Cheryl Guttman Krader, BS, Pharm

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	Take-home: Findings of a literature review highlight the need for more studies to compare SMILE and WFG LASIK for treatment of myopia and myopic astigmatism.

David P. Piñero, PhDProponents of small incision lenticule extraction (SMILE) are advocating this all-femtosecond laser refractive surgery technique for having advantages compared with LASIK. However, examination of the peer review literature shows there is still a lack of high level scientific evidence to support many of the claims, said David P. Piñero, PhD.

	“Good clinical results have been reported for SMILE, and compared with wavefront guided (WFG) LASIK, SMILE appears to be associated with less postoperative dry eye and avoids flap-related complications. However, SMILE shares other complications in common with LASIK and published data do not show that SMILE is superior to WFG LASIK in terms of visual, aberrometric, or biomechanical outcomes,” he said.

	“Whereas the efficacy and safety of WFG LASIK and enhancement procedures are well established, experience with SMILE is still limited, available follow-up is relatively short-term, and information is needed about methods of retreatment and their efficacy. These issues need to be addressed through future research that ideally will include head-to-head comparison trials. Clearly, more data are needed before refractive surgeons should feel confident adopting SMILE into their practices.”

	Dr. Piñero is assistant professor, departments of optics, pharmacology, and anatomy, University of Alicante, Spain. Setting out to compare outcomes of the two refractive surgery procedures when performed with modern technology, he conducted a search of the published literature that was restricted to January 2012 to September 2015.

Courtesy of David P. Piñero, PhDThe search identified 72 articles reporting on SMILE and WFG LASIK outcomes for the treatment of myopia or myopic astigmatism. Most eyes were treated for low to moderate myopia (up to -6.00 D), although one study of SMILE included eyes with higher myopia. Data were extracted on uncorrected and best corrected visual acuity (UCVA and BCVA), higher order aberrations (HOAs), dry eye, corneal backscattering, corneal biomechanics, and complications.

	In his review, Dr. Piñero found that efficacy, measured by the percentage of eyes achieving distance UCVA of 20/25 or better, was similar for the SMILE and WFG LASIK groups, ranging from about 83% to 100%. Mean postoperative logMAR UCVA values reported in the articles reviewed ranged from 0.02 to -0.17 for SMILE and from -0.04 to -0.18 for WFG FS-LASIK.

	There were also no clear differences noted between the two procedures in their safety outcomes, considering an analysis of the percentage of eyes losing one or more lines of BCVA.

	“According to the peer-reviewed literature, the percentage of eyes gaining 1 line of CDVA ranged from 0% to 57.10% and from 14% to 51% for SMILE and WFG FS-LASIK techniques, respectively,” Dr. Piñero said.

	The review of visual outcomes also showed the expected “wow” effect of LASIK with rapid recovery of excellent visual acuity. However, eyes that underwent SMILE took slightly longer to achieve a high level of uncorrected vision.

	Dr. Piñero noted that ultrastructural studies using OCT imaging identify microdistortions in Bowman’s layer as being present after both WFG LASIK and SMILE. However, their number is greater in the SMILE eyes.

	“The microdistortions act to increase light backscattering intensity in the anterior stroma, and that phenomenon may be a contributing factor in the slower visual recovery after SMILE,” Dr. Piñero said.

	The safety comparison of the two techniques also considered the development of dry eye. Findings from studies that assessed dry eye based on subjective questionnaires (Ocular Surface Disease Index or the McMonnies questionnaire) showed early worsening after both SMILE and WFG LASIK procedures. The changes were greater after WFG LASIK, but generally returned to preoperative values by 1 to 3 months following both types of surgery.

	“The difference in dry eye outcomes may be explained by a less severe decrease in subbasal nerve density after SMILE,” Dr. Piñero said.

	Analyses of aberrometry data showed better control of HOAs in eyes that underwent WFG LASIK compared with SMILE. In particular, there was a trend for an increase in coma after SMILE that Dr. Piñero suggested might be explained by a tendency for mild treatment decentration in eyes undergoing that procedure.

