Widefield wavefront sensor for multidirectional peripheral retinal scanning

Abstract

The quantitative evaluation of peripheral ocular optics is essential in both myopia research and the investigation of visual performance in people with normal and compromised central vision. We have developed a widefield scanning wavefront sensor (WSWS) capable of multidirectional scanning while maintaining natural central fixation at the primary gaze. This Shack-Hartmann-based WSWS scans along any retinal meridian by using a unique scanning method that involves the concurrent operation of a motorized rotary stage (horizontal scan) and a goniometer (vertical scan). To showcase the capability of the WSWS, we tested scanning along four meridians including a 60° horizontal, 36° vertical, and two 36° diagonal scans, each completed within a time frame of 5 seconds.

Fig. 1.

Schematic diagram of the SH wavefront sensor’s optical layout. The beam-splitter (BS1) redirected collimated light with a wavelength of 850 nm toward the eye. The reflected backlight from the eye followed the red-line pathway, passed through BS1, and then hit the 4-F telescopic system comprising lens 1, lens 2, and BS2. This system was used to relay the wavefront information from the entrance pupil to the lenslet array. The blue-line pathway represents IR light (950 nm) from the ring-LED that illuminated the eye's pupil whose image was captured by the pupil camera. A cold mirror was used to maintain eye natural fixation during the peripheral scans.

Fig. 2.

Front view of the actual scanning wavefront sensor highlighting the motorized scanning mechanism. The SH wavefront sensor was mounted on the rotational stage consisting of a horizontal rotational table (R1) and a vertical goniometer (G1). The red dashed lines represent horizontal and vertical rotational axes. Both the rotational axes and optical axis (yellow dashed line) are coupled at the system’s center of rotation (orange circle) corresponding to the eye’s pupil center. The orange arrows represent the rotational path along the horizontal and vertical scans. The scanning process can be seen in the supplementary video (see Visualization 1).

Fig. 3.

The validation of the scanning wavefront sensor by comparing theoretical peripheral aberrations with model eye data. The theoretical peripheral aberration was determined by Zemax ray-tracing (A) through a doublet lens (f = 30 mm; AC-254-030A from Thorlabs, Inc.) with the exit pupil positioned on the lens back surface. The aberration was then measured with the WSWS for a 5.5 mm pupil. B and C illustrate the theoretical and measured peripheral defocus and astigmatism of nasal and temporal model eye, respectively. The Y-axis represents Zernike coefficient in microns and has varying scaling to highlight the validation comparison.

Fig. 4.

Peripheral lower-order aberrations (LOAs): A) defocus ( $Z_2^0$ ); B) defocus relative to the fovea; C) oblique astigmatism ( $Z_2^{-2}$ ); and D) vertical astigmatism ( $Z_2^2$ ). The measured aberrations are plotted at four distinct retinal eccentricities: a horizontal (black line, n = 22) scan covering ±30° from the fovea, a vertical (red line, n = 22) scan, and two oblique scans (n = 8) along 45° (blue line) and 135° (cyan line), each covering ±18° from the fovea. The X-axis displays the degree of retinal eccentricity, with negative values indicating temporal, inferior, infero-temporal, and infero-nasal retinal eccentricities for horizontal, vertical, diagonal 45°, and diagonal 135° scans, respectively. The Y-axis displays the aberration magnitude in microns, while the secondary Y-axis represents the equivalent dioptric power of defocus and astigmatic components (J0 & J45) for a 5.5 mm pupil. The amplitude scales in A & B differ to better illustrate the absolute and relative defocus distribution across retinal eccentricities. The error bars represent the standard deviation at each eccentricity.

Fig. 5.

Higher-order aberrations (HOAs) across the retinal eccentricity: A) vertical coma ( ${\text{Z}}_3^{-1}$ ); B) horizontal coma ( ${\text{Z}}_3^1$ ); C) primary spherical aberration ( ${\text{Z}}_4^0$ ); and D) HOA root-mean-square (RMS). The measured aberrations are plotted at four distinct retinal eccentricities: a horizontal (black line, n = 22) scan covering ±30° from the fovea, a vertical (red line, n = 22) scan, and two oblique scans (n = 8) along 45° (blue line) and 135° (cyan line), each covering ±18° from the fovea. The X-axis displays retinal eccentricity in degrees, with negative values indicating temporal, inferior, infero-temporal, and infero-nasal retinal eccentricities for horizontal, vertical, diagonal 45°, and diagonal 135° scans, respectively. The Y-axis represents the magnitude of aberrations in microns, calculated for a 5.5 mm pupil size. The error bars represent the standard deviation at each eccentric point.

Fig. 6.

Pan-retinal schematic representation of wavefront maps reconstructed from the measured aberrations for a 5.5 mm pupil across all four scanning directions. Plot A shows distribution of peripheral lower-order aberrations. Foveal defocus value is subtracted from each retinal location. Plot B shows the distribution of higher-order aberrations. The colormap shows the amplitude of wavefront height in µm.

Fig. 7.

Average relative defocus (D) across the horizontal meridian (in degrees) in the myopic (red) and non-myopic (blue) groups. The shaded red and blue areas represent the standard deviation at each retinal eccentricity. Positive values on the X-axis indicate the nasal retina, and the thick gray vertical bar denotes the area affected by the optic disc.

Fig. 8.

Average higher-order aberration RMS (for 5.5 mm pupil) across the horizontal meridian (in degrees) in the myopic (red) and non-myopic (blue) groups. The shaded red and blue areas represent the standard deviation at each retinal eccentricity. Positive values on the X-axis indicate the nasal retina, and the thick gray vertical bar denotes the area affected by the optic disc.