**Purpose.**:
To analyze the prevalence and associations of anisometropia with spherical ametropia, astigmatism, age, and sex in a refractive surgery population.

**Methods.**:
Medical records of 27,070 eyes of 13,535 refractive surgery candidates were reviewed. Anisometropia, defined as the absolute difference in mean spherical equivalent powers between right and left eyes, was analyzed for subjective (A_{subj}) and cycloplegic refraction (A_{cycl}). Correlations between anisometropia (>1 diopter) and spherical ametropia, cylindrical power, age, and sex, were analyzed using χ^{2} and nonparametric Kruskal–Wallis or Mann–Whitney tests and binomial logistic regression analyses. Power vector analysis was applied for further analysis of cylindrical power.

**Results.**:
Prevalence of A_{subj} was 18.5% and of A_{cycl} was 19.3%. In hyperopes, logistic regression analysis revealed that only spherical refractive error (odds ratio [OR], 0.72) and age (OR, 0.97) were independently associated with anisometropia. A_{subj} decreased with increasing spherical ametropia and advancing age. Cylindrical power and sex did not significantly affect A_{subj}. In myopes all explanatory variables (spherical power OR, 0.93; cylindrical power OR, 0.75; age OR, 1.02; sex OR, 0.8) were independently associated with anisometropia. Cylindrical power was most strongly associated with anisometropia. Advancing age and increasing spherical/cylindrical power correlated positively with increasing anisometropia in myopic subjects. Female sex was more closely associated with anisometropia.

**Conclusions.**:
This large-scale retrospective analysis confirmed an independent association between anisometropia and both spherical ametropia and age in refractive surgery candidates. Notably, an inverse relationship between these parameters in hyperopes was observed. Cylindrical power and female sex were independently associated with anisometropia in myopes.

^{ 1 }

^{ 2 }The prevalence of anisometropia is 0 to 28%.

^{ 3,4 }Several studies have documented a positive association between the level of anisometropia and the degree of spherical ametropia,

^{ 5 –9 }astigmatism,

^{ 5 }or age.

^{ 1,10 }

^{ 7 }and Qin et al.

^{ 11 }have assessed to which extent anisometropia and spherical ametropia, astigmatism, and age are independently associated. This is an important issue, given that Guggenheim et al.

^{ 12 }reported an association between spherical and cylindrical refractive errors. In the study by Tong and colleagues,

^{ 7 }multiple logistic regression was used to identify explanatory variables (risk factors) that were independently associated with the presence of anisometropia in Singaporean schoolchildren ranging in age from 7 to 9 years. They found that the presence of myopia (odds ratio [OR], 4.60), age (OR, 1.19 per year), and sex (OR, 1.19 in females) were all independently associated with anisometropia. Qin et al.

^{ 11 }showed that there is an independent association between anisometropia and both spherical ametropia and astigmatism in a group of 90,884 subjects attending optometry practices in the United Kingdom.

*n*= 395). The hyperopia group included subjects with SE > 0 D. We defined anisometropia as the absolute difference in SE powers between the right and the left eyes, because a recent analysis has demonstrated that classification of anisometropia on the basis of mean SE power (A

_{MSE}) or spherical ametropia (A

_{SPH}) has no effect on the significance of the test results.

^{ 11 }It was calculated separately for subjective and cycloplegic refraction. Each eye was categorized into one of four anisometropia severity groups. The four groups were defined as nonanisometropia (<1.00 D); mild anisometropia (1.00–1.99 D); moderate anisometropia (2.00–2.99 D); and severe anisometropia (≥3.00 D). Subjects were divided into one of six age categories: group 1, <20 years old; group 2, 20–29 years old; group 3, 30–39 years old; group 4, 40–49 years old; group 5, 50–59 years old; and group 6, ≥60 years old. In addition, analyses were also performed on only those subjects ranging in age from 20 to 40 years (inclusive).

_{0}, J

_{45}) was first described by Thibos et al.

^{ 13 }Advantages of the power vector representation of a spherocylinder lens for numerical and graphical analysis of optometric data are described for the statistical distribution of refractive errors. Therefore subjective refractions in conventional script notation [(S)phere, (C)ylinder, axis (α)] were converted to power vector coordinates by the following formulas: J

_{0}= (−

*C*/2) cos (2α) and J

_{45}= (−

*C*/2) sin (2α).

