8.4 Complications of the Procedures
Description
This article is from the Vision and Eye Care FAQ, by grants@research.canon.com.au (Grant Sayer) with numerous contributions by others.
8.4 Complications of the Procedures
PRK Side Effects -
1. Overcorrection - so you ended up long-sighted and need glasses for
reading. Initially the eye is over-corrected as the cornea has a
tendency to regress to its original state. The regression generally
stabilises after 1-3 months and it is uncommon to end up permanently
over-corrected. If you are you'll need glasses for reading and any
close up work.
2. Undercorrection - so you are still a little short-sighted. You may
regress so much you end up still myopic. If it is severe the procedure
can be repeated. Steroid drops are believed to control regression and
are used for several weeks after the procedure to avoid under-correction.
There is considerable debate in the literature over the benefits of
steroid drops but they seem to be widely used.
3. Decentration - the treated zone isn't centred properly, usually because
the patient didn't focus on the right point during the procedure.
"Measures are undertaken to ensure this doesn't occur" (according to my
brochure).
A study of 97 eyes reported
37% centred within < 0.25mm of pupillary centre
48% within 0.25 to 0.50 mm
13% within 0.50 to 1.00 mm
2% > 1 mm
The largest deviation was 1.5 mm and the average was 0.36 mm. The
higher the attempted correction the higher the degree of decentration.
(J. Cataract. Refract. Surg. 1993 19(2 Suppl) pp 149-54)
4. Post-operative Pain - varies in intensity and duration. The procedure
itself is painless. From conversations with people the opinion varied
from it was painful for:
8 hours;
48 hours;
3 days; and
4-5 days
and varied from
painful but not too bad;
agonising on the first day, painful on the second, uncomfortable
on the third; to
as bad as child birth!
The "typical" experience seems to be that it is very painful on the
first day, not nearly so bad on the second and merely uncomfortable on
the third and then painless after that.
5. Delayed Epithelial Healing - this is the outer layer of the eye. It
usually heals in 2 to 4 days but can take longer (generally uncommon).
appears to be very uncommon.
6. Corneal Haze - this gradually gets worse after the procedure and is at
its maximum severity around 6 weeks. It settles by 3 to 6 months and at
this point is generally not detectable by the patient but only by
an ophthalmologist using magnification. If it is severe it can impair
your ability to determine fine detail. The steroid drops are believed
to also control the degree of haze as well as the amount of regression.
If the scarring is severe the laser can be used to remove it and for
reasons which aren't known yet it doesn't re-occur.
From a study of 1821 patients (2920 eyes) corneal haze of grade 2 or
more occurred in 0.38% (11 eyes). Three of these patients (4 eyes)
were re-treated. Grade 2 or higher haze can cause myopia as the scar
tissue reduces the flexibility of the cornea.
(J. Refract. Corneal Surg 1994 Mar-Apr 10(2 Suppl) pp 226-30)
7. Halo effect - this can occur when the pupil enlarges beyond the
treated area at nighttime. They use larger treatment zones these days
(6mm instead of 5 or 4mm) so this is less common. It is also less
noticeable when the second eye is done.
8. Sensitivity to Glare - both eyes often become very sensitive to bright
light after PRK. Treatment - wear sunglasses. This goes away after
the first few months.
9. Other complications - theoretically possible but extremely unlikely
(ie listed to cover their arse (US: ass)).
corneal infection, intra-ocular infection, failure of healing,
corneal decompensation, persistent corneal oedema, corneal perforation,
corneal or anterior ocular neoplasia and cataract.
10. Damage to Bowman's layer - The sculpting burns away Bowman's Membrane,
the 2nd layer of the cornea. This layer is the one implicated in
keratoconus, a genetic disease whereby the cornea becomes irregular.
Keratoconus is treated with specialized rigid contact lenses. The
question here is: will PRK result in a keratoconus-like syndrome over
the long term? Keratoconus takes years and years to really get rolling.
Opinions from Ophthalmologists indicate that this issue is not a concern.
However a histological study (the original work is cited in a review by
Trokl, 1989, J. Cataract Refract. Surg. 15 : 373-782). This work
demonstrated, using both light and transmission electron microscopy,
the presence of a "pseudomembrane" covering surfaces which had been
laser ablated. This membrane apparently exhibits ultrastructural
properties characteristic of true membranes and also some of funtional
properties of true membranes, for example, it acts as a template for
re-epithelialization.
Another observation which suggests that destruction of Bowmans layer as
a result of PRK may not have negative implications in the long term, is
the fact that destruction of this layer as a result of trauma to the
cornea apparently does not result in Keratoconus or other disorders.
11. From a study of 615 PRK procedures with a follow-up of up to 2 years:-
"intraoperative complications with experienced surgeons extremely
rare"
gross eccentricities of ablative zone (of 1.0 to 1.5 mm) occurred
in 2 eyes (0.3%)
"epithelial disorders rare"
"recurrent erosions did not occur"
increased intraoculur pressure due to steroid treatment (of either
0.1% dexamethasone or 1% prednisolone) occurred in 30% of patients
with initial corrections of <= -9.0 D and 50% in patients with
> -9.0 D.
increased intraoculur pressure was correlated with increased risk
of over-correction
scarring severe enough to interfere with vision occurred in 0.5%
of patients with <= -6.0 D and 10% of patients with > -10 D.
scarring correlated with degree of attempted correction
most serious complication - noninfectious corneal ulcer in patient
with systemic lupus erythematosus
(Klin. Monatsbl. Augenheilkd. 1992 Jun 200(6) pp 648-53).
RK:
Major risks include; glare at night, fluctutations in vision from
morning to night, loss of BCVA (best-corrected Visual Acuity) - rarer
with RK than PRK, over/undercorrection, trauma (v. rare), infection
(rare). See Survey of Ophthalmology article by Rashid and Waring on
complications of keratotomy surgery ~1989 [ reference details to follow].
LASIK/ALK:
Risks basically the same as with PRK except no corneal haze occurs, but
you can get irregular astigmatism from an irregular cut. Perhaps 5%
of eyes done by experienced surgeons lose BCVA of 2 lines or more. Also
possible epithelial ingrowth between cornea and outerlayer which needs
to be removed.
Continue to:
My Books
