Clinical Results of 75 cases for Myopia and Hyperopia combined Astigmatism with Kera IsoBeam D200

Dr. Eduardo Murube Jiménez, Marcos Garcia PérezCentro Oftamologico Retire-Lasik Center, Madrid, Spain

Abstract

This paper presents our LASIK results for myopic astigmatism and hyperopic

astigmatism. The experimental set-up consisted of splitting a 193nm excimer laser

beam into two laser beams which simultaneously ablated the corneal surface in a

symmetrical, flying spot fashion (dual flying spots). Each beam with 0.6mm square

size was guided by an independent X-Y positioning device. The randomly non-

sequential ablation positions were determined from a pre-calculated linear pattern

database (random projection). The fractal algorithm was also applied to achieve

diopter by diopter ablation (fractal). Eye fixation was achieved by a concentric ring

together with a line that was projected by a distant illumination light and tracking.

The Lasik Center, located in Madrid, Spain, registry consisted of 54 eyes with myopia

combined with astigmatism. These patients were enrolled between September, 2002 to

December, 2002. The pre-operative spherical equivalent ranged from -1.0D to -

12.75D. The correction factors attempted ranged from 1.0D to 12.0D. Follow up was

12 months. Fifty-two eyes that underwent LASIK myopia and astigmatism were

within 1.0D of the intended spherical equivalent refraction correction and forty-eight

eyes were within 0.5D of the intended spherical equivalent refraction correction. The

Lasik Center registry had 21 eyes with hyperopia combined with astigmatism. These

patients were enrolled between September, 2002 to December, 2002. The pre-

operative spherical equivalent ranged from +0.25D to +5.75D. The correction factors

attempted range from -0.75D to -5.75D. Follow up was 12 months. Nineteen eyes that

underwent LASIK for hyperpoia and astigmatism were within 1 D of the intended

spherical equivalent refraction correction and fourteen eyes were within 0.5D of the

intended spherical equivalent refraction correction.

1. Introduction

Excimer lasers (at 193nm wavelength) have long been used, both safely and

effectively, in the ablation of cornea tissue for refractive corrections such as myopia,

hyperopia and astigmatism. Great care must be taken, however, in transferring energy

from the laser to the cornea so that the laser energy distribution on the surface is both

spatially and temporally homogeneous. Diaphragm-related delivery methods, (1,2)

where a “wide spot” or “line-shape” laser beam is passed through a computer

controlled diaphragm, have shown uncertain ablation predictability and central islands

due to has difficulty in treating dependent hydration effects. (3, 4 and 5) The

diaphragm method also has difficulty in treating hyperopia and astigmatism and can

not handle irregular corneas. The scanning delivery method, (6) where a single small

laser beam scans sequentially over the corneal surface, can result in uneven hydration

effects leading to lateral islands.

In this paper we present a new “dual flying spot, random projection” delivery method

designed to solve both spatial and temporal energy distribution problems discovered

in other delivery approaches by matching the random nature of the factors in

refractive surgery that can not be avoided or adequately predicted, such as hydration,

ablation debris, energy stability and eye movement. A new fractal algorithm was also

used to achieve diopter by diopter ablations. Results of clinical studies performed

using these new delivery approaches and covering a range of refractive procedures are

reported. Procedures include LASIK for the correction of myopic astigmatism (54

cases), correction of hyperopic astigmatism (21 cases). Follow up data of twelve

months are also presented.

2. Principle of System

In the dual flying spot, random projection method a single source laser beam (193nm)

is split into two small flying spots that have the same timing, power and beam

characteristics but are 90 degree out of phase spatially. Each spot is focused to a

0.6mm square size and positioned by the system’s (galvanometric) optics

symmetrically about the optical axis on the patient’s cornea. The flying spots are

flexible enough to perform a wide range of refractive corrections including myopic,

hyperopic and astigmatism (both myopic and hyperopic) corrections as well as

enhancement features for corneal irregularities. By using two beams simultaneously,

however, the frequency of the laser is effectively doubled (from 300 Hz to 600 Hz).

This significantly shortens corneal ablation time thus reducing centration related

problems.

The ablation patterns are computer randomly generated from a sequential scanning

data base. The new non sequential data base were stored in a linearly array for

delivering through optical system to corneal surface. These dual flying spots

simultaneous ablations at symmetrical locations balance the hydration effect and

compensate spot energy profiles both spatially and temporally, while the random

projection effectively matches the random nature of such factors as hydration,

ablation debris, energy stability and eye movement.

“Flat” layer ablations, as performed by most current excimer laser systems, cover only

portions of the optical zone at various times, which would limit the full benefits of

random projection delivery. Therefore the fractal algorithm was constructed to divide

the entire treatment procedure into similar sub-treatment procedures. In this algorithm

each ablation “layer” covers the entire optical zone to varying depths rather than

successive portions of the zone at one “flat” depth. Thus true temporal averaging can

occur throughout the procedure. The unique combination of both the random and

fractal methods is called “Fractal Projection”.

