Optical Signals for Accommodation and Emmetropization.
Mechanisms & Pathways for Accommodation and Emmetropization.
High-speed infrared optometry is used to monitor accommodation continuously while dioptric (pertaining to refraction and chromatic dispersion) and pictorial aspects of the retinal image are manipulated under computer control. Special lenses are used to neutralize, double, or reverse the normal chromatic aberration of the eye, to examine the effect of chromatic aberration on accommodation. Most observers depend on chromatic aberration for effective focusing. This is surprising because the conventional view is that aberrations reduce image quality, and thus they should impair accommodation. Another approach uses computer-generated simulations of blurred images to drive accommodation. These experiments suggest that the visual system compares cone-contrasts measured separately by long-, middle- and short-wavelength-sensitive-cones to determine the sign of defocus (positive or negative wavefront spherical curvature). All three cone types contribute to reflex accommodation and both luminance and chromatic pathways transmit accommodation signals.
The issue is complicated because some individuals accommodate effectively in the absence of chromatic aberration, and without feedback from blur. One possibility is that directionally sensitive foveal cones respond directly to changes in the vergence of light reaching the retina. The issue is examined by controlling the angle of incidence of light reaching the retina by restricting incident light to one or the other side of the natural pupil, while subjects view blurred edges. Other hypotheses being tested are that a decentered Stiles-Crawford effect provides directional information, and that the eye monitors wavefront vergence at blurred edges as a modulation of light across the pupil, and not simply as blur of the retinal image.
The approach assumes that the optical signals that control everyday accommodation also control the long-term focusing process termed emmetropization (coordinated growth and development of the optical components and axial length of the eye).
SELECTION OF PUBLICATIONS
1. Aggarwala K.R., Mathews S., Kruger E.S. and Kruger P.B. (1995) Spectral bandwidth and ocular accommodation. Journal of the Optical Society of America, 12, 450–455.
2. Kruger, P.B., Mathews S., Katz M., Aggarwala K.R. and Nowbotsing S. (1997) Accommodation without feedback suggests directional signals specify ocular focus. Vision Research, 37, 2511-26.
3. Lee, J.H., Stark, L.R., Cohen, S. and Kruger, P.B. (1999) Accommodation to static chromatic simulations of blurred retinal images. Ophthalmic and Physiological Optics, 19, 223-235.
4. Kruger, P.B., Lopez-Gil, N. and Stark L.R. (2001). Accommodation and the Stiles-Crawford effect: Case study and theoretical aspects Ophthalmic and Physiological Optics, 21, 338-350.
5. Rucker, F.R. and Kruger, P.B. (2001). Isolated short-wavelength sensitive cones can mediate a reflex accommodation response. Vision Research, 41, 911-922.
6. Stark, L.R., Lee, R.S., Kruger, P.B., Rucker, F.J. & Fan, H.Y. (2002). Accommodation to simulations of defocus and chromatic aberration in the presence of chromatic misalignment. Vision Research, 42, 1485-1498.
7. Rucker, F.J. and Kruger, P.B. (2004) The role of short-wavelength sensitive cones and chromatic aberration in the response to stationary and step accommodation stimuli. Vision Research, 44, 197-208.
8. Rucker, F.J. and Kruger, P.B. (2004) Accommodation responses to stimuli in cone contrast space. Vision Research, 44, 2931-2944.
9. Kruger, P.B., Stark, L.R. and Nguyen, H-N. (2004) Small foveal targets for studies of accommodation and the Stiles–Crawford effect. Vision Research, 44, 2757-2767.
10. Kruger, P.B., Rucker, F.J., Hu, C., Rutman, H., Schmidt, N.W. and Roditis, V. (2005) Accommodation with and without short-wavelength-sensitive cones and chromatic aberration, Vision Research, 45, 1265-1274.
11. Rucker, F.J. and Kruger, P.B. (2006) Cone contributions to signals for accommodation and the relationship to refractive error. Vision Research, 46, 3079–3089.
12. Chen, L., Kruger, P.B., Hofer, H., Singer, B. and Williams, D.R. (2006) Accommodation with higher-order monochromatic aberrations corrected with adaptive optics. Journal of the Optical Society of America A, 23,1-8.
13. López-Gil, N., Rucker, F.J., Stark, L.R., Badar, M., Borgovan, T., Burke, S. & Kruger, P. B. (2007) Effect of third-order aberrations on dynamic accommodation, Vision Research, 47, 755–765.
14. Stark, L. R., Kruger, P. B., Rucker, F. J., Swanson, W. H., Schmidt, N., Hardy, C., Rutman, H., Borgovan, T., Burke, S., Badar, M. & Shah, R. (2009). Potential signal to accommodation from the Stiles–Crawford effect and ocular monochromatic aberrations. Journal of Modern Optics, 56, 20, 2203-2216.
15. Kruger, P. B. (2009). Aberrations of the Eye – Crude Flaws or Ecological Design? Journal of Optometry, 2, 4,162-164.