June 2013
Volume 54, Issue 15
Free
ARVO Annual Meeting Abstract  |   June 2013
Why ISNT Rim Area Greater for Superior Optic Disc?
Author Affiliations & Notes
  • William Swanson
    School of Optometry, Indiana University, Bloomington, IN
  • Victor Malinovsky
    School of Optometry, Indiana University, Bloomington, IN
  • Mitchell Dul
    SUNY College of Optometry, State University of New York, New York, NY
  • Footnotes
    Commercial Relationships William Swanson, None; Victor Malinovsky, None; Mitchell Dul, None
  • Footnotes
    Support None
Investigative Ophthalmology & Visual Science June 2013, Vol.54, 5919. doi:
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      William Swanson, Victor Malinovsky, Mitchell Dul; Why ISNT Rim Area Greater for Superior Optic Disc?. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5919.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract
 
Purpose
 

Histological data show greater retinal ganglion cell (RGC) density in superior than inferior retina (Curcio & Allen 1990 JCN 300:5), but neuroretinal rim area and retinal nerve fiber layer (RNFL) thickness are not greater for superior optic disc. The hypothesis was that this can be accounted for by macular visual field projection to inferior temporal (IT) but not superior temporal (ST) optic disc sectors (Hood et al, 2012 TVST 1:3).

 
Methods
 

One eye each of 61 patients with glaucoma and 71 age-similar control subjects was tested with HRT-III for rim area, Stratus OCT 3.4 for RNFL thickness, and 24-2 SITA Standard for visual field (VF) sensitivities. ST and IT optic disc sectors were defined by the 2002 Garway-Heath map (IOVS 43:2213), and estimates of RGCs from VF and RNFL values were derived with the 2007 Harwerth model (IOVS 48:763). Bivariate Gaussian ellipses at p = 0.90 characterized control data, and tangents yielded confidence limits for patients. Each sector maps to 14 VF locations: the first 13 locations are mirror images across the horizontal midline, and the 14th location is at 4° for IT and 21° for ST.

 
Results
 

Controls had equal rim areas for ST and IT (0.21 mm2), and lower RNFL thickness for ST than IT (127 ± 26 vs. 136 ± 26 μm), yielding fewer RGCs for ST: 165 ± 38 vs. 176 ± 39 x 103 (t = -3.3, p < 0.002). With 14 locations, VF also yielded fewer RGCs for ST: 279 ± 38 vs. 352 ± 58 x 103 (t = -17, p < 0.0001). With 13 locations, ST yielded more RGCs than IT: 269 ± 36 vs. 239 ± 36 x 103 (t = +11, p < 0.0001). The 14th location provided an average of 10 x 103 RGCs for ST and 113 x 103 RGCs for IT. In both cases, patient data fell within the confidence limits, and above the line of equality (i.e., RGC estimates were greater for VF than RNFL).

 
Conclusions
 

Ganglion cell estimates from perimetry agreed with histological findings of greater ganglion cell density in superior retina, for 13 locations per sector but not 14 locations. This result underscores the role of mapping the macula to the optic disc in structure-function analyses.

 
 
RGC estimates for 14 visual field locations per sector. Circles show estimates of RGCs for VF & RNFL. Red circles show control data, ellipses are confidence limits at p=0.90, red horizontal and vertical lines are means. Black diagonal line for equality, red diagonal lines for linear mean (solid) and confidence limits (dashed).
 
RGC estimates for 14 visual field locations per sector. Circles show estimates of RGCs for VF & RNFL. Red circles show control data, ellipses are confidence limits at p=0.90, red horizontal and vertical lines are means. Black diagonal line for equality, red diagonal lines for linear mean (solid) and confidence limits (dashed).
 
 
RGC estimates for 13 visual field locations per sector, rest as in Figure 1.
 
RGC estimates for 13 visual field locations per sector, rest as in Figure 1.
 
Keywords: 627 optic disc • 642 perimetry • 610 nerve fiber layer  
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