	Corneal biomechanics data were analyzed because it has been purported that compared with LASIK, SMILE has an advantage for maintaining better corneal biomechanical integrity. “However, the evidence supporting this idea is an estimation derived from a mathematical model,” Dr. Piñero said.

	“Results of published studies using different instrumental methods to assess corneal biomechanics provide no clinical evidence that the cornea has better biomechanical behavior after SMILE than after WFG LASIK.”

	Review of complications associated with the two procedures showed that SMILE avoids events that can occur with flap creation. However, other complications associated with LASIK-diffuse lamellar keratitis, decentrations, and ectasia-were still reported in the SMILE studies.

	“In conclusion, both SMILE and WFG LASIK are effective and safe procedures for the correction of myopia and myopic astigmatism, but more research is still necessary to confirm the potential superiority of one technique over the other,” Dr. Piñero said.

	This article is based on a presentation given by Dr. Piñero during the XXXIII ESCRS Congress in Barcelona Spain. A paper by Dr. Piñero and Miguel A. Teus, MD, PhD, reporting on the literature review has been accepted for publication in the 

Articles

Findings of a literature review highlight the need for more studies to compare SMILE and WFG LASIK for treatment of myopia and myopic astigmatism.

What you should know about SMILE and wavefront guided LASIK

In 2018, almost a decade after the first femtosecond laser for cataract surgery became commercially available, laser cataract surgery (LCS) continues to have a limited role in clinical practice. Although they may be in the minority, surgeons who have adopted the technique and become expert LCS users firmly believe that the laser adds value now and holds great promise for the future.

During the 36th Congress of the ESCRS in a meeting led by Julian D. Stevens, MD, Moorfields Eye Hospital, London, an international panel of LCS expert users shared their experiences with the aims of learning from each other and identifying directions for new research.

The consensus of the group was that, even for routine cases, there is a role for using the femtosecond laser because it makes cataract surgery more straightforward, more reproducible, and safer. In addition, because laser pre-treatment shortens the non-laser portion of the procedure, LCS reduces surgery-related ergonomic stress that can shorten a cataract surgeon’s career.

The experts’ discussion particularly highlighted the benefit of using the femtosecond laser for treating preexisting astigmatism, which has relevance in a large percentage of routine cases, and brought to the forefront its role in complex situations, including eyes with a dense black or intumescent cataract. Looking ahead, the participants agreed that with the expected evolution towards capsulotomy-fixated implants, access to LCS will have an unequivocal advantage for enabling delivery of optimal refractive and functional outcomes.

Compared with manual penetrating astigmatic keratotomy (AK), femtosecond laser-assisted AK (FS-AK) has advantages for providing better rotational/angular alignment, better patient comfort, and reduced risk of infection. Data presented during the expert users’ meeting provided evidence that FS-AK is more effective than the manual approach and its result is more stable.

Professor David O’Brart, MD, St Thomas’ Hospital, London, presented findings from analyses of outcomes in groups of patients who underwent FS-AK or manual limbal relaxing incisions (LRIs) in the context of a randomised controlled trial comparing LCS and conventional surgery [J Cataract Refract Surg. 2018;44:955-963]. The analyses included eyes with no visually significant comorbidities that were treated for >1 D of corneal astigmatism with a plano refractive target.

At 1 month after surgery, postoperative cylinder was ≤0.50 D in 18 (42%) of 43 eyes in the FS-AK group and in only 8 (20%) of 41 eyes in the LRI group. Professor O’Brart reported that there were statistically significant differences favoring FS-AK in analyses of difference vector and correction index.

