RGP lens material choice
obsrving
first on your list?
Assumptions: Normal tears, slight propensity for dry (computer) eye,
and no history of o2 depravation due to soft contacts. Slight
astigmatism and low (-2.5) prescription. Eyes are otherwise within
normal shape and consistency. Desire for clearer vision than soft
contacts can provide, comfort level has not been an issue in the
past. Cost (within reason) is not a consideration. Lasik is not an
option for personal reasons, but tests show that "it would be a slam
dunk" and that the corneal thickness is "very good".
Overnight wear would be preferred, but not required. (3-5nights max)
The two materials that pop up most often in web and usenet searches
are the Boston XO2 and the Menicon Z materials.
Advantage to xo2 seems to be a slightly stiffer lens (hard to put into
a true comparison with the MZ lens though) with similar dk and what
they consider to be a better/easier wetting capacity without plasma
treatment.
Disadvantages to xo2 appear to be short time active in the USA and
daily wear only. I am assuming the daily wear status is solely due to
FDA paperwork and studies required for overnight wear, but suffice it
to say that it cannot be currently prescribed in that manner.
Advantages to the MZ (or MZa) lens material appears to be that it is
very thin, excellent wettability (via plasma treatment), extended wear
compatible and has been on the doctors shelves for years so plenty of
experience with fitting and use. Easy to replace due to wide
availability in the USA.
Disadvantages to the MZ material appears to be shorter lifespan due to
plasma treatment, "older" material (though that might not actually be
a disadvantage), possibly less wettable.
Other materials that pop up are the Hydro 2 for a very low wetting
angle and the Boston ES for ubiquity.
Don
> If you were to choose an (r)GP lens material today, which would be
> first on your list?
>
> Assumptions: Normal tears, slight propensity for dry (computer) eye,
> and no history of o2 depravation due to soft contacts. Slight
> astigmatism and low (-2.5) prescription. Eyes are otherwise within
> normal shape and consistency. Desire for clearer vision than soft
> contacts can provide, comfort level has not been an issue in the
> past. Cost (within reason) is not a consideration. Lasik is not an
> option for personal reasons, but tests show that "it would be a slam
> dunk" and that the corneal thickness is "very good".
>
> Overnight wear would be preferred, but not required. (3-5nights max)
>
> The two materials that pop up most often in web and usenet searches
>
> Advantage to xo2 seems to be a slightly stiffer lens (hard to put into
> a true comparison with the MZ lens though) with similar dk and what
> they consider to be a better/easier wetting capacity without plasma
> treatment.
>
> Disadvantages to xo2 appear to be short time active in the USA and
> daily wear only. I am assuming the daily wear status is solely due to
> FDA paperwork and studies required for overnight wear, but suffice it
> to say that it cannot be currently prescribed in that manner.
>
> Advantages to the MZ (or MZa) lens material appears to be that it is
> very thin, excellent wettability (via plasma treatment), extended wear
> compatible and has been on the doctors shelves for years so plenty of
> experience with fitting and use. Easy to replace due to wide
> availability in the USA.
>
> Disadvantages to the MZ material appears to be shorter lifespan due to
> plasma treatment, "older" material (though that might not actually be
> a disadvantage), possibly less wettable.
>
> Other materials that pop up are the Hydro 2 for a very low wetting
> angle and the Boston ES for ubiquity.
I strongly recommend the Menicon Z lenses. I wore the same pair
of Boston Equalens RGP contacts for over 10 years on an extended wear
basis (removed one night per week). They were approved for extended
wear back then, but were since change to daily wear and I never
learned about that (not that it would have mattered since I had no
problems).
When I needed trifocal multifocal lenses at age 54, I
investigated my options like you have, and was strongly sold by the
huge DK of Menicon Z lenses. I have had them for 5 months now and
wear them continuously except for one night per week. They are
FANTASTIC! I LOVE them! My eyes feel better in the morning than at
night. According to one study I found, the oxygen transmissibility of
Menicon Z lenses is higher that what the eye experiences at night with
the eyelids closed. Humans actually have slight corneal edema in the
morning from oxygen deprivation from having their eyes closed all
night. Well, Menicon Z has higher DK than that. I have zero
spectacle blur when I take my contacts out. My glasses prescription
is crystal clear.
Another study I found was interesting. FDA data shows that
extended wear rigid lenses are slightly safer than extended wear
soft. I think this is because their smooth surfaces make them easier
to clean well, unlike soft lenses that are somewhat sponge-like.
Anybody that can learn to tolerate Rigid GPs should use them over Soft
GPs for this reason alone. They are also much cheaper because the
rigid lens lasts forever. My experience has been that optometrists
shy away from Rigid lenses for this reason. They make less money.
I wanted to try multifocal lenses to get away from wearing
bifocals over my contacts. My optometrist first tried a concentric
ring design, but with the bifocal curve on the back surface of the
lens. This created spectacle blur such that my glasses were not in
prescription for about two days due to a temporarily deformed cornea.
Next he tried weighted lenses (just like trifocal glasses) but they
were not satisfying. Rapid eye movement, while changing lanes for
example, caused the bifocal lens to create blurred vision until they
settled down. We then tried the Menifocal Z concentric ring design
with the bifocal curve on the front surface. They are a MIRACLE! The
lenses magically adjust to near, intermediate (computer), or far
without me giving it a thought. For anyone thinking about trifocal
contacts, I recommend trying these.