Jörgen Gustafsson

Resolution of static and dynamic stimuli in the peripheral visual field

In a clinical setting, emphasis is given to foveal visual function, and tests generally only utilize static stimuli. In this study, we measured static (SVA) and dynamic visual acuity (DVA) in the central and peripheral visual field on healthy, young emmetropic subjects using stationary and drifting Gabor patches. There were no differences between SVA and DVA in the peripheral visual field; however, SVA was superior to DVA in the fovea for both velocities tested. In addition, there was a clear naso-temporal asymmetry for both SVA and DVA for isoeccentric locations in the visual field beyond 10° eccentricity. The lack of difference in visual acuity between static and dynamic stimuli found in this study may reflect the use of drift-motion as opposed to displacement motion used in previous studies.

Symmetries in peripheral ocular aberrations

A mirror symmetry in the aberrations between the left and right eyes has previously been found foveally, but while a similar symmetry for the peripheral visual field is likely, it has not been investigated. Nevertheless, the peripheral optical quality is often evaluated in only one eye, because it is more time efficient than analyzing the whole visual field of both eyes. This study investigates the correctness of such an approach by measuring the peripheral wavefront aberrations in both eyes of 22 subjects out to ±40° horizontally. The largest aberrations (defocus, astigmatism, and coma) were found to be significantly correlated between the left and right eyes when comparing the same temporal or nasal angle. The slope of the regression line was close to ±1 (within 0.05) for these aberrations, with a negative slope for the horizontally odd aberrations, i.e. the left and right eyes are mirror symmetric. These findings justify that the average result, sampled in one of the two eyes of many subjects, can be generalized to the other eye as well.

The accommodative pupil responses of children and young adults at low and intermediate levels of ambient illumination

Accommodative pupil constrictions were compared between 27 children (9-10 years) and 13 young adults (22-26 years) in order to clarify the issue whether or not children have such a response. Accommodative stimuli of 4 and 7 diopters were used to elicit the response and experiments were performed at 5 and 100 lux in order to investigate whether the level of ambient light has different effects on developing and mature visual systems. The accommodative pupil response is present in children, but weaker than in adults. Different levels of ambient light lead to only minor additional differences between children and adults. The weaker accommodative pupil response of children may be a consequence of their superior accommodative ranges, which make it unnecessary to close the pupil to increase depth of field. Adults, in contrast, may do better with smaller pupils that reduce accommodative demand because of increased depth of field. A mature human visual system may furthermore be better tuned to handle dimmer and thus noisier images in the photopic range than the developing visual system of a child.