Aberrations of chick eyes during normal growth and lens induction of myopia

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 −15D lenses and in 6 chicks developing naturally. There is no significant difference in higher-order 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.     

Chick eye optics: zero to fourteen days

Ocular dimensions and refractive state data for chicks 0 to 14 days of age were obtained from 234 untreated control eyes of birds treated unilaterally in previous work involving various defocussing lenses and/or translucent goggles. Refractive state and corneal curvatures were measured in vivo by retinoscopy and ophthalmometry respectively. Intraocular dimensions were measured by A-scan ultrasonography, after which the eyes were removed, weighed and measured. In some cases (n=52) intraocular dimensions and lens curvatures were obtained from frozen sections of enucleated eyes. The hyperopia of hatchling chicks (+6.5+4.0 D) initially decreases rapidly and then more gradually to + 2.0 ± 0.5 D by 16 days. The distribution of refractive errors is very broad at Day 0, but becomes leptokurtotic, with a slight myopic skew, by Day 14. Corneal radius is constant for the first four days, possible as a result of pre-hatching lid pressure, and then increases linearly, as do all lens dimensions, axial diameter and equatorial diameter. Schematic eyes were developed for Days 0, 7, and 14.     

Animal Models of Myopia: Learning How Vision Controls the Size of the Eye

As they grow up, approximately 25% of children in the United States become myopic (nearsighted). A much smaller fraction become significantly hyperopic (farsighted), while the majority develop little or no refractive error and are emmetropic. The causes of refractive error, especially myopia, have been the subject of debate for more than a century. Some have held that myopia is primarily an inherited disorder, and others, that myopia is caused by protracted near work and, especially, by accommodation during protracted near work. It has not been possible, based solely on clinical observations, to resolve the relative roles of heredity versus environment in the development of refractive error. In the mid-1970s, several animal models were developed to study the mechanisms underlying refractive error. Using animal models, it was found that the visual environment exerts a powerful influence on refractive state by controlling the axial length of the eye during the postnatal developmental period. Although several species have been examined, three have emerged as primary models and have played complementary roles: tree shrews (mammals closely related to primates), chicks, and monkeys. Each has advantages and disadvantages. Collectively, research on animal models has provided evidence on three issues, namely that (1) the visual environment can produce refractive error; (2) an emmetropization mechanism normally guides eyes to low refractive error; and (3) under-accommodation, rather than excessive accommodation, may cause myopia. Two decades of research on animal models have provided criteria that may be used to evaluate the usefulness of additional species as models of emmetropization.     

Visual-optical characteristics of caged and semifree-ranging monkeys

Five species of macaques and one species of mangabey comprising a total of 324 monkeys (132 males and 192 females) were given visual examinations which included measures of corneal curvature, depth of the anterior chamber, thickness of the lens, depth of the vitreous chamber, total axial length, total power of the eye and intraocular pressure as well as the refractive error of eye under cycloplegia in the anesthetized monkey. Cercocebus and Macaca mulatta demonstrated the greatest amount of myopia and Macaca fascicularis the least, with M. speciosa, M. fuscata, and M. nemestrina in order between these extremes. The M. nemestrina eye approximates that of the chimpanzee in size and relationship of the components. The findings indicate that males have larger eyes than females, the curvature of the cornea decreases as the axial length increases, and there is a close relationship between the length of the eye and the amount of myopic refractive error. There is some evidence that amount of myopia and the percentage of animals showing a myopic refractive error are related to the visual conditions and the behavior patterns of the different species.     

A detailed paraxial schematic eye for the White Leghorn chick

We studied the normal ocular development of the chick (Gallus gallus domesticus, White Leghorn) up to 15 days of age using both longitudinal and cross-sectional methods. The change in refractive error, corneal curvature and axial ocular distances were used to construct schematic eyes. Equations are presented which allow prediction of refractive error changes associated with changes in vitreous chamber depth. The mean refractive error was +3.2 D at hatching, which reduced by 66% over the first 3 days and stabilized by 11 days of age. The lens thickened and the anterior chamber deepened from hatching, but vitreal elongation and corneal flattening were delayed until after the first 3 days, suggesting that normal eye growth may be initially inhibited or inactive during an initial emmetropization period, and subsequently activated in response to myopic defocus arising from the continually expanding lens. Finally, when compared with published data on other chick strains, we find differences in the degree of hyperopia at hatching due to differences in lens thickness. However, the rate of ocular and vitreal expansion and the developmental changes in corneal power are similar, making the schematic eyes presented here generally applicable to different strains of chickens.     

