What Defition of High Myopia do we use?
Over the years, different research groups have chosen to use a range of different definitions of "high myopia". We define high myopes as subjects with a spectacle prescription of greater than or equal to -6.00 Dioptres in the least minus meridian of both eyes.
Examples.
From their spectacle prescriptions, we would classify the following three subjects as high myopes:
R - 6.00
L - 6.00
R - 7.00 / -1.25 x 20
L - 6.00 / -0.25 x 180
R - 9.50 / -0.25 x 35
L - 10.00
We would classify the following three subjects as not being high myopes:
R - 6.00
L - 5.75
R - 7.00 / -0.25 x 20
L - 5.50 / -0.25 x 180
R - 7.50 / +0.25 x 35
L - 7.50 / +2.00 x 115
Why choose such a stringent threshold?
Only about 1 - 2% of the population have "high myopia" by our definition. Selecting families containing one or more individuals with this level of myopia should increase our chances of detecting genes that have a major influence on refractive error.