Chicks use changes in luminance and chromatic contrast as indicators of the sign of defocus

In chicks, with hyperopic defocus, the cone contrast comparison will be between S-cones and double cones, since the spectral sensitivity of L- and M-cones is attenuated at short wavelengths.

“In chicks, with hyperopic defocus, the cone contrast comparison will be between the Scones and the double cones, since the spectral sensitivity of the L-and M-cones is attenuated at short wavelengths (Rucker & Wallman, 2008).”

• cites Rucker & Wallman, 2008 sourcePartly supported

  The Introduction describes double cones as sensitive into the short-wavelength region, and Methods (‘Chick cone sensitivity functions’; page unavailable) describes short-wavelength filtering in M- and L-cones, with a sharper cutoff in L-cones than in double cones. But the paper does not establish that hyperopic defocus is assessed by comparing S-cone and double-cone contrast; the Discussion says it did not directly test whether longitudinal chromatic aberration is used in lens compensation. (LLM, conf=0.82)

  Experimental — accuracy not yet measured

Both L- and S-cones are used in lens compensation in chicks.

“Therefore, it is important to note that both L-and S-cones are used in lens compensation in chicks (Rucker & Wallman, 2008).”

• cites Rucker & Wallman, 2008 sourcePartly supported

  The Results report lens compensation in both red and blue light, supporting a role for long- and short-wavelength cone pathways in chicks. But the Methods say the experiment could not distinguish L-cones from double cones or S-cones from UV-cones, so it does not establish that both named cone types individually are used. The indexed copy provides no page numbers for these passages. (LLM, conf=0.86)

  Experimental — accuracy not yet measured

The eye has been shown to be able to use a comparison of the contrast of the red, green, and blue components of the retinal image in order to guide emmetropization.

“In support of this hypothesis, the eye has been shown to be able to use a comparison of the contrast of the red, green, and blue components of the retinal image in order to guide emmetropization (Rucker & Wallman, 2009).”

• cites Rucker & Wallman, 2009 sourceSupported

Spatial simulations of the color signals produced by longitudinal chromatic aberration with hyperopic and myopic defocus can cause compensatory ocular changes in chicks.

“We have previously shown that spatial simulations of the color signals produced by longitudinal chromatic aberration (LCA) with hyperopic and myopic defocus can cause compensatory ocular changes in chicks (Rucker & Wallman, 2009).”

• cites Rucker & Wallman, 2009 sourceSupported

The −15.16 D/mm change in eye length is slightly less than the −18 to −25 D/mm change in vitreous chamber depth found in earlier experiments.

“This is slightly less than the À18 D to À25 D/mm change in vitreous chamber depth found in earlier experiments (Kee, Marzani, & Wallman, 2001;Rucker & Wallman, 2008), probably because the choroidal changes reduced the refractive changes (the correlation between the vitreous chamber depth and refraction was only r 2 ¼ 0.04).”

• cites Kee, Marzani, & Wallman, 2001Not checked — no full text of the source
• cites Rucker & Wallman, 2008 sourceSupported

In chicks, despite sustained refractions over the two-week period of exposures and recovery periods, eye length continued to change in a manner dependent on the illuminant.

“In sum, despite the sustained refractions over the two-week period of exposures and recovery periods, the eye length continued to change in a manner that was dependent on the illuminant.”

In chicks, color flicker produced much greater changes in eye length than luminance flicker.

“Changes in refraction were mainly due to changes in eye length, with color flicker producing much greater changes in eye length than luminance flicker (R/G Color: 102 lm; B/Y Color: 98 lm; LUM: 66 lm).”

In chicks, eye length changes during recovery after luminance flicker were significantly greater than in all other conditions.

“Eye length changes of chicks recovering after being exposed to luminance flicker were significantly greater than in all other conditions (LUM vs R/G Color t-test: p ¼ 0.0009; LUM vs Low LUM t-test: p ¼ 0.007; No Flicker vs LUM t-test: p ¼ 0.0003; Color þ LUM vs R/G Color t-test: p ¼ 0.04).”

In chicks, changes in vitreous chamber depth after flicker exposure were dependent on the illumination condition.

“Changes in vitreous chamber depth were dependent on the illumination condition (ANOVA p ¼ 0.04).”

In chicks, changes in vitreous chamber depth reflected changes in ocular length.

“Changes in vitreous chamber depth reflected the changes in ocular length.”

In chicks, exposure to R/G Color and B/Y Color flicker produced a daily increase in vitreous chamber depth of the right eyes that was 1.68 times that after luminance flicker.