Wnt Signaling in Form Deprivation Myopia of the Mice Retina

Background

The canonical Wnt signaling pathway plays important roles in cellular proliferation and differentiation, axonal outgrowth, cellular maintenance in retinas. Here we test the hypothesis that elements of the Wnt signaling pathway are involved in the regulation of eye growth and prevention of myopia, in the mouse form-deprivation myopia model.

Methodology/Principal Findings

(1) One hundred twenty-five C57BL/6 mice were randomly distributed into form-deprivation myopia and control groups. Form-deprivation myopia (FDM) was induced by suturing the right eyelid, while the control group received no treatment. After 1, 2, and 4 weeks of treatment, eyes were assessed in vivo by cycloplegic retinoscopic refraction and axial length measurement by photography or A-scan ultrasonography. Levels of retinal Wnt2b, Fzd5 and β-catenin mRNA and protein were evaluated using RT-PCR and western blotting, respectively. (2) Another 96 mice were divided into three groups: control, drugs-only, and drugs+FDM (by diffuser). Experimentally treated eyes in the last two groups received intravitreal injections of vehicle or the proteins, DKK-1 (Wnt-pathway antagonist) or Norrin (Wnt-pathway agonist), once every three days, for 4 injections total. Axial length and retinoscopic refraction were measured on the 14th day of form deprivation.Following form-deprivation for 1, 2, and 4 weeks, FDM eyes had a relatively myopic refractive error, compared with contralateral eyes. There were no significant differences in refractive error between right and left eye in control group. The amounts of Wnt2b, Fzd5 and β-catenin mRNA and protein were significantly greater in form-deprived myopia eyes than in control eyes.DKK-1 (antagonist) reduced the myopic shift in refractive error and increase in axial elongation, whereas Norrin had the opposite effect in FDM eyes.

Conclusions/Significance

Our studies provide the first evidence that the Wnt2b signaling pathway may play a role in the development and progression of form-deprivation myopia, in a mammalian model.     

Visual acuity measures do not reliably detect childhood refractive error--an epidemiological study

Purpose

To investigate the utility of uncorrected visual acuity measures in screening for refractive error in white school children aged 6-7-years and 12-13-years.

Methods

The Northern Ireland Childhood Errors of Refraction (NICER) study used a stratified random cluster design to recruit children from schools in Northern Ireland. Detailed eye examinations included assessment of logMAR visual acuity and cycloplegic autorefraction. Spherical equivalent refractive data from the right eye were used to classify significant refractive error as myopia of at least 1DS, hyperopia as greater than +3.50DS and astigmatism as greater than 1.50DC, whether it occurred in isolation or in association with myopia or hyperopia.

Results

Results are presented from 661 white 12-13-year-old and 392 white 6-7-year-old school-children. Using a cut-off of uncorrected visual acuity poorer than 0.20 logMAR to detect significant refractive error gave a sensitivity of 50% and specificity of 92% in 6-7-year-olds and 73% and 93% respectively in 12-13-year-olds. In 12-13-year-old children a cut-off of poorer than 0.20 logMAR had a sensitivity of 92% and a specificity of 91% in detecting myopia and a sensitivity of 41% and a specificity of 84% in detecting hyperopia.

Conclusions

Vision screening using logMAR acuity can reliably detect myopia, but not hyperopia or astigmatism in school-age children. Providers of vision screening programs should be cognisant that where detection of uncorrected hyperopic and/or astigmatic refractive error is an aspiration, current UK protocols will not effectively deliver.     

Defects of the Lamina Cribrosa in High Myopia and Glaucoma

Purpose

We evaluated the prevalence and characteristics of the defects of the lamina cribrosa (LC) in high myopia and glaucoma, and compared them with control eyes using swept-source optical coherence tomography (SS-OCT).

