[Susceptibility of guinea pig eyes to form deprivation myopia and its age-related recovery].

OBJECTIVE: Young guinea pigs are susceptible to become myopic during form deprivation. They can also quickly recover from the myopia after removal of the form deprivation. This study investigated whether mature guinea pigs are sensitive to form deprivation and its refractive recovery from deprivation myopia. METHODS: It was an experimental study. Thirty-nine guinea pigs were arranged to 3 groups according to age. Group 1: 9-week old (n = 18). Group 2: 12-week old (n = 10). Group 3: 15-week old (n = 11). All the animals were performed refraction measurement prior to the experiment, then wore a facemask that covered one randomly assigned eye for three weeks. The masks were then removed and refraction was measured in both eyes immediately, 2 and 7 days after. RESULTS: After form deprivation, the refraction of the MFD (monocular form deprivation) eyes shifted to myopia, which had significant difference compared to the unmasked eye in all the groups (t = -5.691, -2.203, -2.760; P < 0.05), the relative myopia compared to the unmasked eye in 9 weeks old animals were (-2.53 ± 1.89) D, 12 weeks old (-1.43 ± 1.57) D, 15 weeks old (-0.60 ± 1.48) D. There was significant difference between 9 weeks old animals and 15 weeks old animal in the refractive error right after the form deprivation (F = 2.823, P < 0.05). And the distribution of refractive error tended to lower degree of myopia as the guinea pigs grew older. None of the three groups showed significant reduction in relative refractive error during the recovery, but a trend of recovery was found in 9 weeks old animals. CONCLUSIONS: The guinea pigs are sensitive to the form deprivation even when they are sexual mature, but both the susceptibility and the ability of recovery decrease as they grow older but in different patterns. The ability of recovery in short term (7 days) diminishes when guinea pig is older than 12 weeks while the sensitivity to form deprivation last until 15 w.

[Form deprivation myopia in C57BL/6 mice].

OBJECTIVE: To investigate the changes of refraction and ocular biometric parameters in form deprived myopia, and try to find the effective duration to induce significant myopic shift in C57BL/6 mice. METHODS: It was an experimental study. Seventy-four C57BL/6 mice, approximately 23 days old, were divided into three groups randomly: FD (Form-deprivation), Recovery and Normal control groups. FD group was treated with diffuser worn on one eye for 2 weeks (n = 12), 3 weeks (n = 20) and 4 weeks (n = 18), respectively. In Recovery group, diffusers were removed after 4 weeks form deprivation, and vertical meridian refraction and other biometric parameters were performed immediately on 4(th) and 7(th) day. The same measurements were performed in the normal control group at the same time-points. Refraction was measured by photoretinoscopy and corneal radius of curvature (CRC) was measured by a modified keratometry. Corneal thickness (CT), anterior chamber depth (ACD), lens thickness (LT), vitreous chamber depth (VCD), and axial length (AL) were measured by optical coherence tomography (OCT) with focal plane advancement. RESULTS: The FD eyes were approximately -0.85 D more myopic compared to the fellow and the normal control eyes after 2 weeks form deprivation (P > 0.05). After 3 weeks form deprivation, treated eye had a obvious myopic shift (about -4.27 D) compared to fellow eye, with increased vitreous chamber depth and axial length, however, there was no statistic difference among FD eye, fellow eye and control eye. And after 4 weeks form deprivation, treated eyes were induced significant myopic shift (about -5.22 D) compared with the fellow eye. The difference in refraction of form-deprived and fellow eyes was significantly correlated with the difference in vitreous chamber depth and axial length, which indicate that the induced myopia was mainly axial. The relative myopia shifted rapidly diminished in 4 days after removing the diffuser, followed by a slower recovery. A complete refraction recovery occurred by 7 days after removal of the diffuser compared to the fellow and normal control eyes (P > 0.05). CONCLUSION: Form deprivation myopia can be induced in C57BL/6 mice, but it required longer period than other animals; A complete recovery occurred by 7 days after removal of the diffuser.Optical Coherence Tomography is a useful instrument to measure mouse eye dimension.

Microdissection of guinea pig extraocular muscles.

The guinea pig, a widely used experimental animal, has been used in myopia research in recent years. The structure of the extraocular muscles is important in research on eyeball movement, regulation of movement, binocular vision and surgical intervention. In this study, the anatomy and the structure of the extraocular muscles of guinea pigs were investigated. Five guinea pig eyes were dissected under a surgical microscope immediately after sacrifice, and an additional five were fixed in 10% formaldehyde solution and dissected under a surgical microscope 1 week after sacrifice. The guinea pig eye has seven extraocular muscles: two medial rectus muscles, one superior rectus muscle, one inferior rectus muscle, one superior oblique muscle and one inferior oblique muscle. The retractor bulbi muscle fibers surround the optic nerve longitudinally and insert circumferentially into the posterior pole of the eyeball. The lateral rectus was not found. Our results showed that there is a disparity between the structure of guinea pig extraocular muscles and that of humans.