Dr Thomas Laube, MD, private practice, DÃ¼sseldorf, Germany, presented results from a retrospective study demonstrating the efficacy and stability of FS-AK for reducing corneal and refractive astigmatism [Open Journal of Ophthalmology. 2017;7:262-272]. The study included 42 eyes with 0.5 D to 1.5 D of regular corneal astigmatism and total corneal irregular astigmatism <0.300 Î¼m. The AKs were 8.0 mm diameter paired symmetrical arcs centred according to the scanned capsule and created at a depth between 20% and 80% of corneal pachymetry. Reference marks were placed on the conjunctiva using a sterile disposable ink pen (Devon utility marker, Covidien) that is visible on the Catalys OCT image. Maximum arc length in Dr Laube’s series was 65°. Dr Stevens noted, however, that arc lengths of 90° have been safely used for FS-AK.

“With the intrastromal cuts, there are anterior and posterior belts of intact tissue, and the corneas are relatively stiff in cataract patients who tend to be older,” he explained.

Dr Laube analysed astigmatic change using the Alpins vector method and found manifest cylinder was reduced significantly from 0.94 ± 0.62 D preoperatively to 0.64 ±0.45 D at 1 month after surgery (P=0.03). Continued follow-up showed no significant change after 12 months (P=0.90) at which time manifest cylinder was ≤0.5 D in 60% of eyes compared with just 38.1% preoperatively.

“The majority of patients were happy that they no longer needed glasses for distance vision,” Dr Laube said.
	Dr Stevens noted that with LRIs, the astigmatic effect can continue to regress for up to 10 years. In contrast, he has collected data showing that the effect of FS-AK achieves stability early on and remains unchanged for at least 5 years. 
	Providing some tips for performing FS-AK, Dr Stevens noted that gas generated by the treatment is needed to break corneal fibers and separate the arc walls.

Therefore, it is important to use sufficient power, especially in younger patients.

Dr Stevens also said that there is an increased risk for pupil constriction when performing FS-AK because the laser treatment is commonly placed over the iris. To mitigate this effect, he pretreats the eyes with ketorolac drops and schedules the cases to minimise the delay between the laser and OR portions of the procedure.


	Dr Frank Goes Jr, MD, private practice, Antwerp, Belgium, presented his experience using the Catalys Precision Laser System (Johnson & Johnson Vision) to perform “ultrafast” capsulotomy in an eye with an intumescent cataract.
	“I have no doubt it was a good idea to use the laser when operating on an intumescent lens,” said Dr Goes.

He explained that, during manual capsulorhexis or standard laser capsulotomy, release of intralenticular pressure in an eye with an intumescent cataract creates a risk for radial tearing of the anterior capsule. Dr Goes adjusted the settings for performing the capsulotomy to shorten his capsulotomy time to just 0.3 seconds (Table 1). Importantly, the increase in speed did not compromise quality, he said.

Using trypan blue in the OR to aid visualisation, Dr Goes saw that the capsule disk was not free-floating, but it was free of tags, and he removed it successfully without any radial tearing.

The meeting participants agreed that more evidence is needed to support use of the modified settings as a standard for laser capsulotomy in eyes with an intumescent cataract. Dr Stevens noted that because a significant number of such cases present to Moorfields, he might have the opportunity to amass a series for a prospective study.

It was also noted that a double capsulotomy technique, involving an initial “mini” opening and a second larger capsulotomy, has been described as an alternative for safe capsulotomy in eyes with an intumescent cataract [J Refract Surg. 2014;30(11):742-745]. In this method, the first capsulotomy allows for release of intralenticular pressure. After fluid lens material is removed from the anterior chamber, the eye is redocked for the second capsulotomy. 

Dr Stevens observed that the need for redocking adds time to the procedure and increases the risk for subconjunctival hemorrhage. Because of those issues, he called for manufacturers to modify their systems and eliminate the need for redocking after operators remove their foot from the pedal.

Dr Goes’s case also prompted a discussion about reducing capsulotomy time in routine cases in order to minimise the potential for eye movement that would affect the accuracy of laser pulse placement. Dr Stevens suggested that because the lasers work well “out of the box” with the use of the manufacturer-recommended settings, surgeons are reluctant to experiment with modifications because they are worried about higher rates of incomplete capsulotomy.


