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Morphology of the normal visual field in a population‐based random sample: Principal components analysis
Author(s) -
Oden Neal
Publication year - 1992
Publication title -
statistics in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.996
H-Index - 183
eISSN - 1097-0258
pISSN - 0277-6715
DOI - 10.1002/sim.4780110902
Subject(s) - principal component analysis , sample (material) , eigenvalues and eigenvectors , statistics , variation (astronomy) , mathematics , population , field (mathematics) , visual field , optometry , demography , medicine , physics , ophthalmology , pure mathematics , astrophysics , sociology , quantum mechanics , thermodynamics
I applied principal components analysis to Humphrey central 24‐2 threshold values from both eyes of 304 clinically normal persons selected by simple random sample from Barbados, WI. The first component, accounting for 62 per cent of the variation, is equivalent to the average threshold value within persons. The first eigenvector, when represented by grey scale maps depicting a pair of eyes, reveals that, as average threshold increases, the visual field rises and flattens, like an umbrella that, initially closed, is simultaneously opened and thrust upwards. I verify three numerical predictions based upon this umbrella description. Much less important sources of variation involve disparity between fellow eyes, and hemimeridional and other symmetric differences within eyes. I discuss briefly possible physiologic explanatory mechanisms.