Methods

One hundred fifty-nine eyes of 108 participants were divided into four subgroups; high myopia with glaucoma (MG, 67 eyes of 46 subjects), glaucoma without high myopia (G, 22 eyes of 13 subjects), high myopia without glaucoma (M, 35 eyes of 29 subjects), and a control group with neither glaucoma nor high myopia (C, 35 eyes of 20 subjects). The LC defects were identified and located using a standardized protocol in serial horizontal OCT scans. The prevalence rates of the defects were compared among the groups. Demographic and ocular factors were compared between eyes with and without defects.

Results

LC defects were observed in one eye (0.03%) in the C group, 8 eyes (22.9%) in the M group, 11 eyes (50%) in the G group, and 28 eyes (41.8%) in the MG group. The prevalence rates of the defects differed significantly among the groups (P = 0.0009). Most eyes with defects in the G and MG groups (79.5%) had damage in the corresponding visual hemifields. Other factors such as visual acuity, intraocular pressure, axial length, refractive error, disc ovality, or parapapillary atrophy area did not differ significantly between eyes with and without LC defects.

Conclusions

High myopia and glaucoma significantly increased the risk of LC damage. The LC damage in non-glaucomatous highly myopic eyes may at least partly explain the increased risk of developing glaucoma in myopic eyes.     

Refractive Errors in 3–6 Year-Old Chinese Children: A Very Low Prevalence of Myopia?

Purpose

To examine the prevalence of refractive errors in children aged 3–6 years in China.

Methods

Children were recruited for a trial of a home-based amblyopia screening kit in Guangzhou preschools, during which cycloplegic refractions were measured in both eyes of 2480 children. Cycloplegic refraction (from 3 to 4 drops of 1% cyclopentolate to ensure abolition of the light reflex) was measured by both autorefraction and retinoscopy. Refractive errors were defined as followed: myopia (at least −0.50 D in the worse eye), hyperopia (at least +2.00 D in the worse eye) and astigmatism (at least 1.50 D in the worse eye). Different definitions, as specified in the text, were also used to facilitate comparison with other studies.

Results

The mean spherical equivalent refractive error was at least +1.22 D for all ages and both genders. The prevalence of myopia for any definition at any age was at most 2.5%, and lower in most cases. In contrast, the prevalence of hyperopia was generally over 20%, and declined slightly with age. The prevalence of astigmatism was between 6% and 11%. There was very little change in refractive error with age over this age range.

Conclusions

Previous reports of less hyperopic mean spherical equivalent refractive error, and more myopia and less hyperopia in children of this age may be due to problems with achieving adequate cycloplegia in children with dark irises. Using up to 4 drops of 1% cyclopentolate may be necessary to accurately measure refractive error in paediatric studies of such children. Our results suggest that children from all ethnic groups may follow a similar pattern of early refractive development, with little myopia and a hyperopic mean spherical equivalent over +1.00 D up to the age of 5–6 yearsin most conditions.     

Identification of apolipoprotein A-I as a "STOP" signal for myopia

Good visual acuity requires that the axial length of the ocular globe is matched to the refractive power of the cornea and lens to focus the images of distant objects onto the retina. During the growth of the juvenile eye, this is achieved through the emmetropization process that adjusts the ocular axial length to compensate for the refractive changes that occur in the anterior segment. A failure of the emmetropization process can result in either excessive or insufficient axial growth, leading to myopia or hyperopia, respectively. Emmetropization is mainly regulated by the retina, which generates two opposite signals: "GO/GROW" signals to increase axial growth and "STOP" signals to block it. The presence of GO/GROW and STOP signals was investigated by a proteomics analysis of the retinas from chicken with experimental myopia and hyperopia. Of 18 differentially expressed proteins that were identified, five displayed an expression profile corresponding to GO/GROW signals, and two corresponded to STOP signals. Western blotting confirmed that apolipoprotein A-I (apoA-I) has the characteristics of a STOP signal both in the retina as well as in the fibrous sclera. In accordance with this, intraocular application of the peroxisome proliferator-activated receptor alpha agonist GW7647 resulted in up-regulation of apoA-I levels and in a significant reduction of experimental myopia. In conclusion, using a comprehensive functional proteomics analysis of chicken ocular growth models we identified targets for ocular growth control. The correlation of elevated apoA-I levels with reduced ocular axial growth points toward a functional relationship with the observed morphological changes of the eye.     

