Tilted Optic Disks

Abstract

Tilted optic disks are a common finding in the general population. An expression of anomalous human development, the tilted disk appears rotated and tilted along its axes. Visual sequelae described with tilted optic disks include myopia, astigmatism, visual field loss, deficient color vision, and retinal abnormalities. Although the natural course of tilted optic disks is nonprogressive, the anomaly can be mistaken for tumors of the anterior visual pathway, edema of the optic nerve head, or glaucoma. A thorough examination of patients with tilted disk includes refraction, dilated fundus examination, and visual field testing. At times, neuroimaging may be necessary to arrive at the correct diagnosis. Until normative data are validated for tilted disks, the role of new imaging technologies for the optic nerve head is limited. Familiarity with the spectrum of ophthalmoscopic appearance and the clinical manifestations of tilted disks may be the most critical factors in avoiding misdiagnosis.

Introduction

The congenital tilted optic disk (or tilted disk) appears as if the optic nerve enters the eye at an oblique angle while being rotated along its anterior–posterior axis. The anomaly is a relatively common anatomical variant, having been reported in 0.4–3.5% of populations (Table 1).31, 46, 94, 115, 129, 137 This nearly nine-fold range reflects both the wide phenotypic spectrum of the anomaly and the criteria used to define tilted disk. Most papers published on tilted disks do not objectively define the condition, which could tend to underestimate borderline or equivocal cases.31, 94 Overlapping features with myopic disks may explain the variation in prevalence in some studies. You et al,¹³⁷ for instance, excluded eyes with myopia greater than 8 diopters (D), when other population-based studies did not.¹²⁹ To avoid confusion with myopic disks, some investigators use inferior or nasal tilting as inclusion criteria.¹²⁹

In one cross-sectional study of 316 randomly selected children enrolled in the Singapore Study of Myopia, 44.9% had tilted disks, which indicates the condition referred to as “tilted disk” is not nosologically distinct from the myopic disk.¹²³ The Singapore Study illustrates that frequency data can become easily biased if myopes are disproportionally represented in a sample population.

Apart from the confounding aspects of definition, the clinical spectrum of tilted disk is broad, ranging from subtle variants of normal shape and contour to conspicuous malformations (Fig. 1, Fig. 2). The frequency of bilateral tilted disks range from 37.5% to 80%, and here, too, inclusion criteria explain some of this variation. Many people have asymmetric involvement that may go unrecognized in the less affected eye.31, 57, 94, 129, 138 No sex predilection has been associated with this phenotype.3, 46, 94, 129

Tilted disks have been referred to as Fuchs's coloboma, congenital crescents, heterotypical crescents, obliquely inserted disks with inferior conus, nasal fundus ectasia, segmental hypoplasia, and dysversion of the optic nerve head in older medical literature.22, 61, 94 None of these names offer an advantage over tilted disk, and some infer an established pathogenesis when such knowledge is still lacking.

Tilted disks are associated with other ocular abnormalities and with visual dysfunction including refractive error, visual field defects, and abnormal color vision. The optic disk abnormality itself, however, is believed to be nonprogressive,3, 138 although good longitudinal studies have yet to be published. The lack of progression has been supported by the fact that neither the prevalence nor severity of tilted disk increase with age.46, 129

The differential diagnosis of tilted disks includes conditions that are sight- and life-threatening, including glaucoma, papilledema, and tumors of the anterior visual pathway.