Effects of muscarinic receptor modulators on ocular biometry of guinea pigs.

PURPOSE: This study investigated whether pilocarpine and cyclopentolate induce changes in ocular biometry of guinea pigs, in order to understand if guinea pigs have a similar response to these two agents as humans do. METHODS: Under general anaesthesia, refraction, axial components and surface curvature in various optical interfaces of the eye were measured in 10 guinea pigs (age of 2 weeks) at baseline (0 min) and different time points (5, 10, 20, 30, 60, 90 min) after topical administration of pilocarpine or cyclopentolate. The interval between the two drug treatments for the same animals was at least 24 h. RESULTS: Eyes treated with pilocarpine developed approximately 6D myopia (p < 0.001 from 0 to 90 min) with a decrease in anterior lens radius of curvature (ALRC) (p < 0.001 from 0 to 90 min, repeated measures anova). This myopic shift was moderately correlated to the decreased ALRC (r(2)  = 0.48, p < 0.001). Furthermore, a small but significant increase in the VCD (p < 0.001 from 0 to 30 min, repeated measures anova) with an unchanged AL (p = 0.85 from 0 to 90 min, repeated measures anova) after the drug treatment suggested a transient and mild forward movement of the lens. Cyclopentolate dilated the pupil in all eyes (p < 0.001 from 0 to 90 min, repeated measures anova) but did not change other ocular parameters. CONCLUSIONS: The muscarinic agonist, pilocarpine induced a myopic shift mainly due to a decrease in ALRC, suggesting that guinea pigs have an accommodative mechanism similar to that in humans. The minimal changes produced by cyclopentolate could be due to the use of general anaesthesia, which may have reduced the susceptibility of the eye to topical cyclopentolate in the induction of cycloplegia.

Interocular evaluation of axial length and retinal thickness in people with myopic anisometropia.

PURPOSE: To investigate the changes in axial length and retinal thickness and their relationships with myopia in highly myopic anisometropia. METHODS: A total of 87 Chinese subjects (25.28±11.98 years, mean±SD) were divided into two groups: anisometropia (n=38) and nonanisometropia (n=49). All eyes were measured for axial length, refractive status, and macular thickness (optical coherence tomography). Ocular biometric results were compared between eyes of subgroups. Linear correlation between refractive error and other biometric results was performed. RESULTS: In the anisometropic group, the inner ring macula and part of the outer ring macula (nasal and inferior quadrants) in the higher myopic eyes were significantly thinner than in the fellow eyes (P≤0.007), but the foveal thickness (minimum and average) was similar (P≥0.050) between the two eyes. However, the minimum and average foveal thicknesses were found to be significantly thicker in the highly myopic eyes than those in the emmetropic to moderate myopic eyes (P≤0.016) in the nonanisometropic group. Among the eyes ranging from emmetropia to high myopia, the refractive error was negatively correlated to the axial length of the eye (P<0.001) and the thinning of inner ring macula is consistent with the increase in both myopia and axial length. There was a negative correlation in refractive error and axial length but no correlation in parafoveal thickness between eyes of the same subjects (P<0.001) in the anisometropic group. CONCLUSIONS: In people with myopic anisometropia, the higher myopic eye has a longer axial length but a thinner parafoveal region than its fellow eye. The axial growth in the development of high myopia seems to be centrally regulated; however, the changes in parafoveal thickness are likely manipulated by local mechanisms within the eye.

Inhibition of experimental myopia by a dopamine agonist: different effectiveness between form deprivation and hyperopic defocus in guinea pigs.

PURPOSE: The dopamine (DA) system in the retina is critical to normal visual development as lack of retinal DA signaling may contribute to myopic development. The involvement of DA in myopic development is complex and may be different between form deprivation and hyperopic defocus. This study evaluated effects of a non-selective DA receptor agonist, apomorphine (APO) on refractive development in guinea pigs treated with form deprivation or hyperopic defocus. METHODS: APO was subconjunctivally injected daily for 11 days in form-deprived (0.025 to 2.5 ng/µl) and defocused (0.025 to 250 ng/µl) eyes. Changes in ocular biometry and retinal concentration of DA and its metabolites (DOPAC) were measured in the 2 animal models to assess the level of DA involvement in each of the models (the less the change, the lower the involvement). RESULTS: Similar myopic degree was induced in both the deprived and defocused eyes (-4.06 D versus -3.64 D) at 11 days of the experiment. DA and DOPAC levels were reduced in the deprived eyes but did not change significantly in the defocused eyes compared to the fellow and normal control eyes. A subconjunctival injection of APO daily for 11 days at concentrations ranged from 0.025 to 2.5 ng/µl inhibited form deprivation myopia in a concentration-dependent manner. By contrast, the APO treatment ranged from 0.025 to 250 ng/µl did not effectively inhibit the defocus-induced myopia and the associated axial elongation. CONCLUSIONS: DA signaling may play a more critical role in form deprivation myopia than in defocus-induced myopia, raising a question whether the mechanisms of DA signaling are different under these two types of experimental myopia.