	Jose Luis RodrÃ­guez-Prats, MD, Clinica Visahermosa, Oftalvist, Alicante, Spain, also presented a case in which use of the laser for capsulotomy proved beneficial. The case involved an eye with anterior lenticonus associated with Alport syndrome.

“Performing anterior continuous curvilinear capsulorhexis in these eyes is difficult due to the structurally abnormal anterior capsule,” he explained.

The patient described by Dr RodrÃ­guez-Prats underwent bilateral FLACS with the Catalys laser using the device’s software calipers to manually delineate the anterior capsulotomy. Multifocal toric IOLs were implanted with the aid of intraoperative aberrometry for power selection.

Preoperative UCVA was 0.8 OU in moderate photopic conditions; subjective refraction was -5.25 -7.25 x 180 OD and -6.75 -8.50 x 165 OD. Postoperatively, the patient achieved distance UCVA of 0.9 OU. BCVA was 1.0 OU, and his refraction was plano -0.50 x 5 OD and +0.50 -1.0 x 170 OS. At 45 days after surgery, both IOLs remained well centred.

Javier Mendicute, MD, Donostia University Hospital and Innova Begitek Ophthalmology Clinics, Donostia-San SebastiÃ¡n, Spain, reviewed the benefits of LCS when operating on very dense (black) cataracts (VIDEO). In his opinion, the possibility of using the laser in black cataracts depends on the imaging system’s ability to identify anatomic structures in the situation where there is poor media transparency as well as the accuracy and penetration ability of the laser.

The type of OCT, its working wavelength, and the speed of image capture determine the quality of the image obtained through opaque media and the possibility of identifying the posterior capsule when there is limited lens transparency. Dr Mendicute stated that he thinks swept source OCT is the best option for posterior capsule identification because it has faster acquisition time and deeper penetration than Scheimpflug technology or time domain or spectral domain OCT. He noted, however, that he has had the opportunity to use all femtosecond platforms in the market and that all of the equipment available today allows the automatic identification of anatomical references.

“Because of the imaging technology that allows identification of the posterior capsule and their precision, femtosecond lasers can be used to safely treat the lens close to the posterior capsule,” Dr Mendicute said.

The best fragmentation pattern to achieve the minimum use of energy and maximum efficiency when treating a dense black cataract is debatable. Dr Mendicute said that a grid pattern can require a lot of energy and result in a lot of bubble generation. His approach uses a pattern that he named “Microcrater, Divide & Conquer” in recognition of Dr Howard Gimbel. Using the femtosecond laser, he creates a 2-mm central disc and three radial cuts.

“After phacoemulsification of the central disc, there is a point of support to split the lens into six fragments that are easily removable,” Dr Mendicute said.

Bernardo Mutani, MD, Torino, Italy, presented his experience with LCS using the Catalys laser in an eye with a foldable posterior chamber phakic IOL (Visian ICL, Staar Surgical) (VIDEO). Because the imaging system did not recognise the anterior surface of the cataract, Dr Mutani said he needed to manually customise the anterior capsule to fit on the anterior surface of the lens. Thereafter, he was able to use his routine laser settings to successfully complete both the capsulotomy, which was centred on the pupil, and lens fragmentation.

Dr Mutani noted that trapping of cavitation bubbles in the space between the phakic IOL and the anterior lens capsule, which could impair laser energy delivery for the fragmentation step, was not a problem in this case that involved a cortical cataract.

“It is our experience that less gas is generated when treating a cortical cataract compared with a nuclear cataract,” Dr Mutani said.

In the discussion following Dr Mutani’s presentation, concern was also raised that in eyes with a phakic IOL, the laser’s imaging system may give erroneous readings of the capsule surfaces. Dr Stevens noted that due to these challenges, he chooses to do standard cataract surgery in eyes with a phakic IOL.

Dr Mutani also shared a video involving a case of IOL exchange in which he used the femtosecond laser to cut the in situ IOL (VIDEO). Dr Mutani noted that manually customising the surfaces to include the IOL into the treatment area and slightly increasing the femtosecond laser energy enabled easy cutting of the IOL.
	“This technique allows less traumatic removal of the implanted IOL,” he said.

