Transient increases in choroidal thickness are consistently associated with brief daily visual stimuli that inhibit ocular growth in chicks (original) (raw)
Related papers
Experimental Eye Research, 2017
It is generally accepted that myopic defocus is a more potent signal to the emmetropization system than hyperopic defocus: one hour per day of myopic defocus cancels out 11 hours of hyperopic defocus. However, we have recently shown that the potency of brief episodes of myopic defocus at inhibiting eye growth depends on the time of day of exposure. We here ask if this will also be true of the responses to brief periods of hyperopic defocus: may integration of the signal depend on time of day? If so, are the rhythms in axial length and choroidal thickness altered? Hyperopic defocus: Birds had one eye exposed to hyperopic defocus by the wearing of −10D lenses for 2 or 6
Experimental Eye Research, 2017
Animal models have shown that myopic defocus is a potent inhibitor of ocular growth: brief (1-2 hours) daily periods of defocus are sufficient to counter the effects of much longer periods of hyperopic defocus, or emmetropic vision. While the variables of duration and frequency have been well-documented with regard to effect, we ask whether the efficacy of the exposures might also depend on the time of day that they are given. We also ask whether there are differential effects on the rhythms in axial length or choroidal thickness. 2-week-old chickens were divided into 2 groups: (1) "2-hr lens-wear". Chicks wore monocular +10D lenses for 2 hours per day for 5 days at one of 3 times of day: 5:30 am (n=11), 12 pm (n=8) or 7:30 pm (n=11). (2) "2-hr minus lens-removal". Chicks wore monocular −10D lenses continually for 7 days, except for a 2-hr period when lenses were removed; the removal occurred at one of 2 times: 5:30 am (n=8) or 7:30 pm (n=8). Both paradigms exposed eyes to brief myopic defocus that differed in its magnitude, and in the visual experience for the rest of the day. High frequency A-scan ultrasonography was done at the start of the experiment; on the last day, it was done at 6-hr intervals, starting at noon, over 24-hr, to assess rhythm parameters. Refractive errors were measured using a Hartinger's refractometer at the end.
Experimental Eye Research, 2002
When form deprived, young chicks rapidly develop axial myopia, from which they recover if the treatment is ceased at a suf®ciently early age. The increased axial growth of the eye is accompanied by choroidal thinning and decreased choroidal blood¯ow (ChBF). In contrast, during the early part of the recovery process, the choroid thickens, shifting the retina towards the new plane of focus. Little information is available about ChBF during recovery from myopia. Because of the possibility that choroidal thickening during recovery from myopia might be driven by an increase in ChBF, the temporal relationship of ChBF and choroidal thickness changes was examined during such recovery. White Leghorn chicks were form deprived from 3 days of age for 2±3 weeks using detachable plastic diffusers. Axial ocular dimensions, including choroidal thickness, were then measured by high frequency A-scan ultrasonography at various times after the diffusers were removed up to 240 hr. ChBF was measured transclerally immediately following the A-scan ultrasonography, using laser Doppler owmetry. In the chicks measured immediately after diffuser removal, the vitreous chamber was 29. 9 % longer, the choroid was 6. 4 % thinner and ChBF was 13. 7 % less in the treated than in the non-treated control eyes. These changes are characteristic of myopic chick eyes and are reversible in young eyes. Thus, in chicks examined 7 hr after diffuser removal, the ChBF in recovering eyes was now greater than that in control eyes. This ChBF increase peaked about 19 hr after the diffusers were removed. The mean increase in ChBF in treated eyes for the 7±30 hr monitoring period was 187 %, relative to control eyes. ChBF in the treated eyes gradually returned to the control level after this time. By contrast to the early, transient increase in ChBF, signi®cant choroidal thickening was not observed in treated eyes until 30 hr after diffuser removal, and continued to increase relative to control eyes over the remainder of the monitoring period, reaching a ®nal mean value of 182 %. This study demonstrates, in chick eyes recovering from form deprivation myopia, large increases in ChBF that preceded increases in choroidal thickness and were also more transient than the latter. These results raise the possibility that the increase in ChBF may trigger or even drive the subsequent onset of choroidal expansion, perhaps by facilitating the ®lling of the choroidal lymphatic lacunae that are well developed in the avian eye.
