Background The skull base is the most common site of the craniofacial skeleton to be affected
by fibrous dysplasia (FD). A significant proportion of such FD patients present with
compression of the optic nerve, which can cause visual impairment, but most patients
initially do not experience vision loss. Controversy exists regarding whether to proceed
with a prophylactic surgical decompression of the optic nerve or to elect for “watchful
waiting.” Optical coherence tomography (OCT), a physiologic imaging modality widely
used to assess the condition of the retinal nerve fiber layer (RNFL), has been useful
in the monitoring of other compressive lesions on the optic nerve including pituitary
tumors and craniopharyngioma, and may have a beneficial role in managing patients
with FD involving the optic nerve.
Methods Six patients with suspected optic nerve compression who had received OCT imaging
as part of their neuro-ophthalmic exam were reviewed over a 2-year period at a tertiary
medical center. Patient records were primarily evaluated for the presence of optic
neuropathy grouped by either normal age-adjusted RNFL thickness (above the fifth percentile)
or abnormal (below the fifth percentile) as measured by OCT. Other visual exam measures
including visual acuity, visual field defects, and optic cup-to-disc ratio and radiographic
measures including optic canal size and the presence of optic nerve encasement or
compression on computed tomography (CT) were also analyzed.
Results Two patients were found to have mild optic neuropathy in one eye each. The mean (±
SD) RNFL thickness on OCT was 93.1 ± 12.0 μm, with 3 of 12 eyes falling below the
age-adjusted fifth percentile. Abnormal age-adjusted RNFL thickness was associated
with the presence of optic neuropathy (p < 0.05, see [Table 1]). Visual field defects, optic canal size, and optic nerve encasement differed by
the presence of optic nerve compression on CT (p < 0.05), but the occurrence of optic neuropathy did not differ by optic nerve compression
(p = 0.45).
Conclusion Based on the case series of this rare condition, abnormal RNFL thickness as measured
by OCT better predicted the presence of optic neuropathy than CT alone. OCT may therefore
be a valuable imaging modality to monitor FD patients for development of optic neuropathy
during periods of conservative “watchful waiting” to determine the best timing for
intervention if necessary.
Table 1
(P083) Presence of optic neuropathy by age-adjusted optical coherence tomography RNFL
thickness percentiles and by optic nerve compression on CT imaging
|
Age-adjusted RNFL thickness
|
p-Value
|
Optic nerve compression
|
p-Value
|
|
Bottom 5% (n = 3)
|
Top 95% (n = 9)
|
Present (n = 6)
|
Absent (n = 6)
|
|
Optic neuropathy
|
2 Mild, 1 No
|
0 Mild, 9 No
|
0.045
|
2 Mild, 4 No
|
0 Mild, 6 No
|
0.45
|
Abbreviation: RNFL, retinal nerve fiber layer.