^{ 12 }

^{ 11 }) and only data for the less ametropic eye were included in this study. For statistical analysis, data description was based on medians and quartiles of the respective anisometropia calculations. Arithmetic means and SD were calculated for further descriptive comparison. Because of the nonnormal distribution of the data, nonparametric tests were used throughout the study. The χ

^{2}test or, depending on expecting values of the cells, the Fisher's Exact Test (expecting value <5) were used for comparisons of categorical data between groups. Due to the complexity of the Fisher's Exact Test it could technically not always be applied. The Kruskal–Wallis or Mann–Whitney tests were used for comparisons of continuous measures between groups. The two-sample Kolmogorov–Smirnov test was used to compare distributions. A value of

*P*< 0.05 was considered statistically significant.

^{ 11 }To evaluate these associations more closely, additional logistic regression models were computed in which age was analyzed as a categorical variable with 10-year intervals. In these groups, ORs for anisometropia were calculated for each decade compared with the preceding decade in subjects ranging in age from >20 to >60 years, with adjustment for spherical ametropia, astigmatism, and sex, whereas other variables were controlled for.

_{subj}) in the whole study population was 0.37 D (0.12–0.75 D; 25th to 75th quartiles) and the prevalence of A

_{subj}> 1 D was 18.5%. Mild anisometropia was observed in 13.9%, moderate anisometropia in 3.2%, and severe anisometropia in 1.4% of the subjects. The median level of A

_{cycl}was 0.37 D (0.12–0.75) and mean overall prevalence of A

_{cycl}> 1 D was 19.3%.

_{subj}in myopic subjects and a 16.6% prevalence in hyperopic subjects. Clinical characteristics and descriptive statistics of parameters for the myopic and hyperopic candidates are shown in Table 1.

Factor | Anisometropia | |||||
---|---|---|---|---|---|---|

<1 | ≥1 | Total | ||||

Number | % | Number | % | Number | % | |

Patients | 11,031 | 81.5 | 2,504 | 18.5 | 13,535 | 100.0 |

Male | 4,748 | 43.0 | 942 | 37.6 | 5,690 | 42.0 |

Female | 6,283 | 57.0 | 1,562 | 62.4 | 7,845 | 58.0 |

Myopia | 9,832 | 81.3 | 2,265 | 18.7 | 12,097 | 81.7 |

Hyperopia | 1,199 | 83.4 | 239 | 16.6 | 1,438 | 18.3 |

Range | Mean (±SD) | Range | Mean (±SD) | Min/Max | Mean (±SD) | |
---|---|---|---|---|---|---|

Age, y | 18–74 | 35.7 (±10.0) | 20–68 | 37.0 (±9.7) | 18–74 | 35.9 (±10.0) |

Myopia | ||||||

SE | −12.9/−0.13 | −3.7 (1.9) | −11.5/−0.13 | −0.39 (1.9) | −12.9/−0.13 | −3.7 (1.9) |

SubjectiveSph | −12.0/2.8 | −3.2 (1.9) | −11.0/2.3 | −3.4 (1.9) | −12.0/2.8 | −3.3 (2.0) |

SubjectiveCyl | −6.5/0.0 | −0.9 (0.8) | −6.5/−0.13 | −1.1 (0.96) | −6.5/0.0 | −0.9 (0.9) |

Hyperopia | ||||||

SE | 0.0/7.13 | 2.3 (1.2) | 0.0/−0.13 | 1.9 (1.1) | 0.0/7.1 | 2.2 (1.2) |

SubjectiveSph | 0.5/8.25 | 2.9 (1.2) | 0.75/−0.13 | 2.5 (1.1) | 0.5/8.25 | 2.8 (1.2) |

SubjectiveCyl | −6.8/0.0 | −1.25 (1.3) | −5.8/−0.13 | −1.2 (1.2) | −6.8/0.0 | −1.2 (1.2) |

^{ 11 }

_{subj}(Fig. 1B) and A

_{cycl}(Fig. 1C) with increasing ametropia. Of note, there were no subjects with hyperopia > +4 D showing moderate or severe A

_{subj}(Fig. 1B). To investigate the relationship between anisometropia and spherical ametropia more quantitatively, we examined the median level and mean rank of anisometropia in each of the refractive error categories. A positive association was evident in myopes (Fig. 1D; Fisher's Exact Test,

