Temporal properties of the myopic response to defocus in the guinea pig
Article first published online: 12 MAY 2013
Ophthalmic & Physiological Optics © 2013 The College of Optometrists
Ophthalmic and Physiological Optics
Special Issue: Understanding & Controlling Myopia - Where We Are Now. A compilation to honour the research achievements and mark the passing of Josh Wallman
Volume 33, Issue 3, pages 227–244, May 2013
How to Cite
Temporal properties of the myopic response to defocus in the guinea pig. Ophthalmic Physiol Opt 2013; 33: 227–244. doi: 10.1111/opo.12062, , , .
- Issue published online: 12 MAY 2013
- Article first published online: 12 MAY 2013
- Manuscript Accepted: 14 MAR 2013
- Manuscript Received: 29 NOV 2012
- International Sciences Linkage. Grant Number: CG120160
- guinea pig;
- hyperopic defocus;
- inhibition of myopia;
- refractive error;
Hyperopic defocus induces myopia in all species tested and is believed to underlie the progression of human myopia. We determined the temporal properties of the effects of hyperopic defocus in a mammalian eye.
In Experiment 1, the rise and decay time of the responses elicited by hyperopic defocus were calculated in 111 guinea pigs by giving repeated episodes of monocular −4 D lens wear (from 5 to 6 days of age for 12 days) interspersed with various dark intervals. In Experiment 2, the decay time constant was calculated in 152 guinea pigs when repeated periods of monocular −5 D lens-wear (from 4 days of age for 7 days) were interrupted with free viewing periods of different lengths. At the end of the lens-wear period, ocular parameters were measured and time constants were calculated relative to the maximum response induced by continuous lens wear.
When hyperopic defocus was experienced with dark intervals between episodes, the time required to induce 50% of the maximum achievable myopia and ocular elongation was at most 30 min. Saturated 1 h episodes took at least 22 h for refractive error and 31 h for ocular length, to decay to 50% of the maximum response. However, the decay was an order of magnitude faster when hyperopic defocus episodes were interrupted with a daily free viewing period, with only 36 min required to reduce relative myopia and ocular elongation by 50%.
Hyperopic defocus causes myopia with brief exposures and is very long lasting in the absence of competing signals. However, this myopic response rapidly decays if interrupted by periods of ‘normal viewing’ at least 30 min in length, wherein ocular growth appears to be guided preferentially by the least amount of hyperopic defocus experienced.