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RESULTS
Out of the 122 individuals recruited in the study, there were 38 Malays (31.2%), 42 Chinese (34.4%) and 42 Indians (34.4%). In terms of the gender proportion of the sample, there were 67 females (54.9%) compared to 55 males (45.1%). The mean age was (54.58±12.44) years. The age, weight, height and basic metabolic index (BMI) were normally distributed (Table 1).
In the 244 eyes included in the study, the mean vertical optic disc diameter was (1.96±0.20)mm, the mean horizontal optic disc diameter was (1.84±0.20)mm and the mean optic disc area was (2.84±0.56)mm2 (Table 2).
In this study, Indian showed larger vertical disc diameter and disc area compared with Malay and Chinese. However, the differences between the three ethnic groups were not statistically significant for vertical optic disc diameter (P=0.54), horizontal optic disc diameter (P=0.72) and optic disc area (P=0.69) (Figure 1). The diameters of optic disc published in earlier reports from different countries are given in Table 3.
The mean vertical optic disc diameter in the present study is slightly higher than the readings reported by Quigley et al[9], Winder et al[10], GarwayHeath et al[11], Kashiwaqi et al[12], and Jonas et al[13], but lower than the reports of Sekhar et al[14] and Landers et al[15]. Similarly, the mean horizontal optic disc diameter was higher than the figures of Quigley et al[9] and Jonas et al[13], but lower than Sekhar et al[14].
In this study, Chinese had longer axial length compared to Malay and Indian. These differences account for 19% of variations in axial length among the three ethnic groups (η2=0.19, ANOVA). However, the axial length showed no statistically significant relationship with the optic disc diameters and area among three ethnic groups (P=0.335, P=0.254 and P=0.277 respectively). A significant, but weak, negative correlation was found between the age progression and the axial length (P=0.014, r=0.163). This might be attributed to the increase in the echoic density of the lens with age progression, which results in a false shorter axial length with age progression since sound travels faster in hard lens than soft lens.
Vertical and horizontal optic disc diameters and optic disc area were statistically independent of gender [P=0.32 (95% CI: 0.020.07);P=0.45 (95% CI: 0.030.07) and P=0.40 (95% CI: 0.080.21) respectively]. The intraocular pressure showed a negative but weak correlation with vertical optic disc diameter and optic disc area (P=0.02; r=0.15 and P=0.01; r=0.16 respectively), but not with the horizontal disc diameter (P=0.29).
Table 1Case characteristic of 122 subjects(略)
Table 2The vertical disc diameter, horizontal disc diameter and disc area among the three ethnic groups(略)
Figure 1Measurements of vertical disc diameter, horizontal disc diameter and disc area among the three ethnic groups which constitute the sample of the study(略)
DISCUSSION
When one measures optic disc area using fundus photography, the error caused by magnification should be taken into consideration. Many formulae were used to calculate this magnification error caused by the camera optical system and the patients refractive error. The camera used in our study has the facility of automated correction of magnification error based on Littmanns formula[16]. This requires entering the data of corneal radius of curvature and refractive error of the eye into the camera software program before the measurements on the optic disc.
The majority of studies done to assess the effect of aging on optic disc diameter found no significant correlation[11,17,18]. However, some other studies found increasing optic disc diameter with age[5,19]. In our study, there was no significant correlation between age and optic disc diameter.
Table 3The mean vertical and horizontal optic disc diameters as found in our study compared to previous similar studies(略)
Ramrattan et al[3] found a weak correlation between height and optic disc area, but they did not study the correlation of the height with other optic disc dimensions (such as vertical and horizontal diameters). In this study, a similar correlation with area, and, in addition, significant correlations between height and optic disc diameters (vertical and horizontal) were observed. An attempt was made to correlate between weight and body mass index (BMI) and the optic disc area, but there was no correlation between the two parameters.
Many studies discussed the relationship between gender and optic disc size. Some postulated larger optic disc size in males than females[2,6,20], and some did not[12,17]. In this study, there was no significant correlation between gender and optic disc size.
In this study, the Malay and Chinese groups were found to have the same mean optic disc area [(2.82±0.50)mm2 and (2.82±0.57)mm2 respectively]; on the other hand, Indian group had a larger mean optic disc area compared to the other two groups [(2.88±0.59)mm2]. Thus, Malay population is considered to have optic disc size similar to that of Chinese.
Jonas et al[18] studied the predictive factors that affect the progression of primary open angle glaucoma, and found no significant correlation between the optic disc size and the presence and progression of glaucoma. However, Burk et al[21] found that subjects with large optic discs are more susceptible to glaucomatous optic disc size. In this study, the presence of glaucoma was associated with larger optic disc compared to nonglaucoma subjects.
Oliveira et al[22] found a significant correlation between the axial length of the eye and optic disc. However, there was no significant correlation between the axial length and the optic disc area in our study.
In conclusion, the optic disc size in Malaysian population was larger than that of Caucasians. However, in Malaysia the vertical optic disc diameter and optic disc size were slightly larger in Indians than in Malays and Chinese.
【参考文献】
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