You might think so.

No it's Otis who recommends undercorrection.

Overcorrection gives an illusion of "crispness" without improving measured
acuity. At least that's the definition I use.

-MT

Well, it seems really doubtful that many people have even considered doing
such a thing.  But I would presume that anyone smart enough to figure out
how to get the test lenses, and the right ones, would be smart enough to
avoid overcorrection.  

Of course, you could argue that most people do not need to read signs
when they drive at night.  That might even be your Professional Opinion.
You do not have to see very well in order to get licensed to drive, so it
could be considered just an arbitrary preference to want to read signs.

--
Dicky  

With this technique, without careful coaching, many people choose -050
or -075 more than they really need.

-MT

That is consistent with my experience.  Myopes will usually find themselves
undercorrected, an progressively so, if they happen to be progressive myopes.
That is why it is good to have a -0.25D and a -0.50D test lens.  Sit with
those, in your car on a city street, and hold them before each lens in your
new eyeglasses.  You will find the best (-) addition for reading signs and
seeing the fluorescent displays the most sharply.  With those two lenses,
you can achieve up to -0.75D addition.

Refining the cylinder axes and power is a bit more complicated, but it can
be done indoors.  I would comment further if there seemed to be interest.

You might then go back to the place where you got your glasses and ask
to have your lenses changed.  But if they give you any sh.t, as they most
likely will, you can just figure out what your prescription should have been,
and order some Zennis.  That could be much cheaper if you are asked to pay
for your new "glass".

I should add that you may prefer to be a bit undercorrected if you are getting
presbyopic and don't feel quite ready for bifocals or fancier.

--
Dicky
(legitimate nonprofessional)

Given all the information, -1.75 seems way too much power.  I doubt you
would be comfortable driving w/o correction if indeed that was your
true prescription.  Because of this, your eyes have a tendency to
"prefer" more minus.  Going from -1.75 to plano would seem rather
extreme, and you would probably "reject" that prescription.  The other
prescriptions do not seem "significantly different" from each other.
There is built-in error in every measurement, and the process of
refraction is designed to truncate the error in favor of more plus
rather than too much minus.

Take it from there.

DrG

Hi Dr G,

well, re: power , the average of
0.00
0.25
0.50
and
0.75,

= 0.25, OR 0.50

Should I go for the lower one?

Also, I gave Optometrist A my prescription sunglasses, so he knew what
my previous prescription was, as did the Eye Specialist (Prescription
C).  Prescriptions B and D were done with no mention of my previous
prescription. Could this have been a factor? How relevant is my past
prescription in determining my prescription today?

Andy

Calculate the average?

DrG

To all people who know more about Optometry than 1:

Hi,

Short version:
I'm trying to find the best prescription for my eyes, but my initial
attempt to get a second opinion has resulted in me going to 3
Optometrists, and 1 eye specialist, and now I have 4 different
prescriptions! They are pretty close, and of course no Optometrist is
going to say that the *other* optometrists prescription is the one to
go for, so im stuck! Which one should I choose?

Long version:
I'm 41,  musician / IT person, and last time I got an eye test (late
90's) was prescribed -1.75. I lost my glasses years ago, and have been
simply getting around without them. Main problem is driving, especially
at night, and I occasionally use disposable contacts (My old contect
lens box says -1.75, BC9.0, dia 14.2, if that helps) and marvel at how
sharper everything is. However I needed new glasses, and hence a new
prescription

The first Optometrist (A) prescribed this:

Prescription A:

-0.75    -1.0    x110
-0.75    -1.0     x60

When I put the mock-up frames on they seemed too strong (as he said
they would). He said it would take a couple of weeks to adjust! I've
been getting around for ages without glasses, and this seemed just
counter-intuitive. I said no offense but Id like a second opinion, he
said no problem.

So I rang my eye specialist/doctor, but he was away. His secretary
recommened Optometrist B. I made sure I got enough sleep, and spent
less time in front of the computer (in case these factors had affected
Prescription A)

Optometrist B gave me

Prescription B:

-0.25    -1.0     x95
-0.25    -0.75    x55

Ok, so its different, weaker power, and from what I understand
'significantly' different axis's (?) for the astigmatism. This
Optometrist B said I needed to see an Eye Specialist, so I thought,
cool, whilst I'm there I can get a third definitive opinion.

A few months go by, but the Eye Specialist was very fast and very
dismissive. I explained my dilemna, and showed him the two
prescriptions. He smiled, and said my eyes are fine, and that I didnt
need glasses. I said "well, when im driving at night things can look
pretty blurry", in the end he rushed through a few really quick tests
(took him less than 5 minutes). I did show him the two previous
prescriptions so his contribution IS biased, but anyway here's what
the Eye Specialist recommended:

Prescription C:

-0.50    +0.5    x15
-0.50    +0.5    x165

I realised this was a different code to the other two, and he admitted
that he did this on purpose so I wouldnt worry about it anymore. I
didnt really appreciate this condescending attitude. When I asked him
whether this result was close to presciption A or B, (or in between),
he refused to answer the question, and flippantly kept saying 'This
is the right  prescription for your eyes'. I was not impressed.

I walked into another optometrists shop, and got the guy there to
translate Prescription C to match the notation (?) of the other two,
and got

Prescription C:

0.00    -0.50    x105
0.00    -0.50    x75

So, he didnt think I needed *any* power correction (VERY different to
Prescription A), and the astigmatism seemed different yet again!

I thought to myself , 'well, I'll just go with Prescription B, it seems
the middle of the road between the two'.

But I couldnt help thinking about how flippant the Eye Doctor was, and
since his 1st response was that I didnt need glasses, mabye I sould
discard his prescription from consideration. I knew there had to be a
4th Prescription. And so it came pass, that I walked into another
optometrists, and explained the situation, and without showing them my
previous results, obtained:

Prescription D:

-0.50    -1.00    x90
-0.50    -0.75    x55

Ok, this was very close to Prescription B, and seems to be in between A
which was stronger, and C which had 0.0 power..

I realise these are very similar, and I'm currently trying to decide
between B and D, with the main issue being whether to go for 0.50, or
0.25. On one hand I'm told to get the one which made me read more
letters ( 0.50 rather than 0.25), but otoh, will 0.25 encourage my eyes
to work more, and be 'better for me'? I'll be wearing them mostly
for driving, movies, and other outdoor situations (looking at views
trees, clouds )

Do these results reflect the competency of the optometrists, or my
subjective performance during the test? Factors such as:
1.    How much sleep I'd had
2.    Whether I was regularly blinking during the examination or staring,
which was drying up my eyes
3.    How stressed I felt (in general) on the day.
4.    How much time Id spent in front of the computer that week.

If Optometrist B thought I needed 0.25 power, doesn't that mean that
that's how well my eyes can perform? Ie therefore I wasn't at my
'peak' when I needed 0.50?

your comments welcome,

Andy