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.
* Patent of RF, 24.06.98
Material and methods
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.
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 evaporation of epithelium, 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
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.
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.
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). 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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