As capsulotomy-fixated IOLs are now commercially available and showing benefit compared with capsule-fixated lenses, cataract surgeons may have a new reason to incorporate LCS into their practice.

“I think the development of capsulotomy-fixated IOLs will provide a strong argument for adopting the femtosecond laser because for the first time, the type of implant a patient receives will be determined by whether or not a surgeon has the laser for making the capsulotomy,” Dr Stevens said.

Reviewing his experience with the currently available capsulotomy-fixated Femtis IOL (Oculentis), Dr Stevens reported that it has demonstrated “exceptional” visual stability in a series of nine eyes he has followed since 2013.

“Capsulotomy fixation prevents tilt or lateral displacement of the lens. Therefore, it is an ideal platform for a toric IOL, but for all lenses, capsulotomy fixation makes biometry much more predictable and can lead to better outcomes,” Dr Stevens said.

Although other technologies are now available for automated capsulotomy creation, Dr Stevens said that the femtosecond laser has an advantage for delivering more accurate centration. Looking farther into the future, Dr Stevens said that lens technology offering predictable and stable centration opens the door to more sophisticated designs, such as lenses with more customised spherical aberration correction or that can accept an add-on lens.

“I believe patients would find it very appealing to be able to choose a lens that would give them the opportunity to take advantage of any upgrade that becomes available in the future,” Dr Stevens said.

DR FRANK GOES JR., MD
	e: frankjr@goes.be
	DR THOMAS LAUBE, MD
	e: thomas@drlaube.de
	Dr Laube receives speakers’ fees from Johnson & Johnson GmbH.
	DR JAVIER MENDICUTE, MD
	e: jmendicu@chdo.osakidetza.net
	Dr Mendicute is a consultant to and receives research grants and support from Alcon, Johnson & Johnson Vision, and Carl Zeiss Meditec, and he is a member of the speakers bureau for Alcon and Bausch + Lomb.
	DR BERNARDO MUTANI, MD
	e: bernardo.mutani@oculisticaclk.it
	PROF. DAVID O’BRART, MD
	e: davidobrart@aol.com
	Professor O’Brart has been a consultant to and received a non-commercial research grant from Alcon.
	DR JOSE LUIS RODRÃGUEZ-PRATS, MD
	e: jlrodriprats@gmail.com
	DR JULIAN STEVENS, MD
	e: jds@uk.com
	Drs Goes, Mutani, RodrÃ­guez-Prats and Stevens have no relevant financial interests to disclose. 
	The meeting of expert users was organised by targomed GmbH and supported by an educational grant from Johnson & Johnson Vision.

Insights on laser cataract surgery

	Take-home:  A prospective masked study enrolling eyes with low to moderate myopia with or without astigmatism found significantly better efficacy, safety, and predictability with wavefront-guided LASIK compared with small incision lenticule extraction (SMILE). 

Results of a prospective, masked study show significant differences favoring wavefront-guided (WFG) LASIK compared with small-incision lenticule extraction (SMILE) for the treatment of low to moderate myopia with or without astigmatism.

	The study, which was conducted by Dr Mounir A Khalifa and colleagues in Egypt, included 110 eyes with spherical equivalent (SE) up to -6 D who were followed for six months after their refractive procedure. All patients but one underwent bilateral surgery.

	WFG LASIK was performed in 51 eyes of 51 patients with the Star S4 IR excimer laser (Abbott) using a high-resolution wavefront aberrometer (iDesign system, Abbott), mechanical microkeratome (M2, Moria), 6.0 mm optical zone, and 8.0 mm treatment zone. Fifty-nine eyes of 59 patients underwent SMILE using the VisuMax femtosecond laser (Carl Zeiss Meditec) to create a 6.5 mm lenticule.