Interocular Difference of Peripheral Refraction in Anisomyopic Eyes of Schoolchildren

Purpose

Refraction in the peripheral visual field is believed to play an important role in the development of myopia. The purpose of this study was to investigate the differences in peripheral refraction among anisomyopia, isomyopia, and isoemmetropia for schoolchildren.

Methods

Thirty-eight anisomyopic children were recruited and divided into two groups: (1) both eyes were myopic (anisomyopic group, AM group) and (2) one eye was myopic and the contralateral eye was emmetropic (emmetropic anisomyopic group, EAM group). As controls, 45 isomyopic and isoemmetropic children were also recruited with age and central spherical equivalent (SE) matched to those of the AM and EAM groups. The controls were divided into three groups: (1) intermediate myopia group (SE matched to the more myopic eye of AM group), (2) low myopia group (SE matched to the less myopic eye of AM group and the more myopic eye of EAM group), and (3) emmetropia group (SE matched to the less myopic eye of EAM group). Peripheral refraction at 7 points across the central ±30° on the horizontal visual field with a 10° interval was measured with an autorefractor. Axial length (AL), corneal curvature (CC), and anterior chamber depth (ACD) were also determined by using the Zeiss IOL-Master.

Results

The relative peripheral spherical equivalent [RPR(M)] and relative peripheral spherical value [RPR(S)] of the more myopic eye was shifted more hyperopically than the contralateral eye in both the AM and the EAM groups (both p<0.0001). The RPR(M, S) of the less myopic eyes in the AM and EAM groups showed a relatively flat trend across the visual field and were not significantly different from the emmetropia group. The RPR(M, S) of less myopic eyes in the AM group were shifted less hyperopically than in the isomyopic low myopia group and the more myopic eye of the EAM group [RPR(M), p = 0.007; RPR(S), p = 0.001], although the central SEs of the three groups were not significantly different from each other. However, RPR(M, S) of the more myopic eyes were not different from the corresponding isomyopic groups. There was also no significant difference in the relative peripheral astigmatism [RPR(J0, J45)] between the more and the less myopic eyes in either the AM or the EAM group.

Conclusion

Refraction of anisomyopia differs between the two eyes not only at the central visual field but also at the off-axis periphery. The relative peripheral refraction of the more myopic eye of anisomyopia was shifted hyperopically, as occurs in isomyopia with similar central subjective SE values. Less myopic eyes were much less hyperopically shifted in relative peripheral refraction than the corresponding isomyopic eyes, but are comparable to emmetropic eyes. This emmetropia-like relative peripheral refraction in less myopic eyes might be a factor responsible for slowing down the progression of myopia.     

Retinoscleral control of scleral remodelling in refractive development: a role for endogenous FGF-2?

AIMS: Studies in avian models of myopia have shown that refractive error development can be influenced by exogenously delivered fibroblast growth factor (FGF)-2. The present study sought to determine whether endogenous FGF-2 was associated with retinoscleral signalling or scleral remodelling during changes in refractive error in a mammalian model of myopia. METHODS: Myopia was induced in tree shrews over a 5-day period. One group of animals was then allowed 3 days of recovery from the induced myopia. Endogenous levels of FGF-2 were measured in scleral and retinal homogenates using ELISA. Real-time PCR was used to investigate scleral FGF-2 and FGF receptor (FGFR)-1 mRNA expression. RESULTS: No difference in FGF-2 content was found in posterior scleral or retinal extracts of myopic eyes (scleral -4+/-9%, retinal +23+/-17%) or recovering eyes (scleral -10+/-18%, retinal +1+/-13%), when compared with contralateral control eyes. In addition, no significant changes were found in scleral FGF-2 mRNA expression in myopic or recovering eyes (+106+/-56% and +14+/-12% respectively, P=0.21). However, FGF-2 concentration was significantly higher in anterior, relative to posterior, scleral regions in all animals (1602+/-105 vs 1030+/-50pg/mg respectively P<0.001). Expression of scleral FGFR-1 mRNA was upregulated in myopic eyes (+186+/-32%, P=0.01) but returned to control eye levels during recovery (+63+/-20%). CONCLUSIONS: The findings indicate that alterations in endogenous retinal or scleral FGF-2 levels are not associated with changes in scleral remodelling in this mammalian model of myopia. However, the reversible changes found in FGFR-1 expression in the sclera of myopic eyes mean that an indirect role for FGF-2 in the control of scleral remodelling is implicated. The anteroposterior difference found in scleral FGF-2 concentration indicates a role for this cytokine in the control of normal scleral growth and development and, presumably, eye size.     

