August 2013

 

NEWS & OPINION

 

2013 ASCRS•ASOA Symposium & Congress Best Papers of Session


   

Once again, the ASCRS•ASOA Symposium & Congress has provided tremendous scientific advancements to help ophthalmologists deliver state-of-the art care to patients. One of the great challenges of such a big meeting is filtering through all of the great material to find the highest of the high yield. During each paper session, the panelists awarded a Best Paper of Session. From these papers, a "best of the best" was chosen by the EyeWorld Editorial Board to provide concise summaries of some of the best papers. Dr. Reinstein used a mathematical model to help us understand the tensile strength of anterior lamellar stroma versus posterior stroma and the implications of different refractive procedures such as LASIK, PRK, and SMILE. Dr. Durrie showed results of a new ocular shield on improving vision after SBK and PRK. Dr. Gordon presented data on a novel subjective refraction device that uses a point spread function instead of Snellen letters to determine visual acuity.

John Berdahl, MD, Refractive Editorial Board member

Mathematical model to compare the relative tensile strength of the cornea after LASIK, PRK, and SMILE

Dan Z. Reinstein, MD, Timothy J. Archer, MA(Oxon)

Small incision lenticule extraction (SMILE) is a keyhole form of keratomileusis in which a femtosecond laser creates two interfaces that define a refractive lenticule of stromal tissue and therefore leaves anterior lamellae intact. As this is the strongest part of the stroma, it has biomechanical advantages over both PRK and LASIK. We derived a model to calculate the stromal tensile strength after PRK, LASIK and SMILE based on previously published data of depth-dependent stromal tensile strength. The model predicted that the postop tensile strength after SMILE was approximately 10% higher than PRK and 25% higher than LASIK. For example, the postoperative relative total tensile strength would be 60% for an ablation depth of 73 μm in LASIK (approximately 5.75 D), 132 μm in PRK (approximately 10.00 D), and 175 μm in SMILE (approximately 13.50 D), translating to a 7.75 D difference between LASIK and SMILE for a cornea of the same postoperative relative total tensile strength. This model demonstrates that SMILE does not follow the same criteria as LASIK for under the flap residual stromal bed thickness limits and hence can be expected to correct higher levels of myopia within the cornea than is currently possible with LASIK or PRK.

Quantifying and improving the speed of visual recovery in first 24 hours after keratorefractive laser surgery

Daniel S. Durrie, MD, Stephen Slade, MD, Jason P. Brinton, MD, Michele R. Avila, OD, Erin D. Stahl, MD, Theodore A. Pasquali, MD

This is a prospective multicenter study of 199 eyes from 103 myopic (+/ astigmatic) patients that compared the speed of visual recovery after ASA and SBK with and without a four-hour application of the NexisVision Ocular Shield (NexisVision, Menlo Park, Calif.). Long-term binocular UDVA was equivalent among the SBK groups. However, the shielded group attained a faster average monocular visual recovery with a UDVA of 20/25+2 immediately, compared to 20/40+1 in the non-shielded group. Both groups were 20/20 by four hours. Binocularly, vision was also improved in shielded eyes with 74% achieving 20/20 at 30 minutes compared to 23% of non-shielded eyes. With ASA, the difference was dramatic with 100% of shielded eyes achieving 20/40 or better at day one (64% saw 20/20) compared to 42% of non-shielded eyes. Subjectively, shielded patients had an overall greater comfort and a more rapid return to functional vision.

Use of point spread function in refractive exams

Alison Gordon, MD, Kris A. Morrill

The manual phoropter has been the standard tool employed for subjective vision assessments for 90 years now, with little evolutionary improvement. However, the use of this device can be time consuming and necessitates a long learning curve to use it effectively. In addition, the phoropter is limited to measurements in 0.25 D increments. A new system for subjective refraction that we have been using in our practice for about two years now utilizes point spread function (PSF) targets rather than Snellen letters to perform the refraction and assess visual acuity. We have found that the PSF Refractor (Vmax Vision, Maitland, Fla.), which measures in 0.05 D increments, provides us with a more accurate, more efficient means of performing this routine step of the patient exam.

In order to fully evaluate the difference between these two approaches, we performed a head-to-head comparison with 10 patients (20 eyes). Each patient underwent a subjective refraction with a manual phoropter and then the PSF Refractor. Of the 20 eyes tested, 19 were able to read an increased number of targets with the PSF Refractor compared to the standard letter targetsan average of 2.5 additional letters/ targets in the right eyes and 3.4 additional letters/targets for the left eyes. Further, nine out of 10 patients preferred the subjective refractive exam with the PSF Refractor compared to the manual phoropter, reporting that it was a faster test.

The concluding point is that this new tool for subjective refraction provides better or equal results in terms of accuracy and reliability in refractive end points. In addition, it is more time efficient for performing subjective refractions and patients prefer it.

2013 ASCRS 2013 ASCRS
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