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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



GTS-assisted DLK useful alternative to PK for keratoconus

By Cheryl Guttman

PHILADELPHIA - Deep lamellar keratoplasty (DLK) using the guided trephine system (GTS) is a safe, effective and preferred alternative to penetrating keratoplasty (PK) in keratoconus eyes with a viable endothelium and otherwise good visual potential.

Speaking at the annual ASCRS Symposium on Cataract, IOL and Refractive Surgery, Jorg H. Krumeich MD reported that the postoperative visual rehabilitation course was nearly identical in a series of 228 cases of DLK and 429 cases of PK.
BCVA averaged 20/40 after three months and was 20/30 among eyes which reached the one-year visit (DLKP n=107; PKP n=227). At one year, cylinder was no more than -2.75 D in both groups.

However, several benefits were noted in the DLK eyes. Compared to the PKP group, suture removal between 12 and 16 months resulted in little refractive change in the DLK cohort.

Moreover, endothelial cell counts were unaltered compared to preoperative values and there were no cases of immune rejection at one-year post-DLK compared to four in the PK group.

"The introduction of preservative agents for donor buttons has had a detrimental effect on graft survival after PK. In studying more than 2,000 PK eyes during the last 10 years, we have learned there is a continuous decay of endothelial cell counts that can be as much as 50% in the first year.

"As a result, re-operation rates reach 10% five years after PK and 35% after 10 years. Immunological reactions occur in at least another 5% of eyes," Dr Krumeich said.
He added that for patients needing a corneal transplant who have a healthy endothelium, standard treatment with PK can no longer be justified because it does not offer a permanent cure.

"DLK is a less invasive alternative minimising the risk of intraocular infection and, most importantly, has the potential for much better long-term graft survival," Dr Krumeich remarked.

Although DLK was introduced about 30 years ago, it was not pursued widely because visual acuity with stroma-to-stroma adaptation was suboptimal.
More recently, thanks to the introduction of new techniques that provide separation of donor and recipient stroma and prevent interface healing, DLK is yielding better visual acuity results, he explained.

Currently, there are three main techniques for performing DLK. M. Anwar MD in Saudi Arabia has developed the "big bleb" technique in which air is injected over Descemet's membrane to separate it from the parenchyma.

Despite Dr Anwar's success using that approach, Dr Krumeich noted that since a sharp needle has to be used to achieve the separation, the incidence of perforations of Descemet's membrane occurs in about 50% of eyes in less experienced hands.
In a second approach developed by the Netherlands' Gerrit Melles MD, PhD, the recipient site is prepared with a special spatula working from the limbus and removing Descemet's membrane over the entire cornea with oscillating movements.

That technique is associated with less risk of perforation. But its drawback is that because Descemet's membrane is removed from the periphery, it jeopardises the possibility of performing PK in the future if that procedure becomes necessary.
Dr Krumeich stated his technique using the GTS - which makes even, circular undercuts with high precision at the intended plane - overcomes the limitations of the other alternatives.

With his method, the donor button is obtained on the anterior chamber bench to match an identical bed on the recipient and under pressure conditions that are the same as those in the in vivo eye.

The same trephine is used in the recipient eye. After obtaining pachymetry measurements, the GTS is zeroed and the trephine is lowered to 90% of the parenchymal tissue. Then the corneal parenchyma is lifted close to the level of Descemet's membrane.

"This level is found inside the trephination site with a probe made from a fine Paufique without teeth. The aim is to avoid perforation and prepare Descemet's membrane free of stromal tissue. The preparation to the centre is facilitated by injection of air into the posterior stroma," Dr Krumeich explained.

Finally, the endothelium is stripped off the donor button and fixated in the bed with a double-running anti-torque suture.

The Guided Trephine System is available from Rhein Medical Systems. Dr Krumeich licensed the system but has no financial interest in it.

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