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T. Y. Chui, Z. Y. Zhong, A. Bradley, S. A. Burns; The Relationship Between Optic Disc Crescent and Axial Length: Implications for Differential Eye Growth. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2201.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the relationship between size of optic disc crescent (ODC) and axial length (AL).
1. Infrared fundus imaging and spectral domain optical coherence tomography (SDOCT) (Spectralis HRA+OCT, Heidelberg Engineering, Germany) was performed on 72 healthy adults (72 eyes; age range 20-67; Rx +2.00D to -13.75D; AL 22-27.88mm). On the infrared fundus images, we measured (a) the distance between the foveola and the temporal edge of the optic disc (FOD) and (b) the distance between the foveola and the temporal edge of the crescent (FOC) (if present) after correcting the retinal magnification induced by different AL as described in Bennett et al (1994). The foveola on the infrared fundus image was defined as the corresponding location of minimum retinal thickness on the SDOCT foveal b-scan in each subject.2. SDOCT and adaptive optics scanning laser ophthalmoscope (AOSLO) imaging were performed on the temporal edge of the ODC in 6 of the eyes (1 emmetrope, 5 myopes)..
1. ODC presented in 64% of the subjects. The FOD and FOC were 4.22mm±0.46 and 3.97mm±0.25, respectively. Both the FOD and FOC were significantly correlated with AL with regression slopes of y=0.22x-1.17 (R2=0.41) and y=0.05x+2.82 (R2=0.06), respectively.2. SDOCT images at the ODC showed gradual thinning of the outer nuclear layer from the temporal edge of the ODC towards the temporal edge of the optic disc. Disruption of the inner/outer segment junction and atrophy of the RPE were observed within the ODC. AOSLO images at the ODC showed normal retinal nerve fiber layer striation. Cone photoreceptors were observed at the edge of the ODC and agreed with SDOCT estimates of the position of the margin of the photoreceptor layer. Several RPE cells were visualized at the retina adjacent to the ODC.
As AL increased by 10%, the FOD increased by 13%, but the outer neural retina only expanded by 3% (as indicated by the FOC). This result emphasizes that retinal stretching may not mirror scleral growth, and the existence in some eyes of a difference between the photoreceptor margin and RPE margin suggests that within the retina there could be slippage. This finding is consistent with our finding that cone packing density between the fovea and optic nerve changed less than predicted by eye growth (Chui et al., 2008), with the retina beneath the papillomacular bundle maintains a more constant size.
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