As an optometrist, I am sometimes asked in the consulting room whether people’s eyes are ‘generally the same’. This got me thinking about the number of different lenses we use to examine people’s eyes and the possibility that each pair truly is unique.
So if we consider the possible combinations.
Sphere (range +20.00 to -20.00 in 0.25 steps) ~ 160 options
Cyl (range +4.00 to -4.00 in 0.25 steps) ~ 32 options
Cyl axis (range 0 to 180 in 1 degree steps) ~ 180 options
Prism – horizontal (range 0 to 4 in 0.5 steps) ~ 8 options
Prism – vertical (range 0 to 2 in 0.5 steps) ~ 4 options
Add (range +1.00 to +3.00 in 0.25 steps) ~ 8 options
Number of eyes ~ 2
Therefore, we can calculate the odds of a spectacle prescription being unique at nearly 1 in 471,000,000 (160x32x180x8x4x8x2). With a UK population of about 60 million, the chances are that your eyes are one of kind.
This may not be 100% statistically or scientifically accurate, but it gives a good feel for just how individual your eyes are. But I am sure you all knew you were unique already.