	Visual and refractive outcomes were good with both procedures. WFG LASIK, however, was associated with faster visual recovery compared with SMILE as well as significantly better efficacy, safety, predictability, and preservation of visual quality with less induction of higher-order aberrations (HOAs) and less contrast sensitivity loss.

	The recovery of UDVA in relation to preoperative CDVA (efficacy index with time) was slower in the SMILE group than in the WFG LASIK-treated eyes, and the difference between groups was more prominent in eyes with low myopia versus those with moderate myopia because of a virtually flat efficacy index curve in the WFG LASIK group (see Figure on Page 24).

	“Previously published studies comparing SMILE and LASIK primarily included eyes treated with conventional LASIK and found visual and refractive outcomes were similar for the two procedures whereas results for visual quality and aberrometry were more variable,” said Dr Khalifa, professor of ophthalmology, Tanta University, and chairman, Horus Vision Correction Center, Alexandria, Egypt.

	“SMILE offers some advantages compared with LASIK because there is no flap, and we found it to be an efficacious and safe procedure for correction of myopia with or without astigmatism,” he said.

	“However, WFG LASIK remains the state-of-the-art laser vision correction technique,” Dr Khalifa added. “It offers more predictable outcomes and better aberrometric control and delivers rapid visual recovery and better UCVA outcomes, which are important factors influencing overall satisfaction of refractive surgery patients.”

	Dr Khalifa performed all of the LASIK procedures at the Horus Vision Correction Center. The SMILE procedures were done by Dr Ahmed Ghoneim, professor of ophthalmology, Tanta University, Tanta, Egypt.

	
	The two refractive surgery groups were well-balanced with respect to mean age, sex, mean manifest spherical equivalent (MSE), and distribution of eyes with low (≤-3.0 D) and moderate (>-3.0 to -6.0 D) myopia.

	Preoperatively, mean UDVA was significantly better in the WFG LASIK group whereas the SMILE eyes had a significantly better mean CDVA.

	Based on data collected at the 6-month postoperative visit, mean UDVA and CDVA were significantly better in the WFG LASIK group compared with SMILE, and the proportion of eyes achieving logMAR UDVA 0.00 or better was also significantly greater in the WFG LASIK group compared with SMILE (90.2% versus 78.0%). The mean efficacy index was 1.12 for WFG LASIK and 0.92 for SMILE, and the difference was also statistically significant.

Corresponding with the functional differences, the refractive outcomes analyses showed significantly lower values for mean manifest cylinder and SE in eyes that had WFG LASIK compared with the SMILE group.

	In addition, there were statistically significant differences favoring WFG LASIK versus SMILE in analyses of the proportion of eyes with postoperative SE ±0.50 D of target (98.0% versus 81.5%) and residual cylinder ≤0.50 D (100% versus 84.7%).

	Vector analyses of astigmatic change also showed statistically significant differences favoring WFG LASIK for TIA, SIA, and DV.

	“Our finding that SMILE may undercorrect astigmatism up to 4.0 D is consistent with results reported by Zhang et al. showing better astigmatic outcomes after WFG LASIK compared with SMILE,” Dr Khalifa said.

	“The lack of iris registration and cyclorotation compensation when performing SMILE but not the potential off-axis application of the treatment may explain the better astigmatic correction achieved with WFG LASIK,” he added. “Treatment decentration with SMILE, however, may be the reason why induced more coma than WFG LASIK.”

	HOAs in both groups were measured with the same high-resolution aberrometer and analysed for changes from baseline since there were significant differences between groups preoperatively.

	Compared with WFG LASIK, SMILE induced a significantly higher level of total HOAs and primary coma.

	“The greater induction of primary coma after SMILE as well as an increase in ocular scattering after that procedure may explain our finding of greater loss of CDVA after SMILE compared with WFG LASIK,” Dr Khalifa said.

	Safety analyses showed WFG LASIK was associated with a significantly higher safety index compared with SMILE (1.20 vs 0.98) and no loss of CDVA. In the SMILE group, 6.8% of eyes had a one line or greater decrease from baseline CDVA.

