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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