“Exposure to R/G Color flicker and B/Y Color flicker produced a daily increase in vitreous chamber depth of the right eyes, which was 1.68 times (67 6 10 lm and 50 6 9 lm, respectively) that found after exposure to luminance flicker (39 6 8 lm).”

In chicks, if color contrast was present, eye length changes increased compared to all other conditions.

“If color contrast was present, then eye length changes increased compared to all other conditions.”

In chicks, if color contrast was present, vitreous chamber depth increases were greater than if luminance contrast was present.

“If color contrast was present, then vitreous chamber depth increases were greater than if luminance contrast was present (LUM vs Color t-test: p ¼ 0.02).”

In chicks, increases in vitreous chamber depth after No Flicker, Color+LUM, and Low LUM were similar to those after luminance flicker.

“Increases in vitreous chamber depth after exposure to No Flicker, Color þ LUM, and Low LUM conditions (46 6 7 lm; 28 6 5 lm; 42 6 8 lm) were similar to those after exposure to luminance flicker.”

In chicks, eye length changes after flicker exposure were dependent on the illumination condition.

“Eye length changes were dependent on the illumination condition (ANOVA p ¼ 0.004).”

In chicks, exposure to R/G Color or B/Y Color flicker produced almost double the daily change in eye length compared to luminance flicker.

“When the change in eye length is averaged over the two weeks, chicks exposed to R/G Color flicker or B/Y Color flicker showed almost double the daily change in eye length (R/G: 102 6 7 lm”

• Also stated in: § Abstract · plain

  “with color flicker producing much greater changes in eye length than luminance flicker (R/G Color: 102 lm; B/Y Color: 98 lm; LUM: 66 lm).”

In chicks, changes in refraction after flicker exposure were mainly due to changes in eye length.

“Changes in refraction were mainly due to changes in eye length, with color flicker producing much greater changes in eye length than luminance flicker (R/G Color: 102 lm; B/Y Color: 98 lm; LUM: 66 lm).”

The choroidal thinning with luminance flicker was similar to that in the Low LUM condition (−34 ± 8 μm per day).

“For both exposures, luminance flicker caused a mean choroidal thinning in the right eyes of À23 6 4 lm per day, similar to the choroids in the Low LUM condition (À34 6 8 lm per day).”

Thirty-seven percent of the change in refraction was due to changes in eye length (r2 = 0.37) that occurred with the illumination condition.

“Thirty-seven percent of the change in refraction was due to changes in eye length (r 2 ¼ 0.37) that occurred with the illumination condition.”

During recovery, there was a general increase in eye length in all conditions.

“During recovery, there was a general increase in eye length in all conditions, although chicks exposed to luminance flicker showed a much greater rate of ocular elongation.”

Choroidal increases in the other conditions were very small, ranging from 8-10 μm per day.

“Choroidal increases in the other conditions were very small, ranging from 8-10 lm per day, indicating that the choroidal changes induced during the exposure were sustained during recovery.”

The changes in eye length after color flicker were much greater than normal.

“The myopic shift in refraction after exposure to color flicker was similar to that seen in normal emmetropization, but the changes in eye length were much greater than normal.”

Choroidal changes were dependent on the illumination condition (ANOVA p = 0.006).

“Nevertheless, the choroidal changes (Figure 7) were still dependent on the illumination condition (ANOVA p ¼ 0.006).”

The eye length continued to change in a predictable manner after exposure to color and luminance flicker and during the recovery periods.

“However, the eye length continued to change in a predictable manner after exposure to color and luminance flicker and during the recovery periods, suggesting the eye length was still responding to an error signal.”

Choroids thinned in response to exposure to luminance flicker instead of the predicted thickening.

“Choroids thinned in response to exposure to luminance flicker instead of the predicted thickening.”

The hyperopic shift in refraction seen with luminance flicker was a shift in the opposite direction than that of normal emmetropization.

“The hyperopic shift in refraction seen with luminance flicker was especially significant because it was a shift in the opposite direction than that of normal emmetropization.”

Luminance flicker produced a hyperopic shift in refraction.

“Luminance flicker produced a hyperopic shift in refraction, while color flicker produced a myopic shift in refraction, and both refractive shifts occurred as a result of changes in eye length.”

When color and luminance contrast were combined, as in B/Y Color and Color + LUM, the refractive changes were similar.

“When color and luminance contrast were combined, as in B/Y Color and Color þ LUM, the refractive changes were similar, but the eye length changes were dependent on the relative amounts of color and luminance contrast.”

