Human parallels to experimental myopia? A literature review on visual deprivation

Factors associated with progressive anisometropia after bilateral intraocular lens implantation in patients with pediatric cataract

OBJECTIVES

To identify factors associated with progressive anisometropia after bilateral intraocular lens (IOL) implantation in patients with pediatric cataract.

METHODS

Clinical and standardized questionnaire data were collected for Sixty-eight patients with pediatric cataract (136 eyes) who underwent bilateral IOL implantation and at least 1 year of follow-up. Univariate and multivariate linear regression models were used to identify factors associated with postoperative anisometropia.

RESULTS

The median age at IOL implantation was 3.2 years (range: 1-12.4 years), and median follow-up time was 5.7 years (range: 1.1-14 years). At 1 month postoperatively and at the last follow-up, there were 19 (27%) and 31 (46%) cases of anisometropia ≥1 D, 9 (13%) and 15 (22%) cases of anisometropia ≥2 D, and 2 (3%) and 9 (13%) cases of anisometropia ≥3 D, respectively. Compared with 1 month postoperatively, the amount of anisometropia increased in 45 (67%) patients. Greater anisometropia one year or more after bilateral IOL implantation was associated with larger intereye difference in IOL power (P = 0.032, 95%CI 0.013 to 0.285), intereye difference in preoperative axial length (P = 0.018, 95%CI -1.247 to -0.123), presence of strabismus (P = 0.017, 95%CI 0.063-0.601), anisometropia at 1 month postoperatively (P = 0.001, 95%CI 0.126-0.478), and intereye difference in axial length at the last follow-up (P = 0.047, 95%CI 0.005-0.627).

CONCLUSION

Anisometropia might progress after bilateral IOL implantation in patients with pediatric cataract. Greater intereye difference in IOL power, presence of strabismus might increase the potential of progressive anisometropia.

Dynamic response to initial stage blindness in visual system development

Sensitive periods and experience-dependent plasticity have become core issues in visual system development. Converging evidence indicates that visual experience is an indispensable factor in establishing mature visual system circuitry during sensitive periods and the visual system exhibits substantial plasticity while facing deprivation. The mechanisms that underlie the environmental regulation of visual system development and plasticity are of great interest but need further exploration. Here, we investigated a unique sample of human infants who experienced initial stage blindness (beginning at birth and lasting for 2–8 months) before the removal of bilateral cataracts. Retinal thickness (RT), axial length (AL), refractive status, visual grating acuity and genetic integrity were recorded during the preoperative period or at surgery and then during follow-up. The results showed that the development of the retina is malleable and associated with external environmental influences. Our work supported that the retina might play critical roles in the development of the experience-dependent visual system and its malleability might partly contribute to the sensitive period plasticity.

Altered Refractive Development in Mice With Reduced Levels of Retinal Dopamine

Purpose

The neuromodulator dopamine (DA) has been implicated in the prevention of excessive ocular elongation and myopia in various animal models. This study used retina-specific DA knockout mice to investigate the role of retinal DA in refractive development and susceptibility to experimental myopia.

Methods

Measurements of refractive error, corneal curvature, and ocular biometrics were obtained as a function of age for both untreated and form-deprived (FD) groups of retina-specific tyrosine hydroxylase knockout (rTHKO) and control (Ctrl) mice. Retinas from each group were analyzed by HPLC for levels of DA and its primary metabolite (DOPAC).

Results

Under normal visual conditions, rTHKO mice showed significantly myopic refractions (F(1,188) = 7.602, P < 0.001) and steeper corneas (main effect of genotype F(1,180) = 5.1, P < 0.01) at 4 and 6 weeks of age compared with Ctrl mice. Retina-specific THKO mice also had thinner corneas (main effect of genotype F(1,181) = 37.17, P < 0.001), thinner retinas (F(6,181) = 6.07, P < 0.001), and shorter axial lengths (F(6,181) = 3.78, P < 0.01) than Ctrl mice. Retina-specific THKO retinas contained less than 15% of DA and DOPAC compared with Ctrl retinas, and the remaining DA had a significantly higher turnover, as indicated by DOPAC/DA ratios (Student's t-test, P < 0.05). Retina-specific THKO mice showed similar, yet more variable, responses to 6 weeks of FD compared with Ctrl mice.

