A pupil tracking system for adaptive optics retinal imaging

Lévecq

et al. 2012

Biomed. Opt. Express

Self Cite

Adaptive optics, when integrated into retinal imaging systems, compensates for rapidly changing ocular aberrations in real time and results in improved high resolution images that reveal the photoreceptor mosaic. Imaging the retina at high resolution has numerous potential medical applications, and yet for the development of commercial products that can be used in the clinic, the complexity and high cost of the present research systems have to be addressed. We present a new method to control the deformable mirror in real time based on pupil tracking measurements which uses the default camera for the alignment of the eye in the retinal imaging system and requires no extra cost or hardware. We also present the first experiments done with a compact adaptive optics flood illumination fundus camera where it was possible to compensate for the higher order aberrations of a moving model eye and in vivo in real time based on pupil tracking measurements, without the real time contribution of a wavefront sensor. As an outcome of this research, we showed that pupil tracking can be effectively used as a low cost and practical adaptive optics tool for high resolution retinal imaging because eye movements constitute an important part of the ocular wavefront dynamics.

Section: Methodsmentioning

confidence: 99%

Adaptive optics with pupil tracking for high resolution retinal imaging

Lévecq

et al. 2012

Biomed. Opt. Express

Self Cite

“…The high correlation of the pupil position and the wavefront RMS suggests that the control algorithm for adaptive optics with pupil tracking can be used to estimate the aberration of the shifted pupil. First, Δ x s x , Δ y s x , Δ x s y and Δ y s y , the derivatives of the x and y slopes data of the reference wavefront measurement on x and y axis were calculated using the Equation 6. Second, the displacements of the model eye on the pupil plane (Δx, Δy) were converted to the displacements of the wavefronts on the optoelectronic sensor plane (a, b) by the Equation 9.…”

Section: Resultsmentioning

confidence: 99%

“…The algorithm of the pupil tracking system and its performance were discussed in detail in our previous conference proceedings. 6,7 It was specially constructed to track minute fixational eye movements in high resolution that span ±5 • of visual angle; its detection range is restricted to ±3 mm on x and y axes. After its adaptation to the retinal imaging system rather than being a stand alone system, its accuracy is now 13 ± 5 μm and its image acquisition time is 50 ms, 10 ms of which is the exposure time.…”

Section: Introductionmentioning

confidence: 99%

Retinal imaging system with adaptive optics enhanced with pupil tracking

Ophthalmic Technologies XXI

Lévecq

et al. 2011

Self Cite

A compact retinal camera with adaptive optics which was designed for clinical practice was used to test a new adaptive optics control algorithm to correct for the angular ray deviations of a model eye. The new control algorithm was based on pupil movements rather than the measurement of the slopes of the wavefront with an optoelectronic sensor. The method for the control algorithm was based on the hypothesis that majority of the changes of the aberrations of the eye are due to head and eye movements and it is possible to correct for the aberrations of the eye by shifting the on axis correction according to the new position of the pupil. Since the fixational eye movements are very small, the eye movements are assumed to be translational rather than rotational. Using the new control algorithm it was possible to simulate the aberrations of the moving model eye based on pupil tracking. The RMS of the residual wavefront error of the simulation had a magnitude similar to the RMS of the residual wavefront error of the adaptive optics correction based on optoelectronic sensor for angular ray deviations. If our hypothesis is true and other factors such as the tear film or the crystalline lens fluctuations do not cause changes in the aberrations of the eye as much as motion does, the method is expected to work in vivo as it did for a model eye which had no intrinsic factors that cause aberration changes.

Performance assessment of a pupil tracking system for adaptive optics retinal imaging

Harms

1st Canterbury Workshop on Optical Coherence Tomography and Adaptive Optics

2008

Adaptive Optics (AO) is particularly suitable for correction of aberrations that change over time -a necessity for high resolution imaging of the retina. The rapidly changing aberrations originating from eye movements require wavefront sensors (WFS) with high repetition rates. Our approach is enhancing aberration correction by integrating a Pupil Tracking System (PTS) into the AO loop of the retinal imaging system. In this study we assessed the performance of the PTS developed for this purpose. Tests have demonstrated that the device achieves an accuracy of <15 µm in a ±2 mm range of eye movements with a standard deviation <10 µm. PTS can tolerate ±5 mm defocus with an increase of 4 µm in mean standard deviation. In vivo measurements done with temporarily paralyzed pupils have resulted in a precision of approximately 13 µm.