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A corneal refractive technique can combine monovision and extended depth of field to create a wide, seamless range of functional vision. This can provide independence from spectacles.
The treatment of presbyopia has historically relied on reading glasses or bifocal/varifocal lenses, which can be poorly tolerated, particularly by patients who do not routinely wear glasses.
Today, several surgical options offer patients the chance of having spectacle-free near vision without compromising on intermediate and distance vision. In patients who do not have cataract, one of the safest and most versatile options for achieving this is the use of presbyopia-correcting laser refractive surgery.1
Corneal refractive surgery or lens exchange?
Laser refractive surgery avoids the potential complications of refractive lens-exchange procedures, which include the loss of contrast sensitivity and stereopsis as well the risks of intraocular surgery.2 Corneal laser ablation is a less invasive procedure that enables a greater degree of customisation to accommodate the lifestyle needs of patients.
Additionally, some corneal-based procedures, such as corneal inlay surgery, have the advantage of being reversible.3
Corneal laser ablation retreatment allows for the management of refractive surprise and postoperative refractive changes, ultimately leading to improved patient satisfaction and visual outcomes.4 Recent advancements in presbyopia refractive laser surgery techniques have further improved outcomes. One of these techniques is Presbyond laser blended vision (LBV).
Presbyond LBV is a femtosecond-LASIK procedure for treating presbyopia, which involves modifying the corneal surface. The technique combines the principles of monovision and extended depth of field to create a blend zone that enables a smooth transition from distance to intermediate to near vision between the two eyes.
In our practice, we use the MEL 90 excimer laser (Zeiss) to achieve an aspheric laser ablation profile and the CRS-Master (Zeiss) to implement a micro-monovision (−1.50 D) protocol. The intended postoperative refraction is plano for the dominant eye and in the range of −1.00 to −1.50 D for the non-dominant eye.5
Also known as micro-monovision, the extended depth of focus technique is employed to correct the dominant eye for distance and intermediate vision while the non-dominant eye is corrected for intermediate and near vision: the blend zone is created by the brain mixing the images.
This is considered a cost-effective option for presbyopia management and has reduced postoperative consequences compared with traditional refractive lens-exchange procedures. Its high efficacy and safety in treating ametropia and presbyopia are established compared with its IOL counterparts.6
The advantages of an excimer laser are its speed and accuracy. A larger spot size leads to a shorter procedure duration, meaning that patients will not need to fixate for long. Ultimately, decreasing the duration of the procedure improves outcome predictability.
Furthermore, the larger spot size decreases the number of pulses required, which in turn reduces heat production.7 The device’s accuracy is achieved through its infrared eye tracker, which operates at 1050 Hz and tracks the pupil border and corneal limbus. This tracker can be offset manually to enable treatment to be centred on the coaxially sighted corneal light reflex as opposed to the entrance pupil centre.5
One of the major advantages of the MEL 90 excimer laser is its ‘flexiquence’ switch function to reduce ablation depth.8 The Triple-A ablation profile achieves this by integrating the original MEL 80 aberration smart ablation profile for low myopic corrections and the tissue-saving ablation profile for high myopic corrections into a single profile.
We recently published our findings on the use of this platform to treat phakic presbyopic patients using corneal refractive surgery. Our first study retrospectively compared clinical outcomes 12 months after LASIK for myopia performed using MEL 90 versus Schwind Amaris 750S excimer laser in 328 eyes of 328 participants. Excellent safety and comparable results were observed in terms of postoperative corrected and uncorrected distance visual acuity (CDVA and UDVA), residual refraction and efficacy with both lasers in a single surgeon setting.8
Our second study assessed functional outcomes and reading speed 6 months after Presbyond LBV on 60 hyperopic and myopic eyes (n=30) using the MEL 90. It was found that the procedure consistently yielded significant improvements in reading speed and everyday reading ability (both subjective and objective) compared with preoperative reading ability.
In comparison with previous reports of other refractive presbyopia-correcting procedures, this technique provides a wide range of functional vision without permanent changes to stereoacuity and contrast sensitivity. The binocular UDVA and CDVA achieved are shown in Figure 1.5
The procedure has improved results in relation to visual outcomes, stereopsis, contrast sensitivity, reading speed and dysphotopsias. In this study, defocus curve testing showed a functional vision of 0.2 log MAR (20/32) or better from +0.50 to −2.00 D of defocus, suggesting a theoretical depth of defocus of 2.50 D.
Furthermore, a functional level of stereoacuity was maintained postoperatively, with 93% of patients measuring at 200 arcsec or better and 68% of patients measuring at 100 arcsec or better. Contrast sensitivity was found to be unaffected 6 months after the procedure, and reading speed was significantly improved, at 164±18 wpm versus a preoperative speed of 150±7.3 wpm.
Regarding dysphotopsia, the 6-month review revealed that no patients complained of severe glare or halos; 6.6% of patients reported mild glare. The safety of the procedure is evident in CDVA outcomes: 92% of patients did not lose any lines in their CDVA, and no patients lost more than two lines.
Patient satisfaction for distance, near and intermediate visual tasks was 93.3%, 86.6% and 100%, respectively. Postoperative spectacle independence was also high with distance, near and intermediate prevalence being 93.3%, 86.7% and 100%, respectively. Quality of life was improved following the procedure as a result of patients achieving better or maintained reading abilities.
In summary, we find that Presbyond LBV offers non-cataract patients a safe and effective treatment option for presbyopia, providing the chance of spectacle independence while avoiding intraocular surgery. Our recent studies have shown that patients experience a high level of spectacle-free reading ability postoperatively, which results in improved reading speeds and high patient satisfaction.