Disposable microkeratome use is increasing in Europe due to tighter regulatory guidelines governing the sterilization of medical instruments. Many surgeons feel that it is no longer sufficient to use a new blade for each patient and autoclave the microkeratome; however, more thorough in-house or centralized sterilization is financially and logistically impractical for a busy refractive center.
Our colleagues in the United Kingdom report an even more stringent regulatory environment. Ever since the 1996 outbreak of variant Creutzfeldt-Jakob disease (vCJD; a form of bovine spongiform encephalopathy), Britain has been on heightened alert. Although no cases of vCJD were spread from instrument contamination, the trend over the past decade has been to move toward single-use microkeratomes, especially since the government announced that benchtop autoclaves do not remove the prion proteins that cause vCJD. The UK Department of Health now requires either centralized sterilization or single-use devices, and clinics are evaluated each year on compliance with these rules. Full compliance was required by 2007.
Fortunately, new single-use microkeratomes are both available and in the pipeline. Moria (Antony, France) first introduced the One Use-Plus 130 (Figure 1), an automated version of the One-Use disposable microkeratome. Two versions of the 130—the standard head for 9-mm flaps and the Large Cut head for 9.5-mm flaps (Table 1)—are already available worldwide. In early 2008, the company will introduce the One Use-Plus 90 for thin-flap LASIK.
Two separate motors are found on the One Use-Plus microkeratomes (Figure 2). Blade oscillation is set at 15,000 rpm, and the blade advancement can be switched to a faster or slower forward speed. The direction of the cut is horizontal, and the hinge is nasal. This keratome can be used for small or deep-set eyes and those with narrow fissures in choosing the correct suction. When space is tight, the suction ring may also be used without a speculum. An up-top adjustable stop makes it possible to customize the hinge width and stromal bed diameter and avoid free caps.
The One Use-Plus microkeratomes run on the same Evo 3e console used for other Moria microkeratomes—the Epi-K and the DSAEK. One advantage of this console, especially in suspect eyes, is that the surgeon can reduce the vacuum level on the reverse pass, limiting the duration of elevated intraocular pressure to as little as 10 seconds.
The transparent plastic ring makes centration easy. Moreover, the surgeon can easily visualize the cornea and the blade action through the ring. The keratome is easy to assemble, as there is virtually no risk of blade damage.
Given the current European regulatory environment, a fully disposable microkeratome is advantageous. Each microkeratome head/ring of the One Use-Plus combination is used on one patient, so there is less chance of diffuse lamellar keratitis or pathogen/prion transmission from contaminated instruments.
STUDY RESULTS
I recently participated in a prospective multicenter clinical study with the Moria One Use-Plus 130-µm head. In our center, 68 eyes (34 patients) were treated. Full data have not yet been compiled.
We used the Allegretto EYE-Q 400 excimer laser (WaveLight AG, Erlangen, Germany) for all laser ablations. Flap thickness was measured by subtractive pachymetry (Corneo-Gage Plus; Sonogage, Cleveland). At least six measurements were taken, and the thinnest was selected. The flap dimensions were measured with calipers: (1) average flap thickness was 123 ±12 µm (97–149 µm), where other investigators have had similarly tight standard deviations from the mean, (2) mean vertical flap diameter was 9.3 ±0.17 mm (9.0–9.5 mm), and (3) mean hinge size was 4.21 ±0.97 mm (4.2–5.75 mm). The shape of the flap and bed quality were uniformly excellent. There were no serious complications, however, I noted some irregular margins along the hinge in some eyes. This held no clinical impact. Centration was excellent, although one does have to be sure to decenter slightly nasally.
I also had the opportunity to work with the One Use-Plus 90 for thin-flap LASIK. The average flap thickness in my first 14 consecutive cases was 113 ±8 µm (101–123 µm). The flap in the first and the fellow eye were in average 115 and 112 µm, respectively. This procedure has the advantage of cutting through a more superficial layer of the cornea, where the corneal tissue is less likely to form tension lines/wrinkles. It also appears to preserve the larger corneal nerve trunks, which should have a positive impact on dryness and corneal sensation postoperatively.
Less epithelial trauma is induced with a thinner flap, and the visual recovery may be faster than standard LASIK. By leaving more tissue in the bed, the surgeon can treat a broader range of patients without encroaching upon the 250-µm threshold. This may mean that a patient with borderline thin corneas can still be treated, or that a postoperative patient can be enhanced to improve his visual outcome.
Mark Wevill, MD, of Manchester, United Kingdom, recently conducted a study with 32 eyes (17 patients) using the One Use-Plus for thin-flap LASIK. He used a new head on each eye (not just each patient), as required in the United Kingdom. Pachymetry was measured immediately before and after microkeratome use with a DGH ultrasound pachymeter (DGH Technology, Inc., Exton, Pennsylvania), and central flap thickness was calculated by the subtraction method. Dr. Wevill used the 7.75- or 8-stop and the -1 ring in all eyes. Mean flap thickness was 118 ±16 µm (93–147 µm). The quality of the flaps and beds was consistently good, and no significant complications were noted.
Dr. Wevill also reported that patients' eyes were clear postoperatively, and patients were comfortable after the flap was made with the One Use-Plus. By contrast, he found that femtosecond flaps sometimes produced transient light sensitivity.
Gustavo Tamayo, MD, of Bogot?, Colombia, looked at 34 consecutive eyes (17 patients) treated with an earlier ring version of the Moria One Use-Plus for thin-flap LASIK. Using the One Use-Plus 90, he achieved an average thickness of 109.8 ±11.9 µm (79–131 µm). Flap and bed quality as well as consistency were excellent, and there were no complications.
The subtraction method we used may over- or underestimate the actual flap pachymetry: Its accuracy is surgeon dependent. Even anterior segment optical coherence tomography measurements do not allow for precise measurement of the flap. Nevertheless, they show that the One Use-Plus flap is very close to planar, with central thicknesses that are approximately 12 to 14 µm thinner than those in the periphery (Figure 3).
We can conclude that the flap created by the One Use-Plus keratome is consistent in terms of its thickness, shape, and size. Large flap diameters that can accommodate astigmatic or hyperopic ablation profiles may be achieved with the Large Cut head version. The Moria One Use-Plus has become my microkeratome of choice, and I believe it will be a valuable addition to the armamentarium of surgeons in countries where disposability is key. Because I prefer to perform thin-flap LASIK, I am conducting a study with the One Use-Plus 90 involving a large number of eyes, with excellent results to date.
Jérôme C. Vryghem, MD, practices at Brussels Eye Doctors, in Brussels, Belgium. Dr. Vryghem states that he has no financial interest in the products or companies mentioned. He is a member of the CRST Europe Editorial Board. Dr. Vryghem may be reached at +32 2 741 6999; info@vryghem.be.