Changes in protein profiles of guinea pig sclera during development of form deprivation myopia and recovery.

PURPOSE: To investigate changes in protein profiles of posterior sclera in guinea pigs during development of form deprivation myopia and recovery. METHODS: Three groups of guinea pigs (developing form deprivation myopia, recovering from the myopia and normal control) were evaluated for protein profiles of the posterior sclera using two-dimensional gel electrophoresis. Protein spots with a different intensity of at least threefold among the 3 groups were further identified with mass spectrometry. Key proteins associated with ocular growth (crystallins) were examined at mRNA levels using RT-PCR. RESULTS: Moderate myopia was induced at 7 weeks of monocular deprivation and then more gradually recovered toward the previous refractive status 4 days after re-exposure of the eye to normal visual conditions. The profile of all protein spots at the posterior sclera was similar for both the deprived and the recovery eyes but distinct between either of the 2 experimental eyes and the normal control eyes. Twenty-six and 33 protein spots were differentially expressed in the deprived and the recovery eyes, respectively, compared to the normal control eyes. In contrast, the number of proteins differentially expressed between the deprived and the recovery eyes was only 5. Among the different subtypes of crystallins, ßB2-crystallin was down-regulated and ßA4-crystallin was upregulated in the deprived eyes at both protein and mRNA levels compared to the normal control eyes. The trend of expression for ßA3/A1-crystallin was also similar at both mRNA and protein levels for the deprived eyes. However, αA-crystallin mRNA in the recovery eyes was upregulated while αA-crystallin itself was down-regulated. A similar inconsistency in expression of ßA3/A1-, ßA4-, and ßB2-crystallins between the protein and mRNA levels also occurred in the recovery eyes. CONCLUSIONS: Proteomic analysis provides a useful survey of the number of proteins whose levels change during form deprivation myopia and the subsequent recovery. In particular, the crystallins changed during the development of form deprivation myopia and recovery. The changes in crystallin protein levels were consistent with that in mRNA levels during the development stage of form-deprivation myopia (FDM). However, the changes of most crystallin protein levels were mismatched with mRNA levels during the recovery stage.

Axial myopia induced by hyperopic defocus in guinea pigs: A detailed assessment on susceptibility and recovery.

This study investigated whether adolescent guinea pigs can develop myopia induced by negative lenses, and whether they can recover from the induced myopia. Forty-nine pigmented guinea pigs (age of 3 weeks) were randomly assigned to 4 groups: 2-week defocus (n=16), 4-week defocus (n=9), 2-week control (n=15) and 4-week control (n=9). A -4.00D lens was worn in the defocus groups and a plano lens worn in the control groups monocularly. The lenses were worn from 3 weeks to 5 weeks of age in the 2-week treatment groups with the biometry measured at 2, 4, 6, 10 and 14 days of lens wear. The lenses were worn from 3 weeks to 7 weeks of age in the 4-week treatment groups with the biometry measured immediately and at 2, 4, 6, 10 and 14 days after lens removal. Refractions in the defocused eyes developed towards myopia rapidly within 2 days of lens wear, followed by a slower development. The defocused eyes were at least 3.00D more myopic with a greater increase in vitreous length by 0.08 mm compared to the fellow eyes at 14 days (p<0.05). The estimated choroidal thickness of the defocused eyes decreased rapidly within 2 days of lens wear, followed by a slower decrease over the next 4 days. Relative myopia induced by 4 weeks of negative-lens treatment declined rapidly following lens removal. A complete recovery occurred 14 days after lens removal when compared to the fellow controls. The refractive changes during the recovery corresponded to a slower vitreous lengthening and a rapid thickening of the choroid. The plano-lens wearing eyes showed a slight but significant myopic shift (<-0.80D) with no associated biometrical changes. Guinea pigs aged 3 weeks can still develop negative lens induced myopia and this myopia is reversible after removal of the lens. The myopia and recovery are mainly due to changes in vitreous length and choroidal thickness.

