الفهرس 
Advances in analysis of corneal topographyOnly 14 pages are availabe for public view
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Abstract
A total of 32 eyes of 32 patients suffering from rhegmatogenous
retinal detachment were included in this study. They were divided
into 3 groups based on the surgical procedures. Group A included 5
eyes that underwent radial buckling, group B included 9 eyes that
had radial buckling with encircling, and group C contained 18 eyes
that received segmental circumferential buckling with encircling.
All these cases were operated in Benha Ophthalmology department
between March 2003 and May 2004.
The mean age of cases was 44.8 y. (29 y – 68 y). The maculae
were detached in 26 cases (81.2 %).
The Orbscan called (slit scanning corneal topography and
pachymetry system) analysis up to 240 data points per slit, and
calculates the elevation of the anterior and the posterior surfaces of
the cornea relative to best fit sphere, and the anterior and posterior
borders of the slit in each image were identified by the computer.
This instrument is also capable of measuring corneal thickness at
any point on the cornea with one procedure. It also can measure the
anterior chamber depth, angle of the anterior chamber, and pupillary
size besides other important applications.
We had used the Orbscan corneal topography system in
evaluating the corneal data preoperatively and postoperatively (1
month and 4 months).
The following data were evaluated and studied in every patient,
the induced keratometric cylinder (SimK), corneal astigmatic power
(CAP), average corneal power (ACP), anterior corneal elevation
(ACE), posterior corneal elevation (PCE), maximum and minimum
corneal powers (K1 and K2), corneal pachymetry (central point and
thinnest point), and anterior chamber depth (ACD). We also studied
the axial length (AxL) changes using the A – scan echographic
mode.
This study revealed that all types of scleral buckles could
produce corneal shape alteration, although the pattern of change
differed depending on the surgical procedure. It was noticed that the
Summary and conclusions ١٢٩
radial buckle produces the most remarkable effect on corneal shape
and power where it increases the average corneal power due to
increased steepening of the cornea and produce significant
astigmatism, which is irregular and long lasting.
Furthermore, most cases with radial buckles showed localized
corneal steepening corresponding to the site of the sponge, while
most cases with encircling bands showed central steepening and
peripheral flattening.
We also found that radial buckles induced hyperopia (due to axial
shortening of the globe) which is nullified by the induced refractive
myopia due to increased corneal steepening. On the other hand
encircling band produced a significant myopia (due to axial
lengthening of the globe besides the anterior displacement of the
crystalline lens).
In recent years, the success rate of scleral buckling surgery has
improved markedly. Surgeons should select surgical procedures that
will not simply reposite the retina, but also ensure favorable visual
acuity recovery. With this goal surgeons should not fasten a tire or a
silicone sponge so tightly as to cause changes to the shape of the
cornea, resulting in refractive errors. In addition, the observation of
continous changes in refractive errors within six months after
surgery should prevent unnecessary prescription of glasses. So, long
term studies are needed to determine if these corneal changes persist
over longer time.