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November 2002
IN THIS ISSUE

Wavefront seeks a higher order of vision correction
New laser system for intraoperative measurement of LASIK flap thickness
Visual prostheses use neurotransmitter retinal chips to stimulate retinal function
Wavefront emerges as powerful tool for night vision
Allegretto promising for hyperopia and hyperopic astigmatism
Topography's role in wavefront systems
IOP measurement after LASIK may be unreliable
LASEK may only play support on refractive stage
Solid-state laser PRK yields favourable results for myopia
GTS-assisted DLK useful alternative to PK for keratoconus
Glaucoma common after PK bodes poorly for visual outcome
Classic drawbacks of PRK succumb to new strategies
New insight into LASIK dry eye pathogenesis
Use of anti-inflammatories after capsulotomy questioned
Good quality training leads to good quality cataract surgery
One line of regained visual acuity is a snip at just €120
Mitomycin-C provides effective haze prophylaxis
Long-term concerns linger on safety of Mitomycin-C
German politicos promise health reforms
Honey forms biblical basis for corneal oedema
Routine two-step LASIK after PK unnecessary
Plasma knife provides clean and accurate cut for capsulorhexis
Glaucoma therapy targets apoptosis and trabecular meshwork
Viscocanalostomy viable choice for cataract-glaucoma
Device allows needle-free injections into smallest vessels
New river blindness therapy may provide panacea for 18m people
Daytime running lights may soon be compulsory in all EU states
Intracorneal lamellar implants still a questionable option
Aqualase system viable for small incision cataract removal
Unilateral von-Hippel disease with optic nerve head
FEATURES
From The Editor
Reflections on Refractive Surgery
In Your Good Books
An Eye On Travel
Bio-ophthalmology
Outlook on Industry
Regulatory Matters



Solid-state laser PRK yields favourable results for myopia

By Cheryl Guttman

PHILADELPHIA - Photorefractive keratectomy (PRK) with a 213 nm solid-state laser (Eye:Q) is safe and effective for treating low levels of myopia but larger studies are needed to assess its value in the treatment of hyperopia.
Robert Paul MBBS, FRANZCO and Ian Constable FRACO, FRACS conducted a single-centre study at the Lions Eye Institute/Sir Charles Gairdner Hospital, Perth, Australia. Dr Paul presented two-year follow-up results at the annual ASCRS Symposium on Cataract, IOL and Refractive Surgery.

He was a senior training registrar when the patients were treated and currently practises as a corneal/external eye disease and refractive surgeon at Fremantle Hospital, Perth.

The study's participants included 12 myopes and five hyperopes who had preoperative errors ranging from -5.75 D to +5.75 D and less than 3.0 D of astigmatism. Baseline UCVA was 20/200 or worse in 67% of eyes, with BCVA of 20/20 or better in 80%.
Excluding data from three eyes which underwent LASIK re-treatment with an excimer laser, the results were within 1.0 D of intended in 82% of eyes and within 0.5 D in 63%.

A total of 90% of eyes achieved a UCVA of 20/40 or better. No eye lost more than one line of BCVA, while 50% gained one or more lines. BCVA values remained unchanged in 40% of cases.

There were no cases of induced astigmatism or significant haze during follow-up. Trace amounts of haze were present in 57% of eyes at three months. This declined to 44% after two years.

"Our outcomes compare favourably with results achieved with excimer laser PRK, especially in terms of the uncorrected vision that is most important to the patients," Dr Paul said.

Evaluating the myopes and hyperopes separately, he noted the results were best for the low myopes. Among those treated for less than 3.0 D of myopia, all had UCVA of 20/40 or better and 50% saw 20/20 or better. For those with 3.0 D to 6.0 D of myopia, 83.3% achieved UCVA of better than 20/40.

Follow-up of refraction over time showed the myopes as a group were initially over-corrected, experienced regression and were close to emmetropia at two years.
In contrast, the hyperopes fared worse in terms of UCVA outcomes and exhibited greater variability in refraction during the postoperative course, Dr Paul reported.

"Given the very small number of hyperopic eyes treated, it is not possible to interpret the results to reach any conclusions about PRK treatment of hyperopia with this solid-state laser," he said.

LASIK re-treatment with an excimer laser was performed safely in two myopes and one hyperope after stable refraction was demonstrated. Both myopes were treated initially for more than 5.0 D of error.

One had regressed and the other was under-treated and regressed. Both maintained BCVA of 20/20 at one year after the re-treatment. The hyperope regressed +2.0 D and was re-treated twice at 10 and 13 months with the excimer laser. After one year, there was a single line loss of BCVA to a level of 20/25.

Regression in two other patients was not re-treated. One individual refused treatment and the other was a hyperope with vitelliform dystrophy.
The solid-state laser is a quintupled Nd:YAG device that emits a wavelength one fifth that of a standard Nd:YAG laser because the initially produced infrared beam passes through a crystal system where it is converted to 213 nm.

Compared to gas-based excimer lasers, the solid-state laser has the benefit of being much more compact as well as easier and less costly to maintain, Dr Paul said.
"Another potential benefit is that the 213 nm wavelength penetrates better through the balanced salt solution (BSS) compared to the 193 nm excimer laser beam, and thus the solid-state device offers the possibility of performing wet-field surgery," he added.
The solid-state laser features an infrared, video-based 200 Hz eyetracker and a variable size (0.5 mm to 4.0 mm) flying spot. It has a beam fluence of 170 mJ/cm2, operates at an ablation rate of up to 20 Hz and removes 0.25 microns of tissue per pulse.

The ablation zone measures 6.2 mm for myopic corrections and 6.0 mm to 9.5 mm for treatment of hyperopia.

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