Abstract
Purpose :
Adaptive optics (AO) enables cellular-resolution retinal imaging and stimulation, and enhanced visual performance. This capability requires that the AO control system track and correct temporal changes in ocular aberrations in real time. Here, we study how fast an AO system needs to run in clinically-relevant scenarios and show the advantages of going fast.
Methods :
We developed an ultrafast ophthalmic AO system that achieves a 233 Hz loop rate (discontinuous-exposure scheme; loop gain = 1) and 37.5 Hz bandwidth. We used the wavefront sensor to measure ocular aberrations at 342 Hz in order to characterize their temporal frequency content in multiple clinically-relevant scenarios. These included accommodating eyes, an eye with nystagmus, a blinking eye with a −6.5 D contact lens, a blinking eye with artificial tears to reduce the effect of dry eye, and an eye sequentially fixating for 1 s at different target locations separated by 2° (larger than expected isoplanatic patch size). The latter mimics imaging multiple retinal locations within a 5-s acquisition. We used the measured aberration temporal power spectra to calculate residual wavefront error as a function of AO loop rate, assuming a loop gain of 1 and a data-transfer+processing time of half the loop period. We acquired AO-OCT retinal images with ultrafast (233 Hz) and conventional (10 Hz) AO on the same eyes and compared performances.
Results :
Aberration power spectra in these clinically-relevant scenarios were 1−2 orders of magnitude larger than normal scenarios where AO systems typically operate. The nystagmic eye power spectrum had the largest magnitude with a local spike at the nystagmus frequency of 3 Hz. Predicted wavefront errors show that conventional AO is too slow to achieve diffraction-limited performance (averaged over measurement window) in these scenarios: a loop rate of ~110 Hz is needed for a nystagmic eye and ~90 Hz is needed after an eye blink with high-viscosity artificial tears. ~55 Hz is needed in 3 scenarios: (1) with an accommodating eye of 6 mm pupil; (2) after blink wearing a contact lens; and (3) during sequential fixation at multiple locations. Ultrafast AO improves aberration correction and retinal image quality, because it better corrects both low and high temporal frequency aberrations.
Conclusions :
Current AO systems need to run faster to correct aberrations encountered in clinically-relevant scenarios.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.