Luminance flicker caused a mean choroidal thinning in the right eyes of −23 ± 4 μm per day.

“For both exposures, luminance flicker caused a mean choroidal thinning in the right eyes of À23 6 4 lm per day, similar to the choroids in the Low LUM condition (À34 6 8 lm per day).”

Color contrast prevented the predicted choroidal thinning.

“Conversely, color contrast prevented the predicted choroidal thinning.”

The eye length changes in Color + LUM were smaller than those in B/Y Color.

“However, the eye length changes in Color þ LUM were smaller than those in B/ Y Color, probably because of the weaker color signal in Color þ LUM than in B/Y.”

There was no significant difference in anterior chamber depth between conditions.

“There was no significant difference in the anterior chamber depth between conditions.”

The eye length changes in combined color and luminance conditions were dependent on the relative amounts of color and luminance contrast.

“When color and luminance contrast were combined, as in B/Y Color and Color þ LUM, the refractive changes were similar, but the eye length changes were dependent on the relative amounts of color and luminance contrast.”

Luminance flicker, high or low contrast, caused thinning of the choroid when compared to all other conditions.

“Luminance flicker, high or low contrast, caused thinning of the choroid when compared to all other conditions (LUM vs R/G Color t-test: p ¼ 0.002; LUM vs Color þ LUM t-test: p ¼ 0.008; Low LUM vs R/G Color: t-test: p ¼ 0.0006; Low LUM vs Color þ LUM t-test: p ¼ 0.009).”

In chicks, large refractive changes occurred during the first exposure and were then sustained through subsequent changes in the visual environment despite a four-day recovery period between the exposures.

“Large refractive changes occurred during the first exposure, which were then sustained through subsequent changes in the visual environment despite a fourday recovery period between the exposures (Figure 5).”

In chicks, eye length changes were remarkably repeatable across the two exposures on subsequent weeks.

“These changes were remarkably repeatable, as shown by the two exposures on subsequent weeks.”

Color flicker caused no change in choroidal thickness in R/G Color, No Flicker, B/Y Color, and Color + LUM conditions.

“Color flicker, in eyes exposed to R/G Color, No Flicker, B/Y Color, and Color þ LUM conditions, caused no change in choroidal thickness (À4 6 3 lm; À9 6 6 lm; À10 6 4 lm; À3 6 5 lm, per day respectively).”

There was no significant difference in choroidal thickening between conditions while in the brooder.

“There was no significant difference in choroidal thickening between conditions while in the brooder.”

In chicks during the first week, the hyperopic shift in the right eyes seen in LUM was significantly more hyperopic than in R/G Color, Low LUM, and No Flicker.

“During the first week, the hyperopic shift in the right eyes seen in LUM was significantly more hyperopic than in R/G Color (p ¼ 0.006), Low LUM (p ¼ 0.04), and No Flicker (p ¼ 0.02).”

In chicks, none of the refractive changes in Week 2 were significant since the refractions induced in Week 1 were sustained.

“None of the refractive changes in Week 2 were significant since the refractions induced in Week 1 were sustained.”

The myopic shift in refraction after exposure to color flicker was similar to that seen in normal emmetropization.

“The myopic shift in refraction after exposure to color flicker was similar to that seen in normal emmetropization, but the changes in eye length were much greater than normal.”

Choroidal thickness did not respond to luminance and color flicker in a way suggesting that luminance flicker simulated myopia or color flicker hyperopia.

“In contrast to the refractive error and eye length responses, the choroidal thickness did not respond to luminance and color flicker in a way that would suggest that luminance flicker simulated myopia or color flicker hyperopia.”

Color flicker produced a myopic shift in refraction.

“Luminance flicker produced a hyperopic shift in refraction, while color flicker produced a myopic shift in refraction, and both refractive shifts occurred as a result of changes in eye length.”

The anterior chamber depth increased in all conditions over the three-day exposure period during both weeks.

“The anterior chamber depth increased in all conditions over the three-day exposure period during both weeks.”

The change in refraction was associated with a −15.16 D/mm change in eye length.

“The change in refraction was associated with a À15.16 D/mm change in eye length.”

In chicks during the first exposure, changes in refraction were dependent on the illumination condition.

“During the first exposure, changes in refraction were dependent on the illumination condition (ANOVA p ¼ 0.007).”

Chicks exposed to luminance flicker showed a much greater rate of ocular elongation during recovery.