	Measurements of contrast sensitivity at 6 months showed decreases from baseline after both refractive procedures, but the loss was significantly greater after SMILE compared with WFG LASIK at the spatial frequencies of 6, 12, and 18 cycles/degree.

	“Changes to reduce bridges and the size of the cavitation bubble created with the femtosecond laser, including increasing its frequency, shortening the focal length, reducing the pulse energy, and reducing spot distance, should significantly improve the predictability of SMILE,” Dr Khalifa added. “In addition, implementation of axial and torsional automatic registration should provide benefits for reducing coma induction and improving astigmatic correction.”

	Dr Khalifa received an unrestricted educational grant from AMO Germany GmbH. Dr Ghoneim has no relevant financial interest to report.

A prospective masked study enrolling eyes with low to moderate myopia with or without astigmatism found significantly better efficacy, safety, and predictability with wavefront-guided LASIK compared with small incision lenticule extraction (SMILE).

Exploring laser vision correction for myopia with/without astigmatism

Wavefront-guided photorefractive keratectomy (WFG PRK) performed using a proprietary high-definition aberrometer (iDesign, Abbott Medical Optics) and excimer laser system (VISX STAR S4 IR, Abbott Medical Optics) appears to be a safe and effective option for improving vision in eyes with keratoconus that achieve stability after corneal collagen crosslinking (CXL), according to the experience of Mohamed Shafik, MD, PhD.

	Results from analyses of data collected in a consecutive series of 34 eyes of 25 patients followed for up to 12 months post-WFG PRK were reported in a paper published online in 

 on May 17, 2016. The outcomes show statistically significant improvements in uncorrected and corrected distance visual acuity (UCDVA and CDVA) corresponding to statistically significant reductions in mean manifest sphere and cylinder. Statistically significant improvements were also achieved in some topographic corneal irregularity indices and in higher order aberrations (HOA), including total HOA, primary coma, and trefoil.

	No eyes lost CDVA or developed significant haze-the surgical protocol included mitomycin-C 0.02% applied to the ablated tissue for 20 seconds-and there was no evidence of keratoconus progression after WFG PRK.

	Dr Shafik noted that the high-definition aberrometer has made WFG PRK feasible in eyes with keratoconus because the device can capture an accurate wavefront in highly aberrated corneas and thereby allows a reliable ablation profile. And, he told 

that he considers the WGF ablation superior to a topography-guided approach for this indication. In addition, he believes that there is an advantage for performing surface ablation sequentially rather than simultaneously with CXL. Now, further studies are needed to validate the theories underlying these ideas, said Dr Shafik, Professor of Ophthalmology, University of Alexandria, and medical director, Horus Vision Center, Alexandria, Egypt.

	“Excimer laser surgery to correct the refractive error in eyes with keratoconus treated by CXL has been controversial because of concerns that it would further compromise biomechanical stability. However, surface ablation has less effect on corneal biomechanics than LASIK, and the eyes in my series have maintained good stability so far,” he stated.

Keratoconic eye experience with a long-arc intrastromal corneal ring

	“In addition, the functional and refractive outcomes achieved with WFG PRK in eyes with keratoconus stabilised by CXL compare favourably with those reported in the literature for topography-guided PRK performed in combination with CXL or as a second procedure. Nevertheless, longer follow-up in more eyes is needed to confirm the safety of WFG PRK after CXL and comparative studies are needed to evaluate outcomes using different ablation protocols.”

	All eyes in the consecutive series had grade I or II keratoconus (Amsler-Krumeich classification) and had undergone CXL at least 1 year earlier. In addition, they had to meet the following criteria: <0.5 D variation on subjective refraction at three consecutive monthly visits; <0.75 D increase in the cone apex keratometry in the previous 6 months; manifest spherical equivalent refraction ≤6 D; logMAR CDVA 0.5 or better; clear cornea within the pupillary area; and thinnest pachymetry ≥400 microns. Presence of dry eye syndrome or history of herpetic eye disease, autoimmune disease, or active anterior and posterior segment pathologies are considered contraindications to performing WFG PRK after CXL.

