Lag of accommodation does not predict changes in eye growth in chickens

Abstract

Emmetropization is controlled by the defocus in the retinal image. It is a classical problem how changes in focus, introduced by accommodation, are taken into account. We have quantified accommodation errors in chickens wearing negative lenses to find out whether they can predict subsequent eye growth. Two groups of chicks, aged 10 to 13 days, wore lenses (-7D) monocularly for 4-7 days. Fellow eyes remained untreated. Vitreous chamber depth (VCD) was measured in alert hand-held chickens with high resolution, using the Lenstar LS 900 (Haag-Streit, Koeniz, Switzerland). Non-cycloplegic refractive state was measured by automated infrared photoretinoscopy with and without the lenses in place. In group 1 (n = 6), measurements were done 5 times a day to obtain detailed VCD growth curves. In group 2 (n = 10), measurements were only taken twice, at 9 am and 4 pm, to reduce the risk of recovery from induced myopia due to the frequent removal of the lenses. As expected from the negative power of the lenses, refractions measured through the lenses were more hyperopic although not as much as predicted by the lens powers, indicating that chickens partially refocused their eyes by accommodation. Among different animals, accommodation errors varied from 1.1 ± 0.9 to 3.6 ± 1.1D (group 1, mean ± 1 standard deviation) and 0.22 ± 1.25 to 1.72 ± 1.23D (group 2). No correlations were found between the magnitude of the accommodation errors in individual animals and subsequent changes in VCD. With negative lenses, VCD grew both during day and night while fellow eyes grew only during the day but shrank during the night. In conclusion, accommodation errors did not predict future eye growth. This raises the question as to why brief periods of clear vision, when lenses are taken off, have a strong inhibitory effect on myopia development while periods of clear vision due to accommodation have apparently no effect. A possible explanation is that, in addition to retina-driven control of eye growth, there is a second neural pathway for the control of eye growth that carries the signal of accommodation - although it is striking that no neuronal and structural correlate has been identified to date.

Emmetropic, But Not Myopic Human Eyes Distinguish Positive Defocus From Calculated Blur

“…Finally, recent publications argue against a role of accommodation in emmetropization -accommodation appears to be largely ignored. [40][41][42][43] In summary, we believe that our results are not explained by differences in accommodation.…”

Optical mechanisms regulating emmetropisation and refractive errors: evidence from animal models

“…However, accommodative performance before lens treatment did not predict the amount of myopia induced, suggesting that the increased lag was a consequence of myopia, not a cause. Similarly, a recent study in chicks showed that accommodative lag does not predict the magnitude of lens‐induced myopia …”

“…Similarly, a recent study in chicks showed that accommodative lag does not predict the magnitude of lens-induced myopia. 126 On the other hand, Diether and Wildsoet 127 investigated whether accommodation influenced the chick eye's ability to decode focusing errors and the relationship with spatial frequency and contrast. They found that when accommodation was eliminated through ciliary nerve section, decoding of, and compensation for, imposed defocus was impaired.…”

Probing the Potency of Artificial Dynamic ON or OFF Stimuli to Inhibit Myopia Development

“…24 Axial lengths and vitreous chamber depths were measured in alert hand-held chickens, using a low coherence interferometer (Lenstar LS 900; Haag-Streit, Koeniz, Switzerland). 25 Measurements of Human Subfoveal Choroidal Area and Thickness. Subfoveal choroidal area was imaged with SD-OCT (HRAþOCT Spectralis), as previously described.…”