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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
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Routine two-step LASIK after PK unnecessary

By Cheryl Guttman

PHILADELPHIA - Creation of the LASIK flap does not significantly affect refraction in eyes that have undergone penetrating keratoplasty (PK) and have low keratometry values, new research shows.
Telma Pereira MD presented the results of a prospective study measuring refraction and keratometry values in 10 eyes of nine patients undergoing LASIK at the annual ASCRS Symposium on Cataract, IOL and Refractive Surgery.
A complete ophthalmological examination was performed prior to creating the flap and the eyes were reassessed 15 days after the lamellar keratectomy.

Mean baseline pre-keratectomy values for spherical equivalent (SE), cylinder and keratometry were -3.99 ± 4.17 D, -4.85 ± 2.43 D, and 44.07 ± 2.08 D, respectively.
At 15 days after flap creation, the corresponding values for those parameters were -3.71 ± 3.50 D, -4.72 ± 2.16 D and 43.65 ± 1.99 D.
The mean changes from baseline of -0.28 D in SE and -0.13 D for cylinder were not statistically significant. The mean -0.42 D decrease in keratometry trended towards significance (P=0.0593), Dr Pereira reported.

"We conclude from this investigation that it is not necessary to routinely perform LASIK as a two-step procedure in all post-PK eyes, beginning with the creation of the lamellar flap as the first stage followed by a delay to the laser ablation until refraction and keratometry are stable.
"As caveats, however, we note that our cohort included patients with low preoperative keratometry values and we believe our findings should be confirmed in a larger population," Dr Pereira said.

She observed that in a paper published in the American Journal of Ophthalmology [2001; 131: 507-8], Dada and colleagues reported a case where post-PK astigmatism was markedly reduced after creation of a lamellar corneal flap using the Hansatome microkeratome.
In that study, the patient had a net corneal astigmatism of 7.3 D two years after PK which was reduced to 3.9 D at one month and further to 2.3 D three months after keratectomy.

However, that patient had a preoperative keratometry value of 54.9 D, Dr Pereira noted.
"That value is much steeper than the maximum mean keratometry value in our series, which was 46.93 D. It appears from our experience that any effect of the microkeratome cut is minimal in relatively flatter corneas," Dr Pereira said.

The 10 eyes included in the study were all operated on at least one year post-PK. The mean time since the graft procedure was 33.1 ± 23.91 months. All eyes had clear corneal grafts, the sutures had been removed and the refraction was stable for a minimum of six months.

One surgeon performed 9.5 mm lamellar flaps under topical anaesthesia using a Hansatome microkeratome equipped with the 160 micron head.
After the cut, the flap was not lifted but the stromal bed was irrigated with a balanced salt solution (BSS) to remove debris. No microkeratome-related flap complications were encountered, Dr Pereira reported.

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