I’m looking forward to seeing you all next week in the beautiful city of Istanbul. Our meeting, International Refractive Surgery: Art and Science, held in partnership with the Turkish Cataract and Refractive Division of the Turkish Ophthalmological Society, promises to be an extraordinary educational (including live surgery demonstrations) and networking opportunity. For those who can’t make it, our next issue of Refractive Surgery Outlook will feature some of the highlights and best papers of the meeting, as voted on by attendees. For those of you who plan to attend, travel safely and we’ll see you soon. -- Marguerite B. McDonald, MD, FACS
- A primer on Mitomycin C in surface ablation
- Differentiating interface fluid syndrome from DLK or infectious keratitis following LASIK
- Novel method for calculating IOL power after myopic LASIK shows promise
- Onset of presbyopia symptoms appears delayed in post-PRK eyes
- Variability in higher-order aberration measurements between the LADARWave and Visx WaveScan aberrometers
- Corneal keratocyte deficits continue to persist up to five years after PRK and LASIK
- Intracameral cefuroxime appears to reduce the risk of endophthalmitis after cataract surgery
- Intracameral cefazolin appears to reduce the risk of endophthalmitis after cataract surgery
- Evidence for declining in vitro susceptibility and increasing resistance to fluoroquinolones
- ISRS/AAO now accepting abstracts for the 2006 ISRS/AAO Subspecialty Day program
- Housing and tour information for the 2006 ISRS/AAO meeting in Turkey
- Will you need a U.S. visitor's visa to attend the 2006 ISRS/AAO meeting in Las Vegas?
- Online EyeCare Volunteer Registry makes becoming an international volunteer easier than ever
- Upcoming Meetings
- FDA approves WaveLight for mixed astigmatism
- FDA grants approval for Alcon’s new, high-speed laser
A primer on Mitomycin C in surface ablation
Marguerite B. McDonald, MD, who performs only surface ablation procedures in her corneal refractive surgery practice, offers advice on how to safely use MMC to reduce haze.
Differentiating interface fluid syndrome from DLK or infectious keratitis following LASIK
This retrospective study included eight patients (13 eyes) divided into two groups according to the incorrect preliminary diagnosis: those having a DLK-like reaction (11 eyes) and those diagnosed as having infectious keratitis (two eyes). In the DLK group, steroids were stopped and topical anti-glaucoma therapy was started. The interface edema decreased, and at the end of follow-up the corneal transparency was restored and IOP dropped to normal values. In the infection group, after elevated IOP was detected, steroids and antibiotics were stopped and topical anti-glaucoma therapy was started, resulting in the resolution of the interface edema. The authors conclude that interface fluid syndrome should be taken into consideration as a differential diagnosis for eyes developing late DLK and not responding to topical steroidal therapy. Appearance on slit-lamp microscopy should be the cornerstone in distinguishing interface fluid syndrome from DLK or microbial keratitis along with repeated measurements of IOP at the corneal periphery. Topical anti-glaucoma therapy with elimination of topical steroids is considered the treatment of choice in such cases. Journal of Refractive Surgery, May 2006
Novel method for calculating IOL power after myopic LASIK shows promise
This retrospective chart review included nine patients (nine eyes) who had phacoemulsification after LASIK. IOL power was determined using a method that assumes the patient never had myopic LASIK. It targets the IOL power at the pre-LASIK amount of myopia, bypassing the post-LASIK corneal power. Pre-LASIK keratometry values, pre-LASIK manifest refraction and the current axial length are plugged in the Holladay formula to determine the correct IOL power, assuming the patient had satisfactory LASIK results. In all nine eyes, this method consistently chose the most accurate and precise IOL compared with other methods. The mean spherical equivalent postoperative refraction was +0.03 diopter D ± 0.42 SD (range -0.625 to +0.75 D). Journal of Cataract & Refractive Surgery, March 2006
Onset of presbyopia symptoms appears delayed in post-PRK eyes
This retrospective study compared outcomes of 10 myopic patients (20 eyes) treated with first-generation PRK lasers at a minimum of 10 years after surgery with a control group of 10 normal patients. All subjects were older than age 40. PRK patients had better UCNVA than the control group, which tended to be accompanied by reduced distance vision, although this was not statistically significant. Among the PRK group, 90 percent of eyes had a favorable end point (UCNVA of J2 or better) and 60 percent had a UCNVA of J1+. Among the controls, 45 percent of eyes had a favorable end point, and only 20 percent had a UCNVA of J1+. The authors conclude that the delayed onset of symptoms associated with presbyopia and improved uncorrected near acuity in these patients can be explained by an additional 1-D pseudoaccommodative effect resulting from an increase in corneal spherical aberration and/or depth of field after PRK. They also suggest that it is possible, by controlling and purposefully introducing fixed levels of additional spherical aberration into the eye, that surgeons can enhance depth of field and delay symptoms of presbyopia. Ophthalmology, May 2006
Variability in higher-order aberration measurements between the LADARWave and Visx WaveScan aberrometers
Higher-order aberrations were measured in 17 myopic volunteers (33 eyes) and analyzed with varying pupil diameters controlled by a tunable light intensity source and after instillation of tropicamide 1 percent and phenylephrine 2.5 percent. HOAs increase at different rates and by different magnitude with pupil size and optical zone. Spherical aberration increases the most and is the steepest, followed by coma and then trefoil.
