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Photoastigmatic Refractive Keratectomy
with the“Profil-500”for
Correction
of Compound Myopic Astigmatism
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The paper analyses clinical and functional results of the transepithelial PARK
with the excimerlaser device "Profi1−500" performed in 250 eyes of 131 patients
between the ages of 18 and 45 with compound myopic astigmatism to 5.0 D and
myopia to 10.0D.The follow−up was 3years． In 90％ of cases visual acuity of
0.5−1.0 without correction or with weak myopic correction not more than −2.0D
was achieved by the operation. Complete correction of astigmatism was obtained
in 74％ of cases, residual astigmatism from -0.5 to -0．75D（physiological) was
found in 22.8％ of cases, from -1.0 to -1.5D in only 3.2％ of cases and only in
eyes with initial astigmatism of 4.0−5.0 D. The refractive result agreed with
the calculated data in 96.1％ of cases．
The method of excimerlaser
correction of compound myopic astigmatism，i.e.，Photo astigmatic refractive
keratectomy（PARK），acquires the growing popularity among eye surgeons in Russia
and worldwide．
However most specialists dealing with this problem and using
different excimer laser devices agree that the most accurate and predicted
result is achieved in spherical rather than in cylindric refraction component.
From literature, PARK decreases spherical refraction component by 75-95%, on
average, and cylindric one by 47-81%. After operation, the best visual functions
are recorded, as a rule, in correction of astigmatism to 2.0 D with myopia to
6.0 D [2-9].
It's should be stressed that from 1986 workers of the Center of
Laser Surgery at the Svyatoslav Fyodorov SI IRTC "Eye microsurgery" have pioneer
inventions of several generations of ophthalmic laser devices "Profil".
In
1995 the forming optical system of "Profil-400" which worked on the basis of
absorptive gas cell was modified. "Profil-500" contains basically new laser
system* which was created in cooperation with the Center of Physics
lnstrument-making at the Institute of General Physics of Russian Academy of
Sciences headed by the Nobel Prize winner A.M. Prokhorov. This device allows
simultaneous correction of not only myopia of any value [1] but correction of
compound myopic astigmatism due to formation of ellipsoid profile of laser ray
distribution with the set spatial configuration and selective reprofiling of the
corneal surface.
The objective of the study is the analysis of clinical and
functional results of PARK in correction of compound myopic astigmatism with the
"Profil-500" with the follow-up of 3 years.
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* Patent of RF, 24.06.98
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Material and methods
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Preoperatively, we examined 250 eyes of 131 patients between the ages of 18 and
45 with compound myopic astigmatism to 5.0 D and myopia to 10.0 D. The first
group comprised 54(21.6%) eyes with initial astigmatism to -1.5 D, the second
135 (54.1%) eyes with astigmatism from -1.75 to -3.0 D (Fig. 1), the third
61(24.3%) eyes with astigmatism from -3.25 D to -5.0 D.
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Direct astigmatism was foundiin 185(74%) eyes and reverse one in 65(26%) eyes.
Spherical refraction component to 3.0 D was recorded in 31(12.4%) eyes, from
3.25 to6.0 D in 137(54.8%), and from 6.25 to 10.0 D in 82(32.8%) eyes.
Visual acuity without correction exceeded 0.05 in none of the cases. Visual
acuity with maximal glass correction was 0.1-0.2 in 7 (2.8%) eyes, 0.3-0.4 in
33(13.2%) eyes, 0.5-0.7 in 139 (55.6%), and 0.8-1.0 in 71 (28.4%) eyes. Thus,
corrected visual acuity of 0.5-1.0 was recorded in 210 (84%) eyes
preoperatively. The similar retinal visual acuity was. in 235 (94%) eyes.
In
all cases PARK was performed by transepithelial method, i.e., with subsequent |
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Bowman's membrane, and superficial layers of the corneal stroma. Refraction
effect was calculated using software elaborated at the Center of Laser Surgery
of the SI IRTC "Eye microsurgery" in Windows system.
The operation lasted
not more than 1.5 min without any intraoperative complications |
Results and discussion
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Complete correction of astigmatism by 6-l2 months and more after PARK was
recorded in 48 (89.2%) eyes from the 1st group, in 98 (72.6%) from the 2nd
group, and in 39 (63.9%) eyes from the 3rd group.