Conclusions

Diminished retinal DA induced spontaneous myopia in mice raised under laboratory conditions without form deprivation. The relative myopic shift in rTHKO mice may be explained by steeper corneas, an unexpected finding. The chronic loss of DA did not significantly alter the FD myopia response in rTHKO mice.

What is the influence of parents' myopia on their children's myopic progression? A 22-year follow-up study

PURPOSE

To study the connection between parental myopia and their children's myopia from school age to adulthood.

METHODS

Two hundred and forty myopic schoolchildren (119 boys, 121 girls, mean age 10.9 years) with no previous spectacles for myopia were recruited to a 3-year treatment trial with different use of spectacles. Follow-ups were performed at mean ages of 13.9, 23.7 and 33.2 years for 238, 176 and 170 subjects respectively. Subjective refraction was calibrated to the spherical equivalent at corneal level (SEcor). Corneal refractive power (CR) and axial length (AL) were measured. Parental myopia was assessed with a questionnaire and the children assigned accordingly to one of three hereditary groups: both parents myopic H++, one myopic parent = H+- and no myopic parents = H-.

RESULTS

At baseline, no significant gender differences in age or SEcor were found in the different hereditary groups. Among girls, CR was significantly higher in hereditary group H++ (45.20 ± 1.08 D) than in group H+- (44.19 ± 1.28 D; p = 0.006) or H- (43.84 ± 1.18 D; p < 0.001). Among boys, the differences in CR between the hereditary groups were smaller and significant at follow-up 2 only. At follow-up end, among males, no significant differences between the hereditary groups were found in SEcor, CR, AL or myopic progression. Among females, myopic progression was 4.21 ± 1.81 D if one or both parents were myopic and -3.19 ± 1.36 D if neither parent was myopic (p = 0.035), but no significant difference was observed in AL.

CONCLUSIONS

The main difference between the hereditary groups was higher CR and myopic progression among females with myopic parents than non-myopic parents, but with no significant difference in AL with respect to parental myopia at study end.

Astigmatism among myopics and its changes from childhood to adult age: a 23-year follow-up study

PURPOSE

To study the prevalence of and changes in astigmatism from the onset of myopia at school age.

METHODS

Two hundred and forty myopic schoolchildren (mean age 10.9 years), with no previous spectacles, were recruited during 1983-1984 to a randomized 3-year clinical trial of bifocal treatment of myopia. Three annual examinations with subjective cycloplegic refraction were performed for 237-238 subjects. Subsequent examinations were performed at the mean ages of 23.2 and 33.9 years for 178 and 163 subjects, and the last examination, including data from prescriptions of different ophthalmologists, for 32 subjects. Corneal topography was studied at baseline, at the 3-year follow-up and at the two adulthood follow-ups. Prevalence and changes in refractive astigmatism (RA), in its polar values J0 and J45, and corneal astigmatism (CA) were studied.

RESULTS

Mean RA of the right eye increased during follow-up from 0.26 D (SD) ± 0.30 to 0.79 D ± 0.74. Mean CA was 1.07 D ± 0.74 at study end. The prevalence of RA ≥0.25 or ≥1.00 D increased from 54.9 and 3.8% to 83.4 and 34.4%, respectively. The main direction of the axis of RA and its polar value J0 and CA changed mainly through sphericity, from against the rule (ATR) to with the rule during the follow-up. There was a negative correlation between RA and spherical refraction in the ATR group at end of follow-up. Changes in RA were associated with increase in myopia and with changes in CA.

CONCLUSIONS

The prevalence and mean amount of RA associated with CA increased, and the axis of astigmatism changed among myopics during the 23-year follow-up.