Refractive Surgery 2005: Simply the Best, the annual meeting of the ISRS/AAO, will be held on October 14 and 15, 2005 at McCormick Place in Chicago.

We hope that you will also join us for the 2005 Gala Dinner on Friday, October 14, 2005, from 7 p.m. til midnight at the Hotel Inter-Continental, Renaissance Room. You will enjoy live music and dancing, and the presentation of prestigious awards.

Please note that to continue receiving this newsletter, as well as the other great benefits of ISRS/AAO membership, including the Journal of Refractive Surgery and a discount on meeting registrations, your membership dues need to be paid by August 31. If you have already renewed, thank you. If you haven't, please renew now.

Also, if you have any colleagues that would like to join us, we would love to have them. Please have them complete an application and submit it by the August 31 deadline.

As always, your questions and comments are most welcome.

Sincerely,
Marguerite McDonald, MD, FACS
Medical Editor, Refractive Outlook

IN THIS ISSUE
- Editor's Note: LightTouch Technique a Major Leap Forward for NearVision CK
- Journal Update: Laser in Situ Keratomileusis for Primary and Secondary Mixed Astigmatism
- Journal Update: Nerve Growth Factor Concentration and Implications in Photorefractive Keratectomy vs. Laser in Situ Keratomileusis
- Journal Update: Ex Vivo Confocal Microscopy of Human LASIK Corneas with Histologic and Ultrastructural Correlation
- Q & A

LightTouch Technique a Major Leap Forward for NearVision CK

H. L. “Rick” Milne, MD, and Marguerite B. McDonald, MD, FACS

Since its approval for hyperopia (2002) and presbyopia (2004), conductive keratoplasty has proven to be a very successful procedure. More than 90 percent of patients in the clinical trial for presbyopia, for example, achieved near vision of J3 or better. Still, there are always ways to improve on good procedures. The new LightTouch technique, in which much less pressure is applied to the cornea during application of the treatment spots, has improved predictability of the procedure in everyone’s hands, and nearly eliminated the underresponse or induction of cylinder that some experienced.

Although it might seem counterintuitive to get more response from less pressure, it makes more sense when one considers the theory of conductive keratoplasty. In this procedure, radiofrequency energy heats tissue, causing the tissue to shrink toward the source of heat. During the energy pulse, more tissue will be drawn into the circle of effect from the pulse if there is no other mechanical force acting upon this tissue.

When the cornea is compressed, on the other hand, there is a mechanical stretching effect on the corneal fibers that resists the natural tendency of the tissue being drawn toward the pulse. It turns out that with the standard pressure technique, we were actually fighting against ourselves by maximally stretching the collagen fibers just as we were trying to shrink them with radiofrequency energy.

This not only explains the varied response to standard CK treatments, it also helps explain the incidence of astigmatism in some surgeons’ hands. We now know that a variable degree of compression from one spot to the next could result in variable responses at each location.

LightTouch Technique
Using the standard pressure technique, most surgeons vigorously compressed the cornea, creating a dimple of 5-7 millimeters. For NearVision CK with LightTouch, the surgeon should aim to compress the cornea just enough to get a 1 mm to 2 mm dimple.

Centration and marking are still very important to the outcome and should be performed the same as previously. When the Keratoplast tip is first inserted into the cornea, enough pressure should be applied to indent the cornea to the point that striae extend to the pupil and the ring light reflex is displaced away from the probe. However, before depressing the foot pedal to deliver the radiofrequency energy, gradually release the pressure until there is minimal indentation of the cornea and the striae or dimple around the probe tip is only about 1mm to 2 mm. The ring light reflex should return to its original position.

Surgeons who perform CK with this technique will notice a marked tissue response and a noticeable flattening of the light ring in the sector of the delivered pulse.

With the LightTouch technique, the cornea tends to contract away from the probe with each spot. As this is happening, it is very important to gently “ride” or follow the contraction to ensure that the probe tip remains properly seated in the cornea and the full radiofrequency energy is delivered. This results in deeper bands and greater stability and reduces the chance of an incomplete treatment spot.

Also, because one is using much less pressure than before, it is important to maintain a steady hand position at the time of energy delivery and to instruct the patient on the importance of fixation during the procedure. If there is any concern regarding the patient’s ability to fixate, the surgeon can soak a surgical sponge in tetracaine, hold it against the conjunctiva for a few seconds in one quadrant, and hold the eye still with fixation forceps held on this spot. With proper instruction to the patient, however, this is rarely necessary.

If there is any induced cylinder, which is much less common than with the standard pressure technique, it should be treated postop, rather than intraoperatively. One spot placed on the flattest meridian in the same optical zone as the initial CK treatment is usually sufficient, regardless of the amount of astigmatism. It is rare that a second balancing spot is necessary with the new technique.

LightTouch Nomogram
Because the effect is so much more robust, nomograms for NearVision CK with LightTouch must be more conservative than a standard CK nomogram. One should plan to use fewer spots and treat at a larger optical zone.

