Parapapillary choroidal dense pigmentation in young healthy eyes: a cross-sectional study

BACKGROUND: While observing fundus photographs from exploratory research investigating individual differences in the fundus, we discovered a black band around the optic nerve head that had not been reported in previous studies. Such eyes with parapapillary choroidal dense pigmentation (PCP) have a pigmented conus visible on color fundus photography. This study aimed to determine the prevalence of PCP in young healthy eyes and examine its relationships with axial length, optic disc tilt, and conus area. METHODS: This prospective, observational, cross-sectional study included the right eyes of 133 participants, who were examined between November 1, 2010 and February 20, 2012. Among them, 117 right eyes of 117 patients were finally analyzed. Participants underwent comprehensive ophthalmologic examinations, including axial length measurement, fundus photography, and optic disc optical coherence tomography (OCT). Based on their color fundus photographs and optic disc cross-sectional OCT images, eyes were categorized into the non-PCP, temporal-PCP, and circum-PCP groups. Optic disc tilt was evaluated using a sine curve based on the retinal nerve fiber layer B-scan images. The conus area in the color fundus images was calculated using ImageJ and corrected using Bennett's formula. The Steel-Dwass test was used to perform multiple comparisons of the axial length, optic disc tilt, and conus area among the three groups. RESULTS: The mean age and axial length of the participants were 25.8 years and 25.5 mm, respectively. Of the 117 eyes, 49, 17, and 51 had non-PCP, temporal-PCP, and circum-PCP, respectively. The axial length (p = 0.011) and conus area (p = 0.047) were significantly shorter and smaller, respectively, for the circum-PCP group than for the non-PCP group. No significant differences were observed in the other intergroup comparisons. CONCLUSIONS: OCT findings revealed that PCP appears black due to choroidal pigment. The eyes with circumferential PCP had shorter axial lengths and smaller conus areas than that of those without, suggesting that it may occur more likely in eyes with less axial elongation.