PRESBYOPIC LASIK

LASIK approaches that combine increased depth of field with micro-monovision are yielding some of the best results yet for laser correction of presbyopia. However, the approximately 1.5 D add effect achieved with presbyLASIK is not enough for most older patients, presenters told the 2013 American Society of Cataract and Refractive Surgery (ASCRS) symposium.

“The procedure is time limited. Presbyopia increases with age as well as with changes in the crystalline lens,” said W Bruce Jackson MD, FRCSC, University of Ottawa, Ontario, Canada.

Improvements in near vision with presbyLASIK also come at the expense of some loss of distance vision, and some patients have trouble adjusting, Dr Jackson added. Outcomes are generally less predictable than with standard LASIK, resulting in retreatment rates ranging up to 30 per cent. Ocular surface instability is another factor that affects patients' vision and satisfaction, and must be well controlled for best results, Dr Jackson said.

Monovision, with the ideal correction of plano in the dominant eye and about -1.5 D in the non-dominant eye, remains the most common laser presbyopia treatment. It is also the only currently approved option in North America.

Patient satisfaction with monovision in published studies ranges from 72 per cent to 96 per cent, with two per cent to seven per cent wanting reversals, Dr Jackson said. Enhancement rates run about 20 per cent, with retreatment of the distance vision eye more common. Drawbacks include a slight decrease in binocular distance visual acuity, reduced contrast sensitivity and problems with stereopsis.

Contact lens trials are not always a good predictor of monovision success, Dr Jackson said. Patient selection is critical and expectations must be reasonable as glasses are often required for distance or near vision.

Several manufacturers, including VISX/ AMO, Schwind and Technolas PerfectVision, offer presbyLASIK ablation profiles with a near vision zone in the corneal centre, Dr Jackson said. In a company-sponsored trial he conducted with the VISX/AMO S4 using a bilateral wavefront-guided hyperprolate central 3.0mm near ablation profile, 100 per cent of 66 patients achieved 20/25 distance and J3 or better near at 12 months, with 88 per cent at 20/25 and J1 or better.

Mesopic contrast sensitivity declined slightly from pre-op values, but remained well within normal range. Sixty per cent lost no distance Snellen lines, 28 per cent lost one line and 10 per cent lost two lines, while 1.7 per cent gained one line. Distance vision improved between six months and 12 months after surgery, with improved control of tear film mostly responsible, he reported.

Spectacle free              

“We met our target of 20/25 and J3 in all eyes at one year. However, only one-third were spectacle free, with the others using glasses at some time during the day or week,” Dr Jackson said.

Overall, published studies show about 85 per cent of patient treated with central near presbyLASIK performed with VISX, Schwind and Technolas systems achieved 20/25 to 20/30 and J3, with three to 10 per cent losing two lines corrected distance vision from pre-op refractions of -7.0 to +3.5 D, Dr Jackson said.

However, outcomes with the same equipment and parameters are variable depending on patient selection and technique, he noted. Generally, though, hyperopes were more satisfied and myopes more spectacle dependent with the central near add approach.

VISX, Technolas, Nidek and Wavelight all offer peripheral, or paracentral, near add profiles, which induce negative spherical aberration about 2.5mm from the corneal vertex, increasing depth of field. Studies show about 80 per cent achieved 20/25 to 20/30 and J3 from -8.25 to +4.0. Myopes were more satisfied than hyperopes with the peripheral add approach. Enhancements range from 2-30 per cent. However, peripheral add performance is highly pupil dependent, said Sri Ganesh MD, Bangalore, India. “Miotic near performance is degraded and when the pupil dilates, distance vision is compromised.”

Dual construction  

By contrast, central add performance is enhanced by pupil constriction. Peripheral add also requires more neuroadaptation and distance vision recovery takes longer, he added. Treatment times are also longer with more tissue removed.

Laser blended vision, pioneered by Dan Reinstein MD with the Carl Zeiss Meditec MEL 80 excimer laser, uses non- linear aspheric ablation profiles to increase depth of field in both eyes, combined with monovision. The dominant eye target depth of field is plano to -0.75 D and the non- dominant nominally -1.5 D with a field depth from -0.75 to -2.25. The overlap in field depths is intended to promote stereopsis and improve distance, intermediate and near vision with low corrections.

In a test of a similar approach with a Nidek system, 60 eyes of myopes underwent optimised prolate ablation for presbyopia, with a spherical aberration target of -0.3 microns in both eyes and the non-dominant eye targeted at -0.75 D, Dr Jackson said. Seventy-six per cent achieved 20/25 and J2 uncorrected. “The new generation of bi-aspheric centre near ablation profile combined with micro- monovision shows promising results. Laser blended vision with enhanced depth of field in both eyes may be a good option,” Dr Ganesh said.