Higher-order aberrations displayed by the LADARWave correlate well with those of the Visx WaveScan but were higher than the latter in terms of total HOAs and spherical aberrations. Also the measured coma shows more variability between machines than the trefoil. The authors advise surgeons make sure pupil size is at least 0.5 mm larger than the target optical zone when measuring with the Visx WaveScan to ensure valid peripheral data and accurate higher-order profile, especially spherical aberration. They also find that dilation with mild cycloplegic with phenylephrine 2.5 percent and tropicamide 1 percent does not appear to clinically affect the HOA degree and pattern as measured by both aberrometers, as long as the center of the physiologic daytime pupil is taken as reference. Journal of Cataract & Refractive Surgery, February 2006
Corneal keratocyte deficits continue to persist up to five years after PRK and LASIK
This prospective study included 12 patients (18 eyes) who had PRK to correct a mean refractive error of -3.73 ± 1.30 D and 11 patients (17 eyes) who had LASIK to correct a mean refractive error of -6.56 ± 2.44 D. Keratocyte density decreases for at least five years in the anterior stroma after PRK and in the stromal flap and the retroablation zone after LASIK. After PRK, keratocyte density in the anterior stroma decreased by 40 percent, 42 percent, 45 percent and 47 percent at six months, two years, three years and five years, respectively. At five years, keratocyte density decreased by 20 percent to 24 percnet in the posterior stroma. After LASIK, keratocyte density in the stromal flap decreased by 22 percent at six months and 37 percent at five years. Keratocyte density in the anterior retroablation zone decreased by 18 percent at one year and by 42 percent at five years. At five years, keratocyte density decreased by 19 percent to 22 percent in the posterior stroma. American Journal of Ophthalmology, May 2006
Intracameral cefuroxime appears to reduce the risk of endophthalmitis after cataract surgery
This partially-masked, placebo-controlled study randomized 16,000 patients from 24 sites throughout Europe to receive either intracameral cefuroxime injection after surgery or perioperative levofloxacin eyedrops. The rate of endophthalmitis among patients not treated with cefuroxime was almost five times as high (23 cases in 6862 patients) as that among patients treated with cefuroxime (5 cases in 6836 patients). Though this estimate has a wide confidence interval, the authors are confident this antibiotic provides positive protection, and encourage physicians to consider its adoption as standard procedure for cataract surgery. The authors expected to recruit 32,000 patients, but halted the study in January 2006 after reviewing follow-up records for 13, 698 patients and reported the results before completing follow-up procedures for all 16,000 patients. Journal of Cataract & Refractive Surgery, March 2006
Intracameral cefazolin appears to reduce the risk of endophthalmitis after cataract surgery
This non-controlled, retrospective study included all cases of postoperative endophthalmitis recorded at a single hospital over a four-year period. The first group (3,650 patients) had surgery between January 2001 and December 2002 (a time in which no intracameral cefazolin was instilled); the second group, between January 2003 and December 2004 (3,618) patients. The second group received 1 mg of cefazolin in the capsular bag at the end of cataract surgery. This second group had a lower rate of endophthalmitis (0.055 percent) than the first group (0.63 percent). No patient treated with intracameral cefazoline developed corneal endothelium or retinal toxicity. Despite the positive results, the authors call for more and larger studies to determine the effectiveness of cefazolin and its nontoxic effect on corneal endothelium levels. Journal of Cataract & Refractive Surgery, March 2006
Evidence for declining in vitro susceptibility and increasing resistance to fluoroquinolones
This study evaluated the in vitro susceptibility and cross-resistance of gatifloxacin and moxifloxacin compared with older fluoroquinolones among coagulase-negative staphylococci recovered from patients with clinical endophthalmitis. Gatifloxacin and moxifloxacin – the newest and most potent fluoroquinolones – demonstrated an in vitro efficacy of less than 80 percent against coagulase-negative staphylococci endophthalmitis. Ciprofloxacin resistance may serve as a surrogate for concurrent in vitro resistance for gatifloxacin and moxifloxacin. The authors find resistance increased significantly during the last five years, and conclude that declining in vitro susceptibility to gatifloxacin and moxifloxacin may have important implications for the prevention and treatment of postoperative endophthalmitis. Archives of Ophthalmology, April 2006
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ISRS/AAO now accepting abstracts for the 2006 ISRS/AAO Subspecialty Day program
Abstracts will be accepted from now until June 14 for Refractive Surgery 2006: The Times They Are A-Changin'. The meeting is in Las Vegas, from Nov. 10 to 11. You can now view the Subspecialty Day program schedule online. Registration will open for members on June 28; for nonmembers, on July 12.