The duration of normal visual exposure necessary to prevent form deprivation myopia in chicks
Vision Research, 1995
The aim of this study was to determine the minimum daily period of exposure to normal visual stimulation required to prevent occlusion induced myopia in chicks. Chicks were treated with monocular translucent occlusion in a 12 hr light]12 hr dark cycle. Occluders were removed for 0 (constant occlusion), 15, 20, 30, 40, 60, 75, 90, 120, 150, 240 or 720 (no occlusion) minutes each day for either 2 or 3 weeks. Fellow eyes and the eyes of normal chicks (bilaterally unoccluded) were used as controls. Occlusion-induced myopia and axial elongation were found to decrease significantly (P<0.01) with increasing daily exposure to normal visual stimulation. Application of a time series equation to the data estimates that 30 and 130 min of normal visual exposure per day reduces myopia by 50 and 95% respectively. This study demonstrates that the regulation of ocular growth is affected strongly by short periods of normal visual stimulation in the presence of long periods of abnormal stimulation.
Optometry and Vision Science, 2004
Purpose. Studies in humans and primates suggest that early visual experience may influence eye growth and refractive development later in life. In this study, we asked whether experimentally-induced myopia in 1-week-old chicks influences the responsiveness to form deprivation at a later age (4 weeks old). Methods. A group of White Leghorn chicks ("twice deprived," N ؍ 12) were monocularly deprived of form vision with white translucent diffusers at 3 days of age for 4 days. The diffusers were then removed, and the chicks were allowed 3 weeks of normal vision to age 27 days before being deprived again for 4 days. Another group of chicks ("once deprived," N ؍ 9) were monocularly deprived of form vision at age 27 days for 4 days. Refractive errors, corneal curvatures, and axial ocular dimensions were measured by retinoscopy, infrared videokeratometry, and A-scan ultrasonography, respectively. Measurements were performed daily during the periods of deprivation and at approximately 3-day intervals in between treatments and after the final treatment period. Results. The magnitude of the form-deprivation myopia induced by 4 days of deprivation at 27 days of age was significantly smaller than that induced by the same treatment at 3 days of age (؊4.1 vs. ؊9.8 D; paired t-test, p < 0.01). This difference in induced myopia reflects optical scaling with increasing eye size because the deprivation-induced changes in vitreous chamber depth were not significantly different for the two deprivation periods (0.37 vs. 0.35 mm, paired t-test, p ؍ 0.65). The induction of myopia at the younger age did not affect the susceptibility to form-deprivation myopia at the older age; there was no difference in the response to form deprivation at the older age between the once-deprived and twice-deprived groups (؊3.5 vs. ؊4.1 D; unpaired t-test, p ؍ 0.50). There was also a significant correlation between the amount of axial elongation induced in individual eyes during the first and second periods of deprivation (r ؍ 0.631, p < 0.05). Conclusions. The induction of form-deprivation myopia at a young age does not affect the response to form deprivation at a later age. The significant correlation between the axial elongation induced in individual eyes over the two successive periods of deprivation suggests individual differences, possibly genetic in origin, in the susceptibility to form-deprivation myopia in chicks.
Vision Research, 1997
The aim of this study was to determine whether an integrator of neural activity influences the amount of myopia and axial elongation resulting from deprivation of form vision. The effects on ocular parameters of a continuous period of 30 min per day of normal vision was compared to two exposures of 15 min duration each, or three exposures of 10 min each. For the remaining time, chicks had monocular translucent occlusion in a 12 hr light/12 hr dark diurnal cycle, for either 2 or 3 weeks. Fellow eyes and the eyes of bilaterally unoccluded chicks were used as controls. We found that several short periods of normal visual stimulation per day were more effective in preventing the development of form deprivation myopia and axial elongation than was one single period of the same total duration, after both 2 and 3 weeks of treatment. This study suggests that the level of neural activity in the retina may have a cumulative effect in influencing ocular growth. 0 1997
Journal of Comparative Physiology A, 2005
Eyes of young chickens show diurnal oscillations in axial length and choroidal thickness that are out of phase. In eyes responding to myopic defocus induced by prior form deprivation, the two rhythms shift into phase. In order to elucidate the possible role for these rhythms in ocular growth regulation, they were measured under visual conditions that altered ocular growth rate. (1) Form deprivation to myopic defocus. Eyes of chicks were monocularly deprived for 5 days. Diffusers were removed. (2) Myopic defocus to hyperopic defocus. Eyes wore positive lenses for 6 days; lenses were removed. (3) Hyperopic to myopic defocus. Eyes wore negative lenses for 5 days; lenses were removed. Eyes were measured using A-scan ultrasonography at 6-h intervals for 24 h over various cycles. The rhythms shift into phase in eyes slowing their growth in response to myopic defocus in all three conditions. This shift precedes by 1 day the decrease in growth in both lens conditions, and is concomitant with it in recovering eyes. There is a positive correlation between the phase difference and growth rate. In conclusion, there is a consistent association between growth rate and phase relationships of the rhythms in axial elongation and choroidal thickness.
