Treatment of presbyopia has historically been limited to corrective lenses such as reading glasses, bifocals, multifocals, and contact lenses. Recent advancements in corrective eye surgery have expanded the number of available modalities for presbyopia correction. With more patients valuing freedom from spectacles and contact lenses, safe and effective surgical correction of presbyopia has become increasingly important.
Intraocular procedures for presbyopia correction include intraocular lens implantation with either a multifocal or accommodative lens. Extraocular procedures include corneal inlays and laser refractive surgery, which can be further subdivided into monovision LASIK, presbyLASIK, INTRACOR, and photorefractive keratectomy (PRK).
The most widely studied corneal inlay, the Kamra inlay, was approved by the FDA in April 2015. The Kamra corneal inlay improves near and intermediate vision by way of its small central aperture, placed in the area on or between the pupil center and the corneal vertex, thereby creating a “pinhole effect” and increasing depth-of-focus. The earliest prospective studies on emmetropic presbyopes found significant improvements in UNVA and UIVA after Kamra inlay implantation at one and two-year follow-up. UDVA remained unchanged throughout the two year follow up period. Kamra inlays have also been shown to be effective in improving functional abilities such as reading performance. Studies looking at long-term improvements in reading performance after Kamra inlay implantation found significant improvements in all reading parameters including: mean reading distance, mean reading acuity, mean reading speed, and smallest print size that could be read.
Kamra inlays have been shown to be a safe treatment option, with reports of only mild visual disturbances. Mean endothelial cell count, central corneal thickness, and contrast sensitivity remained relatively stable throughout a two-year follow up period. Of note, a few studies reported the development of corneal epithelial iron deposits in a half-moon shape along the margin of the inlay, with no demonstrable effect on visual acuity.
The Raindrop Near Vision inlay was approved by the FDA in June 2016 as a treatment for presbyopia following the results of a large prospective, multi-center FDA clinical trial that demonstrated long-term improvement in near vision with minimal adverse events. The Raindrop inlay differs from the Kamra inlay in that works by reshaping the surface of the cornea, creating an effect much like that of a multifocal lens. In a prospective clinical trial encompassing 373 emmetropic presbyopic eyes implanted with the Raindrop Near Vision inlay, mean binocular UDVA, UIVA and UNVA improved to 20/20 at one year following Raindrop inlay implantatiom.
The Raindrop inlay was thought to have a good safety profile with most studies reporting stable CDVA and CNVA with no eyes losing more than two lines of corrected vision at one year follow-up.  However, central corneal haze developed in 14% of subjects in the large, multicenter clinical trial and was found to be correlated to more superficial implantation of the inlay. A safety communication from the FDA issued in October 2018 recommended the Raindrop inlay stop being implanted after a post-approval study found 75% of patients experienced corneal haze.
Refractive corneal inlays
The refractive inlays act to change the central refractive index of the cornea, creating a multifocal effect. These include the Flexivue Micro-Lens, the Invue Lens, and the Icolens. The mechanism of action of this inlay lies in its multifocality, with light passing through the central zone of the inlay brought into focus on the retina during far vision, and light passing through the peripheral zone focused onto the retina during near vision.
While UNVA was found to improve significantly after refractive inlay implantation, two studies using the Icolens and Flexivue lense reported a small, but statistically significant decline in UDVA in the inlay eye. 
Laser Refractive Surgery
Monovision is a correction strategy that corrects one eye for near vision and the other eye for distance vision (usually the dominant eye). LASIK-induced monovision is overall very effective at bringing about good functional near and far vision. In a retrospective study of 82 myopic presbyopes who underwent monovision LASIK, 95% of patients improved to UNVA of J1 or better in the near eye and 100% of patients achieved UDVA of 20/25 or better in the distance eye. The induction of micro-monovision--essentially monovision with a lower degree of anisometropia--has been shown to be equally efficacious.
While highly efficacious, monovision LASIK involves inducing a degree of anisometropia. With higher degrees of anisometropia comes a loss of stereopsis and contrast sensitivity. A reduction in near and distance stereopsis has been reported in numerous studies on monovision LASIK. 
PresbyLASIK is a multifocal excimer laser approach, which aims to reshape the cornea for both near and far vision in each eye. PresbyLASIK creates an increased depth of field as a way to improve visual acuity for both near and distance. This can be achieved by creating a central hyperpositive area of the eye for near vision, leaving the peripheral cornea for distance vision. This is called central PresbyLASIK. Another approach is peripheral presbyLASIK which shapes the central cornea for distance vision and the peripheral cornea for near vision. Both ablation profiles have been demonstrated to significantly improve both distance and near vision in presbyopes. 
Both central and peripheral presbyLASIK have been reported to result in a significant decrease in contrast sensitivity at 3, 6, 12, and 18 cycles/degree.  A small number of patients undergoing peripheral presbyLASIK experienced visual night disturbances with 4.5% reporting glare and 14% reporting night halo. Similar rates of patient-reported visual disturbances are seen in central presbyLASIK. 
INTRACOR is a procedure that traditionally involves placement of 5 intrastromal rings in the center of the visual axis using a femtosecond laser, leading to central corneal steepening, and an increased depth of focus.   This procedure is designed primarily for presbyopes and hyperopic presbyopes but is not suitable in myopic presbyopes due to subsequent myopic shift. Multiple studies utilizing INTRACOR with placement of five intrastromal rings demonstrated a significant increase in binocular UNVA.  However, INTRACOR has not been shown to significantly improve mean UDVA, with UDVA remaining relatively stable at follow-up .
The primary advantage of INTRACOR lies in leaving Bowman’s layer and the epithelium intact, thus reducing risk of infection or intraocular complication. However, this procedure comes at a cost. Loss of CDVA is consistently seen across multiple studies, with patients losing 1-2 lines on average.    Another common complication of INTRACOR is the resultant myopic shift ranging from -0.3 to -0.5 D observed in multiple studies, making it unsuitable for myopes.  
Photorefractive keratectomy (PRK) like LASIK is a surgical procedure that uses an excimer laser to reshape the surface of the cornea. However, unlike LASIK, no flap is created. Rather, the central 8.5-9 mm of the corneal epithelium is removed. As a result, PRK comes with a unique set of advantages, including better wound healing and postoperative clarity, and the avoidance of flap-related complications. However, patients must wait for re-epithelialization to occur and there can be a significant amount of postoperative pain. Furthermore, other complications such as corneal haze, decreased efficacy in high myopes, reduced visual quality and regression can occur. Nevertheless, PRK maintains good outcomes, producing improved visual acuity for both near and far in presbyopic patients. 
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