The work analyzes the clinical course of PARK performed
using the "Profil-500" in 250 eyes with compound myopic astigmatism to
5.0D with myopia to 10.0D. Operation was done through transepithelial access.
ln all cases complete epithelialization of the cornea was recorded within
24-48h. By 6-12 months postoperatively and until 3years of follow-up
the cornea of eyes operated on was comPletely transparent in 91.2% of
cases; opacities of 0.5-1 degree Were found in 8.8% of cases which did
not affect final refractive result.
Numerous studies investigating the condition of the cornea at different terms after photorefractive keratectomy(PRK) and photoastigmatic refractive Keratectomy(PARK) indicate tnat tne corneal syndrome is the typical feature of clinical course in the early postoperative period of these excimerlaser interventions in myopia and myopic astigmatism. The degree of syn drome indetermined by the type and area of erosion surface,time and period of cornea epithelialization,and condition of corneal epithelium anu stroma by the moment of completing epithelialization. Many authors consider the above facts to play an important role in the further development of subepithelial fibroplasia which forms corneal opacities of different degrree leading to unpredictable regression of postoperative refractive result[1,3,6,9,12,13]
Notably, from literature, the techniques of PRK and PARK
with different foreign excimer laser devices are performed with preliminary
scarification of the corneal epithelium [4,5,7,8]. Thus, it's necessary
to stress that the device "Profil-500" elaborated at the Center of Laser
Surgery of the Eye Microsurgery Complex, like all previous Profil models
of several generations ,allows transepithelial correction of myopia and
myopic astigmatism i.e., without preliminary scarification of epithelium.
The objective of the work is to study clinical course
of the postoperative period after transepithelial PARK with "Profil-500"
on the basis of postoperative results.
Material and methods
PARK was performed in 250 eye sof 131 patients aged
18 to 45 years with compound myopic astigmatism to 5.OD with myopia to
1O.OD. The follow-up was 3 years.
In all cases the operation was performed by transepithelial
method, i.e., with subsequent evaporation of epithelium, Bowman's membrane
and superficial layers of the corneal stroma. The operation lasted not
more than 1.5 min. No intraoperative complications were recorded.
Biomicroscopy of the anterior sector in eyes operated
on was performed using slit-lamp("opton”,Germany). To evaluate tne pattern
and duration of corneal epithelialization and find defects in it, we used
fluorescein probe according to routine method with the
use of 1% fluorescein solution.
We evaluated in the postoperative period(a) the degree
of corneal syndrome and subepithelial fibroplasia according to the classification
developed at the Eye microsurgery Complex(Kornilovsky I.M.,1995) [2]; (b)
degree of corneal opacities according to the world numeric classification
accepted in excimer laser practice.
Results and discussion
In most eyes operated on (184eyes-73.6%),irrespective
of the degree of initial astigmatism and sphere equivalent(SE),We found
epithelial form of corneal syndrome manifested by minimal involvement of
corneal stromal layers adjacent to ablation zone. In these cases ablation
zone was completely covered with epithelium within 24-36h postoperatively;
edema of superficial corneal stromal layeres adjacent to intervention zone
was rather mild or almost absent. Photophobia and lacrimation disappeared
1-2 days postoperatively as a rule. In 66 eyes(26.4%) stromal type of the
corneal syndrome was recorded which was accompanied by moderate edema of
all stromal layers in ablation zone. Notablv, in these eves the initial
SE varied from 8.25 to 15.0 D, being more than 10.0 D on average. This
required the removal of great volume of tissue and, thus, the use of greater
energy and pulse number for photochemical evaporation of the cornea. Complete
epithelialization in these eyes was recorded 36-48 h postoperatively; stromal
edema gradually decreased with epithelialization and almost disappeared
by day 5-7 postoperatively. Notably, we found no cases of mixed type of
the corneal syndrome consisting in longer epithelialization to 72 and more
hours postoperatively and pronounced stromal edema of entire ablation zone
with signs of descemetitis. This was confirmed by fluorescein probe allowing
detailed evaluation of corneal epithelialization and exclusion of uneven
and chaotic epithelialization with poorly fixed and mobile epithelium.
Thus, uncomplicated postoperative course after transepithelial PARK was
recorded in almost all cases By day 5-7 postoperatively the anterior eye
sector was calm, the cornea was smooth, bright and transparent. Only in
some cases biomicroscopy revealed slightly thickened epithelial layer of
the cornea with mild subep ithelial opalescence; its intensification accompanied
by appearance of whitish inclusions in the cornea are considered to be
the first signs of development of subep ithelial fibroplasia [2]. We analyzed
clinical course of transepithelial PARK at different terms of postoperative
period and recorded no visible signs of fibroplasia(degree 0) in 136(54.4%)
eyes from the first days after surgery and during the whole follow-up to
3 years. As a rule, SE in these cases did not exceed 8.5 D. In 92(36.8%)eyes
8-14 days postpperatively and irrespective of the value of initial refraction,
reversible form of subepithelial fibroplasia was recorded. Its symptoms
intensified during 1-3 months postoperatively and gradually disappeared
by 6-12 months postoperatvely. From our viewpoint, timely and correct topical
corticosteroid and resolving therapy affected the rate of fibroplasia regression
that in agreement with data of other authors[10, 11] Partially reversible
type of fibroplasia was recorded in 22(8.8%) eyes. Average SE was higher
tnan 10.0 D ln these eyes. Due to medication (corticosteroid and resolving
therapy) only delicate and spotty opacities of 0.5-1 degree remained at
tne periphery and in tne center of ablation zone by 6-l2 months after PARK
which almost did not affect postoperative visual acuity and did not cause
its decrease as compared to that with glasses preoperatively.
We found irreversible subepithelial fibroplasia with
signs of pronounced fibrosis in the corneal stroma and accompanied by significant
decrease of refractive effect in none of the cases. This data correlate
with results of clinical observations at the Center of Laser Surgery of
Eye Microsurgery Complex analyzing 40,000 PRK and indicating that this
type of fibroplasia is rather rare and its occurrence is not more than
1.4% of cases. The degree of manifestation of postoperative corneal opacities
in ablation zone is presented in Table.
Thus, 6-12 months after PARK and during the further follow-up
until 3 years corneal opacities caused by subePithelial fibroplasia were
recorded in only 8.8% of cases. Transepithelial access in PARK technique
using "Profil-500" allows significant degrease of degree and duration of
corneal syndrome and decreases 1.5-2 times the period of complete epithelialization
of the cornea that, in turn, sharply reduces the degree of subepithelial
fibroplasia in postoperative period and significantly increases the percentage
of high and stable refractive results.
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