Correlation between myopia and major biometric parameters of the eye: a retrospective clinical study.

PURPOSE: To investigate the relationship between myopia and changes in ocular biometry and macular thickness in young adults. METHODS: Two hundred sixteen eyes from 108 adults (23.3 +/- 6.3 years old, mean +/- SD) were measured for refractive status, corneal curvature, and axial components of the eye. Macular thickness was measured in 118 eyes (59 subjects) by optical coherence tomography. All eyes were categorized into emmetropia, low, moderate, or high myopia based on the refractive status. Biometric results from right eyes of all subjects were compared between sub-groups with the linear correlation analyzed between refraction and other parameters for each group. RESULTS: The vitreous chamber depth was longest in high myopia, followed by the moderate myopia group, the low myopia group and finally the emmetropic group (p < or = 0.004). Average thickness of the inner and outer ring macula in all the myopia groups was significantly thinner than in the emmetropia group (p < or = 0.021). Among different macular regions, the inferior quadrant of the outer ring was consistently the thinnest in myopia. Corneal curvature, anterior chamber depth, and lens thickness measures were not associated with myopia. CONCLUSIONS: Myopia in young adults is associated with an increase in vitreous length and a decrease in para-foveal thickness. The thinness in the retinal region inferior to the fovea appears to be more highly correlated with myopia than any other retinal region.

Recovery from axial myopia induced by a monocularly deprived facemask in adolescent (7-week-old) guinea pigs.

PURPOSE: Guinea pigs have been increasingly used as an animal model for experimental myopia. Infant guinea pigs are susceptible to recovery from myopia within 2 weeks of form deprivation. This study investigated whether adolescent guinea pigs are susceptible to recovery from myopia after a longer period of form deprivation. METHOD: Twenty-two guinea pigs (age of 3 weeks) were randomly assigned to two groups: MDF (monocularly deprived facemask, n=11) and normal control (free of form deprivation, n=11). All animals underwent biometric measurement (refraction, corneal curvature and axial length) prior to the experiment. Animals in the MDF group wore a facemask that covered the right eye for 4 weeks. The MDF was then removed and biometric measurement was performed immediately and at 2, 6, 10 and 14 days. The same measurement was performed in the normal control group at time-points matching those of the MDF group. RESULTS: The MDF eyes were approximately 4D more myopic with a greater increase in vitreous length by 0.12 mm compared to either the fellow or the normal control eyes after form deprivation (p<0.01). This relative myopia shifted rapidly towards hyperopia within 2 days after removal of the MDF, followed by a more gradual recovery. A complete recovery occurred by 6 days after removal of the MDF compared to the fellow and normal control eyes (p>0.05). Vitreous length in the MDF eyes slightly reduced within 2 days after removal of the MDF and then remained steady. The MDF eyes were similar to both the fellow and normal control eyes in vitreous length (p>0.05) 6 days after removal of the MDF. There was no significant difference between the MDF, fellow and normal control eyes in the other axial components during the form deprivation and recovery period. CONCLUSION: Adolescent guinea pigs are susceptible to recovery from MDF-induced myopia. The refractive recovery is mainly correlated to the inhibited axial elongation of the vitreous chamber of the previously deprived eyes.

Feasibility of two-dimensional gel electrophoresis used for proteomic analysis of human scleral fibroblasts.

