Laser-intraocular lenses interaction: Aspects to consider for in situ vision correction

Abstract

Today, 60 years after the laser discovery, the long experience in refractive surgery, the evaluation of the accumulated clinical outcomes and the limitations of kerato-refractive surgery generated the demand to develop alternative methods for treating vision defects. In the frame of this new philosophy for vision correction, the use of polymeric intraocular lenses (IOLs) provides sufficient predictability and optical quality. The new Ophthalmology era takes their use one step further, through the IOLs' customization, aiming at the long desired personalized treatment. Inspired by the need to correct some post-operative complications in cataract surgery and IOLs implantation, the laser use is proposed, for in situ refractive modification of the implanted polymeric material, without any alteration in IOL's light transmittance behavior. In this work we present a brief literature overview of new perspectives in this field, enriched with some of our experimental studies. Through discussion of the laser-material interactions we intend to present the prospects, the limitations and the aspects that have to be considered in the route for in situ laser-based IOL-surgery and finally, vision correction. Lasers in ophthalmology and refractive surgery During the first laser era, both development and applications of laser radiation were impressive, particularly in life sciences (in all areas: diagnosis, treatment and biomedical research and technology). Just a couple of years after the construction of the first ruby laser by Maiman in 1960, lasers were immediately applied for retinal photocoagulation. Especially in ophthalmology, the laser-based refractive surgery transformed the myopia correction to one of the most effective and rapidly developing eye operations for the general population worldwide. The reader should bear in mind that from the very beginning of laser discovery, the application of laser radiation was easier in ophthalmic tissues, as the human eye is a biophysical optical apparatus which is by its natural assembly customized to accept, transmit and focus ultraviolet, visible and near-infrared (UV, VIS and NIR) photons, in the relevant ocular media, for clear vision. Therefore, the first lasers' biomedical applications were in ophthalmology's field, prior to any attempt of developing light guiding devices (e.g. fibers) to apply laser radiation in internal organs and tissues. A very brief and more or less descriptive review for the first 50 years of ophthalmic laser therapy was reported by Palanker et al. in 2011, as an introductive editorial in Archives of Ophthalmology Journal [1]. Certainly, the early development of laser technology has revolutionized the therapeutical interventions in ophthalmology, mainly in the treatment of the three major causes of blindness: diabetic retinopathy, glaucoma, and age-related macular degeneration. Categorically, for operation in retina the only non-contact, non-invasive interventional possibility has been the use of VIS or NIR laser light. Since the mid-1980s, the most popular application of lasers in ophthalmology, besides retina, has been corneal refractive surgery, a laser-based surgical method of permanent vision correction by changing eyes' refractive properties. Today, most refractive disorders are treated with laser ablation techniques in a procedure generally called "laser-based refractive surgery"; although currently, there is a major ongoing effort to refine it in order to correct other vision defects too. For instance, improvements in the development of biocompatible ocular implants used for cataract surgery (e.g. intraocular lenses-IOLs), have provided another option for patients with particular vision defects, besides conventional myopia. Nevertheless, various age-related eye disorders (e.g. cataract, glaucoma, presbyopia, dry-eye syndrome) can influence the possible options for laser-based or non-laser vision correction attempts. For comprehensiveness reasons, some basic notions of human vision are mentioned. The refractive apparatus of the human eye essentially consists of the cornea, the anterior chamber, the lens and the vitreous. These elements constitute two functional groups for sharp vision, the corneal system and the lens system. The refractive power of the former is approximately 40 to 50 diopters (D), while that of the latter is much lower, approximately 15 to 25 D; as measured at accommodative rest with the eyes focused on a distant point [2]. The most common refractive errors, e.g. errors in the ability to focus light by the eye, are: (a) Myopia, where the eyeball is too long, or the cornea is too steep. In this case, the distance between the cornea and the retina is too long. Hence, light rays from distant objects are focused in the vitreous inside of the eye rather than on the retina, making them look blurry. (b) Hyperopia, where the cornea's curve is too flat. This makes the cornea-retina distance too short. Light rays from close objects focus behind the retina, making them look blurry.