Andrzej Grzybowski - Current Concepts in Ophthalmology

The correction of refractive errorshyperopia, myopia, astigmatism, and presbyopiais of interest to eye practitioners worldwide. Functionally, good vision allows one to do his activities of daily life without assistance. Cosmesis and convenience, especially for people who live active lifestyles, require a decrease or elimination in dependency on spectacles and contact lenses. Refractive surgery aims to improve the refractive state of the eye caused by ammetropia whether due to the globes axial length or through a difference in the refractive power of the cornea and the lensor by pathologies such as keratoconus. Modern means for achieving this include topical medications, surgical remodeling of the cornea, intraocular lens implantation, and crystalline lens extraction and replacement with an intraocular implant.

Several classes of eyedrops that address presbyopia are being developed or are currently under clinical evaluation [].

Another set of eyedrops targets the crystalline lens to treat presbyopia. Pirenoxine eyedrops have been shown to suppress crystalline lens hardening in rats. The same effect was also reported in a small randomized controlled study on 18 Japanese males with early presbyopiano improvement was noted in patients with advanced presbyopia [].

Corneal inlays are implanted in the non-dominant eye, under a stromal flap or within a corneal pocket made by femtosecond laser [ enumerates the advantages and disadvantages of corneal inlay implantation for presbyopia treatment.

Table 1.1

Advantages and disadvantages of corneal inlays

Advantages	Disadvantages
Minimally invasive Reversible No need to remove corneal tissue Quick recovery Does not affect visual field testing Can be combined with other refractive procedures Enables normal visualization of central and peripheral fundus	Requires monovision Decreased distance visual acuity Decreased contrast sensitivity Perception of halos Corneal topography changes (long-term) Induces HOAs Corneal haze (with long-term implantation) Dependent on inlay centration Dry eye

Corneal reshaping inlays enhance near and intermediate vision through a multifocal effect, changing the shape of the anterior curvature of the cornea and making it hyper-prolate to increase power. Refractive inlays alter the refractive index with a bifocal optic. Small aperture inlays improve depth of focus [].

The Raindrop(ReVision Optics, Lake Forest, California, USA), is a reshaping inlay that is no longer commercially available. It changes the anterior corneal surface and creates a hyper-prolate region, resulting in a multifocal cornea []. It was associated with significant increases in total RMS, coma-like RMS and spherical-like RMS for a 4 mm pupil size. The Raindrop has been associated with monocular contrast sensitivity loss, but with no binocular loss. Common reasons for inlay explantation were vision dissatisfaction, inlay misalignment, decreased visual acuity, epithelial ingrowth, and recurrent central corneal haze.

The Flexivue Microlens(Presbia Cooperatief U.A., Amsterdam, Netherlands) is a transparent hydrophilic refractive inlay (Fig. ].

Fig. 1.1

Flexivue Microlens inlay

The Icolens(Neoptics AG, Huenenberg, Switzerland) is a refractive inlay made of a copolymer of hydroxyethyl methacrylate and methyl methacrylate [].