# Parafoveal and Perifoveal Accommodation Response to Defocus Changes Induced by a Tunable Lens
## 2 Materials and Methods
### Procedures  
Subjects viewed a green annular target on a dark background on a computer monitor with their right eye while their left eye was covered with a dark patch. The annular target, with a line width of 1.2 mm, was chosen as it simultaneously covers all points at a fixed radial distance from the fovea. For annular targets with 1\({}^{\circ}\), 2\({}^{\circ}\), 3\({}^{\circ}\), 4\({}^{\circ}\), 5\({}^{\circ}\), 6\({}^{\circ}\), 7\({}^{\circ}\), 7\({}^{\circ}\) and 8\({}^{\circ}\) retinal eccentricity, the corresponding retinal illuminance was 1.51, 1.80, 1.98, 2.11, 2.21, 2.29, 2.35, 2.38 and 2.41 log Td. The monitor was placed at a viewing distance of 1 m from the conjugated pupil plane corresponding to an initial +1 diopter baseline of accommodation. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Subject** & **Age (Years)** & **Sphere (D)** & **Cylinder (D)** & **Ac. Range (D)** \\ \hline \#1 & 29 & \(-\)0.50 & 0.00 & 3.40 \\ \#2 & 28 & \(-\)0.75 & 0.00 & 3.53 \\ \#3 & 34 & \(-\)0.75 & 0.00 & 2.42 \\ \#4 & 24 & \(-\)4.75 & 0.00 & 3.35 \\ \#5 & 23 & \(-\)5.75 & 0.75 (Axis 30\({}^{\circ}\)) & 3.55 \\ \#6 & 25 & \(-\)6.00 & \(-\)2.25 (Axis 15\({}^{\circ}\)) & 3.28 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Refractive error in diopters (D) of subjects’ right eyes. The comfortable accommodative (Ac) range was determined manually with the TL for each subject. Subject #1 is an emmetrope, subjects #2 and #3 are mild myopes and subjects #4–#6 are myopes who all wore their spectacles during measurements. The visual targets were displayed on a screen placed at 1 m distance from the conjugated pupil plane (1 diopter initial bias). Figure 1: Schematic of a monocular vision system which was used to measure foveal, parafoveal and perifoveal accommodation responses to a sequence of random defocus steps. Three 4-f telescopes were used to place the iris, HS-WFS and tunable lens in conjugated pupil planes. Beam splitter 1 is a hot mirror, whereas beam splitter 2 is a 50/50 coated plate. Only a single green ring in the annular accommodation target was shown at any given time. The Zernike defocus coefficient \(\mathcal{C}_{20}\) determined with the wavefront sensor was converted from micrometers (\(\upmu\)m) to diopters (D) as follows:  
\[\frac{1}{f}=-16\times\sqrt{3}\times\mathcal{C}_{20}/d^{2}, \tag{1}\]  
where \(d\) is the pupil size in diameter in mm. The factor of 16 is due to the scaling of the wavefront at the pupil onto the Hartmann-Shack wavefront sensor (HS-WFS). A near-IR laser source of 850 nm wavelength (Edmund OpticsTM: Edmund Optics Ltd., York, UK) was focused onto the retina and served as a probe to sense real-time ocular aberrations at 20 Hz including up to the 4 th radial order of the Zernike aberrations with a CMOS-based HS-WFS (ThorlabsTM WFS20-5C; Thorlabs Ltd., Ely, UK). The irradiance of the near-IR source was approximately 100 \(\upmu\)W. The system was computer controlled via a LabviewTM interface (National Instruments Software: Labview 2016). A 3 mm iris was placed in a conjugated pupil plane to limit the effective pupil diameter to keep the measurement situation identical in all cases. A small pupil limits the impact of higher-order aberrations and increases the depth of focus, resembling vision outdoors. In our earlier study, we found no significant difference in accommodative amplitude between pupil sizes of 2.5, 3.5 and 4.5 mm, and therefore a negligible impact of higher-order aberrations [19]. Subjects were not dilated, but the room was dark to ensure a sufficiently large natural pupil. As only changes in accommodative state were studied, a possible myopic shift caused by the dark environment, i.e., night myopia [21], was of no concern as it would provide a constant offset. A bite bar was used to limit unwanted head motion during measurements.