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, 16.6832 mm, Default)
Rodieck (Human, 16.1 mm)
Gulstrand (Human, 17 mm)
PerryCowey (Rhesus)
Packer (Rhesus)
PennDog (Dog)

Passing a numeric value as source returns that value as the
estimate, independent of species. This is a hack that allows
some debugging.

Passing a string that is a number (that is, something that str2num
will turn into a number) as the source will cause that number to
be returned as the eye length. This is a bit redundant with the
numeric option above.

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.

Finally, if you pass a decimal number as a string, this value
will be returned. Useful for passing arbitrary numbers through
routines that rely on this function.

7/15/03 dhb Wrote it.
2/27/13 dhb Added 17 mm option
3/1/13 dhb Changed ‘17’ to ‘Gulstrand’
dhb Added option of passing a number as a string.
4/12/13 dhb Fix bug introduced in previous update, which may have
been Matlab version dependent.
8/9/13 dhb A few more comments.

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