Abstract
Purpose:
To investigate the baseline position of the central vascular trunk (CVT) and the characteristics of the optic nerve head (ONH) in newborns.
Methods:
CVT position was evaluated based on fundus images obtained from newborns who had undergone eye-screening examinations. It was then graded according to the optic disc area as follows: grade 1, within central 4%; grade 2, within central 9%; grade 3, within central 16%; grade 4, within central 25%; grade 5, outside central 25% of optic disc area. The direction of the CVT position was determined in cases of grade 2 or more as superior, inferior, nasal, and temporal, relative to the optic disc center. The ovality index and the vertical cup-to-disc ratio were determined as well.
Results:
In 1000 fundus images from 1000 newborns, 87.1% showed grade 1 (95% confidence interval 84.7–88.8), and 10.7% showed grade 2. The most common CVT direction was central (87.1%, grade 1), followed by nasal (11.0%) and inferior (1.2%). The ovality index was 1.28 ± 0.09 (range, 1.01–1.61). The ONH shape was vertically oval and highly uniform. The average vertical cup-to-disc ratio was 0.29 ± 0.13 (range, 0.00–0.67).
Conclusions:
The CVT of newborns was located in the central area of the ONH in most cases. The shape of the optic disc was vertically oval, and very similar among the newborns. Considering the high variability of ONH morphology and the diverse location of the CVT in adults, our result suggests that the shape of the ONH and the CVT position might change during eyeball growth.
The morphology of the optic nerve head (ONH) is highly variable among individuals.
1–3 The ONH area shows an interindividual variability of approximately 1:7, and the ovality index (defined as the ratio of the largest diameter to the smallest diameter of the ONH), which is one of the morphologic parameters of the ONH, shows a variability of about 1:2 in the general population.
4 Most studies on the ONH have been conducted with adult populations
2,3,5,6; there are only a few such studies dealing with infants.
7–11 Previous work has revealed that the optic nerve is incompletely developed at birth,
12,13 and that it undergoes rapid development in infancy and early childhood.
14 However, it is not certain whether the morphology of the ONH remains stable or changes during ONH development and eyeball growth.
Recently, our group reported that the shape of the ONH changes and that the central vascular trunk (CVT) of the ONH moves with myopic axial elongation in childhood.
15,16 Because the CVT is embedded in the dense connective tissue of the lamina cribrosa (LC), positional change (i.e., shift) of the CVT could be a clue indicating the extent and the direction of underlying LC shift.
16,17 We identified LC defect in the area opposite to the eccentric location of the CVT in the myopic eyes of healthy children, suggesting that changes in the CVT position and ONH morphology could be related to the risk of later developing glaucoma in myopia.
16 Subsequently, we showed that the position of the CVT relative to the center of the Bruch's membrane opening (BMO) was related to the initial damage location of myopic normal-tension glaucoma,
17 based on the assumption that the CVT was originally located at the center of the ONH.
If structural change of the ONH during infancy or childhood is linked to the long-term risk of developing glaucoma, the evaluation of baseline morphologic characteristics of the ONH in newborns would be important in order to deduce changes of the ONH and deep structures, such as the LC, during eyeball growth. Therefore, the purpose of the current study was to investigate the position of the CVT and the morphologic characteristics of the ONH in newborns based on fundus photographs.
Digital fundus images of the posterior polar retina were consecutively obtained from infant eye-screening examinations performed using the Retcam wide-field digital imaging system (Natus Medical Inc.; Pleasanton, CA, USA) on healthy newborns within a week of birth in 28 local obstetrics and gynecology centers between July and September 2018. The infants' pupils were dilated with 1% tropicamide eye drops. Before the examination, topical anesthesia was instilled and an eyelid speculum was applied. The 130° lens of a digital fundus camera was used. One fundus photograph was acquired per each eye of each infant, as centered on the posterior pole, by a well-trained nurse of each center between 1 and 7 days after birth. All of the fundus images were sent to the Reading Center of Soonchunhyang University Cheonan Hospital, where they were screened by one pediatric ophthalmologist (SYK). The images contained no patient-identifiable information except sex, gestational age, and birth weight. Eyes with congenital abnormalities, retinal hemorrhages, or intraocular inflammation were excluded. Images of poor quality also were excluded. If images from both eyes of an infant were eligible, one eye was randomly selected. This study was performed in accordance with the tenets of the Declaration of Helsinki, and the study protocol was approved by the Soonchunhyang University Cheonan Hospital institutional review board.
Fundus images were independently assessed by two independent observers (MK and KML) to determine the position and direction of the CVT using a measuring tool (
Fig. 1). The outermost measurement circle was fit to the disc margin, and the center of the circle was set as the ‘center' of the disc. The position of the CVT was defined as its area of location in the optic disc (grade 1, within central 4% of optic disc area; grade 2, within central 9%; grade 3, within central 16%; grade 4, within central 25%; grade 5, outside of central 25%). The direction of CVT location was determined in cases of grade 2 or more as superior, inferior, nasal, or temporal relative to the center of the optic disc. The reference line was set as the line connecting the fovea and the ONH center, and each direction was a quadrant measuring 90°. In cases of disagreement between the two observers, a third observer (SHK) was consulted to achieve consensus.
The disc diameter and cup diameter were measured to determine the cup-to-disc ratio and ovality index using ImageJ software (
http://imagej.nih.gov/ij/; provided in the public domain by the National Institutes of Health, Bethesda, MD, USA). The vertical and horizontal cup-to-disc ratios were determined as the ratio between the cup diameter and the disc diameter. The ovality index was defined as the ratio between the largest and smallest disc diameters. All of the measurements were performed independently by two masked observers (MK and KML), and the average values were used in the analysis.
The presence and the type of hypopigmented peripapillary lesion were evaluated by two masked observers (MK and KML). The circular type of hypopigmented lesion was defined as a 360° hypopigmented lesion around the optic disc, and the crescent type was defined as a less than 360° hypopigmented lesion. In cases of disagreement between the two observers (4 cases), a third observer (SHK) was consulted to achieve consensus.
Supported by a clinical research grant-in-aid from the Seoul Metropolitan Government Seoul National University (SMG-SNU) Boramae Medical Center (03-2019-3; Seoul, Korea).
Disclosure: M. Kim, None; S.Y. Kim, None; K.M. Lee, None; S. Oh, None; S.H. Kim, None