Housing and tour information for the 2006 ISRS/AAO meeting in Turkey
To reserve your hotel room, complete the online housing form and return it to United Expo at +90-232-4650086. United Expo is also organizing half day, full day and pre/post meeting tours. To reserve your spot on a tour, complete the online order form and it fax to United Expo at +90 232 465 00 86. Find all the latest information on this year's meeting in Istanbul, including recent updates to the program and faculty listing, from our Web site.
Will you need a U.S. visitor's visa to attend the 2006 ISRS/AAO meeting in Las Vegas?
Find out on the Academy's Web site. To assist you in the visa process, the Academy has compiled a complete review of the documentary requirements for international travelers. You can also download a letter of invitation from our site.
Online EyeCare Volunteer Registry makes becoming an international volunteer easier than ever
After registering on the Foundation of the American Academy of Ophthalmology’s Web site you initiate your own search, locating a match for your interests and skills, including geographic preferences, length and type of service. Among the services available is Orbis' telemedicine program, Cyber-Sight, which allows you to become an international volunteer without leaving your home or office.
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|Upcoming Meetings || || |
May 17-20, 2006
4th SOI International Congress
| || |
June 23-24, 2006
South African Society of Cataract and Refractive Surgery Regional Meeting
Cape Town, South Africa
|May 25-28, 2006 |
19th Congress of German Ophthalmic Surgeons (DOC)
| ||June 28 - July 1, 2006|
XII International Meeting of the Mexican Center of Cornea and Refractive Surgery
May 26-28, 2006
ISRS/AAO Meeting: International Refractive Surgery: Art and Science
| || |
July 8-9, 2006
Indian Intraocular Implant and Refractive Society Convention
|June 16-17, 2006 |
South African Society of Cataract and Refractive Surgery Regional Meeting
Johannesburg, South Africa
|Nov. 10-11, 2006|
ISRS/AAO Subspecialty Day Meeting
Sands Expo at the Venetian Hotel
Las Vegas, Nevada, USA
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FDA approves WaveLight for mixed astigmatism
The U.S. Food and Drug Administration approved the Allegretto Wave excimer laser system to treat naturally occurring mixed astigmatism of up to 6 D. The Allegretto Wave is a wavefront-optimized excimer laser that delivers specific ablation profiles based on each eye's unique corneal asphericity.
FDA grants approval for Alcon’s new, high-speed laser
The company says its LADAR6000excimer laser for use in LASIK and PRK surgery has a 50 percent faster ablation rate than previous Ladarvision platforms, resulting in significantly decreased surgical time, especially in higher refractive correction ranges, and less exposure of the corneal flap. The U.S. Food and Drug Administration (FDA) also granted the industry's broadest wavefront-guided hyperopic indication for Alcon's Customcornea procedure on both the Ladar6000 laser and the Ladarvision 4000 system, allowing surgeons to treat hyperopia and hyperopic astigmatism (+0.75D to +5.00D sphere with up to -3.00D cylinder) in addition to the current range for myopia and myopic astigmatism.
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Q & A
Marguerite McDonald, MD, FACS Question: How Do You Use Mitomycin C in Surface Ablation?