“During recovery, there was a general increase in eye length in all conditions, although chicks exposed to luminance flicker showed a much greater rate of ocular elongation.”

There was greater choroidal thinning in Low LUM during the exposure.

“Refractions were similar in both conditions after the first exposure, but hyperopia was only maintained during the recovery period in the Low LUM condition, and there was greater choroidal thinning in Low LUM during the exposure.”

Hyperopia was only maintained during the recovery period in the Low LUM condition.

“Refractions were similar in both conditions after the first exposure, but hyperopia was only maintained during the recovery period in the Low LUM condition, and there was greater choroidal thinning in Low LUM during the exposure.”

When color and luminance contrast were available, the eye was able to compensate for up to 88% of the eye length changes by changing choroidal thickness.

“When color and luminance contrast were available, the eye was able to compensate for up to 88% of the eye length changes by changing choroidal thickness.”

Refractions were similar in Low LUM and Color + LUM conditions after the first exposure.

“Refractions were similar in both conditions after the first exposure, but hyperopia was only maintained during the recovery period in the Low LUM condition, and there was greater choroidal thinning in Low LUM during the exposure.”

There was a strong correlation between eye length changes and choroidal changes.

“There was a strong correlation between eye length changes and choroidal changes that may explain the sustained refractions.”

When spatial cues are reduced with dim light or astigmatic lenses, the eye can use other color cues that are present only in white light.

“These results suggest that when the spatial cues are reduced with dim light or astigmatic lenses, then the eye can use other color cues that are present only in white light.”

The chick eye can differentiate between hyperopic and myopic defocus on the basis of the effects of change in luminance or color contrast.

“Our results support the hypothesis that the eye can differentiate between hyperopic and myopic defocus on the basis of the effects of change in luminance or color contrast.”

With longitudinal chromatic aberration, short-wavelength blue light is dispersed more strongly than long-wavelength red light through the eye's optical system.

“With longitudinal chromatic aberration, short-wavelength blue light is dispersed more strongly than longwavelength red light through the eye's optical system (Bedford & Wyszecki, 1957).”

• cites Bedford & Wyszecki, 1957 sourceNot checked — no full text of the source

Flicker exposure does not cause a sudden increase in eye growth when the flicker stops.

“We conclude that flicker exposure does not cause a sudden increase in eye growth when the flicker stops.”

• AssumptionRests on an assumption: A brief period of LUM flicker (1.5 days) is insufficient to cause refractive and eye length changes.

The relative difference in cone contrast produced by longitudinal chromatic aberration can provide an indicator of the sign of defocus even under open-loop or brief viewing conditions.

“Thus, the relative difference in cone contrast produced by longitudinal chromatic aberration can provide an indicator of the sign of defocus even under open-loop or brief viewing conditions.”

Cone contrast varies with defocus as a result of longitudinal chromatic aberration.

“Cone contrast varies with defocus as a result of longitudinal chromatic aberration.”

Because L- and M-cones are responsible for detection of small changes in luminance, a decrease in L- and M-cone contrast on either side of the in-focus plane produces a symmetrical decrease in the signal for luminance contrast.

“Because the L-and M-cones are responsible for the detection of small changes in luminance (Vk function), a decrease in Land M-cone contrast on either side of the in-focus plane produces a symmetrical decrease in the signal for luminance contrast.”

The presence of color contrast inhibited the strong hyperopic response seen with LUM.

“Both conditions produced only very small refractive shifts, suggesting that the presence of color contrast inhibited the strong hyperopic response seen with LUM.”

Choroidal changes probably reduced the refractive changes.

“This is slightly less than the À18 D to À25 D/mm change in vitreous chamber depth found in earlier experiments (Kee, Marzani, & Wallman, 2001;Rucker & Wallman, 2008), probably because the choroidal changes reduced the refractive changes (the correlation between the vitreous chamber depth and refraction was only r 2 ¼ 0.04).”

Our results support the hypothesis that the eye can differentiate between hyperopic and myopic defocus based on the effects of changes in luminance or color contrast.

“Our results support the hypothesis that the eye can differentiate between hyperopic and myopic defocus based on the effects of changes in luminance or color contrast.”

Choroidal thickness changes in response to imposed myopic or hyperopic defocus occur within an hour.

“Because choroidal thickness changes in response to imposed myopic or hyperopic defocus occur within an hour (Zhu, Park, Winawer, & Wallman, 2005), we reasoned that if the choroidal changes were a response to the flicker itself, we should see a similarly rapid response”

• cites Zhu, Park, Winawer, & Wallman, 2005 sourceNot checked — no full text of the source

The choroidal changes induced during the exposure were sustained during recovery.

