> In <3gbis1$i0j at onramp.arc.nasa.gov> brp at recon.arc.nasa.gov (Bruce Raoul
Parnas) wrote::
>> >Does anyone have a pointer to material dealing with the
> >density of photoreceptors as a function of radial distance
> >from the retina in humans? A plot of density versus distance
> >would be most welcome.
> In article <3geqge$a3k at eldborg.rhi.hi.is>, thoreys at rhi.hi.is (Thor
Eysteinsson) wrote:
> I think you are looking for a study by Osterberg, published in 1935
> in either Acta Physiologica Scandinavica, or Acta Ophthalmologica.
> This was a light microscopic examination of a retina of an enucleated eye
> from a 16 year old.This is the classic study of receptor density, giving
a plot > of rods and cones as a function distance from the fovea. It
involved basically > detailed counting of receptors from one retina. I
recall seeing a poster at a
> conference some years ago, where the authors had used very sophisticated
> computers and gizzmos to do exactly the same thing. I asked them if there
> was any difference between their results and those of Osterberg.
> Their reply was, essentially, no. So, I said "have a nice day" them, and
> turned to the next poster :-)
>>Osterberg GA Topography of the layers of rods and cones in the human
retina. was published in Acta Ophthalmol in 1935.
I believe caution has to be exercised in using the values from this study
because of methodological considerations.
This study was performed on retinal preparations from a single eye 2x3cm
in size, divided into four quadrants. Correction for shrinkage had been
obtained by using a die with numerous needles in experiments on 3 Ox eyes
and 2 human eyes to determine a factor of 24% radial and 27% circular
shrinkage. Photoreceptors were counted through an eyepiece grid but no
method of marking rods and cones as having been counted is described.
Visual counting of rods and cones in a measuring frame is inaccurate and
in the thick preparations used it is extremely difficult to discriminate
within clumps of rods.
Counts were made in 164 places located on their meridional axis by
distance from the fovea. The retinal preparations were orientated by
drawing with an epidiascope a picture of each quadrant on graph paper at
10x magnification so that distinctive tears could be recognised for
subsequent orientation. The graph paper was reconstructed around a globe
of appropriate size to achieve as close a register of their edges as
possible. Areas were calculated by paper weighing. From this globe
meridians and distances were estimated for areas counted. He was forced to
include counts from a wedge-shaped area of retina spanning 64š arc on the
temporal side and 37 š arc on the nasal side onto his profile for rod and
cone densities for the 0-180 š (equitoral) meridian. He was unable to
count in one quadrant, 8% of which he could not estimate for area. Several
extrapolations and assumptions of uniform density gradients were made. He
himself quotes his estimates as 'a rough calculation'.
In more contemporary publications, a graph of the densty of rods in the
horizontal meridian from the study of Osterberg is reproduced in Ogden, TE
(1976) The receptor mosaic of Aotes trivirgatus: distribution of rods and
cones. J.Comp.Neur. 163: 193-202
