[Theoretic explanation about visual disorder induced by fibrous dysplasia of skull: pressure disequilibrium between lamina cribrosa].

OBJECTIVE: To investigate the causes for changes in optic nerve head and visual impairment caused by fibrous dysplasia (FD) of optic canal stenosis.
METHODS: A total of 12 FD patients, diagnosed by CT, received the fundus and optical coherence tomography (OCT). Those with FD involving optic canal underwent decompression. The examination of OCT showed that lamina cribrosa located at the top was the exposure factor for retinal pigment epithelium (RPE). There were decreased vision or edematous optic nerve and atrophic lesion. Odds ratio was calculated by Fisher's exact test.
RESULTS: The examination of CT showed the results of optic canal stenosis caused by lesions involving 18 sides: 8-sides with normal vision. Among which, 6 showing that lamina cribrosa was located below RPE and a lamina cribrosa plate near RPE at follow-up, 1 side OCT showing lamina cribrosa above RPE with normal optic nerve; a lateral lamina cribrosa was located above RPE with edematous optic nerve. Visual impairment at 10 sides, normal papillary 2 sides, atrophic papillary 8 sides, OCT showed that lamina cribrosa was located above RPE, postoperatively OCT showed that lamina cribrosa below with 7 sides having improved visual acuity. Fisher's exact test was performed (P = 0.000, odds ratio = infinity).
CONCLUSION: The optic canal stenosis causes a rising pressure of lamina cribrosa zone to shift above RPE. The channel becomes distorted so as to squeeze and cut the ganglion cell axons of optic nerve, block the axoplasmic transport and result in blood circulation disorder. The above factors are the etiologies of visual impairments. Postoperatively lamina cribrosa zone pressure drops so that depressed lamina cribrosa and channel deformation recover and visual acuity improves.