Presbyopia Adds

[p***@gmail.com]

Eye community.

I read a research abstract that between the ages of 40 and 50, the average presbyopic addition is .12D/year or about 1.25D during the decade. Thereafter it slows down to an average of 0.02D/year.

Is it reasonable to assume that this implies the average light myope who was wearing a -1.25 correction at 30 would likely be glasses free at 50 for distance? Does that occur often in real life?

Secondly, does the person who has Lasik at 30 with a -1.25 status end up with the same presbyopia effects between 40-50 as say the person with the perfect non-corrected eyesight? i.e. both will end up need plus add for near vision and even for disance vision at about the same rate?

Thanks,
Peter

[Mike Tyner]

"Presbyopic adds" are a treatment, a compensation that depends on habit and
stature, not to mention ordinary bell-shaped variability. It is too variable
to place such significance on an arbitrary figure like "0.12D/year". That
figure might vary doctor-to-doctor because to some degree you'll adopt
whatever working distance the doctor happens to write.

If you want that level of precision, look for tables describing age vs
accommodation. Accommodation begins declining in the second decade and the
progression is relatively uniform and predictable, independent of gender,
height, occupation or the philosophy of the prescribing doctor.

You will find that hyperopes appear to have less accommodation than myopes
and to become presbyopic earlier. I believe that's because most hyperopes
maintain substantial tonic accommodation that influences routine
measurements of their farpoint.

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Post by p***@gmail.com
I read a research abstract that between the ages of 40 and 50, the average
presbyopic addition is .12D/year or about 1.25D during the decade.
Thereafter it slows down to an average of 0.02D/year.
Is it reasonable to assume that this implies the average light myope who
was wearing a -1.25 correction at 30 would likely be glasses free at 50
for distance? Does that occur often in real life?

I don't see how that follows at all. Having a presbyopic add doesn't imply
any change whatsoever in the far point, where myopia is defined. You'd
expect a -125 myope to remain -125 from age 30 to age 50. Probably half of
them would see some "improvement" in their farpoint but it isn't "typical"
for a -125 myope to go all the way to 0.00 at age 50.

Post by p***@gmail.com
Secondly, does the person who has Lasik at 30 with a -1.25 status end up
with the same presbyopia effects between 40-50 as say the person with
the perfect non-corrected eyesight? i.e. both will end up need plus add
for near vision and even for disance vision at about the same rate?

Presbyopia superimposes pretty uniformly on all refractive errors. If a
50-year-old sees perfectly far away with -1.25, wearing his glasses produces
pretty much the same vision as a non-myope who doesn't need glasses; both of
them can be assumed to have < 1D of accommodation and both of them need
about +2 relative to their "habitual correction" in order to see at 20".

[p***@gmail.com]

On Tuesday, November 20, 2012 9:08:05 PM UTC-5, Mike Tyner wrote:> > Secondly, does the person who has Lasik at 30 with a -1.25 status end up

Post by Mike Tyner

Post by p***@gmail.com
with the same presbyopia effects between 40-50 as say the person with
the perfect non-corrected eyesight? i.e. both will end up need plus add
for near vision and even for disance vision at about the same rate?

Presbyopia superimposes pretty uniformly on all refractive errors. If a
50-year-old sees perfectly far away with -1.25, wearing his glasses produces
pretty much the same vision as a non-myope who doesn't need glasses; both of
them can be assumed to have < 1D of accommodation and both of them need
about +2 relative to their "habitual correction" in order to see at 20".

Thanks Mike.

So, to help me clearly understand. If you are -1.25 myope at age 30 and assuming you fall into the group of the majority of people you don't have a far point change by the age of 50, then the odds favor at 50 you will likely need a (bifocal) perscription that would be -1.25D on top and say -.25D on the bottom.

Would that be correct?

Again, apologize for my ignorance if I am asking dumb questions. I am just trying to understand what happens typically (or in the majority of cases) during the presbyopia years.

Thanks,
Peter

[Mike Tyner]

Post by p***@gmail.com
If you are -1.25 myope at age 30 and assuming you fall
into the group of the majority of people you don't have
a far point change by the age of 50, then the odds favor
at 50 you will likely need a (bifocal) perscription that
would be -1.25D on top and say -.25D on the bottom.

The "traditional" answer isn't -.25 it's +1.25. But the "traditional" table
makes two assumptions that don't hold so much today, although it's still
used for training.

The table assumes 1) at age 50 there is no functional accommodation left and
2) everyone wearing near correction wants clear vision at 16" (40 cm).

Assuming no functional accommodation, the TPN (total plus at near) necessary
to focus at 0.40m would be +2.50 diopters (1/0.40). By definition. So the
emmetrope at >50 needs +2.50 single-vision glasses to focus at 40 cm.

The -1.25 myope wearing glasses would be corrected "to emmetropia", so to
speak, and therefore STILL needs a +2.50 add over his glasses, to focus at
40 cm.

When he removes his -1.25 glasses, that's in effect putting on +1.25 of near
power (he focuses at 87 cm), half of his 40-cm value. To focus closer at 40
cm, he needs another +1.25 to add up to a total of +2.50D TPN.

I don't normally assume 16" for a preferred working distance. I usually ask
about their near habits and consider what they've been wearing and what
their complaint may be.

Researching this answer, I came across new papers that defined presbyopia
such that it doesn't even exist in some 60-year-olds. I simply don't find
that relevant to the population I work with.