*P*< 0.001 and Kruskal–Wallis chi-square test: χ

^{2}= 86.371, degrees of freedom [

*df*] = 9 with

*P*< 0.001). In hyperopes, the lowest prevalence and corresponding lowest mean rank of anisometropia were observed in the > +4 D hyperopia subgroup. The correlation was statistically borderline significant (Fig. 1E; Pearson's chi-square test: χ

^{2}= 25.564,

*P*= 0.017; Kruskal–Wallis: χ

^{2}= 12.378,

*df*= 6,

*P*= 0.02. Note that 30% of the cells had expected counts of <5).

_{0}, and J

_{45}) and nonvectorial (spherical and cylindrical powers) approaches were used. In vectorial analyses, both the prevalence and severity of anisometropia varied with the level of astigmatism, but the distribution pattern differed for J

_{0}and J

_{45}. For J

_{0}, we observed an increasing prevalence and severity of anisometropia with increasing positivity of J

_{0}(Fig. 2A; Kruskal–Wallis test χ

^{2}= 72.684,

*df*= 4,

*P*< 0.001). For J

_{45}, we found a symmetrical V-shaped prevalence of anisometropia with a minimum for J

_{45}between −1 D and +1 D (Fig. 2B; Kruskal–Wallis test χ

^{2}= 12.236,

*df*= 3,

*P*= 0.007). A relationship between anisometropia and cylindrical power was evident in nonvectorial analyses. In the eyes of myopes, the prevalence of anisometropia increased significantly as cylindrical power increased (Fig. 2C), as did the severity of anisometropia (Fig. 2G; Kruskal–Wallis test χ

^{2}= 154.121,

*df*= 4,

*P*< 0.001). In contrast, in the eyes of hyperopes, the prevalence of anisometropia did not increase significantly as cylindrical power increased (Fig. 2D). Furthermore, there was no significant increase in the severity of anisometropia with increasing cylindrical power in hyperopes. (Fig. 2H; Kruskal–Wallis test χ

^{2}= 4.700,

*df*= 4,

*P*= 0.319).

^{2}= 58.426,

*df*= 5,

*P*< 0.001).

*P*< 0.001; Kruskal–Wallis test χ

^{2}= 75.405,

*df*= 5,

*P*< 0.001) and decreased in the seventh decade. In hyperopes the prevalence of anisometropia tended to decrease with increasing age up to the fifth decade. In the sixth and seventh decades this trend of negative correlation became more prominent (Fig. 3C; Pearson's test χ

^{2}= 33.313,

*df*= 15,

*P*= 0.004; Kruskal–Wallis test χ

^{2}= 22.678,

*df*= 5,

*P*< 0.001. Note that 37% of the cells had an expected count of <5).

^{2}= 25.261,

*df*= 3; Mann–Whitney test

*z*= −4.1; for both tests

*P*< 0.001). Although the median level of 0.37 D and distribution parameters of quartiles (Figs. 4C, 4D; Q25–Q75, 0.13–0.75) of anisometropia between male and female subjects were equal, the difference between mean ranks of the sex groups reached statistical significance due to higher anisometropia prevalence in female subjects.

^{2}= 25.285,

*df*= 3; Mann–Whitney test

*z*= −4.2, for both tests

*P*< 0.001), whereas in hyperopic subjects the prevalence of anisometropia was not significantly different between both sexes (Fig. 4B; Pearson's χ

^{2}= 1.16,

*df*= 3,

*P*= 0.725; Mann–Whitney test

*z*= −2.17,

*P*= 0.828). Logistic regression analysis revealed that female sex was independently associated with anisometropia in myopic subjects (for males compared with females, OR, 0.802; 95% CI, 0.728–0.883;

*P*< 0.001). These results are shown in Table 2. The only effect reaching statistical significance in hyperopes was in 20- to 40-year-old subjects (for males compared with females: OR, 0.526; 95% CI, 0.318–0.871;

*P*= 0.01), where the significance level would be borderline when taking into account multiple testing.

