Vector analysis of astigmatism before and after excimer laser treatment

"Both the Allegretto IQ 400Hz (Wavelight; Erlangen, Germany) and the Schwind Amaris 750S (Schwind; Kleinostheim, Germany) result in excellent outcomes for myopic or mixed astigmatic patients in terms of mean J0, J45 and S2 vector values after LASIK surgery, with no significant differences between the two platforms or the two patient groups," Dr Alma Biščević (Svjetlost Klinika, Zagreb, Croatia) concluded from a study comparing outcomes that she and her colleagues conducted at the Svjetlost Eye Clinic.
Dr Biščević and her team performed LASIK on patients with myopic (N=245; Allegretto n=127, Amaris n=118) or mixed (N=228; Allegretto n=61, Amaris n=110) astigmatism. The team subjected the pre- and postoperative sphere [S], negative cylinder[C] and axis [ų] of subjective refractions to vector analysis by calculations of the standard J0, J45 and S2, and then compared the pre- and postoperative vectors using standard t test and linear regression.
The team found no significant difference between the outcomes of the two platforms, and no significant difference between the myopic and mixed astigmatic group for mean J0, J45 and S2 values before and after surgery.
Use of both the Allegretto and the Amaris resulted in significant (p "This highly significant fall in J0 and S2 vector values indicates that both the Allegretto and the Amaris produce excellent results in treating both myopic and mixed astigmatism," said Dr Biščević.

Does dry eye testing impact refractive surgery outcomes?

"There is no correlation between results of a preoperative Schirmer's test to diagnose dry eye and tear osmolarity results; 68% of eyes we tested that had normal osmolarity test results went on to have successful refractive surgery," reported Mr Richard Corkin (Wellington Eye Clinic, Dublin, Ireland) during this morning’s free paper session on 'New evaluation tools in refractive surgery'.
Mr Corkin and his team had conducted a consecutive case series of 112 eyes presenting for laser vision correction assessment, to determine if there is a difference in the incidence of this postoperative complication based on the type of preoperative test used to assess the presence of dry eye.
The standard diagnostic method used in the clinic is the Schirmer I tear test; all patients also underwent osmolarity testing with the TearLab Osmolarity System (TearLab Corporation; San Diego, California, USA), and evidence of superficial punctate keratopathy (SPK) was noted and graded.
"Patients were assessed at their 6-week postoperative visit for evidence of dry eye using SPK grading," said Mr Corkin.
The preoperative mean result for the Schirmer test was 11.9±9.7 mm, and mean preoperative osmolarity test was 305 mOsm/l (range: 275–335 mOsm/l). Preoperatively, 93% of eyes demonstrated no evidence of SPK; of the eyes demonstrating SPK, 24% were grade I and 2.7% were grade II. Overall, 57% of patients demonstrated no preoperative symptoms of dry eye.
At 6 weeks postoperatively, 60% of eyes showed no evidence of SPK, with 33.6% and 5.5% showing grade I and grade II SPK, respectively. In line with previously reported results, there was no correlation in the tested eyes between the preoperative Schirmer’s test and the osmolarity results.
"In patients with SPK at six weeks post-op, there was a slight trend of correlation between higher pre-op tear osmolarity and post-op SPK," noted Mr Corkin. Of the patients with normal osmolarity results who went on to have successful refractive surgery (68%), 77% had LASEK and 23% had LASIK.

White-to-white measurements

"White-to-white (WTW) corneal measurements using the Pentacam (Oculus; Wetzlar, Germany) for Scheimpflug-based topography can replace measurements with the Orbscan (Bausch + Lomb; Rochester, New York, USA) for Placido-based topography in the assessment of corneal diameter for planning the implantation of phakic IOLs," says Dr P. Baenninger (Lucerne Cantonal Hospital, Lucerne, Switzerland).
Dr Baenninger, who was presenting study results during the 'Imaging' free paper session this afternoon, and his team had compared the two techniques in 50 patients by having a single examiner take bilateral automated and manual WTW measurements with both the Orbscan and the Pentacam in a single session. The measurement values were limited to one decimal, and pair-wise comparisons were performed.
"Of each pair, the joint distribution was examined using Bland-Altman plots and differences in the mean variance were tested using Pitman’s test of difference in variance," added Dr Baenninger.
The mean values of Pentacam automated and manual measurements were 11.77 mm (range: 10.6–12.6 mm) and 11.74 mm (range: 10.4–12.5 mm) the mean values of Orbscan automated and manual measurements were 11.68 mm (range: 10.4–13.0 mm) and 11.66 mm (range: 10.4–12.5 mm).
“The mean differences (95% confidence interval [CI]) of Pentacam manual versus Pentacam automated, Orbscan manual and automated were -0.029 (-0.050 to -0.008); p=0.010, 0.084 (0.050–0.118); p=0.031, and 0.065 (0.029–0.101); p=0.821. Corresponding values of Pentacam automated versus Orbscan manual and automated were 0.113 (0.085–0.141); p=0.539 and 0.094 (0.062–0.126); p=0.155. The comparison between the manual versus automated values of Orbscan were -0.019 (CI -0.056 to 0.018); p=0.089,” said Dr Baenninger.
Although the automatically generated Pentacam values tended to be higher than the Orbscan values, these differences were clinically insignificant, and on average all parameters were highly concordant across the full range of WTW examined, indicating that the Pentacam can replace the Orbscan.

Visual outcomes excellent after minimally invasive technique

Small incision lenticule extraction (ReLEx Smile) using the 500 kHz VisuMax femtosecond laser (Carl Zeiss; Jena, Germany), a minimally invasive technique that offers patients the opportunity to undergo single-step refractive correction without having a flap cut and without the need for an excimer laser, offers excellent visual and refractive outcomes comparable to the highest standard of modern femtolasik techniques in the correction of myopia and myopic astigmatism, according to Dr Frank Goes (Goes OogCentrum en Bels Lasercentrum, Antwerp, Belgium), who was speaking during this evening’s ‘Refractive Femtosecond’ session.
Dr Goes reported how he used the Visumax Femtosecond in 74 eyes to create a small stromal lenticule, which was dissected using the spatula developed by Dr Ekktet Chansue (TRSC International LASIK Center; Bangkok, Thailand) and extracted with a 0.12 forceps through a 3.5 mm side-cut. After the procedure, the pocket was rinsed and the lenticule was inspected for possible defects, and patients were followed for a further 3 months, with Pentacam (Oculus; Wetzlar, Germany) topography performed at each visit.
Pre SR equiv was -5.06±1.79 D; pre SR sphere was -4.73±1.79 D and cylinder was -0.66±0.60 D. At 3 months, post SR equiv was -0.02±0.55 D; post SR sphere was 0.15±0.56 D and cylinder was -0.33±0.34 D (mean values). In terms of best-corrected visual acuity (BCVA), 9% gained more than one line and no patients lost more than one line; 95% had an uncorrected visual acuity (UCVA) of ≥0.8.
All treated patients had a refractive outcome within 1.0 D of target refraction, and 85% had a refractive outcome within 0.5 D of target.
"In this study, we had a retreatment rate of 0%. The visual and refractive outcomes are excellent, comparable to the highest standard of modern femtolasik techniques," reported Dr Goes. "The advantages of this technique over femtolasik include the lack of influence of room temperature, room humidity and air current; the treatment also takes place in a closed environment, which should further improve accuracy."