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One-year Results of Photorefractive Keratectomy
With and Without Surface Smoothing Using the
Technolas 217C Laser
Sebastiano Serrao, MD, PhD; Marco Lombardo, MD ABSTRACT
PURPOSE: To assess the efficacy, predictability,
Several factors can affect smoothness of the stability, and safety of a smoothing technique in
patients with myopia immediately after photore-
laser beam diameter1, laser beam homogeneity, the fractive keratectomy (PRK) using a scanning-spot
excimer laser.
ejected molecular ablative debris deposited back METHODS: Using the Technolas 217C excimer
onto the corneal surface, and the thermal compo- laser, PRK was performed on 100 eyes of
nent of the ablation process. Most refractive surgery 54 patients. Ablation zone diameter was 6.0 mm and
techniques are associated with irregularities on the transition zone diameter was 9.0 mm. The eyes
corneal surface which, in turn, may cause an were randomized into two groups: in 50 eyes PRK
alone was performed and in the other 50 eyes, a
increase in the number high order aberrations and smoothing technique was performed after the ini-
reduced visual acuity in certain light conditions.
tial ablation. Preoperative mean spherical equiva-
The reduction in the regularity of the first corneal lent refraction was -4.98 ± 1.71 D in the PRK only
surface after the photoablation phase of photore- group (range -2.25 to -8.60 D) and -4.82 ± 1.61 D in
fractive keratectomy (PRK) can lead to three unde- the smoothing group (range -2.00 to -8.00 D). Follow-
up was 12 months for all patients.
sirable phenomena: a decrease in corneal trans- RESULTS: At 1 year after surgery, mean manifest
parency2, regression of refractive outcome3, and a spherical equivalent refraction was -0.61 ± 0.50 D
(range -2.25 to +0.62 D) in the PRK only group and
The irregularity of the ablated surface is the in the smoothing group, +0.02 ± 0.32 D (range -0.75
“primum movens” for delayed wound healing and to +0.75 D). Postoperative regularity topographic
indices were lower in the smoothing group than in
abnormal epithelial and stromal remodeling.
the PRK group (P<.001).
Abnormalities include stromal thickening and CONCLUSIONS: Smoothing after PRK for cor-
epithelial hyperplasia or distortion of the existing rection of myopia up to -6.50 D increased surface
regularity, as expressed by lower topography sur-
In our opinion, none of the laser systems devel- face regularity indices, and reduced the incidence
and severity of postoperative haze. We observed
oped to date produce a sufficiently smooth stromal higher predictability throughout follow-up in the
surface. This, in addition to patient eye and head smoothing group, which may be addressed by a
movements during laser refractive surgery, result in nomogram adjustment in the PRK only group.
erroneous targeting of the surgical beam and hence [J Refract Surg 2004;20:444-449]
a sub-optimal correction.8 Efforts by laser manufac-turers to produce more sophisticated eye trackingdevices9 and to improve the quality of the emittedlaser light have not yet produced an optimal out-come.
From the Catholic University of Rome, Department of Ophthalmology, Rome, Italy (Serrao, Lombardo) and the University of Padua, Department Carones demonstrated that even when the most of Ophthalmology, Padua, Italy (Serrao). effective eye tracking system was employed, The authors have no financial interest in the materials described Maloney's topographic regularity index (BFTI) did Correspondence: Sebastiano Serrao MD, PhD, Via Orazio 31, 00193 not significantly differ from that achieved when Rome, Italy. Tel: 39.380.333.11.00; Fax: 39.380.333.11.00; E-mail: other devices were used. The eye tracker device is advantageous, especially in uncooperative patients Received: December 5, 2002Accepted: March 30, 2004 Journal of Refractive Surgery Volume 20 September/October 2004
PRK With and Without Smoothing Using the Technolas 217C Laser/Serrao and Lombardo
Many authors have evaluated the physical char- corneal surgery.12 In this study, we compare the acteristics of various types of excimer lasers. Huang refractive data and corneal regularity indices of eyes and Arif simulated corneal ablations using different treated using the same excimer laser system beam diameters and beam profiles similar to those (Technolas 217C), with PRK alone and PRK with currently used in commercial excimer laser sys- tems.1 Their aim was to study the efficacy of thescanning laser in correcting high order aberrations.
