Ho trovato questo articolo in cui un Dottore di Jerusalem spiega come mai alcuni portatori di LAC si trovano bene per alcuni giorni e poi male per altri.


Good Eye Days -- Bad Eye Days (GED/BED)

by Bezalel Schendowich, OD, FIACLE

A common complaint of contact lens wears and especially those with
keratoconus is that they can fairly well wear their contact lenses for
several days running and then run up against several days during which they
can't manage even to insert the little beasts. Some patients have termed
this situation Good Eye Days/ Bad Eye Days (GED/BED).



I would like to offer a possible explanation of this phenomenon; a rationale
why GED/BED is likely to be more prevalent amongst the KC contact lens
wearing population than amongst those with non-conical corneas; and
hopefully a possible prevention-cure.



Causes



Of the many possible causes of GED/BED, I think the most likely is simply
overwearing contact lenses. While many people can wear lenses for many
consecutive hours day after day with no readily apparent insult, there
exists a particular corneal structure which tires of bearing the contact
lens-foreign body at some stage. We first became aware of the 'overwear
syndrome' (OWS) many years ago with hard (not gas permeable -- RGP) contact
lenses. After too many hours eyes begin to redden, tear and generally
reject the lenses; the morning after is even worse. Many cases of OWS have
been at least partially remedied with contact lenses made from RGP
materials, but some corneas still can not

handle the stress of long term wear.



I think that in KC we have to consider two additional factors besides the
'foreign body under the lid' aspect: the predisposition of the conical
cornea to react pathologically to stresses on (1) the molecular level and
(2) the cellular level. A series of recent laboratory studies summarized by
Dr. M. Cristina Kenney when she presented the Everett

Kinsey Lecture last year to the Contact Lens Association of Ophthalmologists
and since reprinted in the Spring '99 issue of the NKCF Newsletter and on
their website can help us understand the weakness and susceptibility of the
KC cornea to react badly to physical stress. While the paper ought to be
read in full, I will use some of the results here.



1. Molecularly, several biochemical compounds (amino acids, proteins,
enzymes) have been identified in significantly different concentrations in
normal corneal cells as opposed to their concentrations in keratoconic
cells. Some compounds are more frequently found in keratoconus cells and
others which exist in normal corneas are in some cases non-existent in KC.
The purposes of these chemicals of course varies. In normal corneas the
compounds which are missing in KC aid the cornea in proper healing after
injury, in new cell growth and development, and in maintaining the
structural uniformity and transparency of the cornea. Those that are found
in KC but not in

normals have been shown to weaken the cornea's response to UV-light and
other external stresses.



2. Research has shown that on the cellular level, KC cells will
capitulate and self-destruct (apoptosis) when threatened or injured. Other
work has shown that areas of these cells will more likely heal from injury
and abrasion abnormally. This compromised healing response results in scars
and thinner tissue than would a healthy cornea.



Now back to GED/BED. We know that KC'ers, like most of the visually
unchallenged world, enjoy seeing; and because, seeing is optimized for them
by wearing contact lenses (in most cases), will tend to wear their lenses to
the maximum. Sometimes they overrun the maximum, physiologically safe,
wearing time for their eyes and their lenses. That would have been a Good
Eye Day. Many KC'ers can wear their lenses for many successive GED's
before they suddenly encounter a BED. And then, 'all H--- breaks loose'.
"Why can't I wear my contact lenses?" cries the hapless voice over the
phone. On examination and questioning the careful clinician can discover
that his patient has probably been pushing his lens wear to the limit. He
is now in the throes of what may

be considered to be a complicated OWS with exaggerated responses dictated by
his compromised KC cornea.



So, from these thoughts it seems that when the wearing is good, we have GED;
and after the wearing has been very, very good, it can be followed by the
BED. It also seems that because of the peculiar biochemistry of the cells
of the KC cornea this is more likely to happen to KC'ers than non-KC'ers. I
would like to propose that however so much a KC'er needs (and I imply with
that word a 'need' greater than most of us can comprehend) to wear his
lenses in order to function, he will do far better in the long run by
limiting his continuous wearing time.



Continuous wearing time (CWT) is one of my favorite functions of contact
lens wear. At each follow-up visit I try to ask every patient how long he
has worn his lenses so far today and yesterday and the day before. This
helps me to understand more clearly the intricacies of contact lens
adaptation. I explain to my patient-in-the-chair that when he removed his
lenses for his afternoon nap he essentially divided his wearing day

into distinct units. I, then, ask again how long he wears his lenses
continuously (I also remind him to thoroughly clean his lenses on each
removal).



Treatment



While KC patients have to read, write, work, and compete like the rest of us
in order to survive and they have to cook, clean, drive, plow, and so on as
part of their every day lives; and while they must be able to see
efficiently to perform these functions, it must not be at the expense of
either their immediate eye health or their capacity to wear their contact
lenses on the following day. A common sense approach to CWT for these
patients maintains a balance between necessary binocular wear, incidental
alternating monocular wear, and around the house spectacle wear (for those
who can -- and most can manage something around the house with glasses). We
must use our judgment as

professionals to help our patients find the most efficacious way of avoiding
the pitfalls of GED/BED.

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Bezalel Schendowich, OD, FIACLE