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Lasik corrects refractive errors
after PK in selected patients
Ana Hidalgo-Simón MD, PhD in Gatwick, London
DATA compiled from a recent UK study shows that Lasik is effective
in correcting refractive errors like anisometropia and astigmatism
after PK, provided patients are chosen carefully, Marcela Espinosa
MD told the Cornea 2002 meeting.
Dr Espinosa and Sheraz Daya MD, from the Centre for Sight, Queen
Victoria Hospital, East Grinstead, UK were concerned about the unpredictability
of the correction of refractive errors following PK.
Current therapeutic options for these patients include astigmatic
keratotomy, re-graft, lensectomy with toric IOL implantation, wedge
resection, photorefractive keratotomy and Lasik.
“We found that PRK used to treat refractive errors following
PK resulted in persistent epithelial defects and a substantial amount
of inflammation. This modality also had limited scope for correction
and frequently resulted in haze or scarring.
“Although still controversial, we found that Lasik resulted
in less inflammation. We could also perform an increased range of
corrections and early enhancements when necessary. In addition,
Lasik could be combined with other therapeutic interventions, such
as astigmatic keratotomy,” she explained.
The study included 62 eyes of 57 patients. Exclusion criteria were
poor graft-host apposition, areas of thinning, large pupils, any
graft rejection within the previous 12 months and the presence of
systemic or ocular surface diseases.
The most common original diagnosis was keratoconus which occurred
in 72.6% of cases, followed by herpes virus keratitis, corneal dystrophy
and trauma.
The mean age of participants was 42 years, ranging between 22 and
85, and mean time after PK was 7.6 years, ranging between two and
23.
Preoperative mean sphere was -3.04 D (range –15.75 to 7.75);
mean cylinder was -4.91 D (range 0.0 D to –13.0 D); and mean
spherical equivalent (SE) was -5.50 D (range -17.0 D to 5.8 D).
The follow-up period ranged from six to 60 months and averaged at
27 months, with visits at one day, one week and then one, three,
six, 12 and 24 months.
Enhancements, when necessary, were performed at three months postoperatively.
The follow-up rate at last visit was relatively poor at 44 eyes
or 71%.
All operations were performed with one of two lasers (LS 2000: LaserSight
and Technolas 217: Bausch and Lomb) and one of three microkeratomes
(Chiron ACS: Bausch and Lomb; Flapmaker: Refractive Technologies;
and Hansatome: Bausch and Lomb), although the majority of the operations
were performed with the Hansatome.
“Although there wasn’t a large change between the before
and after cylinder measurements (-4.91 D and –3.22 D), the
decrease in standard deviation was significant. We had to take into
consideration the fact that these eyes have big refractive errors
before the Lasik,” she explained.
Stability over time was excellent, with a slight drift towards myopia
after two years. Not too many eyes had data for more than two years,
so these results need to be confirmed.
Predictability after one and three months and one year was also
good. There was a tendency towards undercorrection, which remained
stable over time, she reported.
Safety evaluations were performed at one, three, six and months
postoperatively. These studies revealed that between 20% and 50%
of eyes showed no change in acuity.
Approximately one third of patients gained one line of vision, with
a few patients gaining two or more lines.
The UCVA results were good. Some 30% of the eyes saw 20/40 or better
at six months, improving to 40% at one year. BCVA was 20/40 or better
in 96% of eyes after one year. In 22.6% of eyes, re-treatment was
necessary (twice in two eyes) and in 16% a combined procedure with
astigmatic keratotomy (AK) was used.
The complications encountered by Dr Espinosa and her team included
one free flap, three partial flaps and three buttonholes. All these
were treated and corrected without further problems. They also had
three cases of epithelial in-growth, one rejection episode, and
one case of herpes simplex virus infection. Four eyes required re-grafting.
“There is a certain amount of controversy about when to use
Lasik after PK. The traditional view recommends waiting some time,
giving the eye a rest to recover after the cut of the flap. We did
not think this was necessary. Currently, our re-treatment rate is
13%. If we wait, that rate of re-intervention would be 100%,”
she explained.
She said that exposing the eye twice is hazardous for the allograft,
with its subsequent inflammation and antigen presentation.
The data from the current study indicates that Lasik is effective
in reducing the refractive error after PK, but not for all patients.
There is an increased chance of flap complications. Lasik can be
combined with other techniques, such as under-flap AK, and more
effectively, bitoric ablations, she explained.
“The important point is to understand that, assuming you are
selective with patients, this technique reduces anisometropia, reduces
astigmatism and helps patients tolerate their spectacles better,”
Dr Espinosa said.
Marcela Espinosa MD
Centre for Sight, Queen Victoria Hospital, UK
Email: marcela@centreforsight.com
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