Daniel Kurtz

Eye position during fixation tasks: comparison of macaque and human.

Two macaques and three humans fixated luminous targets in a dark field. All subjects had greater dispersion of eye position from trial-to-trial (between-trial variability) than would be predicted from sampling error and within-trial variability. Monkeys had greater between-trial dispersion on the vertical meridian than humans because of less precise control of saccades. Mean vertical eye position of the monkeys varied idiosyncratically with the fixation task (spot-dim or line-tilt). Between-trial fixation variability of both monkeys and humans was large enough to affect the interpretation of experiments relating visual performance to retinal anatomy or to neurophysiology.

Variability of the ocular component measurements in children using A-scan ultrasonography.

Knowledge of the precision with which the various ocular components can be measured with available techniques is vital to our ability to track changes in the anatomy of the eye in relation to the development of refractive error. Corneal touch A-scan ultrasound measurements were obtained by either an instrument-mounted or by a hand-held method on 469 children aged 6 to 11 years at their enrollment into the Correction of Myopia Evaluation Trial. Variability of measurements was calculated for overall axial length, anterior chamber depth, lens thickness, and vitreous chamber depth. The mean variability of overall axial length was 0.062 ± 0.043 mm and 0.061 ± 0.056 mm for the right and left eyes, respectively. Mean variability of the ocular component measures was similar. The mean variability was not influenced by the age, gender, level of myopia, or residual accommodation of the subjects. Statistically significant differences between the instrument-mounted and the hand-held method and among certain ethnic groups were found, but the differences were not of a magnitude to be clinically significant. A-scan ultrasonography is sensitive to changes in the axial length and vitreous chamber depth equivalent to 0.25 D and is therefore a useful technique to assess changes in these ocular components in children. The precision of lens thickness is poorer than the equivalent of 1.0 D, and, therefore, A-scan may not be sufficiently precise to be useful in studies of active accommodation or lens growth.

Primate head and body restraint without chronic skin openings or attachments to the animal

We developed a primate restraint system that requires no chronic skin openings or attachments to the animal. The restraining chair has a unique neck clasp; monkeys without chains and collars are easily trained to readily enter the chair and accept restraint with the neck and head held at a comfortable angle. A bite bar, in combination with contact on broad areas of the monkey’s brow and occiput, provides rigid head immobilization. In order to achieve contact with a broad area of the occipital bone, the muscles at the back of the animal’s head are surgically detached from the occiput and reattached to the underlying neck muscles. A strain-gauge, mounted on the head-holder and monitored by a laboratory computer, detects head movements of the monkey and permits the experimenter to teach the monkey to sit still during data acquisition. This system is well accepted by experienced monkeys and helps prevent the risks of infection posed by most earlier methods. Furthermore, the head and shoulders of the monkey are readily accessible for examination and for close positioning of test equipment.