PURPOSE: This study used two-dimensional gel electrophoresis (2-DE) to analyze protein profiles for normal human scleral fibroblasts in order to provide a baseline for future study of proteomics of the sclera in experimental conditions. In addition, differences in the presence and amount of proteins from fibroblasts isolated from the anterior or posterior sclera were analyzed. METHODS: The fibroblasts from anterior and posterior sclera of two healthy donors were cultured separately. Proteins were extracted from the cell lines, run on 2-DE, and stained by Commassie blue R-250. The gel images were analyzed to detect differences in expression levels (at least a fivefold difference in intensity) and location of the protein spots between the anterior and posterior sclera. These protein spots were trimmed from the gels, digested with trypsin, identified by MALDI mass spectrometry, and functionally categorized with human cDNA and protein databases from NCBI. RESULTS: The number of spots detected was 455 and 453 protein spots from the anterior and posterior scleral fibroblasts, respectively. The patterns of gel maps were very similar between the anterior and posterior sclera in each donor and between the donors in either the anterior or posterior sclera. Nine proteins showed a stronger expression in the anterior sclera compared with the posterior sclera. These proteins together with the two proteins that appeared only in the anterior sclera were mainly associated with anabolic metabolism in cells. Eight proteins showed a stronger expression in the posterior sclera, and seven of them were mainly associated with catabolic metabolism in cells. Among all 19 protein spots identified as being differentially expressed between fibroblasts originally isolated from the anterior or posterior sclera, 14 proteins had a pI (3.86-7.95) and molecular weight (23-66 kDa) consistent with those found in human from the database of NCBI and from SwissProt Entry Name. CONCLUSIONS: The distribution and levels of expression in proteins are very similar for both the anterior and posterior sclera in vitro, with only approximately 4% of the proteins demonstrating a differential level of expression (at least fivefold) between the two segments of the sclera.

[A comparison of Chinese reading parameters among rapid serial visual presentation, full screen and printed displays].

OBJECTIVE: This study investigated reading speed of Chinese in rapid serial visual presentation (RSVP), full screen and printed display among young adults with normal vision. The critical font size and critical acuity reserve in RSVP were also evaluated. METHODS: Thirty university students with a visual acuity of at least 20/20 in both eyes (uncorrected or corrected) were recruited in this study. The visual acuity threshold (VAT) (3 m distance) was evaluated for all subjects using a self-designed visual acuity chart presented on a computer screen. The reading speed for Chinese was measured under RSVP (10 font sizes from 4 to 33 pt), full screen and printed display (2 font sizes: 10 and 13 pt). The reading speed (wpm) was expressed as the percentage of words read correctly x 60 x total number of words/time used (second). The acuity reserve (RA) was expressed as RA = SP/ST, where SP was the font size of the reading material for the reader and ST was the acuity threshold expressed as a font size. RESULTS: The visual acuity threshold (VAT) at a distance of 40 cm in these 30 subjects was (2.2 +/- 0.3) pt (mean +/- SD). The reading speed increased significantly with the increasing font sizes until the font size reached (7.8 +/- 0.4) pt where the maximum reading speed (258.0 +/- 34.4 wpm) was achieved. The reading speed remained at a constant value in font sizes ranging from 7.8 to 33 pt. The reading speed increased with the increasing R(A) until the R(A) reached 3.5:1 and then remained unchanged. There was no significant difference in reading speed between full screen and printed displays (P > 0.05). The reading speed in full screen or printed display was significantly faster than in RSVP (10 pt: full screen display versus RSVP: t = -10.15, P < 0.01; printed display versus RSVP: t = -8.77, P < 0.01. 13 pt: full screen display versus RSVP: t = -11.64, P < 0.01; printed display versus RSVP: t = -10.79, P < 0.01). CONCLUSIONS: Young readers who use the computer as a reading tool can achieve a maximum reading speed for Chinese when the font size of the reading text is larger than 7.8 pt. A font size of at least 3.5 times the acuity threshold can attain a maximum reading speed for RSVP.

The effect of topical administration of cyclopentolate on ocular biometry: An analysis for mouse and human models.

Mydriasis with muscarinic antagonists have been used routinely prior to retinal examination and sometimes prior to refractive measurements of the mouse eye. However, biometric changes during topical administration of muscarinic antagonists have not been fully investigated in mice and humans. We found that the mouse eyes treated with cyclopentolate developed a hyperopia with a reduction in both the vitreous chamber depth and axial length. In humans, prior to the cyclopentolate treatment, a 6D accommodative stimulus produced a myopic shift with a reduced anterior chamber depth, choroidal thickness and anterior lens radius of curvature and an increase in lens thickness. After the cyclopentolate treatment, human eyes developed a hyperopic shift with an increased anterior chamber depth and anterior lens radius of curvature and a reduced lens thickness. Therefore, the biometric changes associated with this hyperopic shift were mainly located in the posterior segment of the eye in mice. However, it is the anterior segment of the eye that plays a main role in the hyperopic shift in human subjects. These results further indicate that mouse eyes do not have accommodation which needs to be taken into account when they are used for the study of human refractive errors.

Normal development of refractive state and ocular dimensions in guinea pigs.