Although surgeons may eventually vary their nomograms based on personal experience, Table 1 shows a good starting point for a LightTouch nomogram. This nomogram can be used for all virgin corneas and previous CK-treated eyes. Eyes that have been exposed to previous excimer laser energy over-respond to CK, for reasons that we don’t fully understand. This is especially true in former myopes. In such patients, the LightTouch technique can still be used, but the approach should be very conservative, with a starting point of one treatment ring at an optical zone of 8.5 mm or 9 mm.

Advantages of LightTouch
The greatest advantage of NearVision CK with LightTouch, compared to the standard pressure technique, is the reduced induction of cylinder. Data show that the incidence of any amount of induced cylinder has dropped from 29 to 10 percent or less with the new technique, dramatically reducing the need for postoperative balancing spots and improving patient and surgeon satisfaction with the procedure (Table 2).

Visual outcomes are even better with the new technique and the visual recovery appears to happen more rapidly. CK was always a pretty comfortable procedure for the patient, but with the reduction in the number of spots needed, any discomfort in the first few hours after treatment is truly minimal now. All this has combined to really enhance the “wow factor” for patients in the immediate postoperative period.

For us as surgeons, the ability to treat more (and more predictably) with less surgery is also very appealing.

In the past, with standard pressure CK, the greatest effect that was routinely possible to obtain was about 2.25 D—but that required a spot pattern of 32 spots, a pattern that was less predictable and more likely to induce astigmatism. In practice, most patients were treated with 16 spots and sometimes 24, but surgeons generally turned to laser if more than 2 D of effect was desired. Now, with the most typical LightTouch spot pattern (eight spots at 7 mm), one can achieve up to 1.75 D of effect.

Moreover, most patients can be treated with just one ring of eight spots at a larger optical zone than previously. Previously, three of the four recommended spot patterns required spots in the 6 mm optical zone. With LightTouch, the most robust spot pattern (16 spots) requires treatment at the 7 mm and 8 mm optical zone. This shift farther away from the visual axis reduces the induction of cylinder, preserves more of the cornea for future enhancements and gives us a more peripheral, and therefore more forgiving, procedure.

We would strongly encourage those who may have tried CK in the past and been underwhelmed to try it again with LightTouch. Although it may seem like a minor modification to an established procedure, the difference in predictability of response is so great that it is almost a different operation. In our hands, NearVision CK with LightTouch has been a very important step forward in the evolution of conductive keratoplasty.

TABLE 1: Milne LightTouch Nomogram

TABLE 2: Comparison of NearVision CK with Standard Pressure and LightTouch

Dr. Milne is in private practice at The Eye Center in Columbia, S.C. Contact him at 803-256-0641 or hmilne@aol.com.

Dr. McDonald is Clinical Professor of Ophthalmology at Tulane University School of Medicine and in private practice at Southern Vision Institute in New Orleans, La. Contact her at (504) 896-1242 or margueritemcdmd@aol.com.

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JOURNAL UPDATE

Laser in Situ Keratomileusis for Primary and Secondary Mixed Astigmatism

Jin G, Merkley K.H., Lyle W.A. Am J Ophthalmol. 2005: 139:1019-27.

Purpose:
To evaluate the safety, predictability and efficacy of LASIK for the treatment of primary and secondary mixed astigmatism.

Method:
A retrospective study included 118 eyes having LASIK performed with the LADARVision 4000 excimer laser to correct mixed astigmatism. There were two groups: 64 for primary and 54 for secondary mixed astigmatism.

Results:
Postoperatively, the mean uncorrected acuity was 20/20 in 51 percent of eyes, 20/40 in 97 percent of eyes at the last visit [mean follow up 10.6 mos.] The mean preoperative refractive cylinder was -2.18 D, while postoperatively the mean cylinder was -0.56 D. One eye lost two lines of best spectacle corrected. Vectoral analysis revealed a correction of 87 percent of intended cylinder in primary eyes versus 105 percent in secondary eyes.

Conclusion:
LASIK was safe, effective and predictable to treat primary and secondary and mixed astigmatism.

Comments:
This paper illustrates the safety, efficacy and predictability of treating both primary mixed astigmatism as well as that which developed following LASIK. Interestingly, primary eyes revealed less effective treatment than did eyes which developed mixed astigmatism after LASIK.

Nerve Growth Factor Concentration and Implications in Photorefractive Keratectomy vs. Laser in Situ Keratomileusis

Lee HK, Lee KS, Kim HC, Lee SH, Kim EK. Am J Ophthalmol 2005: 139: 965-71.

Purpose:
To determine whether tear nerve growth factor [NGF] concentration correlates with corneal sensation and ocular dryness after PRK and LASIK.

Methods:
The authors performed a prospective clinical trial analyzing total tear protein level, tear NGF, tear film breakup time and Schirmer’s measurements prior to and after PRK and LASIK.

