Now showing 1 - 3 of 3
  • Publication
    Hartmann–Shack wavefront sensing without a lenslet array using a digital micromirror device
    The common Hartmann–Shack wavefront sensor makes use of a lenslet array to sample in-parallel optical wavefronts. Here, we introduce a Hartmann–Shack wavefront sensor that employs a digital micromirror device in combination with a single lens for serial sampling by scanning. Sensing is analyzed numerically and validated experimentally using a deformable mirror operated in closed-loop adaptive optics with a conventional Hartmann–Shack wavefront sensor, as well as with a set of ophthalmic trial lenses, to generate controllable amounts of monochromatic aberrations. The new sensor is free of crosstalk and can potentially operate at kilohertz speed. It offers a reconfigurable aperture that can exclude unwanted parts of the wavefront.
      632Scopus© Citations 21
  • Publication
    Monocular foveal, parafoveal, and perifoveal accommodation response to random defocus step changes
    (SPIE, 2020-08-21) ;
    Accommodation of the human eye relies on multiple factors, including – object size, monochromatic and chromatic aberrations, and vergence, and corrects defocus even in monocular conditions. Previous studies have been done to understand whether the retina can decode the sign of defocus as this may play a role for emmetropization and possibly also accommodation. Yet, findings have not been unambiguous and questions remain. Thus, in this study we tried to understand how accommodation makes use of defocus blur to detect the sign of defocus by performing experiments using a fast wavefront sensor in a vision testing system while eliminating other visual cues that may otherwise confound the analysis. A new automated method has been introduced to study monocular accommodation by using a currentdriven tunable lens (TL) to induce a random sequence of defocus step changes within the accommodative range of each observer. The response was captured in real time using a Hartmann-Shack wavefront sensor (HS-WFS) operating at 20 Hz while detecting aberrations and Zernike coefficients until 4th radial order across a 3 mm limited pupil. Foveal, parafoveal and perifoveal accommodation has been studied for young emmetropes and myopes to determine until which eccentricity accommodation is triggered. Our findings show that the accommodative range diminishes with eccentricity and at 14° (diameter) and beyond it becomes largely absent.
      9
  • Publication
    Monocular accommodation response to random defocus changes induced by a tuneable lens
    (Elsevier, 2019-12) ;
    Accommodation of the human eye relies on multiple factors and visual cues that include object size, monochromatic and chromatic aberrations, and vergence. Yet, even in monocular conditions, accommodation corrects for defocus. Studies of eye growth in chicks have addressed whether the retina can decode the sign of defocus as this may play a role for emmetropization and possibly also accommodation. However, findings have not been unambiguous and questions remain. Here, we report on monocular accommodation studies of emmetropic and myopic human subjects to clarify whether foveal vision drives accommodation in the correct direction by removing out-of-focus blur potentially before relying on other cues. Subjects viewed monocularly a green target at 1-meter distance while being presented with a random sequence of negative defocus step changes induced by a pupil-conjugated currentdriven tuneable lens. The natural pupil was constricted by a pupil-conjugated motorized iris using three different diameters and target brightness was set with a liquid crystal variable attenuator. A Hartmann-Shack wavefront sensor with an infrared beacon captured real-time changes of defocus and Zernike polynomial coefficients up to 4th radial order. We find that the young adult eye accommodates reliably in the correct direction but with a latency of 300 – 700 ms. The findings are discussed in relation to an absorption model of light in outer segments 2 that breaks the defocus symmetry and thus may serve as a plausible guide for accommodation and emmetropization.
      171Scopus© Citations 8