Congenital anomalies of the OD are rare but they are crucial to diagnose accurately, as they can cause visual impairment or pseudopapilledema apperence. Accurate and precise examination of optic nerve head morphology is important to make correct diagnosis and functional assessment. Substantial interindividual and intraindividual morphological variations and factors such as race and age determine the normal range. Estimating the pervalence of these variations and anomalies is essential because it is representative of the characteristics of the population. After determining which diseases/anomalies are common in a population, by giving priority to the diseases/anomalies with a high prevalence in the population the accurate diagnosis can be easily reached without wasting time, money and energy.
There were a few studies described the prevalences of various OD anomalies [5–10]. To our knowledge this is the first study estimating the prevalence of all congenital OD anomalies from Turkey. In this study, the prevalence of OD anomaly was 3.12%. Bassi et al found it to be 1.1% in the adult South Indian population [5]. The reasons for the difference in prevalence between our study and other studies may be due to the racial differences or age and gender distribution differences between examined population groups. In addition, our study also was a hospital-based study, namely, all patients who presenting with various ophthalmic problems were screened in this study. Bassi et al reported 63.7% were males and 36.3% were females and the mean age at presentation was 51.4±8.9 years [5]. Contrary to Bassi et al, in this study, the gender ratio was almost equal and the mean age of cases was younger. These differences may be caused by the fact that our study was a hospital-based study and there was no difference between the number of male and female patients applying to hospital or the genetic characteristics of our patients because of geographical differences. If our study was population-based rather than hospital-based, the prevalence of ON anomalies could have been lower. In following paragraphs, we separately discussed each congenital OD anomaly that we observed in Turkey.
The prevalence of tilted disc in Turkey population was found 0.83% in our study. As is known the tilted disc and PPA are the characteristic shape of myopic disc [6]. Similar to this information, in our study, SE was compatible with myopic shift in tilted disc and PPA cases. The prevalence of tilted disc was found 1.6% in Australia and 0.49% in Northern China [7, 8]. Both study used inferior or nasal disc tilting as the diagnostic criterion for a tilted disc appearance as in our study. In another study was reported that the prevalence of tilted optic discs was 3.5% in adult Chinese population in Singapour but when the definition of tilted optic discs included tort, the prevalence decreased to 2.4% [6]. They explained that this variation is resultant of diversity in definitions of tilted and torted optic discs, different inclusion criteria, and varying research methods between the studies. Also, the difference of race/ethnicity between the study groups could be explanation of these variety.
PMNF is caused by oligodendrocytes abnormally migrated into the retina, and is a relatively rare finding in a general ophthalmological clinic [9]. You et al. reported PMNF prevalence in adults 0.4% in China, Kodama et al. reported 0.57% in Japan, Bassi et al. reported 0.28% in South India [5, 9, 10]. The prevalance of PMNF was found 0.56% in our study, similar to other studies.
PPA is a non-specific finding. It can occur in both benign and pathologic conditions (glaucoma, myopia) and can also be a result of aging. It is not well understood that how to the peripapillary region is affected in these diseases [11]. Liu at al. reported that the area of PPA was associated with SE power and as SE power increased, the PPA area increased linearly [12]. Similar to literature, two-third of patients with PPA had high myopic SE power in our study.
The true congenital optic disc pigmentation is typically described as discrete, irregular and granular in appearance. Prevalence of OD pigmentation was found 0.03% in a previous study [5]. Contrarily previous study we found higher rate in our study (0.29%).
ODD is acellular deposits located in the optic nerve head which progressively become more calcified and allow them to be visible on ophthalmoscopy. The prevalence of ODD in children is about 0.4% [13]. In adults, the prevalence of ODD was found 2% in previous studies [14, 15]. In our study, ODD was seen less common in Turkish population than literatüre (0.27%).
Epipapillary glial tissue is a source for intrapapillary proliferations, as the glial tissue surrounds the area of cavernous atrophy of the optic nerve and is defined with other optic disc anomalies likewise ODP [16]. Bassi et al. found the prevalence of epipapillary glial tissue 0.28% [5]. The prevalance of epipapillary glial tissue in our study was compatible with the literatüre (0.22%).
A persistent hyaloid artery results from persistant hyaloid vascular system; a small stalk of fibrous tissue on the optic disc is also known as Bergmeister papilla. Its prevalence was reported 0.03% in South India in adults [5]. Unlike to this study, we determined the prevalence of Bergmeister papilla higher (0.2%).
PVL originates from a branch of either retinal artery or vein ending at the disc or surrounding optic disc [17]. The prevalence of PVL was 0.115% in Japan, and 0.15% in Africa [18, 19]. Our result was conformable to previous studies.
ODH is a morphologically and functionally abnormal small optic disc which may appear ophthalmoscopically gray or pale in color and is often surrounded by a peripapillary halo [20]. In the adult Indian population and is seen only in 0.04% [5]. The prevalence of ONH in England was reported that 10.9 per 100,000 [21]. Our study shows similar results with Asian population (0.09%).
The optic disc changes like staphyloma of OD is a common characteristic of highly myopic eyes and may be caused by scleral stretching in the peripapillary region [22]. In our study, staphyloma of OD was associated with high myopic eyes (0.02%)
ODP are focal depressions located at the bottom of the ONH that can be associated with a non-rhegmatogenous serous macular detachment [20]. Its prevalence was found 0.02% in China, and 0.01% in South India similar to our results [5, 23].
Optic disc coloboma (ODC) is a congenital malformation of the optic disc which is caused by a defective closure of the embryonic fissure that can cause severe visual impairment or blindness [20]. Skriapa Manta et all reported prevalence of ODC 0.0089% in chilhood population in Sweden, Bassi et al. reported 0.08% in adult population [5, 24]. During our study, we found the prevalence of ODC like previous studies.
Morning glory disc anomaly has a characteristic appearance and may result from abnormal development of the lamina cribrosa and posterior sclera [25]. Ceynowa et al. reported the prevalance of Morning glory disc anomaly was 0.26% [26]. Our results supportted to literature (0.02%)