Abnormalities of the Optic Nerve in Down Syndrome and Associations With Visual Acuity

Abstract

Background: Various ocular anomalies are present in the vast majority of individuals with Down syndrome; however, we know little about optic nerve abnormalities. The aim of this cross-sectional comparative study was to describe optic disc morphology in patients with Down syndrome and to determine if the differences found are potentially related to visual acuity. Subjects/methods: Assessable fundus images were obtained in 50 children with Down syndrome and 52 children without Down syndrome. Morphological analysis of the optic nerve was performed, including the disc-to-macula distance (DM) to disc diameter (DD) ratio (DM/DD), the cup-to-disc ratio and optic disc ovality. Data relating to ophthalmological status were retrospectively analyzed to evaluate the possible causes of reduced visual acuity. Results: DM/DD was significantly larger (p = 0.0036) and the cup-to-disc ratio was significantly smaller (p = 0.018) in children with Down syndrome, compared to controls. The optic discs were also more frequently torted (p = 0.034), tilted (p = 0.0049) and oval (p = 0.026). Furthermore, crescents (p = 0.0002), peripapillary atrophy (p = 0.0009), and pigment anomalies (p < 0.0001) were also more prevalent in children with Down syndrome than in those without. Visual acuity was significantly lower in children with Down syndrome compared to controls with similar refraction problems and strabismus prevalence (p < 0.0001). The mean DM/DD and the presence of a crescent was not directly related to visual acuity (r = 0.39, p = 0.31), (r = 0.35, p = 0.12) respectively. Visual acuity was diminished in 80% of children with Down syndrome and the smallest discs and in 84% of those with tilted discs. However, other causes may contribute to the diminished visual acuity in these cases. Conclusion: The optic nerve head in children with Down syndrome is affected by various anatomical and developmental abnormalities. Unrelated to refraction (spherical equivalent), the optic discs appear smaller and more frequently mal-inserted in Down syndrome. Optic disc hypoplasia, as well as severe tilting, may reduce vision but they do not represent major contributors to the decrease of vision in such children. As these children often have multiple ocular and neurosensory problems, it remains challenging to relate visual acuity problems with a specific abnormality. Smaller discs may lead to optic disc drusen formation in children with Down syndrome.

Keywords: Down syndrome; optic disc drusen; optic disc size; optic nerve; physiological cup; tilted disc; visual acuity.

Figure 1

Small optic discs in Down syndrome. (A) Small optic disc with vascular tortuosity in a child with Down syndrome. This image exemplifies the formula used in the estimation of the disc-to-macula distance (DM) to disc diameter (DD) ratio (DM/DD): Dfx2+ D₁/D₁+ D₂ (38, 39)_. Both vertical and horizontal disc diameters were considered, to compensate for oval discs. (B) Small, round optic disc with a double ring sign between the black arrows. (C) Hypoplastic disc of a child with Down syndrome. Papillary vascular malformation is evident. A large halo of peripapillary atrophy is seen at 360° (white arrows). The gray arrow indicates an area of pigmented epithelium hypertrophy at the temporal margin of the disc. (D) Small tilted optic disc in a child with Down syndrome and myopia. A scleral crescent is visible at the temporal margin (between the black arrows). The disc is oval and bean-shaped in this case, with a hyperpigmented halo. An extensive area of peripapillary atrophy, with visible choroidal vessels, is evident (white arrows).

Figure 2

Hyperopia and myopia (spherical equivalent) in Down syndrome vs. control (RE, right eye; LE, left eye).

Figure 3

Optic disc ovality in Down syndrome vs. control (RE, right eye; LE, left eye).

Figure 4

Optic nerve crescents in children with Down syndrome. (A) Oval and tilted optic disc with a temporal crescent (black arrows) in a child with Down syndrome and myopia. (B) Choroidal crescent located temporally (black arrows) in a small, tilted disc from a child with Down syndrome and high myopia. (C) Small temporal crescent (black arrows) in a child with Down syndrome and hyperopia. (D) Small, tilted disc with vascular tortuosity. A scleral crescent is located below the disc and extends nasally (black arrows). (E) Tilted disc with situs inversus of the vessels (striped arrows). A large choroidal crescent is evident below the disc and extending into the nasal area (between the black arrows). Peripapillary atrophy is noted at the temporal margin of the disc (white arrows). (F) Tilted disc in which the scleral crescent, although wider below the disc, takes an annular form. Situs inversus, in which the vessels emerge nasally, is also evident (striped arrows). (G) Choroidal crescent, located below the disc with inferonasal and temporal extension (black arrows), in a child with Down syndrome and hyperopia. The disc appears equally tilted in this case. (H) Tilted and torted optic disc of a child with Down syndrome with myopic astigmatism. A choroidal crescent is evident below the disc (black arrows) along with a large zone of temporal peripapillary atrophy (white arrow). Note the bean-shaped optic disc in this case. (I) A smaller choroidal crescent, located below the disc and nasally, in a child with Down syndrome and hyperopia. In the upper and central rows, the optic discs have no physiological cupping.

Figure 5

Relationship between crescent localization and refraction in children with Down syndrome vs. controls. Crescents (black lines) were evident in children with Down syndrome, without association with a specific refractive status. In controls, the crescents were more prevalent in those with myopia and astigmatism. Temporal crescents (red lines) were evident mostly in children with and without Down syndrome with myopia and myopic astigmatism. Crescents below the disc and annular crescents were more prevalent in children with Down syndrome (blue and purple lines). Other localizations (green lines) were rare.

Figure 6

Peripapillary pigmentary anomalies in children with Down syndrome. (A,B) Failure of the pigment epithelium to reach the optic disc margin for 360° of the optic disc margin in two children with Down syndrome (black arrows). (B) Inferotemporal small gray crescent (between the gray arrows). (C) Small intrapapillary pigment dot (red arrow) in an optic disc with temporal peripapillary atrophy (white arrows). (D) Choroidal crescent (gray arrows) below the disc with temporal pigment epithelium hypertrophy (white arrows). (E) Temporally-located conus pigmentosum (white arrows). The pigment extends into the optic disc substance, creating the appearance of a small gray crescent (gray arrows). (F) A tilted disc with an annular crescent (black arrows) and situs inversus of the vessels (striped arrows) in a child with Down syndrome and no refraction error. Two intrapapillary pigment dots are noted on the temporal side of the disc (red arrows).

Figure 7

Optic disc drusen in children with Down syndrome, as evidenced by fundus imaging and ocular B-scan ultrasound. (A,C) Optic disc drusen in two children with Down syndrome; a spoke-like vessel pattern is evident in (A). The optic discs appear smaller, with no physiological cupping. (B,D) Ocular B-scan ultrasound in the same patients, showing ovoid echogenic lesions, with acoustic shadow, at the junction of the retina and the optic nerve.

Figure 8

Visual acuity in children with Down syndrome without opacities of the media vs. controls.

Figure 9

Visual acuity in children with Down syndrome and hypoaccommodation compared to those with normal accommodation and to controls.

Figure 10

Visual acuity in children with Down syndrome with and without nystagmus and in controls.