- See also: Guide:How to measure your eyesight
In general, your measurements actually change wildly within the day. They're mostly useful for checking that you're not going off track with habits changes, or for measuring relative changes in vision in different circumstances. (e.g. diet, time of day, and activity)
As far as what progress you can see, that appears to actually be fairly individual. You need to measure to learn about how you see things. But think of general changes on the span of multiple weeks, or even a month or so.
Measurements are a learning process, not a goal
The cm measurement uses a basic optics formula to calculate the diopters of correction you need to see clearly long distance.
- Hold a ruler up to your eye, and measure how far away you can still read text without blur in centimeters. This is your "cm measurement".
- The ideal precise measurement is from the surface of your eyeball, but this is obviously not safe, so measure from some facial structure near your eye.
- Consistency is more important than accuracy, you want to be able to track your small changes over the course of a day, and larger changes over time.
- Calculate diopters from the measurement: Diopters = -100cm/cm measurement.
- If your result is stronger than -4D, and you wear glasses, you'll need to correct for vertex distance to convert this from contacts diopters to glasses diopters.
- If your result is stronger than -10, you'll likely have problems getting consistent readings.
- EndMyopia Diopter Calculator
- Making the physical measurement easier (EndMyopia blog link)
- Varakari's Vision Log Tool
- Measurement (EndMyopia blog link)
- The iOS Sight Meter App
- The Android Diopter Calculator