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RGP night vision
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biscuit
medicine forum Guru Wannabe


Joined: 24 Apr 2005
Posts: 296

PostPosted: Sun Jul 16, 2006 3:02 pm    Post subject: RGP night vision Reply with quote

Until a few days ago I had never really worn my new-ish RGP lenses at
night due to the long summer days. While my vision during the day is
just about perfect, I noticed a fogginess to my vision at night. The
way it looked really was almost indistinguishable from it actually
being just a little foggy; everything was sharp and in focus, but
bright things had a little haze around them, most notably reflective
street signs in the headlights.

Any thoughts on the cause of this and what could be done to improve
matters? I should mention that in this case I got up before the sun
and cleaned my lenses the night before, so the issue shouldn't be
related to having worn them for a long time.

By the way, I see they have "enzymatic" protein remover stuff for RGP.
My doctor didn't even mention the stuff. Is it a good idea to use it
weekly as suggested on the package?

Thanks.

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Mike Tyner
medicine forum Guru


Joined: 24 Mar 2005
Posts: 1299

PostPosted: Sun Jul 16, 2006 5:22 pm    Post subject: Re: RGP night vision Reply with quote

"Charles" <nospam@nospam.com> wrote

Quote:
being just a little foggy; everything was sharp and in focus, but
bright things had a little haze around them, most notably reflective
street signs in the headlights.

This could be buildup on the lenses, or corneal edema, or (possibly)
decentered lenses with larger pupils at night.

If the haze is gone immediately after you remove contacts and put on
glasses, then it isn't edema.

If it's protein/mucus buildup, then enzyme cleaners (or a more aggressive GP
cleaner) would be appropriate.

Most RGP lenses are compatible with enzyme cleaners. Those cleaners aren't
used so much for RGP because protein doesn't build up on them as it does on
soft lenses (or if it does, it gets rubbed off better with cleaning.)

-MT
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biscuit
medicine forum Guru Wannabe


Joined: 24 Apr 2005
Posts: 296

PostPosted: Sun Jul 16, 2006 6:25 pm    Post subject: Re: RGP night vision Reply with quote

Mike Tyner wrote:

Quote:

"Charles" <nospam@nospam.com> wrote

being just a little foggy; everything was sharp and in focus, but
bright things had a little haze around them, most notably reflective
street signs in the headlights.

This could be buildup on the lenses, or corneal edema, or (possibly)
decentered lenses with larger pupils at night.

If the haze is gone immediately after you remove contacts and put on
glasses, then it isn't edema.

If it's protein/mucus buildup, then enzyme cleaners (or a more
aggressive GP cleaner) would be appropriate.

Most RGP lenses are compatible with enzyme cleaners. Those cleaners
aren't used so much for RGP because protein doesn't build up on them
as it does on soft lenses (or if it does, it gets rubbed off better
with cleaning.)

-MT

Thanks for the reply. My contacts are certainly not centered, although
my doc things they are within tolerance (to me they look very low).
How could this lead to foggy, yet sharp vision?

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biscuit
medicine forum Guru Wannabe


Joined: 24 Apr 2005
Posts: 296

PostPosted: Sun Jul 16, 2006 6:30 pm    Post subject: Re: RGP night vision Reply with quote

Mike Tyner wrote:

Quote:

"Charles" <nospam@nospam.com> wrote

being just a little foggy; everything was sharp and in focus, but
bright things had a little haze around them, most notably reflective
street signs in the headlights.

This could be buildup on the lenses, or corneal edema, or (possibly)
decentered lenses with larger pupils at night.


Forgot to ask: I see edema keep coming up on the net in conjunction
with questions about foggy vision. How widespread/likely is this
condition? It sounds very serious, is it? And, would it normally be
detected with the regular checkup at the optometrist's office, or is it
harder to spot?

Thanks.


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Mike Tyner
medicine forum Guru


Joined: 24 Mar 2005
Posts: 1299

PostPosted: Mon Jul 17, 2006 1:09 am    Post subject: Re: RGP night vision Reply with quote

"Charles" <nospam@nospam.com> wrote

Quote:
Thanks for the reply. My contacts are certainly not centered, although
my doc things they are within tolerance (to me they look very low).
How could this lead to foggy, yet sharp vision?

Generally the contact gives you good vision only through the portion of your
pupil that it covers. If that's 75% of the total area of your pupil, you get
a crisp image from 75% of the rays, but it's surrounded by a blurry image
contributed from the 25% bypassing the contact. This haze would come and go
as the lens moved in and out of place. It would probably be associated with
"flare", a semicircular reflection produced by the meniscus at the lens
edge.

You didn't describe variability, or flare when the lens moves, so poor
centration may not be the problem.

You haven't said whether the haze disappears _immediately_ after switching
to glasses. That's important if you're worried about edema.

Corneal edema (CE, or CCC for Central Corneal Clouding) used to be very
common with PMMA contact lenses, and it always persisted more than a minute
or two after removing contacts.

CE would likely be spotted in the slit lamp if it were present. It stands
out. But probably you weren't examined at night, after several hours of
wear. CE would increase as the day goes on and start reversing soon after
you remove lenses.

If your haze persists after switching to glasses, another possibility is a
GP footprint, a temporary impression of the lens edge pressed into the
corneal epithelium, from a lens that sticks off-center and doesn't move
enough.

So, if the haze goes away after switching to glasses, it's likely buildup or
surface contamination.

Consider using a Q-tip soaked in cleaner, spinning it gently against the
back surface of the contact once a week or two. Sometimes your cleaning
routine misses that surface if your fingers are too big, etc. Make sure your
lenses stay wet after massaging with conditioner. If it beads up, there's
oil on the lens.

-MT
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biscuit
medicine forum Guru Wannabe


Joined: 24 Apr 2005
Posts: 296

PostPosted: Mon Jul 17, 2006 2:43 am    Post subject: Re: RGP night vision Reply with quote

Mike Tyner wrote:

Quote:

Generally the contact gives you good vision only through the portion
of your pupil that it covers. If that's 75% of the total area of your
pupil, you get a crisp image from 75% of the rays, but it's
surrounded by a blurry image contributed from the 25% bypassing the
contact. This haze would come and go as the lens moved in and out of
place. It would probably be associated with "flare", a semicircular
reflection produced by the meniscus at the lens edge.


It doesn't sound like this is my problem, although its tough to tell
for sure from these descriptions. It seems to me more like either a
dry lens surface or a "greasy" lens surface. Sometimes I get these
symptoms to an extent that they are obvious in bright daylight and they
go away instantly with drops or tearing - so I know it's something on
the surface. Maybe I always have it to some extent and only notice it
at night.

Quote:
You didn't describe variability, or flare when the lens moves, so
poor centration may not be the problem.


I'm generally pretty aware lens movement since I can see the edges ever
so slightly. The night fogginess did not appear to be related.

Quote:
You haven't said whether the haze disappears immediately after
switching to glasses. That's important if you're worried about edema.

I'll have to wait until fall and do some experimentation. I've been
wearing my lenses from 7AM to about 8 or 9PM and it doesn't get very
dark until almost 10PM right now.

Quote:

Corneal edema (CE, or CCC for Central Corneal Clouding) used to be
very common with PMMA contact lenses, and it always persisted more
than a minute or two after removing contacts.


Thanks for the info. What you are describing is a temporary thing?
I've been reading about a chronic condition unrelated (or not
necessarily related) to contacts. It sounds pretty scary to me and I
_don't_ want to have it!

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