This study analyzed the data from a national health survey (KNHANES) and determined the prevalence and risk factors for SSOH. SSOH prevalences have been reported in a number of Asian studies. Yamamoto et al. reported that prevalence of SSOH in Japan, as determined by fundus photography, was 0.3% among their subjects and 0.2% among the general population . Han et al., reviewing photographs of 3,905 hospital-based Korean subjects, calculated a 0.08% prevalence . However, those study subjects were not representative of the general Korean population but only of the one institute where they were examined.
Our study demonstrated that the prevalence of SSOH in Korea is actually as high as 0.24%. The discrepancy in the prevalence of SSOH between the present study and Han’s study is attributable to the difference in the study population. Our study participants constituted a representative Korean population, while those in Han’s study are patients who had visited a health promotion center in a tertiary referral hospital. Han et al. noted, as a limitation, the possibility that participants with a known optic disc anomaly might not have been included. Additionally, different examinations were used for SSOH diagnosis. A combination of stereo disc photography, red-free retinal nerve fiber layer, and Humphrey visual field test was used in the study by Han et al., whereas fundus photography and frequency-doubling technology (FDT) perimetry were used in our study. The difference in the diagnostic ability between these examination sets would have led to the difference in the prevalence.
In fact, ours is the first study to investigate the Korean prevalence of SSOH in a representative random population. Considering the ethnic similarity between Koreans and Japanese along with Yamamoto et al.’s result, we believe that the prevalence of SSOH obtained in our study is an accurate estimate of its true prevalence.
SSOH has been noted to occur both unilaterally and bilaterally with relatively equal frequency [2, 6]. The percentage of unilateral SSOH in our series was slightly higher than those reported by other investigators. There were no statistically significant differences in prevalence by age or gender. Although several reports have indicated a female predisposition to SSOH [1, 3, 7], no significant gender difference has yet been documented anywhere. Further research will be necessary for helpful clarification of such issues.
Tendencies toward lower birth weight, shorter gestation time and poorer control of maternal diabetes were associated with increased risk of SSOH . These associations could be due to unfavorable conditions during development that affect fetal growth, general fetal development and the risk of malformation. Brodsky et al. suggested, based on cases of identical twins, genetic susceptibility as a possible risk of SSOH . Unoki et al. also noted a familial case of SSOH . In any case, the pathogenic mechanism of SSOH remains obscure.
The results of this study indicated that maternal history of diabetes and paternal history of IHD are significantly associated with SSOH. Whereas reported risk factors for SSOH have been relatively rare in the literature, several studies have shown a correlation between insulin-dependent diabetic mothers and SSOH in their children [7, 8]. Our present study served to reconfirm the positive relationship between maternal history of diabetes and SSOH in children. A possible pathology is selective interference of the teratologic mechanism of insulin-dependent diabetes mellitus with the early-gestational development of superior retinal ganglion cells.
As for paternal history of IHD, it has gone completely unreported in the literature, and remains to be confirmed in future studies. Our present results, uniquely, showed paternal history of IHD to be an independent risk factor for SSOH. A possible explanation is related to altered levels of growth factors and insulin sensitivity. Several studies have reported an association between optic nerve hypoplasia and endocrine disturbances including growth hormone (GH) deficiency and insulin resistance [10, 11]. Paternal IHD has been reported for offspring with insulin resistance , which association could increase the risk of optic nerve hypoplasia.
Paternal IHD was found to be associated with the GH level of offspring. Previously, paternal IHD has been reported for offspring with polymorphism in angiotensin converting enzyme (ACE) . ACE variation, moreover, has been associated with lower levels of growth hormone and insulin-like growth factors, because the ACE polymorphism site is located nearby the GH gene site . It is not clear if the finding of the association with the GH level of offspring, then, would explain an increased risk of SSOH. However, this association is a possible explanation of genetic susceptibility to SSOH. Because determinative genetic information could not be obtained in this study, and because the association between paternal IHD and congenital malformation remains controversial, further study in efforts to prove that association certainly is warranted.
This study has several limitations. The analysis relied on self-reported data on medical conditions. As a result, the prevalences could have been underestimated or influenced by the individual’s memory. Another limitation of the current analysis is that we were unable to assess disease onset, duration, or severity, as pertinent data were not collected by KNHANES.
Notwithstanding the limitations of the present study, the strength of this study is that the sample size is significantly large, and indeed, KNHANES is based on a representative sample of the Korean population. Therefore, the proportions and odds ratios obtained in this study are representative of the Korean population as well.