“Choroidal increases in the other conditions were very small, ranging from 8-10 lm per day, indicating that the choroidal changes induced during the exposure were sustained during recovery.”

Flicker produced refractive changes by causing changes in eye length.

“To summarize, flicker produced refractive changes by causing changes in eye length.”

Chicks have tetrachromatic color vision.

“Chicks are a good animal model for the role of color in emmetropization because they have tetrachromatic color vision (Osorio, Vorobyev, & Jones, 1999).”

• cites Osorio, Vorobyev, & Jones, 1999 sourceNot checked — no full text of the source

Both refractive shifts occurred as a result of changes in eye length.

“Luminance flicker produced a hyperopic shift in refraction, while color flicker produced a myopic shift in refraction, and both refractive shifts occurred as a result of changes in eye length.”

The eye length was still responding to an error signal after exposure to color and luminance flicker and during recovery.

“However, the eye length continued to change in a predictable manner after exposure to color and luminance flicker and during the recovery periods, suggesting the eye length was still responding to an error signal.”

These results suggest that eye growth is sensitive to the relative amounts of luminance and chromatic contrast.

“Either way, these results suggest that eye growth is sensitive to the relative amounts of luminance and chromatic contrast.”

It is unlikely that the choroidal responses in this experiment were direct responses to the flickering light because no choroidal changes were seen after three hours of flicker exposure.

“We find it unlikely that the choroidal responses in this experiment were direct responses to the flickering light because we saw no choroidal changes after three hours of flicker exposure.”

These results may indicate that the choroidal response responds to different stimuli through different neural pathways than the eye length response.

“These results may indicate that the choroidal response responds to different stimuli through different neural pathways than the eye length response.”

These differences indicate that the eye was able to detect the presence of the small amount of color in the combined Color + LUM stimulus.

“These differences indicate that the eye was able to detect the presence of the small amount of color in the combined Color þ LUM stimulus and that the eye was not simply responding to the reduction in luminance contrast.”

The adjustment of the choroid in response to luminance and chromatic contrast appears to be an almost perfect method of maintaining refraction despite perturbations in the visual environment.

“The adjustment of the choroid in response to luminance and chromatic contrast appears to be an almost perfect method of maintaining refraction despite perturbations in the visual environment, and probably reflects the faster initial choroidal response to induced refractive errors.”

The increase in eye length in chicks that had been exposed to luminance flicker was most likely compensating for the previously induced hyperopia.

“The increase in eye length in chicks that had been exposed to luminance flicker was most likely compensating for the previously induced hyperopia, but since the refraction remained fairly constant, other components such as choroidal thickness must also be changing.”

The eye was not simply responding to the reduction in luminance contrast in the Color + LUM condition.

“These differences indicate that the eye was able to detect the presence of the small amount of color in the combined Color þ LUM stimulus and that the eye was not simply responding to the reduction in luminance contrast.”

The correlation between eye length changes and choroidal changes may explain the sustained refractions.

“There was a strong correlation between eye length changes and choroidal changes that may explain the sustained refractions.”

The chick eye could infer whether it was myopic or hyperopic by determining whether changes in either color or luminance contrast were stronger when the plane of focus shifted.

“The chick eye could infer whether it was myopic or hyperopic by determining whether changes in either color or luminance contrast were stronger when the plane of focus shifted.”

• AssumptionThe authors state this as an assumption: The environment of most neonates does not change dramatically over time.

Our results suggest that the chick eye uses a color signal to guide emmetropization.

“Our results suggest that the chick eye uses a color signal to guide emmetropization.”

The results of this experiment present more evidence of the dissociation of the choroidal and eye-length responses that have been found in earlier experiments.

“The results of this experiment present more evidence of the dissociation of the choroidal and eye-length responses that have been found in earlier experiments.”

Other components such as choroidal thickness must also be changing in chicks exposed to luminance flicker during recovery.

“The increase in eye length in chicks that had been exposed to luminance flicker was most likely compensating for the previously induced hyperopia, but since the refraction remained fairly constant, other components such as choroidal thickness must also be changing.”

The adjustment of the choroid probably reflects the faster initial choroidal response to induced refractive errors.

“The adjustment of the choroid in response to luminance and chromatic contrast appears to be an almost perfect method of maintaining refraction despite perturbations in the visual environment, and probably reflects the faster initial choroidal response to induced refractive errors.”