In my corneal refractive surgery practice, which is now limited to surface ablation, I perform PRK, epi-LASIK, and an alcohol-free form of LASEK that I developed. While the incidence of severe haze and the associated regression has dropped dramatically with the introduction of lasers that create smoother ablations with less physiologically disruptive profiles, haze remains a problem. The risk of haze rises considerably in patients who have had prior corneal surgery.
In a 100% surface ablation practice like mine, where treatments of corneas with prior corneal surgeries (RK, LASIK, PKP, etc) and high-diopter corrections are a significant part of the volume, mitomycin C (MMC) plays a significant role—although I am always mindful of its toxicity and seek to expose patients to the smallest dose of MMC that effectively prevents haze.
Who Receives MMC?
In previously unoperated eyes, I limit the use of MMC to patients with significant corrections, specifically:
- spherical equivalents greater than or equal to -6.00 D (myopes) or +3.00 D (hyperopes), and
- astigmatism greater than or equal to 3.00 D.
All eyes with previous corneal surgery receive MMC, regardless of the degree of correction, except prior surface ablation patients.
I use a single standardized MMC protocol for all patients, irrespective of the correction or other variables. I place 0.02% MMC on a circular Wek-Cel® cellulose sponge and then squeeze it hard until there is no excess liquid at all. I then place the sponge gently on the freshly ablated cornea and keep the sponge in place with my gloved finger for 15 seconds, after which I irrigate profusely with balanced salt solution (BSS).
When they do occur, haze and regression can usually be treated without additional ablation. To treat it, I scrape the cornea and apply MMC. I do not ablate. In most cases, the scraping/MMC procedure will eradicate the new collagen that has caused the regression, so ablation at that point would risk overcorrection.
For therapeutic application I use the same dose of MMC and deliver it in the same way as I do for prophylaxis. The postoperative regimen is the same as well, except that in therapeutic cases I use topical corticosteroids more aggressively.
Selecting a Dose
Just a few years ago, the MMC was delivered in a liquid-filled well that I kept in place for 2 minutes. Awareness of MMC’s toxicity has led many surgeons to reduce the concentration of MMC used and/or shorten the time for which it is applied to the cornea. A side benefit of the current lower dose of MMC is that it allows us to use our standard laser nomogram.
Thornton and others are experimenting even lower concentrations of MMC (0.002%).1,2 Promising preliminary results have been reported at meetings, but I don’t believe a major study has yet been published in the peer reviewed literature. This is a subject I follow closely. Given MMC’s toxicity, my strategy is to use the lowest dose that has been shown to provide effective prophylaxis against haze and regression.
- Have a pharmacy compound the MMC. The downsides of an error in compounding a substance as toxic as MMC outweigh any benefits of compounding it oneself.
- Use a fresh bottle of MMC every day. When we bought MMC in higher volume and kept each bottle sterile and refrigerated as we used it over the course of several weeks, we noticed an increase in inflammation during the first week postoperative (from which the patients all recovered uneventfully, although their eyes clearly looked more inflamed for the first 7 days). The problem disappeared when we changed to using a fresh bottle each day.
- Order MMC in small amounts so that the opened container can be discarded at the end of each day.
- Use MMC on:
- corrections > or equal to -6.00 D or + 3.00 D.
- astigmatism > or equal to 3.00 D.
- all eyes with previous corneal surgery, except prior surface ablation.
- MMC 0.02%.
- Soak circular Wek-Cel® in MMC and squeeze until there is no excess liquid.
- Place on ablated area of cornea for 15 seconds
Irrigate profusely with BSS.
- Same MMC dose and protocol.
- Scrape only; don’t ablate.
- More aggressive postop topical steroids.
- Don’t compound MMC in house. (Use a pharmacy.)
- Use a fresh bottle each day.
- Buy in small quantities.
1. Thornton IL, Puri A, Cox,CA, et al: Low dose mitomycin C as a prophylaxis for corneal haze in moderate and highly myopic photorefractive keratectomy. April 30-May 4, 2006, Ft. Lauderdale, FL, ARVO poster B294.
2. Nassaralla BA, Nassaralla J: Mitomycin C 0.02% X 0.002% to inhibit haze formation after photorefractive keratectomy for high myopia. April 30-May 4, 2006, Ft. Lauderdale, FL, ARVO poster 3605.
The Ocular Surface is a peer-reviewed journal with review articles on medical and surgical topics related to the anterior eye. Visit the for a free sample copy and special offer for ISRS/AAO members.
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