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function eyeLengthMM = EyeLength(species,source)
% eyeLengthMM = EyeLength(species,source)
%
% Return the length of the eye in mm. Length is taken as distance
% between nodal point and fovea. For foveal stimuli, this length
% may be used to convert between degrees of visual angle and mm/um
% of retina. Since the nodal point isn't at the center of eye,
% the same conversion doesn't work for extrafoveal stimuli.
%
% Supported species:
% Human (Default), Rhesus, Dog
%
% Supported sources:
% LeGrand (Human, Default)
% Rodieck (Human)
% PerryCowey (Rhesus)
% Packer (Rhesus)
% PennDog (Dog)
% None
%
% Passing a numeric value as source returns that value as the
% estimate, independent of species. This is a hack that allows
% some debugging.
%
% Passing None is appropriate as an error check -- if a calculation
% uses the eye length when none is passed, NaN's will show up in
% the answer.
%
% 7/15/03 dhb Wrote it.
%
% Fill in defaults
if (nargin < 1 || isempty(species))
species = 'Human';
end
if (nargin < 2 || isempty(source))
source = 'LeGrand';
end
% Handle case where a number is passed.
if (~ischar(source))
eyeLengthMM = source;
return;
end
% Handle case where 'None' is passed.
if (streq(source,'None'))
eyeLengthMM = NaN;
return;
end
% Fill in length according to species, source
switch (source)
% I took the LeGrand number from Wyszecki and Stiles' description of
% his model eye.
case {'LeGrand'}
switch (species)
case {'Human'}
eyeLengthMM = 16.6832;
otherwise,
error(sprintf('%s estimates not available for species %s',source,species));
end
% Rodieck's standard observer, from Appendix B, The First Steps of Seeing.
case {'Rodieck'}
switch (species)
case {'Human'}
eyeLengthMM = 16.1;
otherwise,
error(sprintf('%s estimates not available for species %s',source,species));
end
% Orin Packer provided me with this information:
% Monkey eye size varies a lot, so any particular number
% is bound to be in error most of the time, sometimes substantially.
% That said, I usually reference Perry & Cowey (1985) (Vis Res 25, 1795-1810).
% For rhesus they report an eye diameter of 20 mm and a posterior nodal
% distance of 12.8 mm.
case {'PerryCowey'}
switch (species)
case {'Rhesus'}
eyeLengthMM = 12.8;
otherwise,
error(sprintf('%s estimates not available for species %s',source,species));
end
% Orin Packer also said: For the fovea I usually use a conversion factor of
% 210 um/degree which is the average of Perry & Cowey, Rolls & Cowey (1970)
% (exp Br. Res., 10, 298) and deMonasterio et al (1985) (IOVS 26, 289-302).
% This corresponds to 12.0324 mm.
case {'Packer'}
switch (species)
case {'Rhesus'}
mmPerDegree = 210*1e-3;
eyeLengthMM = 0.5*mmPerDegree/atan((pi/180)*0.5);
otherwise,
error(sprintf('%s estimates not available for species %s',source,species));
end
% PennDog
case {'PennDog'}
switch (species)
case {'Dog'}
eyeLengthMM = 15;
otherwise,
error(sprintf('%s estimates not available for species %s',source,species));
end
otherwise
error(sprintf('Unknown source %s for eye length estimates',source));
end
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