Regulation of human eye growth by the energy density of the radiation in the retina--a biophysical theory in ophthalmology

A number of theoretical and experimental models analyze regulation of eye growth in humans and animals. In this article we introduce a biophysical theory to explain human eye growth from an energetic point of view. We find different energy densities of the electromagnetic radiation in the retina for hyperopic, emmetropic and myopic eyes. We postulate a relation between the different energy densities of the radiation in the retina and growth regulation by the retina. Based on this relation between physics and biology we are modeling emmetropization, missing emmetropization in severe hyperopia and development and progression of myopia in correspondence with a number of clinical and experimental results.     

Social recognition and approach in the chick: lateralization and effect of visual experience

Chicks, Gallus gallus domesticus, tested monocularly on day 3 after hatching recognize familiar versus unfamiliar conspecifics and choose to approach one or other when they use the left eye, whereas they approach familiar and unfamiliar chicks at random when they use the right eye. In experiment 1 we investigated the effects of light exposure of embryos prior to hatching on this particular form of lateralization. Irrespective of whether they hatched from eggs incubated in the dark or from eggs exposed to light during the final days of incubation, chicks using the left eye had higher choice scores (meaning they chose to approach either a familiar or an unfamiliar chick) than chicks using the right eye or both eyes. Therefore, light experience prior to hatching did not influence the lateralization of individual recognition or choice behaviour, although it did affect latency to move out of, and time spent in, the centre of the runway. Experiment 2 showed that visual/social experience posthatching influences choice behaviour: chicks housed in a group in the light for 12 h on day 1 posthatching made a clear choice between familiar and unfamiliar chicks when tested on day 3, but chicks kept in a group in the dark on day 1 did not make a choice, instead alternating between the two stimuli. In experiment 3 we found that posthatching visual/social experience increased the choice scores of chicks using the right eye and thereby removed any lateralization of choice behaviour. The results suggest that visual experience of a social group is required before chicks using their right eye (and left hemisphere) will pay attention to the cues that distinguish one chick from another. Chicks using their left eye (and right hemisphere) recognize the difference between individuals without requiring visual experience with other chicks. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Breed- and gender-dependent differences in eye growth and form deprivation responses in chick

This study investigated the influences of breed and gender on the response to form deprivation and subsequent changes (recovery) when normal vision was restored. Two breeds of chickens, the White Leghorn and broiler cross, were compared, as well as male and female chicks for the White Leghorn breed. Normal eye growth was faster in the more rapidly growing broiler chicks; gender-differences were not as great as breed-differences although male White Leghorns ultimately became heavier and showed slightly greater normal eye growth than females. While both breeds showed high myopia and axial elongation in response to form deprivation, they differed significantly in the magnitude of their response, with White Leghorns showing more myopia and greater axial elongation and also recovering more slowly. Responses to form deprivation were similar for both genders, with respect to both the amount of myopia and axial elongation produced, although the female chicks recovered faster. Together these observations indicate that, although the overall pattern of response of form deprivation is consistent across both breed and gender, related quantitative differences in responses can be expected and need to be taken into account in experimental design and cross-study comparisons.Abbreviations WL White Leghorn chicks - BC broiler cross chicks - M male chicks - F female chicks - N normal eye - T treated eye - FD form deprivation - ACD anterior chamber depth - ALT axial lens thickness - VCD vitreous chamber depth - AL axial length     

Refractive Errors Affect the Vividness of Visual Mental Images

The hypothesis that visual perception and mental imagery are equivalent has never been explored in individuals with vision defects not preventing the visual perception of the world, such as refractive errors. Refractive error (i.e., myopia, hyperopia or astigmatism) is a condition where the refracting system of the eye fails to focus objects sharply on the retina. As a consequence refractive errors cause blurred vision.We subdivided 84 individuals according to their spherical equivalent refraction into Emmetropes (control individuals without refractive errors) and Ametropes (individuals with refractive errors). Participants performed a vividness task and completed a questionnaire that explored their cognitive style of thinking before their vision was checked by an ophthalmologist. Although results showed that Ametropes had less vivid mental images than Emmetropes this did not affect the development of their cognitive style of thinking; in fact, Ametropes were able to use both verbal and visual strategies to acquire and retrieve information. Present data are consistent with the hypothesis of equivalence between imagery and perception.     

