Eyeworld

63 EW REFRACTIVE June 2017 Epi-on PiXL treatment of low-grade myopia; the treatment zone is 4 mm, and the total energy delivered 15J/cm 2 . Note the oxygen mask, which increases the oxygen level to above 90% to increase the treatment effect. Source: Anders Behndig, MD Department of Clinical Sciences/ Ophthalmology, Umea University Hospital, Sweden, who presented the study. "We achieved approxi- mately 1.25 D of myopic correction with this technique so far, 3 months after the treatment, with no signs of regression, meaning that the myopic correction may even increase some- what more over time." Dr. Behndig's investigation involved healthy volunteers over 18 years of age with a stable pre- scription for at least 2 years, who had mean low grade myopia with a spherical equivalent (SEQ) of –1.5 ± 0.5 D (range: –0.5 to –2.6 D). He and his team performed epi-on PiXL treatments in 39 eyes of 20 patients using topical anesthesia and isotonic riboflavin, which was applied every 90 seconds for a 10-minute dura- tion. The eyes were irradiated in the central 4 mm zone of the cornea using pulsed crosslinking (CXL) with 30 mW/ cm 2 for a mean 16.4 minutes at 15 J/cm 2 . The study incorporated two groups: The first group included 12 eyes of six patients that were treated under room air (20% O 2 ) conditions, and the second group included 27 eyes of 14 patients that underwent the same treatment under high oxygen (94.3 ± 1.3% O 2 ) conditions, using an oxygen mask. The primary outcome measure was logMAR un- corrected visual acuity (UCVA), mea- sured preoperatively and at 1 month and 3 months postoperatively. The preoperative mean UCVA was 0.6 logMAR in the room air group and 0.65 logMAR in the high oxygen group. Postoperative UCVA was significantly different between the two groups at the 1-month follow-up (P=.031) as well at the 3-month follow-up (P=.017), with the high oxygen group's UCVA under 0.1 logMAR and the room air group's UCVA at 0.4 logMAR, at 3 months. The mean preoperative SEQ was –1.25 D in the room air group and –1.6 D in the high oxygen group. In the room air group, a slight in- crease in SEQ was seen at 1 month of +0.33 ± 0.15 D, whereas a more pronounced effect was seen in the high oxygen group of +1.18 ± 0.48 D (P<.001). The preoperative Kmean was 43.0 D in the high oxygen group and 43.5 D in the room air group. The high oxygen group had a reduction in Kmean related to the reduction in the SEQ. At 1 month after surgery, the Kmean in the high oxygen group was under 42.5 D and almost 43.5 D in the room air group (P=.022). The endothelial cell count did not change significantly in either group, indicating that the method is safe for the endothelium. Dr. Behndig said although the methods implemented in determining the endothelial cell count could vary somewhat, there were no significant discrepancies in the outcomes. The cell count in room air eyes went from 2,750 cells/mm 2 preoperatively to just under 3,000 cells/mm 2 at 3 months. In high oxygen eyes, the cell count went from 3,000 cells/ mm 2 preoperatively to around 2,800 cells/mm 2 at 3 months. The results of color coded and gray scale back scatter maps showed a much more pronounced effect in the high oxygen patients at 1 month, with further improve- ment by 3 months after treatment. "The corrective effect is much less in room air patients, which corre- sponds to less corneal light back scatter," Dr. Behndig said. "As we go down in the corneal stroma from 0 µm to 425 µm, back scatter changes. Looking at this in more detail, we see a characteristic demarcation ring in the periphery of the treatment zone of the high oxygen eyes at around 3 months after treatment, indicating that the treatment had a superior effect compared to room air treatment." average (P=0.29). Looking at left and right eyes separately, the increase was statistically significant in left eyes (2.73 mm, P=0.014) but not in right eyes. Although one might have expected to see a larger effect from plugs, we also know that the sensi- tivity of Schirmer testing is relatively poor in normal eyes. There were small improvements in visual acuity. For example, at the 1-week mark, UCVA was 20/18 in the plug group versus 20/21 in the control group. Overall, punc- tal occlusion resulted in a small (less than one line) but statistically significant improvement in the right eyes (P<0.001), although the change in the left eyes was not statistically significant. There was no impact on BCVA. This was not unexpected; dry eye-related changes in vision during the early postoperative period do not generally depress Snellen acuity. Most impressive, however, is the noticeably better quality of vision that we see in the OSDI results. The OSDI questionnaire measures not just comfort but also quality of vision and the presence of visual fluctuations. At all postoperative time points, the mean change in OSDI resulted in a lower (better) OSDI score in the eyes with punctal occlusion, and a higher (worse) score in the eyes without plugs (Figure 1). The Extend absorbable plug increased the odds of improving the OSDI score after surgery by nearly six-fold (P<0.001). Ocular surface quality, which was graded 0 to 4 according to the severity of corneal staining, was minimal (0 or 1) in all eyes prior to surgery. After LASIK, staining was unchanged or improved in the majority of eyes in the punc- tal occlusion group. In the control group, about half the eyes had worse staining in the first month after surgery (Figure 2). Insertion of the Extend absorbable plug significantly influenced ocular surface quality (P=0.005), increasing the odds of im- proved corneal staining by approxi- mately three-fold. Tear film osmolarity was in the normal range before LASIK and re- mained so postop, although punctal occlusion at the time of surgery did reduce tear film osmolarity by 3.62 mOsmol/L (P=0.026). Punctal oc- clusion did not appear to have any effect on the presence of inflamma- tion, as measured by MMP-9. In conclusion, this small study demonstrates that punctal plugs can play a role in promoting ocular sur- face health in patients undergoing LASIK. The insertion of an absorb- able plug may be the perfect short- term solution to the short-term problem of post-LASIK dry eye. EW Editors' note: Dr. Donnenfeld has financial interests with Beaver-Visitec International. Contact information Donnenfeld: ericdonnenfeld@gmail.com continued on page 64 LASIK continued from page 61

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