Description
The optic nerve head can be anatomically tilted in any direction. Tilt of the optic nerve head reflects the orientation of the insertion of the optic nerve at the scleral canal. It is most commonly associated with high myopia, where axial elongation and growth of the globe has led to a non-perpendicular insertion of the optic nerve at the posterior surface.
Two configurations are commonly encountered:
(a) Oblique insertion (malinsertion syndrome): The optic nerve does not meet the scleral canal posteriorly at a perpendicular (or ‘right’) angle, but rather is obliquely inserted. The surface of the optic nerve head is tilted about the superior-inferior axis.
(b) Tilted disc syndrome: The optic nerve is rotated, often through about 90 degrees: i.e. the vertical meridian of the optic disc is tilted about the anterior-posterior axis. The optic nerve may also be obliquely inserted.
Symptoms
Usually asymptomatic. Uncommon symptoms include blurred vision, distorted shapes of objects (metamorphopsia) and visual field defects. Acuity is usually normal, unless complications from myopia develop.
Signs
(a) Oblique insertion: The disc may appear small or vertically oval-shaped. There is a “tilt” to the disc surface, with the nasal aspect of the disc being raised and the temporal margin being depressed. There is usually an associated temporal scleral crescent. While the nasal margin of the disc may appear blurred and indistinct, there may still be distinct cupping or other features of the optic nerve head enabling differentiation from papilledema.
(b) Tilted disc syndrome: Like oblique insertion the disc may appear small or oval-shaped; however, the vertical axis of the optic nerve head, is tilted often by about 90 degrees i.e. the superior margin of the optic nerve being rotated away from the 12 o’clock position. There is usually an inferonasal scleral crescent. In addition, the temporal retinal vessels may emerge from the nasal aspect of the disc (situs inversus).
The tilted disc may be associated with an outpouching of the globe in the in the inferonasal quadrant (also known as fundus ectasia, or posterior staphyloma). In these cases, the inferonasal retina appears hypopigmented and oblique astigmatism may be present. In bilateral cases with fundus ectasia, bitemporal depression of visual fields occurs. The retinal changes also carry a slight risk of sub-retinal leakage.
Tilted and obliquely inserted discs are often bilateral, although may be unilateral depending upon refractive asymmetry or other contralateral differences. When bilateral, the optic nerve heads in the right and left eyes are usually mirror images (see Figures 1 and 2).
Prevalence
Very common (approximately 1/10) in association with myopia
Significance
A tilted or obliquely inserted disc is a benign stable condition.
Differential Diagnosis
Oblique insertion and tilted disc may cause concern by simulating signs of intracranial pathology:
- In bilateral tilted discs, bitemporal visual field defects may occur, Significantly, the visual defects often cross the vertical midline: this is not characteristic of compression of the optic tracts by intracranial tumors posterior to the optic chiasm.
- The partially raised appearance of the optic disc in oblique insertion may be mistaken for papilledema.
See Also
Myopic Degeneration.
Management
No treatment is required.
Additional investigations
Visual field assessment should be made. Rule out differential diagnoses.
Refractive correction
Correction of the refractive error in the ectatic area with astigmatic lenses may reduce the size of the visual field defect.
Review
Encourage routine review.
Figure 1
Tilted discs with inferonasal crescent, showing mirror image symmetry (enantiomorphism) in right and left eyes. There was a corresponding visual field defect in each eye.
Figure 2
Obliquely inserted discs, also showing mirror image symmetry. The nasal aspect of the disc is elevated and the temporal aspect is depressed in each eye.