	Mean preoperative central corneal thickness (CCT) was close to 500 microns and minimum corneal thickness (MCT) was about 475 microns. The mean intended central ablation depth was 54.5 microns, the mean change in CCT was 53.7 microns, and the mean change in MCT was 53.7 microns. CCT remained stable during follow-up between 1 and 12 months.

	Dr Shafik observed that UDVA, CDVA, sphere, cylinder, and keratometry values (K1, K2, and Kmax) had already improved significantly by one month after the WFG PRK procedure and continued to improve as follow-up continued.

	At the last available visit, logMAR UDVA averaged 0.14 and was 0.3 or better (Snellen equivalent 20/40 or better) in 97% of eyes.

Why recalibration for EKR devices may be crucial

	“Prior to WFG PRK, only about 75% of eyes had distance BCVA of 20/40 or better. At one year, almost half of the eyes gained at least two lines in distance BCVA and mean logMAR BCVA was 0.05, Dr Shafik said.

	“The reduction in corneal irregularity and HOAs probably explains the improvement in BCVA.

	At 12 months, SE was ±0.50 D in almost two-thirds of eyes and ±1.00 D in more than three-fourths of the cohort. Whereas cylinder magnitude was ±0.50 D in only 11.8% of eyes prior to PRK, almost half of the eyes had <0.5 D of cylinder at 12 months after the procedure.

	Dr Shafik said he performed PRK after CXL rather than at the same session considering evidence suggesting ablation and refractive outcomes are less predictable in diseased corneas compared with healthy eyes.

	“The explanation may relate to the potential for tissue-related differences in laser ablation rates. In addition, manifest refraction measurements may be less accurate in eyes with keratoconus due to an interaction between second order and higher order aberrations, and compensatory epithelial remodeling after surface ablation in eyes with an irregular cornea may also play a role,” Dr Shafik said.

Keeler welcomes optometry students to Windsor headquarters

	“In order to maximise the accuracy of our surgical planning, we measure the refraction a minimum of three times and check for agreement in the values, and in general, the predictability of the refractive outcomes achieved in my series is among the best reported to date.”

	He listed several reasons why a WFG ablation profile provide is more optimal for correcting refractive error and improving visual quality in eyes with keratoconus compared with a topography-guided technique. First, the WFG ablation addresses the HOAs that underlie degradation of image quality in these complex corneas.

	“In other words, it offers a better cause and effect relationship than a topography-guided profile,” Dr Shafik said.

	In addition, the WFG procedure uses actual data from the central zone of the corneal that is mainly responsible for vision degradation in eyes with keratoconus.
	“Topographers do not read the central cornea and so the topography-guided central ablation profile is derived from an extrapolation of data. HOAs in the central cornea, primarily coma, are the main cause of vision degradation in eyes with keratoconus, and the high-definition aberrometer obtains exact measurements to calculate a proper and effective ablation profile,” he explained.

Tapping treatment paradigms for keratoconus

	As another advantage, the WFG procedure allows for precise placement of the laser spots because beam delivery is guided by iris registration that compensates for both cyclotorsion and pupil centroid shift due to supine position and different light conditions under the aberrometer and the laser.

	“Accuracy of the ablation is critical for addressing corneal surface regularity in eyes with keratoconus. Misplacement of spots that hit troughs rather than peaks in the surface can worsen irregularity. Only just recently have topography-guided procedures begun to adjust for cyclotorsion, and they still cannot compensate for pupil centroid shift,” Dr Shafik said.

	The planning software for the WFG procedure also uniquely allows the surgeon to adjust the sphere and cylinder to correct the refractive error and target emmetropia.

	“The topography-guided profile is more crude in this regard as it only targets corneal surface regularisation,” Dr Shafik said.

	Dr Shafik has no relevant financial interests to disclose.

Technique targets the main cause of vision degradation and a large clinical series finds positive results.

Author | Cheryl Guttman Krader, BS, Pharm

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