Purchase this article with an account.
Zheng Shao, Elizabeth L. Irving, Marsha L. Kisilak, Melanie C. Campbell; Both Changes in Eye Power and Optical Eye Length Contribute to Emmetropization of Refractive Error in Early, Normal Development of Chick Eyes. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3445.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
During lens induction of refractive errors, emmetropization to defocus is primarily via changes in ocular length. However, changes in mean ocular refraction (MOR) can be due to changes in either dioptric length (which is inversely proportional to optical length) or in optical power. We wished to determine the contributions of eye power and optical length to emmetropization in the normally developing chick eye.
Using literature values of chicken schematic eye parameters for two different strains, we plotted the rate of change of MOR, and changes in eye power, optical length and dioptric length as a function of age up to day 15. From experimental measurements from our labs of eye length and MOR, we calculated the variation of eye power with age. We compared the behaviours of MOR, optical length, dioptric length and eye power to their behaviours in a uniformly growing eye.
Because the f# of the chick eye was almost constant with age, the retinal blur is expected to be proportional to the amount of MOR. For the different strains considered, MOR showed a similar exponential decrease with age and the change in MOR varied linearly with the amount of retinal blur present over the full age range. The variation of eye power with age was similar when calculated from age dependent schematic eye models and when inferred from optical length and MOR. Changes in optical length and eye power are biphasic, showing different behaviours before and after day 6. The rate of change of eye power becomes increasingly negative between days 0 and 6 during which it is proportional to the amount of retinal blur. Conversely, the change in dioptric length of the eye is relatively constant and larger than the change in eye power until day 6. Beyond day 6, both the rate of change of eye power and of dioptric length increase linearly with time but nonlinearly with retinal blur. These changes in dioptric length and eye power are similar in magnitude. Neither the changes before or after day 6 are predicted by a uniformly expanding eye model.
Emmetropization of the normal chick eye is biphasic due to a change in the variation of eye power around day 6. Before day 6, both changes in eye length and eye power contribute to emmetropization with an almost constant change in the dioptric length of the eye making the larger contribution. However, it is the variable change in eye power over time, proportional to retinal blur, which gives rise to the exponential shape of the decrease in MOR with age. Beyond day 6, changes in both eye power and optical length contribute similarly to emmetropization.
This PDF is available to Subscribers Only