3. Subjects and Methods

3.A Myopia Combined with Astigmatism

The Lasik Center registry consisted of 31 consecutive patients from September, 2002

to December, 2002 who were recruited into a prospective study for a total 54 eyes

treated. All patients signed fully informed written consents. Criteria for patient

participation included: 18 years or older, spherical equivalent of -0.25D to -12.0D,

stable myopic for the past two years, no contact lens worn for at least 2 weeks prior to

preoperative evaluation and surgery, and no active or residual corneal disease in either

eye. Bilateral LASIK surgeries were performed.

The patients were 20 females and 11 males with ages ranging from 19 to 48 years old.

Preoperative best spectacle corrected visual acuities were 20/20. Spherical equivalent

refractions before surgery ranged between -1.0D and -12.75D and attempted

corrections were from 1.0D to 12.0D.

Preoperative examinations included slit lamp microscopy, uncorrected visual acuity,

best corrected visual acuity, manifest and cycloplegic refraction, corneal topography

and pachymetry of the central cornea.

3.B Hyperopia Combined with Astigmatism

The Lasik Center registry consisted of 12 consecutive patients from September, 2002

to December, 2002 who were recruited into a prospective study for a total 21 eyes

treated. All patients signed fully informed written consents. Criteria for patient

participation included: 18 years or older, spherical equivalent of +0.25D to +6.0D,

stable hyperopic for the past two years, no contact lens worn for at least 2 weeks prior

to preoperative evaluation and surgery, and no active or residual corneal disease in

either eye. Bilateral LASIK surgeries were performed.

The patients were 9 females and 3 males with ages ranging from 18 to 47 years old.

Preoperative best spectacle corrected visual acuities were 20/20. Spherical equivalent

refractions before surgery ranged between +0.25D and +5.75D and attempted

corrections were from -0.75D to -5.75D.

Preoperative examinations included slit lamp microscopy, uncorrected visual acuity,

best corrected visual acuity, manifest and cycloplegic refraction, corneal topography

and pachymetry of the central cornea.

4. Surgical Technique

The surgeries were performed with the 193nm Kera IsoBeam D200 laser at a

repetition rate of 300Hz (600Hz effective rep. rate) with dual 0.6mm square spot size

and a fluence of 92mj per cm square each. The eye tracking is a 300 Hz infrared pupil

detection system. For spherical correction, the optical zones were chosen to minimize

the ablated tissue thickness but were larger than 5.5mm with an additional 1mm

transition zone. Cylinder corrections used optical zones with the same sizes as used in

the spherical corrections but with transition zones 2mm larger than the optical zones.

An eyelid speculum was put securely in place and the eye cleaned with a normal solan

sponge. A nasally based, 160 micron flap was made with a Moria’s automatic

microkeratome. After the corneal flap was formed, the microkeratome and its suction

ring were removed and the flap was lifted and displaced nasally. Laser procedure was

performed on the stroma bed with the IsoBeam D200 excimer laser system. After

surgery, the flap was folded back to its original position.

Patients were examined at 24 hours, 1 week, 1 month and 6 months and 12 months

with a slit-lamp microscope, and for uncorrected visual acuity, best corrected visual

acuity, manifest refraction and corneal topography.

5. Clinical Results

Table 1 shows preoperative and postoperative 12 months data for 54 eyes with

myopia combined with astigmatism. Table 3 shows the postoperative unaided visual

acuity and its successful rate. In 54 of 54 eyes an unaided visual acuity of 20/40 or

better was obtained. In 52 of 54 eyes an unaided visual acuity of 20/32 or better was

obtained. In 37 of 54 eyes an unaided visual acuity of 20/20 or better was obtained.

There have no eyes lost more than 1 line of the best corrected visual acuity at 6

months follow up.

Table 2 shows preoperative and postoperative data of 21 eyes with hyperopia

combined with astigmatism. Table 3 shows the postoperative unaided visual acuity

and its successful rate. In 21 of 21 eyes an unaided visual acuity of 20/40 or better

was obtained. In 19 of 21 eyes an unaided visual acuity of 20/32 or better was

obtained. In 12 of 21 eyes an unaided visual acuity of 20/20 or better was obtained.

There have no eyes lost more than 1 line of the best corrected visual acuity at 6

months follow up.

