Volumetric Measurement of Peripapillary Hyperreflective Ovoid Masslike Structures in Patients with Optic Disc Drusen

Abstract

Purpose: To develop a method to determine the volume of peripapillary hyperreflective ovoid masslike structures (PHOMS) and to examine the correlation between PHOMS and anatomic optic nerve head characteristics in a large cohort of patients with optic disc drusen (ODD).

Design: Retrospective, observational study of patients with ODD.

Participants: Patients with ODD seen in a 3-year period.

Methods: We determined the prevalence of PHOMS. We then developed a method to calculate the volume of PHOMS and measured this in all patients where radial scans on OCT were available. We analyzed the correlation between PHOMS volume and patient age, size of Bruch's membrane opening (BMO), ODD visibility, and anatomic location of ODD in the optic nerve.

Main outcome measures: Prevalence and characteristics of PHOMS in patients with ODD.

Results: In 247 (77%) eyes with ODD, PHOMS were found. Among these, 80% were in the first decade of life, 87% were in the second decade, 89% were in the third decade, 85% were in the fourth decade, 74% were in the fifth decade, 73% were in the sixth decade, 58% were in the seventh decade, 40% were in the eighth decade, and 0% were in the ninth decade. The ophthalmoscopic visibility of ODD increased with age. The volume of PHOMS decreased with age, but with no correlation to the size of BMO. The median volume of PHOMS was 0.27 mm³ (interquartile range [IQR], 0.13-0.49 mm³). Predominantly, PHOMS were observed in the nasal peripapillary area (87.5% nasal, 78.5% superior, 67% inferior, and 63.5% temporal).

Conclusions: In patients with ODD, PHOMS are seen frequently, with the highest prevalence in younger individuals. The volume of PHOMS decreases with age, and PHOMS are seen more frequently in patients with superficial ODD.

Keywords: BMO, Bruch’s membrane opening; EDI, enhanced depth imaging; IQR, interquartile range; NAAION, nonarteritic anterior ischemic optic neuropathy; OCT; ODD, optic disc drusen; Optic disc drusen; Optic nerve anatomy; Optic nerve head drusen; PHOMS; PHOMS, peripapillary hyperreflective ovoid masslike structure(s); Peripapillary hyperreflective ovoid masslike structure; Volumetric measurement.

Figure 1

Volume measurement of peripapillary hyperreflective ovoid masslike structure(s) (PHOMS). A, B, A PHOMS encircles the optic disc in 3 dimensions, like a torus. C, In each of the 6 radial OCT scans, it was noted on both side of the Bruch’s membrane opening (BMO) if a PHOMS fragment (blue oval) was present or not. If 2 PHOMS fragments were present in all 6 scans, they were counted as part of 1 large PHOMS extending all the way around the disc like a torus. In each radial scan, for each PHOMS fragment, we measured b = PHOMS fragment cross-sectional width divided by 2, c = PHOMS fragment cross-sectional height divided by 2, w = the distance between the far edge of BMO to the intersection of b and c, and a = w – ½BMO. The minor radii of the torus are b and c; the major radius of the torus is a.

Figure 2

Flowchart showing the inclusion and exclusion of patients. ODD = optic disc drusen.

Figure 3

Bar graph showing peripapillary hyperreflective ovoid masslike structure(s) (PHOMS) and visible optic disc drusen (ODD). The prevalence of PHOMS (blue) decreases with age, whereas the ophthalmoscopic visibility of ODD (red) increases with age.

Figure 4

Scatterplot showing peripapillary hyperreflective ovoid masslike structure(s) (PHOMS) volume and age. The volume of PHOMS decreases significantly with age (P < 0.05). Based on 112 eyes with radial scans available.

Figure 5

Box-and-whisker plot showing peripapillary hyperreflective ovoid masslike structure(s) (PHOMS) volume in patients with buried and visible optic disc drusen (ODD). Patients with buried ODD harbor larger PHOMS (median, 0.33 mm³) compared with those with visible ODD (median, 0.25 mm³). The squares represent the interquartile range (IQR), and the lines represent minimum (quartile 1 – 1.5 × IQR) and maximum (quartile 3 + 1.5 × IQR). The circles represent outliers.

Figure 6

OCT scans demonstrating the NSIT rule of peripapillary hyperreflective ovoid masslike structures (PHOMS): PHOMS are seen most frequently in the nasal peripapillary region, followed by the superior, then the inferior, and finally the temporal peripapillary region. The figure shows 4 different patients with PHOMS extending around Bruch’s membrane opening (BMO) in varying degrees. When PHOMS partially encircle BMO, they are commonly located in the nasal peripapillary areas with varying involvement of the inferior and superior section, whereas superior involvement is seen most frequently. A, A PHOMS encircles the BMO in a complete torus. B, The PHOMS are located in the nasal, superior, and inferior regions. C, The PHOMS is located in the nasal and superior regions. D, The PHOMS is located in the nasal region.