PURPOSE: This study investigated changes in refraction, corneal curvature, axial components and weight of posterior sclera in guinea pig eyes during the normal development from birth. METHODS: Sixty-four guinea pigs were assigned to eight groups (n=8 each). Each group underwent a series of ocular measurements at one of the eight time-points (0, 1, 2, 3, 5, 7, 9 and 11 weeks), including refraction (streak retinoscopy), corneal radius of curvature (CRC; keratometry), anterior segment length (AS: corneal thickness and depth of the anterior chamber), thickness of the crystalline lens (CL), vitreous chamber length (VC; all A-scan ultrasonography) and dry weight of a circular 6mm diameter punch in the posterior sclera (electronic balance). Results of all the measurements were statistically compared between right eye and left eye, male and female and among different age groups. Artifacts of retinoscopy due to small eye artifact were also estimated at different ages. RESULTS: The refraction in guinea pig eyes was +5.22+/-0.23 D (Mean, SE) at birth. This value decreased rapidly during the first 3 weeks followed by a slow decline. The overall decrease in refraction was highly significant from birth to 11 weeks (p<0.001 one way ANOVA). The small eye artifact was approximately 4.00 D at birth, which reduced to 2.76 D at 11 weeks. The guinea pig eyes were emmetropic by 3 weeks of age when the small eye artifact was taken into account. The CRC (3.24+/-0.01 mm at birth), AS (1.20+/-0.01 mm at birth), CL (2.72+/-0.03 mm at birth) and VC (3.28+/-0.01 mm at birth) increased within the first 3 weeks despite a transient decrease in the CRC within the first week. The increase in CRC, CL and VC continued after 3 weeks, however, the AS remained constant after this age. The increase in VC was better correlated to the decline of hyperopia (R(2)=0.70) than the other components (R(2)=0.33-0.39). Dry weight of the posterior sclera increased linearly from birth (p<0.001 between any two close time-points from 3 to 9 weeks) and had a moderately linear correlation with the VC (R(2)=0.60). There were no significant differences between the right eye and left eye or between male and female in all the measurements. CONCLUSIONS: In guinea pigs, the hyperopia present at birth rapidly reduces to emmetropia within the first 3 weeks of age. The emmetropization process in guinea pigs is mainly related to the increase in the vitreous chamber length. This relationship in guinea pigs is similar to that in chickens, tree shrews, primates and humans. The axial development of the vitreous chamber in guinea pigs appears to be associated with tissue growth of the posterior sclera.

The presence of m1 to m5 receptors in human sclera: evidence of the sclera as a potential site of action for muscarinic receptor antagonists.

PURPOSE: The aim of this study was to identify the presence of muscarinic acetylcholine receptors (mAChRs) in human sclera in order to determine whether the sclera is a potential site of action for mAChR antagonists. METHODS: Cell lines of human scleral fibroblasts were cultured in Dulbecco modified Ealge's medium. Reverse transcription-polymerase chain reaction (RT-PCR) and Northern blot analysis were used to detect mRNA expression of muscarinic acetylcholine receptors in the cell lines of the fibroblasts. Western blot analysis and immunocytochemistry were used to detect proteins of mAChRs in the cell lines. Immunohistochemical study was used to further detect the presence of mAChR proteins in the frozen scleral sections. RESULTS: The cultured fibroblasts demonstrated mRNA expression of five mAChRs (m1 to m5) in RT-PCR and Northern blot analysis. The molecular size of mRNA expression was largest for the m3 receptor, followed by the m2, m4, m5, and m1 in both RT-PCR and Northern blot analysis. Proteins of the m1 to m5 receptors were present in cell line fibroblasts under Western blot analysis and immunocytochemistry with a range of molecular weight from 80 kDa (m5) to 60 kDa (m1) in Western blot analysis. The presence of these five receptors was also detected in scleral tissues with immunohistochemistry. CONCLUSIONS: This study demonstrated the presence of mAChR subtypes (m1 to m5) in human scleral fibroblasts at both mRNA and protein levels. This finding indicates that the sclera is a potential site of action for the currently used mAChR antagonists in prevention of human myopia.

[Expression of muscarinic acetylcholine receptor-1 in human retinal pigment epithelium].