Results:
Corneal sensation after LASIK [less than six months], but not PRK was diminished as compared with preoperative values. Mean tear break up time and Schirmer’s values were also lower after LASIK as compared with PRK for six months after surgery. Early postoperative tear NGF/total protein ratio correlated with the six month value for corneal sensation, tear breakup time and Schirmer’s values.

Conclusion:
This study shows that ocular dryness following laser vision correction may be related to early postoperative levels of NGF.

Comment:
This study shows that patients with low levels of NGF/total protein in tears early after LASIK had more signs of ocular dryness. If further studies confirm these results, additional treatments for dryness induced by LASIK may be developed.

Ex Vivo Confocal Microscopy of Human LASIK Corneas with Histologic and Ultrastructural Correlation

Dawson D, Holley GP, Geroski DH, Waring GO, Grossniklaus HE, Edelhauser HF. Ophthalmology; 139: 225-8.

Purpose:
To evaluate the confocal microscopic findings and compare to histologic and ultrastructure analysis of human LASIK corneas.

Methods:
This observational case series involved confocal analysis of 22 corneas from one month to 6.5 years after LASIK.

Results:
Confocal microscopy demonstrated that the epithelium centrally thickened after LASIK from basal epithelial cell hypertrophy, Bowman’s layer has undulations and the interface scar was “easily identified” by interface particles.

Conclusions:
This study shows that eyes after LASIK exhibit both interface and surface features that can be visualized and characterized by confocal microscopy; these include epithelial cell hypertrophy, Bowman’s layer undulations, and interface particles.

Comments:
This study shows that eyes after LASIK undergo healing which can be detected by confocal microscopy.

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Vikentia Katsanevaki, MD, PhD

Noninfectious Stromal Inflammation after LASIK?

Diffuse lamellar keratitis (DLK) is a complication of LASIK, recently described by Smith and Maloney, that typically presents within the first 48 hours after the procedure.¹ They defined DLK as a syndrome of diffuse corneal infiltrates of leukocytes confined to the interface and scattered throughout a large area with multiple faint foci. The patients present with photophobia, blurred vision, little or no anterior chamber reaction, relatively noninflamed conjunctiva and little or no ciliary flush. DLK is not associated with any infectious agent and responds well to steroids.

Since 1998, when this condition was initially identified, additional reports have described both sporadic and widespread cases of DLK in patients who underwent primary LASIK and LASIK enhancements. However, despite the extensive literature describing the clinical presentation and natural history of DLK, little is known about its etiology.

Most cases are considered idiopathic, or are associated with conditions known to increase ocular surface inflammation, such as meibomian gland secretions in the flap bed, bacterial endotoxins and postoperative traumatic flap dislocation. The use of povidone-iodine solution, microkeratome blade debris, carboxymethylcellulose drops and interface hemoglobin have also been proposed as possible pathogenic factors of the syndrome. Sterilizers with reservoirs may play a role in DLK, especially in clustered cases, since many centers have observed that the elimination of these sterilizers significantly reduced the incidence of DLK.

Whatever the causative agent, DLK is exquisitely responsive to treatment with steroids, with only some cases requiring additional flap lifting and manual removal of the inflammatory cells. Early diagnosis and treatment of this condition is important since DLK can result in significant haze or even flap melt, with loss of best corrected vision.

However, even with early recognition and treatment of DLK, refractive surgeons must not overlook the possibility of other clinical conditions that resemble DLK but that may be exacerbated by the use of steroids. Three recent reports2-4 describe patients with prolonged, atypical DLK that would not respond to steroid treatment. All the patients presented at least one week after LASIK, failed to respond to topical steroids and had increased intraocular pressure (IOP). Resolution of inflammation was obtained only by lowering the IOP and discontinuing or fast tapering topical steroids. Belin et al termed this condition “pressure-induced stromal keratitis” (PISK).²

In contrast to DLK, PISK presents late, is associated with increased IOP, and is exacerbated by topical steroids. To avoid exacerbating the interface inflammation, refractive surgeons should assess IOP in atypical DLK patients and aggressively treat elevated IOP. Discontinuation of topical steroids alone may be sufficient to manage this pathological entity.

In summary, stromal inflammation after LASIK must be identified early and be treated accordingly. Patient assessment must always include IOP measurement.

References:
1. Smith RJ, Maloney RK. Diffuse lamellar keratitis: a new syndrome in lamellar refractive surgery. Ophthalmology. 1998;105:1721–1726.
2. Belin MW, Hannush SB, Yau CW, et al. Elevated intraocular pressure-induced interlamellar stromal keratitis. Ophthalmology. 2002;109:1929–1933.
3. Davidson RS, Brandt JD, Mannis MJ. Intraocular pressure-induced interlamellar keratitis after LASIK surgery. J Glaucoma. 2003;12:23–26.
4. Nordlund, Michael L. MD, PhD; Grimm, Sara OD; Lane, Stephen MD; Holland, Edward J. MD Pressure-Induced Interface Keratitis: A Late Complication Following LASIK. Cornea. 23(3):225-234, April 2004.

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