Table 1: 12 months results for myopia combined astigmatism treatment

# Eye Sex Preop Postop UCVA1 OD F -5.5+2.0x90 0 0.82 OS F -4.0+2.0x90 -0.5x180 0.93 OD F -7.5+1.25x30 0 1.04 OS F -9.25+0.75x140 -0.75+0.75x130 1.05 OD F -1.25+1.0x100 0 1.26 OS F -1.25+1.0x100 0 1.27 OD M -4.75+1.75x110 0 1.08 OS M -4.50+0.75x90 -0.25 1.09 OD M -4.25+0.25x90 0 1.210 OS M -4.75+1.0x90 +0.25 1.211 OD F -2.25 0 1.012 OS F -2.0 +0.5 1.0

13 OD M -2.0+1.75x175 0 1.214 OS M -3.0+2.25x5 0 1.215 OD F -7.0+1.5x105 -0.5 0.816 OS F -6.75+0.75x90 0 1.017 OD M -2.25 0 1.218 OS M -2.75 0 1.219 OD F -4.5+0.75x110. -0.5 1.020 OS F -7.5+1.5x65 -0.25+0.25x40 1.221 OD F -3.75+2.25x105 0 1.222 OS F -4.75+1.75x105 0 1.223 OD F -3.75+1.25x90 0 1.024 OD F -6.25+1.25x95 +0.25 1.025 OS F -7.0+2.25x85 -1.25+1.25x125 0.826 OD M -2.0+1.25x80 0 1.227 OS M -2.25+1.25x100 0 1.028 OD F -4.25+1.0x70 0 1.029 OD F -6.0+0.25x90 0 0.630 OS F -6.5+0.5x90 +0.5 0.831 OD M -1.0 0 1.232 OS M -1.5+0.5x160 0 1.533 OD F -3.75+0.5x100 0 1.234 OS F -4.0+1.0x85 0 1.535 OD F -10.25+2.75x95 +0.5 0.636 OS F -11.25+1.75x90 -2.75+2.75x95 0.637 OD F -6.5+1.25x30 -0.75 0.638 OS F -7.5+3.0x140 0 1.039 OD M -2.0+2.0x80 -0.5x18 1.240 OS M -1.75+1.25x115 -0.5x166 1.041 OD M -1.25 +0.75 1.542 OS M -1.5 0 1.243 OS F -3.0 -0.75+0.75x130 1.244 OD F -6.5+1.5x95 -0.5x10 1.045 OS F -7.0+0.75x75 0 0.646 OD M -12.75+1.25x120 -0.5x60 0.847 OS M -11.5+0.5x105 0 0.948 OD F -10.5+2.0x90 0 0.849 OS F -9.0+2.5x105 0 0.850 OD F -5.0+0.5x165 0 1.0

51 OS F -5.0+0.5x135 0 1.052 OD M -6.0+0.5x160 0 0.853 OS M -6.5+0.75x50 0 1.054 OD F -6.75+2.25x90 -0.25-0.25x90 0.8

Table 2: 12 months results for hyperopia combined astigmatism treatment

# Eye Sex Preop Postop UCVA1 OD F +4.25 -0.75+0.5x130 1.22 OS F +4.25+0.5x150 -1.0+0.75x170 1.03 OD F +0.25+1.0x90 -1.25+0.75x70 0.94 OS F +2.0x70 0 1.05 OD M +2.0-0.5x138 +0.25 1.06 OS M -1.0+1.0x10 +0.75 1.07 OD F -0.75+1.25x130 -0.5 1.08 OS F +0.25+1.25x85 -0.75 1.29 OD M +3.25+2.5x85 +0.5 1.010 OS M +3.0+2.0x110 +0.5 1.211 OD F +5.50 +1.0 0.612 OS F +5.57 +1.5 0.613 OD F -0.5+6.25x110 -0.5x10 0.814 OS F +5.25x85 -0.5x160 0.815 OD M +2.5+2.25x100 -0.5x15 0.816 OS M +1.75+1.25x90 0 1.217 OS F -0.75+2.0x80 -0.25 0.818 OD F +0.75+1.75x45 0 1.019 OS F +1.5x120 0 1.020 OD F +3.0+0.5x145 0 1.221 OS F -1.25+2.25x85 -0.5+0.75x45 0.8

Table 3: 12 months post-operative visual acuity achievement chart

20/40 or better 20/32 or better 20/20 or betterMyopic astigmatism 54/54 52/54 37/54

Hyperopic astigmatism 21/21 19/21 12/21

6. Conclusion

The result from the myopia combined with astigmatism and hyperopia combined with

astigmatism clinical study demonstrate that Kera’s IsoBeam D200 excimer laser is a

safe and effective surgical laser system for correcting mild, moderate and severe

refraction defect. The good predictability and lack of island side effects prove the

value of the dual flying spots, random projection, fractal algorithm excimer laser

delivery method.

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Presented by :

Dr. Eduardo Murube Jimérez Marcos Garcia Pérez

April 12th, 2005