Objective: To investigate whether structural differences of the optic nerve head are evident in young people who do not have manifest glaucoma but are known to carry myocilin mutations.
Methods: A case-control design was adopted. Subjects from Australian pedigrees known to have either the Gln368STOP myocilin mutation (cutoff age, <40 years) or the Thr377Met myocilin mutation (cutoff age, <30 years) were examined for signs of glaucoma. Stereoscopic disc photographs were digitalized. Analysis of the optic disc area, optic cup area, and neuroretinal rim area was performed using digital stereoscopy with a Z-screen. Mutation analysis was conducted using direct sequencing. The t test, corrected for multiple comparison testing, was used in analysis.
Results: A total of 29 myocilin mutation-carrying (case) and 33 mutation-free (control) individuals were reviewed. The mean +/- SD ages were 19.9 +/- 9.0 and 22.1 +/- 9.5 years in the mutation and mutation-free groups, respectively (P = .35). There was no significant difference in intraocular pressure between mutation carriers and noncarriers (P = .44). There were no statistically significant differences in the mean disc, neuroretinal rim, and cup areas between the groups. The mean +/- SD neuroretinal rim area was 1.24 +/- 0.24 mm(2) in the noncarrier group and 1.25 +/- 0.23 mm(2) in the mutation group (P = .46). No notch, nerve fiber layer defect, or neuroretinal rim hemorrhage was noted in any eye examined.
Conclusions: Although confounded by penetrance and expressivity, no quantified structural difference in the optic nerve head was observed in individuals who had a myocilin mutation prior to the diagnosis of glaucoma.