I have not myself checked most of the facts listed here.

N.B. "X^2" means X raised to the second power i.e. X squared. And "X^-3"
means X raised to the power -3 i.e. 1 divided by X cubed.

A "mu" means a micron i.e. 10^-6 of a metre (one thousandth of a millimetre).

- There are at least 10 fundamentally different types of eye (using different principles).
- Eyes have independently evolved between 40 and 60 different times.
## Units

- 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); change of 0.3
log10 units is a factor of 2, or 6 dB
## Image Formation

- 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: 1mm -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
## Retina

- Retinal area: 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))

- 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 = 100

- 1.5x10^6 optic nerve fibers/retina
- Ratio of receptors to ganglion cells: in fovea 1:3; for whole retina, 125:1
## Cortex

- 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.

## Sensitivity

- Minimum number of absorptions for: scotopic detection 1-5;
detectable electrical excitation of a rod 1; photopic detection 10-15

- 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 (cpd = cycles per degree of
visual angle)

- 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

## Colour

- 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

(White, black, red, green, yellow, blue, brown, purple, pink, orange, grey)

- Incidence of:

- anomalous trichromacy (3 colours, but a different 3 from the rest of
us), 10^-2 (male), 10^-4 (female);

- protanopia and deuteranopia (long and medium wavelength cones missing), 10^-2 (male), 10^-4 (female);

- tritanopia (short wavelength cones missing), 10^-4;

- rod monochromacy (rods only), 10^-4;

- cone monochromacy (one cone type only), 10^-5

- anomalous trichromacy (3 colours, but a different 3 from the rest of
us), 10^-2 (male), 10^-4 (female);