The phase relationships between the diurnal rhythms in axial length and choroidal thickness and the association with ocular growth rate in chicks

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.     

Association between Childhood Strabismus and Refractive Error in Chinese Preschool Children

PurposeTo investigate the association between concomitant esotropia or concomitant exotropia and refractive error in preschool childrenMethodsA population-based sample of 5831 children aged 3 to 6 years was selected from all kindergartens in a representative county (Yuhuatai District, Nanjing, Jiangsu Province) of Nanjing, China. Clinical examinations including ocular alignment, ocular motility, visual acuity, optometry, stereopsis screening, slit lamp examination and fundus examination were performed by trained ophthalmologists and optometrists. Odd ratios (OR) and 95% confidence intervals (95% CI) were calculated to evaluate the association of refractive error with concomitant esotropia and concomitant exotropia.ResultsIn multivariate logistic regression analysis, concomitant esotropia was associated independently with spherical equivalent anisometropia (OR, 3.15 for 0.50 to <1.00 diopter (D) of anisometropia, and 7.41 for > = 1.00 D of anisometropia) and hyperopia. There was a severity-dependent association of hyperopia with the development of concomitant esotropia, with ORs increasing from 9.3 for 2.00 to <3.00 D of hyperopia, to 180.82 for > = 5.00 D of hyperopia. Concomitant exotropia was associated with astigmatism (OR, 3.56 for 0.50 to 1.00 D of astigmatism, and 1.9 for <0.00 D of astigmatism), myopia (OR, 40.54 for -1.00 to <0.00 D of myopia, and 18.93 for <-1.00 D of myopia), and hyperopia (OR, 67.78 for 1.00 to <2.00 D of hyperopia, 23.13 for 2.00 to <3.00 D of hyperopia, 25.57 for 3.00 to <4.00 D of hyperopia, and 8.36 for 4.00 to <5.00 D of hyperopia).ConclusionsThis study highlights the close associations between refractive error and the prevalence of concomitant esotropia and concomitant exotropia, which should be considered when managing childhood refractive error.     

Application of fluorescence difference gel electrophoresis technology in searching for protein biomarkers in chick myopia

The lens-induced myopia (LIM) in response to concave lens (negative lens) is a well established animal model for studying myopia development. However, the exact visual and neurochemical signaling mechanisms involving myopic eye growth are yet to be elucidated. The feasibility of applying a novel two-dimensional fluorescence difference gel electrophoresis technique for global protein profilings and a search for differential protein expressions in LIM were explored in the present study. Two-dimensional polyacrylamide gel electrophoresis was performed employing a "minimal Lysine labeling" approach and a reverse CyeDye experimental protocol using retinal tissue from chicks. The retinal protein profiles between myopic and control eyes were found to be very similar. More than a thousand protein spots could be detected on a 2D gel. Sixteen and ten protein spots were found to be up-regulated and down-regulated respectively in the myopic eyes according to our preset criteria with the inclusion of an internal pool standard. About 65% of those filtered spots could be successfully identified by peptide mass fingerprinting by matrix-assisted laser desorption ionization-time-of-flight mass spectrometry . Most of the differentially expressed proteins were found to be related to cytoskeletal or oxidative functions. According to the prediction of subcellular locations, most of them (about 84%) were classified as cytoplasmic proteins. The cellular functions for those differentially expressed proteins were reported and their possible involvements in the compensated eye growth were discussed. We have optimized a workable protocol for the study of the differential retinal protein expressions in the LIM using 2D-DIGE approach which was shown to have a number of advantages over the traditional 2D electrophoresis technique.