Scientific Reports, 2019
The amount of compensation to lens-induced defocus of different sign is not symmetric. Tree shrews and primates compensate for imposed hyperopic defocus more completely than to equal amounts of imposed myopic defocus 27,30. However, myopic defocus dominates hyperopic defocus when the stimuli are presented individually 31,32 , successively 33-35 or simultaneously in various species including human 36-39. A relatively small amount of alternated or simultaneous myopic defocus can cancel the compensation of greater amounts of hyperopic defocus 34,36,40,41 , and interrupting hyperopic defocus for even brief periods of time is also known to reduce myopia development in chicks, tree shrews and primates 26,35,42. The sign, frequency, and duration of imposed defocus are important factors that affect compensatory eye growth and refractive change, and may represent how real-world visual experience influences eye growth and the development of refractive state 43. Studies of the temporal integration of defocus signals provide evidence for non-linear integration of the visual signals 31,40,44,45. For example, in terms of the sign of defocus, the retina is more sensitive to myopic than to hyperopic defocus as shown by the preferred compensation to myopic defocus when both myopic and hyperopic defocus are presented simultaneously 36-39. In terms of temporal frequency, multiple brief episodes that stimulate eye growth are more effective than longer less frequent episodes of the same total duration 44,46-a total of 28 mins/day of hyperopic defocus given 2 min/hr can induce increased eye growth in chick eyes whereas the same treatment duration given in 7 minute-periods every 3 hrs is not effective 44. The time required to integrate the visual signal for compensatory eye growth depends on the sign of the defocus. In chicks, the axial and choroidal responses to either hyperopic or myopic defocus rises and saturates in less than 5 minutes 40. However, the effect of myopic defocus takes longer to decline (24 hrs) than the effect of hyperopic defocus (20 mins), and the choroidal response to imposed defocus is also asymmetrical 40. In guinea pigs, 30 mins of exposure to hyperopic defocus triggers 50% of the maximum myopic growth, and episodes of unrestricted vision as brief as 30 mins can interrupt the response 33. Macaques and tree shrews show reduced myopia development when imposed hyperopic defocus from negative lenses is alternated with unrestricted vision compared with alternation with positive lens defocus or full time wear 34,35. How the eye integrates retinal defocus signals to control eye growth and refractive state is important for optimizing optical treatments of myopia 47. In this study using a non-human primate (NHP) model of eye growth and myopia, we examined the effect of interrupting imposed hyperopic defocus with short daily periods of clear vision at either the beginning of treatment or later in treatment. We did this by evaluating the effect that the interruptions had on eye growth, central and peripheral refractive development, and other biometric changes, while measuring and controlling the visual experience and refractive state during the interruption periods.
Investigative ophthalmology & visual science, 2014
Bifocal contact lenses were used to impose hyperopic and myopic defocus on the peripheral retina of marmosets. Eye growth and refractive state were compared with untreated animals and those treated with single-vision or multizone contact lenses from earlier studies. Thirty juvenile marmosets wore one of three experimental annular bifocal contact lens designs on their right eyes and a plano contact lens on the left eye as a control for 10 weeks from 70 days of age (10 marmosets/group). The experimental designs had plano center zones (1.5 or 3 mm) and +5 diopters [D] or -5 D in the periphery (referred to as +5 D/1.5 mm, +5 D/3 mm and -5 D/3 mm). We measured the central and peripheral mean spherical refractive error (MSE), vitreous chamber depth (VC), pupil diameter (PD), calculated eye growth, and myopia progression rates prior to and during treatment. The results were compared with age-matched untreated (N=25), single-vision positive (N=19), negative (N=16), and +5/-5 D multizone len...
Aberrations of chick eyes during normal growth and lens induction of myopia
Journal of Comparative Physiology A, 2006
Understanding the control of eye growth may lead to the prevention of nearsightedness (myopia). Chicks develop refractive errors in response to defocusing lenses by changing the rate of eye elongation. Changes in optical image quality and the optical signal in lens compensation are not understood. Monochromatic ocular aberrations were measured in 16 chicks that unilaterally developed myopia in response to unilateral goggles with À15D lenses and in 6 chicks developing naturally. There is no significant difference in higherorder root mean square aberrations (RMSA) between control eyes of the goggled birds and eyes of naturally developing chicks. Higher-order RMSA for a constant pupil size exponentially decreases in the chick eye with age more slowly than defocus. In the presence of a defocusing lens, the exponential decrease begins after day 2. In goggled eyes, asymmetric aberrations initially increase significantly, followed by an exponential decrease. Higher-order RMSA is significantly higher in goggled eyes than in controls. Equivalent blur, a new measure of image quality that accounts for increasing pupil size with age, exponentially decreases with age. In goggled eyes, this decrease also occurs after day 2. The fine optical structure, reflected in higher-order aberrations, may be important in understanding normal development and the development of myopia.