PATIENTS AND METHODS
They concluded that beam sizes р1 mm should besufficient for elimination of most high order optical Patients
Fifty-four patients (35 women and 19 men) Other authors have compared the operative out- between 22 and 50 years of age (mean 33.8±6.21 yr) come with a broad beam laser to that observed with were recruited for a total of 100 treated eyes.
scanning spot and scanning slit lasers. They con- Patients were randomly enrolled from the excimer cluded that the corneal surface was smoothest fol- laser surgery waiting list of the Department of lowing scanning spot laser surgery.10 At present, it Ophthalmology of the Catholic University of Rome.
is widely held that a smooth postoperative ablation Inclusion criteria were the absence of ocular surface is mandatory if refractive surgery is to be pathology, no previous ocular surgery, refractive considered maximally effective. Benefits of a regu- astigmatism less than 1.50 diopters (D), and at least lar corneal surface include faster re-epithelializa- 1 year of refractive stability. Patients wearing con- tion, less haze and regression, and improved visual tact lenses were asked to discontinue use for at least performance. As suggested by Vinciguerra and col- 4 weeks prior to preoperative evaluation. Informed leagues, the smoothing technique is an effective pro- consent was obtained from all patients.
cedure for achievement of a smoother ablated stro- Preoperative evaluation included the determina- tion of manifest and cycloplegic refraction, uncor- In spite of the fact that the results following PRK rected visual acuity (UCVA) both for reading and performed using the Technolas 217C are satisfacto- distance, best spectacle-corrected visual acuity ry, all users must include some hypercorrection in (BSCVA), and autorefraction (Nidek AR-600, Tokyo, the treatment planning (about 5% to 10% of the Japan). Slit-lamp microscopy, tonometry, and fun- spectacle correction). This is done to avoid the over- dus examination were also performed. Corneal correction consequent to regression of refractive out- thickness was measured using a contact ultrasound come that occurs in the months following surgery.
pachymeter (Optikon 2000, Rome, Italy) and corneal We believe that this regression is due to the irregu- topography was performed with the Keratron Scout larity of the ablated corneal surface. We present (Optikon). Emmetropia was the refractive goal in all results obtained when a smoothing technique was performed after refractive treatment (PRK) using a We randomized the eyes into two groups using a statistical package (Matlab, software version 6.5).
The smoothing technique was used to obtain a In one group (26 patients; 16 women and 10 men, smooth ablation surface, thus eliminating gross and mean age 34.7 ± 4.97 yr; 50 eyes) PRK only was per- small irregularities and flattening the borders of the formed, whereas in the second group (28 patients; ablation edges. This technique is similar to pho- 19 women and 9 men, mean age 31.7 ± 7.45 yr; totherapeutic keratectomy (PTK), which is useful 50 eyes), smoothing was performed immediately for treatment of corneal diseases such as Reis- Bückler's dystrophy or band-like keratopathy, and Mean preoperative refraction (mean cycloplegic in order to achieve corneal smoothness after ptery- spherical equivalent refraction ± standard devia- tion) was -4.98 ± 1.71 D in the PRK only group Other studies2,3 have demonstrated that smooth- (mean cylinder -0.58 ± 0.41 D) and -4.82 ± 1.61 D in ing after PRK using a scanning slit laser, such as the smoothing group (mean cylinder -0.55 ± 0.53 D). the the Nidek EC-5000, facilitates a better optical Statistical comparison of preoperative data in surface, better visual results, and less haze and both groups revealed no significant differences regression. Alió and colleagues demonstrated that (Fischer test, P>.05). Statistically significant differ- the Technolas 217C laser used in PTK mode with a ences between means of the two study groups were masking fluid was useful for treating irregular determined by the Student's paired t-test. P-values corneal astigmatism caused by previous refractive less than .05 were considered significant. Journal of Refractive Surgery Volume 20 September/October 2004
PRK With and Without Smoothing Using the Technolas 217C Laser/Serrao and Lombardo
Mean Cycloplegic Spherical Equivalent Refraction (D) Before and After PRK, With and
Without Smoothing, in 100 Eyes of 54 Patients (Number of Eyes Examined)
Refractive Range (D)
Preoperative
Postoperative
PRK with smoothing
-1.75 to -3.00
PRK only
-1.75 to -3.00
Surgical Technique
until complete re-epithelialization of the cornea, Surgery was performed by one surgeon (SS) sodium diclofenac 0.1% preservative-free eyedrops under topical anesthesia achieved using oxybupro- three times daily for 3 days, topical fluorometholone caine hydrochloride eye drops. The corneal epitheli- 0.1% twice daily for 1 month after complete re- um was removed using the Amoils brush. Laser epithelialization, and sodium hyaluronate 0.18% ablation was performed using the Bausch & Lomb hypotonic solution preservative-free eyedrops five Technolas 217C Planoscan excimer laser (Bausch & times daily for 6 months after surgery. A bandage Lomb Chiron Technolas, Dornach, Germany; wave- contact lens was applied until the third postopera- length 193 nm). Ablation zone diameter was 6.0 mm and transition zone diameter was 9.0 mm.
