Over the past 30 years, the landscape of corneal refractive surgery has undergone significant advances and changes. One unresolved issue that remains is the treatment of presbyopia.

Clinicians and researchers have explored various non-refractive options, including multifocal contact lenses, intraocular lenses, corneal inlays, and scleral implants. With the introduction of the femtosecond laser technology INTRACOR procedure, intrastromal vertical and concentric corneal cuts can be made.

These cuts change the biomechanical force of the cornea, leading to a change in curvature, and improve near visual acuity. As this procedure is a newer option for patients, comparison to gold standards is necessary. This study compared contrast sensitivity in patients using the INTRACOR and LASIK procedures.

A total of 48 eyes were included in the study. Eight hyperopic eyes were treated with INTRACOR. Inclusion criteria were presbyopia with a minimum near add of +4.00 at 40cm and less than 1D of hyperopia. Forty hyperopic and myopic eyes (20 patients) were treated with conventional LASIK.

In addition to traditional testing related to the procedure, contrast sensitivity (CS) was evaluated with the CSV-1000E Vector Vision with and without glare stimulus. CS was measured at four spatial frequencies (3, 6, 12 and 18cpd) before and after surgery.

Pre-surgery, both groups had similar CS at all frequencies except 18cpd. INTRACOR patients, who were significantly older, had higher CS than the LASIK patients (5.68 vs. 4.68). For INTRACOR, a comparison of pre and postoperative CS showed a drop under both glare and non-glare conditions, which was significant at 12 and 18cpd under glare and at 6 and 18cpd under non-glare.

For LASIK, the drop was significant at 6 and 12cpd SF under glare and at 12cpd under non-glare. When comparing the drop between the two procedures under the two conditions, a more severe drop was found at 3 and 6cpd SF under non-glare conditions.

While the corneal refractive procedures are aimed at correcting refractive error, clinicians must understand that vision is more than acuity. CS is one evaluation that is often overlooked but provides benefits to understanding visual function in various situations.

This study showed that the INTRACOR procedure was successful in assisting the patients at near, but the cost came in the form of decreased CS. While for some patients this trade-off would be acceptable, for others, the changes would be debilitating.

Proper education must be part of the procedural work up so that the patient understands the risk and rewards. Further attention to the impact of different corneal refractive procedures on various aspects of visual function should continue to be investigated.

Eksa L.C. Mai, Ie-Bin Lian, David C.K. Chang

International Journal of Ophthalmology 2016;9(12):1798-1801.