Combined Autorefractor and Motorized Visual Fixation Target to Measure Accommodation Response to Step and Ramp Demands

Abstract

Purpose : The purpose of this project is to develop a combined wavefront sensor and programmable motorized visual fixation target that can provide a range of step and ramp stimuli to study and quantify dynamic optical accommodative responses.

Methods : The device combines a custom-built wavefront aberrometer with a motorized fixation target based on the Badal principle. The wavefront aberrometer uses a commercially available Shack-Hartmann wavefront sensor (WFS, Thorlabs, WFS20-5C) with a superluminescent diode emitting at 960nm (Inphenix, IPSDS0901C-0311) as the light source and a standard 4f relay system. The Badal fixation target was designed to produce a maximum vergence of -20 D. The system was designed with two channels to enable both ramp and step stimuli, with a maximum speed of 13.4D/sec for the ramp. The aberrometer and fixation target are coupled using a dichroic mirror. A prototype of the system was assembled on an adjustable slit-lamp table (see Figure 1). Calibration of the system was performed using an eye model. Under an IRB approved protocol, a preliminary test was performed on a 29 y/o subject (SEQ = +1.25) to assess the capability of the system to dynamically record the optical response to an accommodation stimulus ramping from 0D to 3D with a speed of 0.25 D/sec.

Results : The calibration using the eye model shows linearity (y= 0.998x - 0.106) in the sphere range between -20D to +10D with a maximal residual error of -0.4D. The human subjects tests demonstrate the functionality of the system (see Figure 2).

Conclusions : The proof-of principle of the accommodation biometry system with combined ramp/step stimulus was demonstrated.

This is a 2020 ARVO Annual Meeting abstract.

 

Figure 1: Prototype of the combined wavefront sensor and programmable motorized visual fixation target system assembled on an adjustable slit-lamp table.

 

Figure 2: Dynamic recording of 29 y/o subject to 3D ramp stimulus. Red horizontal line shows baseline refraction measured to be 1.46D. Red vertical line shows when ramp accommodation stimulus was applied.