# Biomaterials for Ophthalmic Applications
## 2 Biomaterials in Ophthalmology
### Inlays  
The history of ophthalmic inlays begins in the 1940s, when [PERSON] introduced the idea of correcting corneal refraction through an implant to increase cornea curvature [87]. [PERSON] proved that no existing material could be used due to their lack of biocompatibility (corneal inflammation, nutritional deprivation, lack of precision in refractive correction). The use of living corneal tissue did not prove to be a viable alternative due to difficult surgical procedures [87; 88].  
The discovery of hydrogels deepened the concept of the intracorneal inlay [9]. It was [PERSON], in the late 1960s, who first described the use of a hydrophilic hydrogel polymer to permit nutritional flow. Inlay migration, epithelial growth at the interface and crystal formation represent some of the most common complications. The shapes were limited by the materials and available equipment used to modify surfaces.  
Inlays continued to be improved with the emergence of new biocompatible materials and were more tolerated. Femtosecond lasers developed at the end of 1990s made obtaining  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Component** & **Main Function** & **References** \\ \hline Viscosity-improving agents (Carbomer 940, & \\ Carboxymethyl cellulose (CMC), Hyaluronic acid (HA), & Increase the time of permanence in the eye due to their \\ Hydroxypropylme-thycellulose (HPMC), & mucoadhesive properties & [81; 86] \\ polyvinylpyrrolidone (PVP)) & Maintaining normal cellular metabolism, even under \\ Osmoprotectors & extreme osmotic stress & [71; 79] \\ Trehalose & Bioprotection and osmoprotection & [71; 72; 77; 79] \\ Quercetin, epigallocatechin gallate, n-propyl gallate and & Protecting the corneal epithelium from & [75; 79] \\ gallic acid & oxidative damage & [75; 79] \\ Benzalkonium chloride (BAC), Sodium perborate, & Preservatives & [75; 79] \\ sodium chlorite, Polyquaternium-1 & & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Main components and functions of artificial tears.  
more accurate stromal pouches possible; therefore, a better centralization of the intracorneal inlay and a better estimation of the implementation depth were achieved [9].  
Presbyopia is a progressive decrease in the amplitude of accommodation, related with age, which is responsible for a reduction in near visual acuity. Presbyopia is a growing problem in view of an aging global population and increasingly, patients desire spectacle-free solutions to address this condition. This loss in accommodation amplitude is due to the aging of the zonula, capsule, lens and ciliary bodies. The lens becomes thicker and stiffer, the capsule increases in thickness and decreases in elasticity, and the zonula becomes more fragile and rigid; therefore, the ciliary body remains in a contracted position because of elasticity loss in the lens. Non-invasive methods to correct presbyopia include corrective lenses and contact lenses, however, these do not restore the accommodation process. Surgical methods can reduce visual acuity and quality of vision. Deploying inlays is technically easy and incurs less risk than an intraocular procedure [9].