More than what meets the eye Despite extensive knowledge on eye optics and the neural processing of the optical image, a number of basic questions are surprisingly unclear. A European study investigated the mechanisms by which our vision adapts to daily needs. Health © Shutterstock Our ability to see is a result of the visual processing of light by our visual system. This system includes the eye, the visual cortex and other parts of the brain. The complex processes carried out by this system include the reception of light, the conversion of monocular representations into binocular perception, distance assessment between objects and body movement guidance. Research over the years has provided invaluable insight into the functions and some of the underlying mechanisms implicated in vision but there are many unresolved issues. The EU-funded OPAL (Optical and adaptational limits of vision) project investigated the mechanisms by which the eye can sharpen degraded, aberrant or defocused retinal images. In addition, they addressed the role of diurnal factors in visual performance. Regarding chromatic aberration — when the lens fails to focus all colours to the same convergence point — researchers discovered that lens thickness is partly responsible for the individual differences. In addition, it explained why this phenomenon is more prominent among older people. To correct transverse chromatic aberration (TCA), scientists concluded that in people with central visual field loss, one should avoid inducing additional peripheral TCA. The development of the first fully optical coherence tomography (OCT) based eye models should help towards comprehending ocular optical degradation. Using specific psychophysical routines, the consortium evaluated on- and off-axis vision, in terms of contrast sensitivity and resolution, as well as detection acuity. Interestingly, they discovered that foveal vision improved after prolonged exposure to defocus blur but this effect was suppressed when the periphery was blurred. This highlighted the importance of peripheral vision when designing optics to reduce the progression of myopia. OPAL generated a new integrated optical instrument to measure stray-light into a portable optoelectronic device that was tested in patients with cataract. Results indicated a good correlation with psychophysical data and clinical grading of cataract densities. The findings of the OPAL study have direct implications for optical correction strategies (spectacles, refractive surgery), as well as understanding how different mono- and polychromatic aberrations limit vision and sensitivity in low light environments. Keywords Eye, optics, visual system, transverse chromatic aberration, lens, peripheral vision, cataract