Model* | Variable† ‡ | Regression Coefficient | SE of Coefficient | Significance§ | OR | 95% CI of OR | k ‖ | |
---|---|---|---|---|---|---|---|---|

Lower | Upper | |||||||

Hyperopes | Spherical power | −0.329 | 0.069 | <0.001 | 0.720 | 0.629 | 0.824 | 2.25 |

All ages (n = 1438) | Cylindrical power | 0.025 | 0.067 | NSD | 1.026 | 0.900 | 1.169 | ¶ |

Nagelkerke R = 0.039 | Age, y | −0.024 | 0.007 | <0.001 | 0.976 | 0.964 | 0.989 | 47 |

Sex, male | −0.074 | 0.144 | NSD | 0.929 | 0.701 | 1.231 | ¶ | |

Constant | 0.394 | 0.396 | NSD | 1.483 | — | |||

Myopes | Spherical power | −0.072 | 0.012 | <0.001 | 0.931 | 0.910 | 0.953 | ¶ |

All ages (n = 12,094) | Cylindrical power | −0.289 | 0.026 | <0.001 | 0.749 | 0.712 | 0.788 | −2.5 |

Nagelkerke R = 0.032 | Age at TT | 0.021 | 0.003 | <0.001 | 1.021 | 1.016 | 1.026 | 53 |

Sex, male | −0.221 | 0.049 | <0.001 | 0.802 | 0.728 | 0.883 | ¶ | |

Constant | −2.633 | 0.109 | <0.001 | 0.072 | — | |||

Hyperopes | Spherical power | −0.480 | 0.112 | <0.001 | 0.619 | 0.497 | 0.770 | 1.5 |

Age 20 to 40 years (n = 446) | Cylindrical power | 0.154 | 0.106 | NSD | 1.167 | 0.948 | 1.436 | ¶ |

Age, y | 0.007 | 0.020 | NSD | 1.007 | 0.967 | 1.048 | ¶ | |

Nagelkerke R = 0.108 | Sex, male | −0.643 | 0.257 | 0.013 | 0.526 | 0.318 | 0.871 | ¶ |

Constant | 0.311 | 0.762 | NSD | 1.364 | — | |||

Myopes | Spherical power | −0.076 | 0.014 | <0.001 | 0.927 | 0.901 | 0.824 | −7.00 |

Age 20 to 40 years (n = 8394) | Cylindrical power | −0.314 | 0.032 | <0.001 | 0.731 | 0.686 | 0.824 | −2.25 |

Age, y | 0.022 | 0.005 | <0.001 | 1.022 | 1.012 | 0.824 | ¶ | |

Nagelkerke R = 0.027 | Sex, male | −0.198 | 0.061 | 0.001 | 0.820 | 0.728 | 0.824 | ¶ |

Constant | −2.723 | 0.177 | <0.001 | 0.066 | — |

_{subj}. For hyperopes >50 years the probability of being anisometropic decreased significantly (OR, 0.502–0.336 per decade) with advancing age.

Model* | Variable | Regression Coefficient | SE of Coefficient | Significance | OR | 95% CI of OR | |
---|---|---|---|---|---|---|---|

Lower | Upper | ||||||

Hyperopes | Spherical power | −0.340 | 0.069 | <0.001 | 0.712 | 0.621 | 0.815 |

Age range, 20–99 y | Cylindrical power | 0.004 | 0.065 | NSD | 1.004 | 0.883 | 1.142 |

Nagelkerke R = 0.05 | |||||||

Sex, male | −0.049 | 0.145 | NSD | 0.952 | 0.717 | 1.264 | |

Age: 20–29 y | −0.596 | 0.697 | NSD | 0.551 | 0.140 | 2.162 | |

Age: 30–39 y | 0.017 | 0.392 | NSD | 1.017 | 0.472 | 2.195 | |

Age: 40–49 y | −0.087 | 0.271 | NSD | 0.917 | 0.539 | 1.559 | |

Age: 50–59 y | −0.688 | 0.245 | 0.005 | 0.502 | 0.311 | 0.812 | |

Age: ≥60 y | −1.090 | 0.384 | 0.005 | 0.336 | 0.158 | 0.714 | |

Myopes | Spherical power | −0.071 | 0.012 | <0.001 | 0.931 | 0.910 | 0.953 |

Age range, 20–99 y | Cylindrical power | −0.289 | 0.026 | <0.001 | 0.749 | 0.712 | 0.788 |