OBJECTIVE: The aim of this study was to identify the presence of muscarinic acetylcholine receptors-I (M1 receptor) in human retinal pigment epithelium (RPE) in order to determine the role of M1 receptor in the maintenance of function of RPE and its role in the occurrence and development of myopia. METHODS: The 3rd-5th passages of RPE cells established in our laboratory were used in the present study. Reverse transcription-polymerase chain reaction (RT-PCR) was used to detect mRNA expression of M1 receptor in cultured RPE. Immunocytochemistry was used to detect M1 receptor protein in the RPE cells. RESULTS: Cultured RPE demonstrated mRNA expression of M1 receptor in RT-PCR. Protein of M1 receptor was presented in the RPE under immunocytochemistry. CONCLUSIONS: This study demonstrated the presence of M1 receptor in human RPE at both mRNA and protein levels. M1 receptor plays an important role in the maintenance of function of RPE. Injection of M1 receptor antagonist into the vitreous can delay the occurrence and inhibit the development of myopia, which is possibly related to the inhibition of RPE cells function.

[Expression of muscarinic acetylcholine receptor-1 in human scleral fibroblasts].

OBJECTIVE: The aim of this study was to identify the presence of muscarinic acetylcholine receptors-1 (mAChRs-1) in human sclera in order to determine whether the sclera is a potential site of action for mAChR antagonists. METHODS: Cell lines of human scleral fibroblasts were cultured in Dulbecco Modified Eagle's Medium. Reverse Transcription-Polymerase Chain Reaction (RT-PCR) was used to detect mRNA expression of M1 receptors in the fibroblasts. Immunocytochemistry was used to detect proteins of mAChRs in the cell lines. Immunohistochemical study was used to further detect the presence of M1 receptor in the frozen scleral sections. RESULTS: The cultured fibroblasts demonstrated mRNA expression of M1 receptor in RT-PCR. Protein of the M1 was present in the fibroblasts by examination of immunocytochemistry and immunohistochemistry staining. CONCLUSION: This study demonstrated the presence of M1 receptor in human scleral fibroblasts at both mRNA and protein levels. This finding indicates that the sclera is a potential site of action for the currently used mAChR antagonists in prevention of human myopia.

Effects of the cycloplegic, cyclopentolate, on measurements of refraction in eyes of a strain of wild-type juvenile guinea pig (Cavia porcellus): a comparative study.

OBJECTIVE: To investigate the effect(s) of the cycloplegic, cyclopentolate, on measurements of refraction in eyes of a strain of wild-type guinea pig. METHODS: Both eyes of 13 wild-type juvenile guinea pigs (n=26 eyes) were examined both pre- and post-mydriasis, using streak retinoscopy (SR) and eccentric infrared photoretinoscopy (EIP). On the day of measurement, three SR measurements were taken for each eye at 0900, 1000, 1100, 1400, 1500 and 1600, and three EIP measurements for each eye at 0930, 1030, 1130, 1430, 1530 and 1630. Cyclopentolate hydrochloride (1%) was topically administered three times to each eye at 5-min intervals: 1300, 1305 and 1310. RESULTS: Repeated measurements made by either method revealed that mydriasis did not significantly affect refractive stability (repeated measures, p>0.05). Depending on the stage of mydriasis, however, there were significant differences in measured refractive changes both SR and EIP (0.27 ± 0.65 D, tSR=-2.095, PSR=0.04 and 0.73 ± 1.06 D, tEIP=-3.494, PEIP=0.002, respectively) measurements. CONCLUSIONS: Cyclopentolate had only limited effects on measurements of refraction, indicating that direct SR or EIP measurements of refraction in this wild-type strain of juvenile guinea pig, without the use of a cycloplegic, yield reliable and stable results.

Activation of dopamine D2 receptor is critical for the development of form-deprivation myopia in the C57BL/6 mouse.

