Advances in Therapeutic Contact Lenses for the Management of Different Ocular Conditions

Abstract

In the advent of an increasingly aging population and due to the popularity of electronic devices, ocular conditions have become more prevalent. In the world of medicine, accomplishing eye medication administration has always been a difficult task. Despite the fact that there are many commercial eye drops, most of them have important limitations, due to quick clearance mechanisms and ocular barrers. One solution with tremendous potential is the contact lens used as a medication delivery vehicle to bypass this constraint. Therapeutic contact lenses for ocular medication delivery have attracted a lot of attention because they have the potential to improve ocular bioavailability and patient compliance, both with minimal side effects. However, it is essential not to compromise essential features such as water content, optical transparency, and modulus to attain positive in vitro and in vivo outcomes with respect to a sustained drug delivery profile from impregnated contact lenses. Aside from difficulties like drug stability and burst release, the changing of lens physico-chemical features caused by therapeutic or non-therapeutic components can limit the commercialization potential of pharmaceutical-loaded lenses. Research has progressed towards bioinspired techniques and smart materials, to improve the efficacy of drug-eluting contact lenses. The bioinspired method uses polymeric materials, and a specialized molecule-recognition technique called molecular imprinting or a stimuli-responsive system to improve biocompatibility and support the drug delivery efficacy of drug-eluting contact lenses. This review encompasses strategies of material design, lens manufacturing and drug impregnation under the current auspices of ophthalmic therapies and projects an outlook onto future opportunities in the field of eye condition management by means of an active principle-eluting contact lens.

Keywords: bioavailability; composite; contact lens; drug delivery; gas-permeable; hydrogel.

Figure 1

(A) Schematic representation of different hydrogels, (a) traditional single polymer networks (b–d) double networks and (e,f) cross-linked double networks. This figure is from an open access journal under a CC-BY license source [28]. (B) pH-responsive polymer consisting of amino group (–NH₂) and loaded drug. In a basic pH environment, the amino groups are ionized and they keep the drug within the polymer network; for acidic pH, the amino groups were protonated (NH₃⁺) and electrostatic repulsion between the polymer and drug positive groups takes place, releasing the encapsulated drug. (C) pH-responsive polymer containing a carboxylic group (–COOH) loaded with drug. In the acidic pH environment, the acidic group is unionized and encapsulates the drug in the polymer matrix. For basic pH, the –COOH group ionizes, increases the electron charge density, and releases the incorporated drug. These figures have been taken from an open access journal under a CC-BY license source [29].

Figure 2

Evolution of contact lenses from the first introduction as scleral CLs made of glass to the introduction of customized silicone hydrogel contact lenses (SiHCLs). Reprinted with permission from Elsevier [43].

Figure 3

Stacked column representation of Google Patents indexed documents on the topic of CLs.

Figure 4

Schematic representation of keratoconus eye; current treatment approaches for keratoconus, i.e., rigid contact lens wear and cornea collagen photochemical cross-linking with riboflavin with UVA light.