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Residual astigmatism in groups at the same time postoperatively was the
following: in the 1st group astigmatism to -0.5 D was found in 6(10.8%)
eyes; in the 2nd group astigmatism to -0.5 D was recorded in 22 (16.3%)
eyes (Fig. 2), -0.75 D in 15 (11.1%) eyes, in the 3rd group astigmatism
to -0.5 D was found in 6 (9.8%) eyes, -0.75 D in 8 (13.2%), -1.0 D in 5
(8.2%) and -1.5 D in 3 (4.9%) eyes. Data are presented in Table 1.
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Thus, from the total number of eyes operated on, by 6-12 months after PARK full
correction of astigmatism was diagnosed in 185 (74%) eyes, residual astigmatism
-0.5 and -0.75 D, regarded as physiological, in 57 (22.8%) eyes, from -1.0 to
-1.5D in only 8 (3.2%) eyes from the third group with the high initial
astigmatism. In none of the cases astigmatism exceeded -1.5 D.
In 65 eyes
with residual astigmatism from -0.5 to -1.5 D, its axis remained stable in 35
(14%) eyes and changed within 5-10ﾟ in 30 (12%) eyes. In none of the cases
deviation of the residual astigmatism axis exceeded 10ﾟ.
From the total
number of eyes operated on complete correction of the spherical component of
refraction was achieved in 124 (49.6%) eyes, residual sphere -0.5 D in 87
(34.8%) eyes, sphere from -0.6 to 2.0 D in 39 (15.6%) eyes. Notably, weak myopic
refraction found 6 months - 3 years postoperatively coincided with the
calculated, i.e., planned, one in 96.1% of cases. Such "planned undercorrection"
was related to the age of patients, their social demands and refraction of the
fellow eyes. In none of the cases undercorrection was more than -2.0 D |
Table2). |
Hypercorrection up to +0.25 D from emmetropia, which did not affect
postoperative visual acuity, was found in only 3 eyes 6-l2 months after PARK and
only using refractometry in conditions of cycloplegia (1.2% of cases). It's
should be noted that 1.5-2 years postoperatively, hypercorrection was not
already found in these eyes.
By 6-l2 months postoperatively and during the
whole follow-up, visual acuity 0.5-I.0 without correction or with weak myopic
predicted correction was achieved in 94.4% of cases in the 1st group, in 94% in
the 2nd, and in 77% of cases in the 3rd group. On the whole, there are 225 (90%)
eyes as compared to 210 (84%) eyes with the same visual acuity in glasses
preoperatively (Table 3). |
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The correspondence of this visual acuity to the analogous retinal one was
recorded in 95.7% of cases. It is because of the fact that postoperatively, we
found increase of visual actlity in 30 eyes by 0.1-0.2 as compared to the
analogous visual acuity with glass correction preoperatively.
Dynamics study
showed that the corneal refraction, according to the data of ophthalmometry, by
6-12 months postoperatively and during the whole follow-up to 3 yearswas 37.59 ±
0.72 D, on average. Thickness of the corneain the centerwas not less than 300 um
in any case that showed correct choice of individual ablation
reglmen.
Clinical and functional results of the study are confirmed by the data of
keratotopographical examinations indicating the following things: achievement of
the smooth ablation profile of the cornea with the maximal refractive effect in
the central zone and gradual change of the corneal refraction in the each point
of the cornea along the entire zone of the excimer laser influence in all cases;
symmetrical flattening of the cornea along the axis which has had the greatest
refraction preoperatively; multifocali-zones with smooth over fall of refraction
from 1.0 to 3.0 D without sharp intermediate zones both inside each zone and
between them, along the whole zone of influence; absence of defects in
keratotopographic images such as "crescent", "key-hole", and "central islets";
rear decentrations of ablation zone with regard to the center of the pupil and
the cornea not greater than 0.75 mm and 0.18-0.32 mm, on average.
The above
data of keratotopography which was performed at different terms after
transepithelial PARK using "Profil-500" explain the fact that most patient did
not complain of negative subjective feelings as lights, crepe, dazzling, and
halos and, besides, many of them did not use glasses for the work at near
distance [1].
Thus, the results obtained show that the developed technology
of transepithelial PARK using "Profil-500" is safe, highly effective and
predictable refractive excimer laser interference which allows simultaneous
complete correction of myopia and compound myopic astigmatism of different
degree |
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