtended 0.33 deg and the outer ring diameter was 4 deg. Viewing was monocular, with an IR-pass filter used for occlusion so that refractive state could be recorded from both eyes. Spherical lenses, ranging from -5 to +5, were placed in front of the occluded eye for at least 5 seconds each. Data were collected twice in a dimly-lit room.
The change in measured anisometropia induced by each lens was calculated, relative to a baseline before the lens was applied. For each participant, each eye and each viewing distance, the slope of a linear regression describing anisometropia as a function of lens power was determined. There were individual differences based on (i) eye being assessed (up to 30% change in the slope) and (ii) viewing distance (up to 40% change in the slope) that fell outside the range of measurement repeatability.
The eccentric photorefraction calibration function for a given individual can depend on viewing distance. Depending on the sensitivity desired, it may be important to calculate the slope of the calibration function for subjects at each distance.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
This PDF is available to Subscribers Only