Charts · 29
What your eye actually renders
Hold your gaze still and the scene seems sharp and complete from edge to edge. The retina disagrees. Cones, which give you detail and colour, are packed into a pit at the centre and thin out tenfold within a millimetre of it. Rods, which work in dim light, are missing from the very centre. And where the optic nerve leaves the eye there is nothing to detect light at all. Find that hole in your own eye first, then see the counts it sits in.
Find your blind spot
Why that distance: the centre of the blind spot sits 15.5° out from where you are looking, so the dot has to be seen at that angle, and 1 / tan 15.5° is 3.61. The blind spot is about 6.4° wide, which is why there is a range rather than a single point.
What the retina samples
The centre of the fovea
196,890 cones · 0 rods per mm²
Only cones. The very centre of your gaze has no rods at all, which is why a faint star can vanish when you look straight at it.
The data: every measured point on the horizontal meridian
| Side | mm | Degrees | Cones per mm² | Rods per mm² |
|---|---|---|---|---|
| Temporal | 17.91 | 67.7 | 3,359 | no value |
| Temporal | 16.91 | 62.9 | 3,070 | no value |
| Temporal | 15.92 | 58.8 | 3,176 | 60,889 |
| Temporal | 14.93 | 54.9 | 3,336 | 69,000 |
| Temporal | 13.93 | 50.8 | 3,368 | 76,106 |
| Temporal | 12.94 | 46.6 | 3,436 | 83,973 |
| Temporal | 11.94 | 42.9 | 3,539 | 90,966 |
| Temporal | 10.95 | 39.3 | 3,763 | 98,807 |
| Temporal | 9.95 | 35.7 | 3,888 | 105,756 |
| Temporal | 8.96 | 32.1 | 4,208 | 112,405 |
| Temporal | 7.96 | 28.6 | 4,477 | 120,700 |
| Temporal | 6.96 | 25.0 | 4,780 | 126,964 |
| Temporal | 5.97 | 21.4 | 5,103 | 134,004 |
| Temporal | 4.97 | 17.9 | 5,786 | 137,095 |
| Temporal | 3.98 | 14.3 | 7,030 | 138,390 |
| Temporal | 2.98 | 10.7 | 9,118 | 132,354 |
| Temporal | 1.99 | 7.1 | 11,703 | 109,264 |
| Temporal | 0.99 | 3.6 | 19,699 | 68,997 |
| Temporal | 0.90 | 3.2 | 21,165 | 64,875 |
| Temporal | 0.80 | 2.9 | 24,144 | 60,097 |
| Temporal | 0.70 | 2.5 | 29,027 | 53,390 |
| Temporal | 0.60 | 2.1 | 34,223 | 45,316 |
| Temporal | 0.50 | 1.8 | 38,380 | 36,675 |
| Temporal | 0.40 | 1.4 | 45,420 | 26,877 |
| Temporal | 0.30 | 1.1 | 57,712 | 13,439 |
| Temporal | 0.20 | 0.7 | 80,004 | 3,864 |
| Temporal | 0.15 | 0.5 | 98,424 | 1,022 |
| Temporal | 0.10 | 0.4 | 121,619 | 74 |
| Temporal | 0.05 | 0.2 | 162,414 | 13 |
| Centre | 0.00 | 0.0 | 196,890 | 0 |
| Nasal | 0.05 | 0.2 | 154,441 | 0 |
| Nasal | 0.10 | 0.4 | 115,399 | 24 |
| Nasal | 0.15 | 0.5 | 92,992 | 204 |
| Nasal | 0.20 | 0.7 | 74,233 | 969 |
| Nasal | 0.30 | 1.1 | 53,432 | 11,023 |
| Nasal | 0.40 | 1.4 | 42,975 | 22,395 |
| Nasal | 0.50 | 1.8 | 36,493 | 33,699 |
| Nasal | 0.60 | 2.1 | 31,530 | 43,492 |
| Nasal | 0.70 | 2.5 | 26,109 | 50,971 |
| Nasal | 0.80 | 2.9 | 23,872 | 57,762 |
| Nasal | 0.90 | 3.2 | 22,339 | 62,923 |
| Nasal | 0.99 | 3.6 | 20,962 | 66,977 |
| Nasal | 1.99 | 7.1 | 12,522 | 111,888 |
| Nasal | 2.98 | 10.7 | 8,849 | 130,967 |
| Nasal | 3.98 | 14.3 | optic disc | optic disc |
| Nasal | 4.97 | 17.9 | 7,179 | 126,595 |
| Nasal | 5.97 | 21.4 | 6,651 | 145,158 |
| Nasal | 6.96 | 25.0 | 6,409 | 144,241 |
| Nasal | 7.96 | 28.6 | 6,232 | 137,114 |
| Nasal | 8.96 | 32.1 | 5,959 | 130,478 |
| Nasal | 9.95 | 35.7 | 5,609 | 123,706 |
| Nasal | 10.95 | 39.3 | 5,348 | 116,888 |
| Nasal | 11.94 | 42.9 | 5,139 | 109,731 |
| Nasal | 12.94 | 46.6 | 4,989 | 102,422 |
| Nasal | 13.93 | 50.8 | 4,886 | 93,008 |
| Nasal | 14.93 | 54.9 | 4,807 | 83,995 |
| Nasal | 15.92 | 58.8 | 4,726 | 78,266 |
| Nasal | 16.91 | 62.9 | 4,721 | 71,644 |
| Nasal | 17.91 | 67.7 | 4,717 | 59,557 |
| Nasal | 18.91 | 72.7 | 4,846 | 56,824 |
| Nasal | 19.90 | 78.0 | 5,234 | 48,666 |
| Nasal | 20.89 | 84.4 | 4,906 | no value |
| Nasal | 21.89 | 91.3 | 5,191 | no value |
Counted
- 199,000cones per square millimetre at the centre of the fovea, on average across the eyes counted. Between individuals it ranged from 100,000 to 324,000, a threefold spread in the sharpest part of human vision. Curcio et al., 1990
- 1.25°the rod-free zone at the centre, 0.35 mm across. Where you look hardest there are no rods at all. Curcio et al., 1990
- 92 millionrods in an average retina (77.9 to 107.3 million), against 4.6 million cones (4.08 to 5.29 million). Twenty rods for every cone, and almost none of them where you are looking. Curcio et al., 1990
- 15.5°from where you are looking, the centre of the blind spot, and 1.5° below it, give or take 1.1° between people. Rohrschneider, 2004
- 6.4° × 7°of visual field with nothing in it, in every eye: the average optic disc, 1.76 mm across and 1.92 mm tall. Jonas, Gusek and Naumann, 1988
Why you never see the hole
With both eyes open, each eye’s blind spot falls on a part of the scene the other eye can see. Your eyes are also never still for long, so nothing stays in the gap. But even with one eye closed and held steady, as in the card above, you do not see a hole. You see whatever surrounds it: the blank card, the line carried straight across, the stripes continued. This is perceptual filling-in, and recordings show that neurons in early visual cortex take part in it (Komatsu, 2006).
What that means is still argued over. Dennett (1991) said the brain simply ignores an absence it has no reason to notice; Pessoa, Thompson and Noë (1998) reviewed evidence that some completion is active, with neural signals that spread into the missing region. Either way, the picture you experience as even and complete is not what the retina sends. It is sharp only in a pit a few degrees across, coarse and almost all rods towards the edge, with a hole in each eye, and it reaches you finished.