Photoinduced Change in Refractive Index of Functional Polymers for Ophthalmic Applications
A cataract is a clouding of the eye’s lens that affects vision, causing images to look blurred or fuzzy. It is the leading cause of blindness worldwide with an estimated 50 million people suffering from this illness. Although the exact causes of cataract formation are still a topic of intense resear...
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|Summary:||A cataract is a clouding of the eye’s lens that affects vision, causing images to look blurred or fuzzy. It is the leading cause of blindness worldwide with an estimated 50 million people suffering from this illness. Although the exact causes of cataract formation are still a topic of intense research, it is thought that most cataracts are related to aging and are usually caused by the denaturing of lens proteins, resulting in crystallization of the lens. The only way to treat cataract is to surgically remove the cloudy lens. The natural lens is then replaced with an artificial polymeric lens, a so-called intraocular lens (IOL). Cataract surgery is one of the safest, most effective and most common procedures and is performed tens of millions of times every year. However, there are some specific related postoperative problems. The aim of this work is to overcome one major drawback of IOLs. A typical postoperative complication in cataract surgery is that the refractive power of the implanted IOL is often not sufficient for optimal vision, requiring the patient to use prescription eye wear. This is mainly because the eye is a complex optical system and the biometric data required for the calculation of the IOL’s shape cannot be determined with sufficient precision before surgery. In particular, vision is strongly influenced by the radius of curvature of the cornea and the length of the eye ball. In addition, the exact location of the IOL in the capsular bag may change unpredictably during surgery or afterwards while the wound is healing, making the initial IOL design no longer optimal.Most patients treated with IOLs need prescription eye wear for optimal vision following cataract surgery or the IOL needs to be explanted and changed to a more suitable one in another surgery. This thesis develops a solution to this problem of poor imaging performance. The focal length of an IOL is tuned postoperatively in a non-invasive manner by changing the refractive index of the implanted lens through a photochemical process. Polymers, suitable for the fabrication of an IOL, were synthesized and characterized. These polymers have a specific photo-active linker group attached to the polymer backbone. Photo-induced cross-linking of these photo-active linker molecules leads to a decrease in the IOL’s refractive index. The maximum change in refractive index of the polymers synthesized here is more than 0.03, enabling a fine-tuning of more than 2.5 diopters in a standard IOL. With such postoperative treatment nearly all patients should not need viewing aids after cataract surgery. Compared with other approaches for tuning the refractive power of an IOL, the system presented here offers further advantages since the focal length change is induced with virtually no delay. This makes a direct analysis and control of the achieved visual acuity possible. Photo-controlled tuning may be performed more than once and even a change back towards the initial value is possible by using another irradiation wavelength.|