- Radiometric units represent physical energy
(e.g., radiance has units of watts sr^-1 m^-2)
- Colorimetric units adjust radiometric units for
visual wavelength sensitivity (e.g. luminance has units of cd m^-2);
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^-2):
starlight 10^-3; moonlight 10^-1; indoor lighting 10^2;
sunlight 10^5; max intensity of common CRT monitors, 10^2
- One Troland (Td) of retinal illumination is produced on the
retina when the eye looks at a surface of 1 cd / m^2 through a
pupil of area 1 mm^2.
- Lens focal length: f (meters); lens power = 1/f (diopters)
- Conversion of linear units (X) to decibels: Y = 20 log10(X);
a change of 0.3 log10 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) x 175 deg (h)
- Binocular visual field measured from central fixation: 200 deg
(w) x 135 deg (h)
- Region of binocular overlap: 120 deg (w) x 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: 5 x 10^6
- Number of rods in each retina: 10^8
- 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 10^5 cones/mm^2;
- Foveal cone size: 1-4 mu (diameter) x 50-80 mu (length);
extrafoveal cone size: 4-10 mu (diameter) x 40 mu (length)
- Size of rods near fovea: 1 mu (diameter) x 60 mu (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
(though the ratio may be higher in the foveola)
- 1.5 10^6 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 10^5 mm^2; 1.7 mm thick
- Total number of cortical neurons: 10^10; density: 10^5 neurons / mm^3
- Synapses: 5 x 10^8 synapses / mm^3
4 x 10^3 synapses/neuron;
- Axons: 3 kilometers / mm^3
- Number of corpus callosum fibers: 5 x 10^8
- Number of macaque visual areas: 30
- Size of each area V1: 3cm 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">.

- Minimum number of absorptions for: scotopic detection 1-5;
detectable electrical excitation of a rod 1; photopic detection 10-15
- The number of photoisomerisations per rod (per sec?) required to
saturate the retinal rod circuit.
- Following exposure to a sunny day, dark adaptation to a
moonless night involves: 10 minutes (photopic); 40 minutes (scotopic);
change in visual sensitivity 6 log10 units
- Highest detectable spatial frequency at high ambient light levels,
50-60 cpd; low ambient light levels, 20-30 cpd
- The contrast threshold (Delta L / L) for a static edge at photopic
luminances is 1%.
- Highest detectable temporal frequency: high ambient large
field, 80 Hz; low ambient, large field 40 Hz.
- Typical localization threshold: 6 arc sec (0.5 mu on the retina)
- Minimum temporal separation needed to discriminate two small, brief
light pulses from a single equal-energy pulse: 15-20 ms
- Stereoscopic depth discrimination: step threshold, 3 arc sec;
point threshold, 30 arc sec

- Visible spectrum: 370-730 nm
- Peak wavelength sensitivity: 507nm (scotopic) and 555 nm (photopic)
- Spectral equilibrium hues: 475 nm (blue),
500 nm (green), 575 nm (yellow), no spectral equilibrium red
- Number of basic English color names: 11
- Incidence of:
anomalous trichromacy, 10^-2 (male), 10^-4 (female);
protanopia and deuteranopia, 10^-2 (male), 10^-4 (female);
tritanopia, 10^-4; rod monochromacy, 10^-4; cone monochromacy, 10^-5