PURPOSE: This study used dopamine D2 receptor (D2R) knockout (KO) mice to investigate the role of D2R activity in the development of form-deprivation myopia (FDM). Sulpiride, a D2R antagonist, was administered systemically into wild-type (WT) mice to validate the involvement of D2R in FDM development. METHODS: The D2R KO and WT C57BL/6 mice were subjected to FDM. Wild-type mice received daily intraperitoneal injections of sulpiride, 8 µg/g body weight, for a period of 4 weeks. The body weight, refraction, corneal radius of curvature, and ocular axial components were measured at week 4 of the experiment. Differences in all ocular parameters between the experimental and control groups were compared statistically. RESULTS: Form-deprivation myopia in D2R KO mice (FD-KO) was significantly reduced compared with their WT littermates (interocular difference, -2.12 ± 0.91 diopter [D] in FD-KO versus -5.35 ± 0.83 D in FD-WT, P = 0.014), with a smaller vitreous chamber depth (0.008 ± 0.006 vs. 0.026 ± 0.006 mm, P = 0.044) and axial length (-0.001 ± 0.007 vs. 0.027 ± 0.008 mm, P = 0.007). Furthermore, FDM was attenuated in animals treated with sulpiride (-2.01 ± 0.31 D in FD-sulpiride versus -4.06 ± 0.30 D in FD-DMSO, P < 0.001) compared with those treated with vehicle, with a retardation in growth of vitreous chamber depth (-0.001 ± 0.006 vs. 0.022 ± 0.004 mm, P = 0.003) and axial length (-0.004 ± 0.007 vs. 0.027 ± 0.005 mm, P = 0.001). CONCLUSIONS: Genetic and pharmacological inactivation of D2R attenuates FDM development in mice, suggesting that dopamine acting on D2R appears to promote the development of FDM in C57BL/6 mice. Further studies are required to confirm these results using animal models in which retinal D2R is selectively blocked.

The effect of temporal and spatial stimuli on the refractive status of guinea pigs following natural emmetropization.

PURPOSE: To understand the visual information essential for maintaining stable refraction after emmetropization, we investigated the effects of spatial and temporal stimuli on the refractive status of guinea pigs. METHODS: Eighty-eight guinea pigs (4 weeks old) were randomly divided into 10 groups. Thirty animals were raised in backgrounds of gray (N = 13), square-wave (N = 9), or sine-wave grating (N = 8). Thirty-one animals were raised in gray backgrounds with three frequencies of flicker: gray-1-Hz (n = 10), gray-6-Hz (n = 12), and gray-20-Hz (n = 9). Eighteen animals were raised in regular cages with different frequencies of flicker (n = 6 respectively in 1-Hz-, 6-Hz-, and 20-Hz-flicker groups). Nine animals were raised in regular cages with no additional stimuli and used as normal controls. Ocular biometry was measured before and after 3 weeks of exposure to the test environments. RESULTS: Guinea pigs raised in the gray background for 3 weeks developed myopia, -6.1 ± 2.1 diopters (D), whereas those exposed to either sine-wave or square-wave gratings, or raised in regular cages, retained stable refractions. Animals in the gray-6-Hz group developed lower myopia, -2.7 ± 2.7 D, than the gray group not exposed to flicker. Animals stimulated with a range of flickering frequencies in regular cages also developed myopia but to a lower degree, -3.1 to 0.2 D, than those in gray backgrounds, -5.0 to -2.7 D. CONCLUSIONS: Guinea pigs require both spatial and temporal stimuli to maintain stable refractions. The influence of temporal stimuli on refraction varies with the type and amount of spatial information available in the visual environment.

Spontaneous high myopia in one eye will affect the development of form deprivation myopia in the fellow eye.

PURPOSE: Whether there is an interaction between eyes of individual subjects in refractive development is an important issue to guide experimental designs and help understand mechanisms involved in development of refractive errors. This study investigated whether spontaneous high myopia in one eye will affect refractive development of the fellow eye treated with form deprivation. METHODS: Thirty-four guinea pigs were divided into four groups: MD (monocularly form-deprived animals with a pre-treatment anisometropia ≤ 2D, n = 8), anisometropic MD (monocular form deprivation on a relatively hyperopic eye in animals with a pre-treatment anisometropia ≥ 10D, n = 9), normal control (non-form deprivation in animals with a pre-treatment anisometropia ≤ 2D, n = 8), and anisometropic control (non-form deprivation in animals with a pre-treatment anisometropia ≥ 10D, n = 9). All eyes in different groups underwent biometric measurements on days 0, 12, 24, and 36 of the experiment. RESULTS: High myopia in one eye reduced form deprivation myopia in the fellow treated eye. The change in refraction from 0 to 36 days in the deprived eyes was -3.07D for the MD group, but -1.22D for the anisometropic MD group (-3.07D vs. -1.22D: p = 0.009, independent sample t-test). The amount of vitreous chamber lengthening over the same period in the deprived eyes was 0.19 mm for the MD group, but 0.12 mm for the anisometropic MD group (0.19 mm vs. 0.12 mm: p = 0.038, independent sample t-test). Myopic development in the anisometropic animals is mainly inhibited within the first 12 days compared to normal MD animals. CONCLUSIONS: These results indicate that an interaction in refractive development may exist temporarily between two eyes of a highly anisometropic animal if the visual environment has been changed.

