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G.S. Bhermi, N. Peter, D. Goh, C. Migdal; Optical Coherence Tomography Measurements of Peri–Papillary Retinal Nerve Fibre Layer Thickness in Patients With Tilted Optic Discs . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2517.
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Purpose:Tilted optic discs can be difficult to distinguish from normal or glaucomatous discs on clinical examination alone and an objective assessment may be more useful. This study investigated the use of optical coherence tomography (OCT) to objectively assess differences in retinal nerve fibre layer thickness (RNFLT) between tilted and normal optic discs. Methods: 28 eyes of 18 patients with ophthalmoscopically tilted optic discs and 24 eyes of 14 patients with normal optic discs underwent OCT examination (OCTIII). All patients had normal intraocular pressures, normal visual fields and no risk factors for glaucoma. Each patient had a 3.6mm diameter circular scan centred on the optic disc. The RNFLT for each circular scan was divided into 30 degree segments and notated using clock hours where 9 O’clock represented the temporal 30 degrees and 12 O’clock the superior 30 degrees. Each measurement was repeated three times and the results averaged for each clock hour. An un–paired, two–tailed student t–test was used to compare RNFLT at each clock hour between the normal and tilted disc groups. The correlation of axial length (measured with laser interferometry) and RNFLT was also assessed. Results: In the following, the term significant refers to statistical significance. The mean age was 57yrs (range 30 to 82) with no significant difference between the tilted or normal disc groups. In comparison with the tilted disc group, the RNFLT was significantly greater in the normal disc group by 16% to 33% in all sectors except the temporal 90deg which did not vary significantly between the two groups. RNFLT did not correlate significantly with axial length in any sector the normal disc group, and correlated negatively in the nasal 150 degrees in the tilted disc group. Conclusions:Peri–papillary measurements of RNLFT were smaller in tilted discs than in normal discs in all but the temporal quadrant. Furthermore RNLFT measurements did not decrease with an increase in axial length suggesting that the thinner RNFL in tilted discs is a function of the tilted disc syndrome rather than a longer axial length. The ophthalmoscopic appearance of a thinner RNFL in the inferior / inferotemporal region often associated with tilted discs is not evident on OCT.
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