Some useful numbers in vision science
(from B. Wandell, Stanford University)
Radiometric units represent physical energy (e.g., radiance has units of watts/sr-m)
Colorimetric units adjust radiometric units for visual wavelength sensitivity (e.g. luminance has units of cd/m); scotopic units are proportional to rod absorptions; photopic luminance units are proportional to a weighted sum of the L and M cone absorptions
Typical ambient luminance levels (in cd/m): starlight 10; moonlight 10; indoor lighting 10; sunlight 10; max intensity of common CRT monitors, 10.
One Troland (Td) of retinal illumination is produced on the retina when the eye looks at a surface of 1 cd/mthrough a pupil of area 1 mm.
Lens focal length: f (meters); lens power = 1/f (diopters)
Conversion of linear units (X) to decibels: Y = 20 (X); a change of 0.3 units is a factor of 2, or 6 dB
The eyes are 6 cm apart and half-way down the head
Visual angle of the sun or moon = 0.5 deg
At arm's length: thumbnail = 1.5 deg; thumb joint = 2.0 deg; fist = 8-10 deg
Monocular visual field measured from central fixation: 160 deg (w) 175 deg (h)
Binocular visual field measured from central fixation: 200 deg (w) 135 deg (h) ??
Region of binocular overlap: 120 deg (w) 135 deg (h)
Range of pupil diameters: 2mm -8mm.
Refractive indices: air 1.000; glass 1.520; water 1.333; cornea 1.376
Optical power (diopters): cornea, 43; lens, 20 (relaxed); whole eye, 60
Change in power due to accommodation, 8 diopters
Axial chromatic aberration over the visible spectrum: 2 diopters
Retinal size: 5 cm x 5 cm; 0.4 mm thick
One degree of visual angle = 0.3 mm on the retina
Number of cones in each retina: 510
Number of rods in each retina: 10
Diameter of the fovea: 1.5 mm (5.2 deg); rod-free fovea: 0.5 mm (1.7 deg); foveola (rod-free, capillary-free fovea): 0.3 mm (1 deg); size of the optic nerve head: 1.5 mm x 2.1 mm (5 deg (w) x 7 deg (h)) location of the optic nerve head: 15 deg nasal
Peak cone density: 1.6 x 10 cones/mm
Foveal cone size: 1-4 (diameter) x 50-80 (length); extrafoveal cone size: 4-10 (diameter) x 40 (length)
Size of rods near fovea: 1 (diameter) x 60 (length)
S cone spacing (foveal): 10 arc min
L and M cone spacing (foveal): 0.5 arc min
Number of (L + M) cones : Number of S cones = 14 (but the ratio may be higher in the foveola)
1.510 optic nerve fibers/retina; ratio of receptors to ganglion cell in fovea 1:3; ratio of receptors to ganglion cells for whole retina, 125:1
Area of entire cortex: 1.3 x 10 mm; 1.7 mm thick
Total number of cortical neurons: 10; density: 10 neurons/mm
Synapses: 5 x 10 synapses/mm 4 x 10 synapses/neuron;
Axons: 3 kilometers/mm
Number of corpus callosum fibers: 5 x 10
Number of macaque visual areas: 30
Size of each area V1: 3 cm by 8 cm
Half of area V1 represents the central 10 deg (2% of the visual field)
Width of a human ocular dominance column 0.5-1.0 mm; width of a macaque ocular dominance column 0.3 mm.