Nagelkerke R = 0.032 | |||||||

Sex, male | −0.220 | 0.049 | <0.001 | 0.803 | 0.729 | 0.884 | |

Age: 20–29 y | 0.285 | 0.262 | NSD | 1.330 | 0.796 | 2.225 | |

Age: 30–39 y | 0.332 | 0.137 | NSD | 1.394 | 1.065 | 1.825 | |

Age: 40–49 y | 0.448 | 0.099 | <0.001 | 1.566 | 1.290 | 1.899 | |

Age: 50–59 y | 0.474 | 0.109 | <0.001 | 1.607 | 1.299 | 1.988 | |

Age: ≥60 y | 0.444 | 0.302 | NSD | 1.559 | 0.862 | 2.820 |

_{cycl}> 1 D) in the whole study population was 19.3% compared with 18.5% for A

_{subj}. Median severity for both A

_{cycl}and A

_{subj}was 0.37 D (0.12–0.75). Mild A

_{cycl}was observed in 14.5% (A

_{subj}13.9%), moderate A

_{cycl}was observed in 3.2% (A

_{subj}3.2%), and severe A

_{cycl}in 1.6% (A

_{subj}1.4%) of the subjects. The prevalence of anisometropia (A

_{cycl}) in myopic subjects was 19.5% and in hyperopic subjects 18.0%, being slightly higher than the prevalence of A

_{subj}in myopic (18.7%) and hyperopic (16.6%) subjects (Figs. 1A, 1B). In summary, the trends and correlations between anisometropia and the analyzed variables were very similar for subjective and cycloplegic refraction with only minor differences.

_{subj}, in logistic regression analysis did not reach statistical significance, when calculated for cycloplegic refraction (OR, 0.801; 95% CI' 0.516–1.244;

*P*= 0.323). Second, the correlation between increasing hyperopia (spherical ametropia) and decreasing anisometropia in the 20- to 40-year-old hyperopes (subjective refraction; Table 2) was not verified by cycloplegic refraction recalculation (OR, 0.868,; 95% CI, 0.754–1.001;

*P*= 0.051). Third, in hyperopes age correlated negatively with A

_{cycl}for subjects older than 60 years (compared with an age range of 50–59 years; OR, 0.289; 95% CI, 0.125–0.670,;

*P*= 0.004). For A

_{subj}statistical significance was also evident in hyperopes ranging in age from 50 to 59 years (compared with the preceding decade). Fourth, in myopes the observed continuous increase in the OR with each decade of advancing age from the third to the fifth decades for A

_{subj}was expanded to the sixth decade when calculated for cycloplegic refraction (>60 years compared with the preceding decade; OR, 1.903; 95% CI, 1.069–3.387;

*P*= 0.029).

^{ 1 }). Yamashita et al.

^{ 14 }reported an anisometropia (SE difference > 1 D) prevalence of 3.1% in school children, whereas Tong et al.

^{ 7 }reported an anisometropia (SE difference > 1.5 D) rate of 1.57% in school children. Another study by Wu et al.

^{ 15 }revealed an anisometropia prevalence of 14.4% in Singaporean males ranging in age from 16 to 25 years, significantly higher than that observed in children. In the Blue Mountains Eye Study, Guzowski et al.

^{ 5 }reported that anisometropia was present in 14.7% of the participants (3402 Australians older than 50+ years), with moderate to high anisometropia present in 2.1% of the subjects. The authors were able to further restrict their analysis to phakic subjects, excluding potential effects of intraocular lens implant power mismatches. Thus, the 18.5% prevalence of A

_{subj}(mild 13.9%; moderate 3.2%; severe 1.4%) and 19.3% prevalence of A

_{cycl}in our cohort of refractive surgery candidates in central Europe is higher than that reported for the general population of developed countries,

^{ 5,8 }but comparable to the approximately 17% prevalence of anisometropia reported by Qin et al.

^{ 11 }

^{ 5 }and Tong et al.

^{ 7 }did not observe a sex difference with regard to anisometropia, Qin et al.

^{ 11 }found that the prevalence of anisometropia was higher in females compared with that in males, with the difference just reaching statistical significance (

*P*= 0.02). We found a statistically significant higher prevalence of anisometropia in female subjects, in particular female myopic candidates (Fig. 4A). In addition our analysis suggests that the female sex is independently associated with anisometropia in myopic subjects (

*P*< 0.001), but since the median level of anisometropia between the two sexes was equal (0.37 D) this effect of higher prevalence in female subjects is not clinically relevant.

