**Abstract**

The focus of this chapter is to review the most recent advances in the diagnosis and treatment of contact-lens-related infectious keratitis, the most sight-threatening complication of contact lens wear. In the last decades, contact lenses technology has confronted several challenges, including the need for safer and more comfortable polymer materials. The development of high coefficient oxygen permeability (Dkt) and low-water content disposable contact lens translated into a significant improvement in ocular discomfort related to dry eye and allergic reactions, decreasing biofilm build-up on the external surface of the lens. Additionally, the emergence and boom-effect of corneal refractive surgery have also driven the development of better contact lens manufacturing. Despite these substantial technological advances, contact lens users continue to be at risk for developing corneal infections. We describe recent epidemiologic data, and advances in understanding the complex pathogenesis of the disease, including the clinical characteristics of the infectious process produced by bacteria, fungi, and protozoans. Finally, the recent development of diagnostic techniques and therapeutic regimens are discussed.

**Keywords:** contact lens, infectious keratitis, bacteria, fungi, *Acanthamoeba*

### **1. Introduction**

Contact lenses are a useful tool for correcting refractive errors; over 125 million people wear them worldwide [1]. The widespread use of contact lenses is associated with a variable range of complications up to 39–60.99% of contact lens wearers. Complications range from mild superficial punctate keratitis to vision-threatening conditions such as contact-lens-related infectious keratitis. Infectious keratitis is a potentially blinding condition, and it rarely occurs in healthy eyes; it comprises bacterial, fungal, and *Acanthamoeba* keratitis. Contact lens wear is, in fact, the predisposing factor in up to 50.3% for infectious keratitis [2–4]. Contact lens wear is the most critical risk factor for microbial keratitis in developed countries and the second one in developing countries after trauma [5–8]. Despite different contact lens materials and wearing modalities, infectious keratitis continues to be a sightthreatening condition in contact lens wearers, with a rate of visual loss of up to

28.6% [3, 9]. The annual incidence rate for contact lens-related microbial keratitis is 2/10 000 for rigid contact lens users, 2.2–4.1/10 000 for those who use daily-wear soft contact lens, 13.3–20.9/10 000 for extended wear soft contact lens users, and 52/10 000 for patients who wear therapeutic contact lenses [10].