Twelve-month follow-up included evaluation of This laser is also equipped with an active eye track- corneal haze, UCVA and BSCVA, refraction, corneal er device and utilizes a 2-mm flying-spot laser topography, evaluation of high order aberrations beam. The fluence at the corneal plane was from the first corneal surface, pachymetry, and 120 mJ/cm², the ablation rate was 0.25 µm per pulse, and the repetition rate (frequency) was 50 Hz.
No nomogram adjustment was used in this study.
Final smoothing was performed with the same At 1-year follow-up, mean cycloplegic spherical laser in PTK mode. The maximum diameter of the equivalent refraction in the PRK only group was ablation zone was 9.00 mm. A viscous solution of -0.61 ± 0.50 D; in the smoothing group it was +0.02 0.25% sodium hyaluronate was used for masking ± 0.32 D (Table). Differences in spherical equivalent the cornea. The fluence, ablation rate, and frequen- refractive error observed in the two groups at cy in the PTK mode were the same as in PRK mode.
1 month (P<.05), 3 months (P<.05), 6 months Before the procedure, we re-targeted the ablation (P<.05), and 1 year (P<.05) following surgery were area at the center of the pupil and fixed it with the The scattergram of the attempted versus the We standardized the smoothing procedure using achieved correction for both groups is shown the Technolas 217C laser. Ablation depth was set at in Figure 1. Twenty-six eyes (52%) had a manifest 10 µm (divided into four intervals for a total of spherical equivalent refraction within ±0.50 D of 428 spots) and a spatula was used to spread the emmetropia in the PRK only group, whereas this masking fluid on the corneal surface.
result was achieved in 46 eyes (92%) in the smooth- The viscous masking solution formed a stable and ing group; 41 eyes (81%) were within ±1.00 D in the uniform coating on the surface of the eye. In partic- PRK only group and 50 eyes (100%) were within ular, it filled the depressed areas on the cornea and ±1.00 D in the smoothing group. Figure 2 shows efficaciously masked the tissue to be protected mean spherical equivalent refraction during follow- Postoperatively, patients were prescribed micro- Preoperative refractive astigmatism ranged from nomicin preservative-free eyedrops six times daily 0 to -1.50 D in both groups, with a mean of -0.58 ± Journal of Refractive Surgery Volume 20 September/October 2004
PRK With and Without Smoothing Using the Technolas 217C Laser/Serrao and Lombardo
Figure 2. Mean (SD) change in cycloplegic refraction during follow-
Figure 1. Scattergram at 1 year after PRK shows slight overcorrec-
up in the two study groups. There was a slight hyperopic shift in the tion of the refractive target in the PRK only group (50 eyes) and the smoothing group during the early postoperative period. A regression high predictability of the refractive results in the PRK with smooth- of the refractive effect occurred in the PRK only group between the ing group (50 eyes). The P-value was calculated using Student's 1st and 3rd postoperative months. P-value was statistically signifi- cant (P<.05) at each follow-up examination.
Figure 3. At the end of follow-up, an increase in the postoperative
Figure 4. At 1 year after PRK with and without smoothing, the ablat-
topographic irregularity index (BFTI) was observed in the PRK only ed first corneal surface showed a mean increase of the 3rd to 6th group. The regression observed in this group may be explained by high order optical aberrations. The smoothing technique performed the more marked irregularity of the ablated corneal surface. The at the end of the PRK procedure reduced postoperative stromal irregularities, facilitating a more even surface with respect to PRKonly. The mean induced high order optical aberrations in the PRKwith smoothing group was less marked (P<.05).
0.41 D in the PRK only group and -0.55 ± 0.53 D in with an efficacy index of 1.03 versus 0.97 in the PRK the smoothing group. At 1 year, refractive astigma- only group, where only two eyes (4%) gained 2 or tism was reduced to a mean -0.37 ± 0.40 D in the PRK only group and +0.05 ± 0.51 D in the smooth- Two eyes (4%) in the smoothing group and six ing group, with no surgically-induced astigmatism.
eyes (12%) in the PRK only group had haze greater No eye lost any Snellen lines of spectacle-correct- ed visual acuity during follow-up. The safety index The regularity of the first corneal surface was was 1.02 in the PRK only group and 1.06 in the determined using two topographic indices: Best Fit smoothing group. In the smoothing group, 10 eyes Topographic Irregularity (BFTI)14 and the high (20%) gained 2 or more lines of Snellen visual acuity order root-mean-square wavefront error (RMS).
