The development of the refractive state in the newborn Thomson gazelle.

Changes in refractive error during the first 3 months of life were studied retinoscopically in six Thomson gazelles ( Gazella thomsoni). Animals were hand-raised to allow repeat testing over time without chemical restraint. Refraction results were correlated with ultrasound measurements of intraocular dimensions, and with values in adult gazelles. Gazelles are born hyperopic with a mean refractive error of 3.44+/-0.31 D. By day 50, the animals are virtually emmetropic (0.13+/-0.21 D) and remain so in adulthood (0.03+/-0.09 D). The refractive error is highly correlated with the axial length ( r(2)=0.96) and with the vitreous chamber depth ( r(2)=0.83), but not with anterior chamber depth. Significant with-the-rule astigmatism was recorded ( P<0.001).

Development of the refractive state in eyes of ostrich chicks (Struthio camelus).

OBJECTIVE: To follow the development of the refractive error in the eyes of ostrich chicks from age 0 to day 37 after hatching. ANIMALS: 35 ostrich chicks. PROCEDURES: Spot retinoscopy was conducted to assess refractive error in ostrich chicks. Seventy eyes of 35 ostrich chicks were examined. Of these, 18 chicks were followed over time. At least 4 serial measurements (at 2- to 7- day intervals) were conducted in each of these chicks from day 1 to 37 after hatching. Seventeen additional chicks were examined on days 0, 3, 12, and 19 after hatching. RESULTS: Ostrich chicks were myopic at hatching, with a mean +/- SD refractive error of -4.47 +/- 0.15 diopters (D). The refractive error rapidly decreased during the first week of life, and by day 7 after hatching, chicks were slightly hyperopic, with a mean refractive error of 0.42 +/- 0.12 D. After day 7, there were no significant differences in the mean refractive error. CONCLUSIONS: The development of optics in the ostrich eye appears to be unique among animals and is characterized by myopia at hatching, rapid onset of emmetropia, and minimal variation in refractive error among chicks.

Presbyopia correction and the accommodation in reserve.

One method of determining the additional correction for presbyopia suggests leaving a percentage of the amplitude of accommodation in reserve. The rationale for this assumption seems logical because using all of the available accommodation is not sustainable without discomfort. However there is no empirical evidence indicating what percentage of the amplitude of accommodation should actually be left in reserve. Common figures adopted have been one-half and one-third. In this investigation the percentage of accommodation used is deduced mathematically after having determined the following: 1. The 'add' by the direct subjective clinical method. 2. Measured the amplitude of accommodation. 3. Measured the reading distance in 305 presbyopes ranging from 40 to 83 years of age. The results showed a small decline in the amplitude of accommodation up to the age of 52, after which age the measurements were scattered about a steady level. This finding suggests that after the age of 52 the results are based on the depth-of-focus of the eye. Females had slightly greater accommodation than males of the same age. The power of the add was significantly correlated to the age of the subject. The mean percentage of accommodation used for the 305 subjects was found to be 50.7%, thus confirming the rule of leaving half of the accommodation in reserve, although there were large variations: there were differences between males and females and with age the percentage of measured accommodation used, after having determined the correct add, diminished. Similarly the percentage of accommodation also decreased for shorter reading distances.