Can it be determined how many diopters a person’s eyesight will change over the course of their presbyopia, or does it depend person to person?

07 Dec Can it be determined how many diopters a person’s eyesight will change over the course of their presbyopia, or does it depend person to person?

The default focal point of the normal human eye is way off at the horizon. To pull the focus up close requires a physical change in the shape and thickness of the natural lens of the eye called “accommodation.” This change in focusing power is measured in the same units as in lens prescriptions called “diopters.” The gradual loss of focusing power for near tasks (such as reading or threading a needle) is inevitable as we age due primarily to the gradual hardening of the natural lens. The accompanying loss of accommodation can also be measured in diopters.

The ability of the natural eye to accommodate in childhood is typically about +14 diopters -way more than we need. [The strongest power reading glasses you can buy in a drugstore is about +3.5 diopters.] There is about a 1½ to 2 diopter decrease in accommodative ability per decade past age 10.

Surprisingly, 2/3 of accommodative ability is lost between the ages of 15 and 35! After age 35, this loss speeds up to about 2½ diopters per decade until it becomes quite noticeable in the mid to late 40s. By the time we reach our early to mid-50s, there is less than 1-2 diopters left which is not enough to focus easily at a typical reading distance. We try to compensate by moving the print further away or turning up the light. Eventually, this is not enough and we have to resort to some kind of help with lenses.

While there can be some variation in these numbers and ages, they are pretty typical and predictable for most everybody.