Journal of Refractive Surgery Volume 20 September/October 2004
PRK With and Without Smoothing Using the Technolas 217C Laser/Serrao and Lombardo
The BFTI is measured in diopters and is fit to the ularities induce a more pronounced healing central 4-mm-diameter circle at the center of the response when compared to a smoother ablation videokeratograph to approximate the size and loca- surface.21 Altered wound healing is the first step tion of the entrance of the pupil; it is defined as the toward the onset of haze and a less than desirable root-mean-square sum of the differences between the measured cornea and the best-fit spherocylinder In our PRK study, we used a 2-mm beam spot size that minimizes the distance between the two sur- device. In one group, smoothing was performed immediately after PRK. Results confirm that the High order RMS is measured in microns and rep- smoothing technique improved the quality of the resents the difference between the measured ablated corneal surface and visual outcome, espe- corneal wavefront and an aberration-free wave- cially in eyes with a spherical equivalent refraction front. We calculated RMS over a 4-mm-diameter up to -6.50 D. The observed hyperopic shift was due pupil and for 3rd to 6th Zernike orders.
to the diameter of the optical zone of the Technolas Figures 3 and 4 show preoperative and 1-year 217C laser. This instrument allows for a maximum postoperative values for BFTI and RMS in the two PTK zone of 6 mm with a 3-mm transition zone.
study groups. Postoperative values were greater When this smoothing technique is performed using than preoperative values, showing that ablation a Nidek EC-5000 laser with a 9-mm PTK zone with- caused an increase in irregularity; the increase was out transition, it did not induce a consistent hyper- less consistent in the smoothing group and the dif- opic shift for such a limited tissue ablation (up to ference was statistically significant (P<.05). A post- operative reduction in RMS was observed in nine Many authors report induction of a hyperopic eyes (18%) in the smoothing group, but in only two shift for attempted correction as the major compli- cation of PTK.23 Various techniques have been pro-posed to minimize the refractive shift: use of a DISCUSSION
masking agent to reduce the real depth of tissue In accordance with other reports3, we observed ablation, use of a large ablation zone with a transi- that the outcome of refractive surgery was influ- tion zone, and setting a low ablation depth.24-27 enced primarily by final optical quality of the ablat- Corneal topography analysis can identify whether ed corneal surface. In experimental settings, a PTK- or not the better result was due only to the hyper- type treatment at the end of PRK allows for a opic shift. For this reason, we analyzed the topo- smoother ablation.10,15,16 Smoothing of the corneal graphic indices and the topographic wavefront. The surface involves the use of a fluid that, when applied BFTi and the RMS over a 4-mm-diameter pupil and to the cornea, masks deeper tissues while at the for 3rd to 6th Zernike orders demonstrated a differ- same time leaves protruding irregularities ence between the two groups: the smoothing group exposed17; subsequent ablation of the irregular had a result closer to emmetropia but it was also anterior stromal surface should therefore focally associated with better topographic indices.
excise elevated corneal tissue, thereby reducing sur- In our clinical study, the eyes in which smoothing was performed postoperatively had higher pre- The ideal fluid to be used in this technique has dictability for the refractive target; this may be not yet been established. The 0.25% sodium explained by the hyperopic shift induced by PTK, hyaluronate masking fluid that we used is a moder- and might also be achieved in the PRK only group ately viscous solution with an ablation rate similar by a nomogram adjustment. In the smoothing to that of corneal tissue. Thanks to these properties, group, we found a more regular first corneal surface it can cover the irregular surface uniformly and not as expressed by topography indices and better visu- run off too quickly, hence, only stromal peaks are al acuity, compared to the PRK only group.
This smoothing procedure, which facilitated a A smoother surface allows for better epithelial smoother anterior stromal surface compared to PRK adhesion and migration. Experimental studies have alone, permitted faster re-epithelialization7,28,29 shown that epithelial migration can be inhibited by with less haze and better visual outcome.
irregularities in the surface of the substratum.18,19 Performing smoothing at the end of PRK was an Correct and rapid re-epithelialization is the prin- effective means to improve corneal regularity after cipal process that regulates epithelial and stromal PRK with a scanning laser system, with a beam size remodeling after PRK. Postoperative ablation irreg- Journal of Refractive Surgery Volume 20 September/October 2004
PRK With and Without Smoothing Using the Technolas 217C Laser/Serrao and Lombardo
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Journal of Refractive Surgery Volume 20 September/October 2004

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