Relative axial myopia induced by prolonged light exposure in C57BL/6 mice.

Ambient lighting is essential for ocular development in many species, however, disruption in diurnal lighting cycle can affect the development in refraction and axial growth of the eye. This study investigated the effects of prolonged daily lighting on refraction and various optical components of the eye by raising C57BL/6 mice under three different light/dark cycles (18/6, 12/12 and 6/18). Egr-1 mRNA expression, apoptosis and histology of the retina and size of the scleral fibrils were evaluated in these three lighting cycles. Results showed that there was a trend of myopic development, increasing vitreous chamber depth and thinning of the retina in eyes from 6/18 to 18/6 groups. Retinal Egr-1 mRNA expression and diameter of scleral fibrils were reduced with the prolongation of daily lighting from 6/18 to 18/6. However, retinal apoptosis was not detected in all the groups. These results suggest that prolonged lighting can induce axial myopia in inbred mice. This model, which uses mice with similar genetic backgrounds, provides an alternative to the currently available models and therefore is useful for evaluation of refractive errors caused by changes in environmental illumination.

Axial myopia induced by a monocularly-deprived facemask in guinea pigs: A non-invasive and effective model.

This study evaluated the efficacy of a facemask, a non-invasive and potentially more reliable method, in inducing axial myopia in guinea pigs. Thirty-six animals were randomly assigned to 3 groups: MDF (monocularly-deprived facemask, n=6), lid-suture (eyelids sutured monocularly, n=24) and normal control (free of form deprivation, n=6). All the groups underwent biometric measurement (refraction, corneal curvature and axial length) prior to the experiment. All animals in the MDF group underwent biometric measurement at each of the 4 timepoints (2, 4, 6 and 8 weeks of form deprivation). In the lid-sutured group, the animals were randomly assigned to 4 subgroups (n=6 each) and each subgroup underwent biometric measurement at one of the timepoints matching those of the MDF group. In the normal control group, all animals underwent biometric measurement at each of the timepoints matching those of the 2 experimental groups. Placement of a facemask on an animal took approximately 10 sec and all the facemasks remained in place at all timepoints. The procedure of lid-suture took at least 20 min for an animal and rupture of the sutures occurred in 50% of the animals after 4 weeks. The MDF eyes developed myopia from -2.21+/-2.11D (Mean+/-s.d.) at 2 weeks to -4.38+/-2.14 at 8 weeks (p<0.05 at all timepoints, compared to the contralateral eyes) with a lengthening of the vitreous chamber from 0.17+/-0.05 mm at 2 weeks to 0.29+/-0.12 mm at 8 weeks (p<0.01 at all timepoints, compared to the contralateral eyes). The lid-sutured eyes developed myopia from -2.38+/-1.21D at 2 weeks to -4.75+/-1.39D at 8 weeks (p<0.05 at all timepoints, compared to the contralateral eyes) with a lengthening of the vitreous chamber from 0.13+/-0.02 mm at 2 weeks to 0.30+/-0.10 mm at 8 weeks (p<0.05 at 2, 4, 8 weeks, but >0.05 at 6 weeks, compared to the contralateral eyes) and an increase in the radius of the corneal curvature (0.20+/-0.07 mm at 4 weeks, p<0.01; 0.17+/-0.05 mm at 8 weeks, p<0.05; compared to the contralateral eyes). Both the MDF and lid-sutured groups had a similar development in myopia and vitreous length (MDF vs lid-suturing: p>0.05 at all timepoints, one-way ANOVA with Bonferroni correction). This development was significantly faster than in the normal control group (MDF or lid-suture vs normal control: p<0.05 to <0.01 from 2 to 8 weeks, one-way ANOVA with Bonferroni correction). The radius of corneal curvature in the lid-sutured group was significantly greater than in either the MDF group or the normal control group since 4 weeks of form deprivation (p<0.05, one-way ANOVA with Bonferroni correction). Treatment with MDFs is as effective as the lid-suture in inducing axial myopia in guinea pigs. This method is non-invasive and allows evaluation of the same group of animals at different timepoints so that the number of animals required could be minimized without affecting the accuracy of the results.