^{ 5 }vs. selected subjects

^{ 11 }and our study), differences in definition of anisometropia (SE difference > 1.5 D

^{ 7 }vs. SE difference > 1 D

^{ 11 }and our study) and differences in recruiting refractive data (spectacle prescriptions,

^{ 12 }cycloplegic autorefraction,

^{ 7 }subjective refraction

^{ 9 }) must be considered when comparing our results with other published data.

^{ 10 }has summarized data on the age-related prevalence of anisometropia from a comprehensive meta-analysis of the literature, and noted a positive linear relationship with the prevalence increasing by approximately 1.4% for each decade increase in age. Qin et al.

^{ 11 }further explored the association between anisometropia and spherical ametropia, astigmatism, age, and sex in a group of 87,759 subjects attending optometry practices in the United Kingdom. One drawback of the Qin study is the inability to exclude subjects who present anisometropia as a result of unilateral cataract extraction or untreated cataracts, because detailed ophthalmological examination was not available. In contrast, information related to ocular history, subjective and cycloplegic refraction, and detailed slit-lamp examination were available for the 13,535 subjects included in the present study. Because the data set of Qin et al.

^{ 11 }comprised only spectacle prescriptions, it is probable that the full extent of myopia might have been overestimated in some younger subjects, due to incomplete relaxation of accommodation, or that some younger hyperopes were prescribed only a partial correction. Both of these events would be less likely to occur in adults, due to the decline in the amplitude of accommodation with age.

^{ 5,9 }However, this association has to be interpreted with caution due to a potential bias as a consequence of the use of spherical equivalent anisometropia.

^{ 16 }Therefore, we used logistic regression analysis to control for the individual effects of spherical ametropia and astigmatism (explanatory variables) on anisometropia and to reveal an independent association of each contributing factor. Qin et al.

^{ 11 }were the first to show an independent association between anisometropia and both spherical ametropia and astigmatism. Our study confirmed the independent association between anisometropia and both spherical ametropia and astigmatism in myopes. Logistic regression analysis was used to control for the effects of all explanatory variables. In contrast to the study by Qin et al.,

^{ 11 }the prevalence and level of anisometropia in hyperopic subjects of our study did not increase as spherical (Fig. 1B) and cylindrical power (Fig. 2D) increased and we did not find a positive linear association between increasing anisometropia and increasing ametropia. In turn our data revealed a decreasing prevalence (Figs. 1B, 1C) and severity (Figs. 1E, 1F) of anisometropia with increasing hyperopic ametropia.

^{ 5,11 }we did not observe a remarkable symmetry in the prevalence of anisometropia as refractive errors diverged from zero.

*n*= 1438) resulting in sampling variation for small hyperopic subgroups might limit the validity of our findings. Young hyperopic subjects with good UDVA and accommodative capacity do not usually visit refractive clinics to correct refractive error. Anisometropic low hyperopes may decide to visit a clinic for laser vision correction, whereas nonanisometropic low hyperopes with good accommodative capacity may not. This resulting selection bias could partly explain the relative abundance of anisometropic hyperopic subjects (<40 years) in our data set and the decreasing prevalence and severity of anisometropia with increasing hyperopia. The possible overrepresentation of anisometropic young hyperopes could, in turn, potentially mask a relationship between increasing anisometropia and increasing age in hyperopic subjects.

^{ 10,17 }This in turn could also affect the outcome of laser refractive surgery at advanced ages (>45 years). Since it is widely accepted that the prevalence of myopia is increasing over the years

^{ 18,19 }and that anisometropia is positively correlated with myopia,

^{ 11 }future longitudinal studies covering all age groups and focusing on the impact of anisometropia on progression of refractive errors will be of great interest. If future longitudinal studies will confirm the observed association between anisometropia/astigmatism and age, refractive surgery for myopia in prepresbyopic subjects may achieve emmetropia for only a limited period.

^{ 11 }found a strong association between anisometropia and age, although our detailed evaluation suggested that the relationship differed in myopic and hyperopic subjects.

^{ 11 }we observed an inverse relationship between anisometropia and spherical ametropia and age in hyperopic subjects: anisometropia decreased with increasing spherical ametropia and advancing age. Cylindrical power and sex did not significantly affect anisometropia in hyperopes.