Preface

Due to its evolving nature, infectious eye disease is one of the most severe sight-threatening conditions, representing a diagnostic and therapeutic challenge to ophthalmologists for centuries. Pathogens have evolved over time, producing more complex infections. Microbes such as *Treponema pallidum*, Mycobacterium *tuberculosis*, and *Toxoplasma gondii* producing syphilis, tuberculosis, and toxoplasmosis persist as important ocular pathogens. Also, the herpes viruses, the most ancestral with significant eye pathogenicity, have evolved from simple epithelial keratitis infections to devastating forms of necrotizing retinitis. During the AIDS era, characterized by a significant virally induced immune suppression, many rare opportunistic pathogens to the eye, like cytomegalovirus, atypical mycobacteria, *Coccidioides immitis*, and *Pneumocystis carinii*, among others, produced devastating infectious retinitis and panuveitis. When highly active antiretroviral therapy (HAART) was established for HIV infection, patient immune recovery drastically reduced most of these opportunistic pathogens to the eye. At present, the COVID-19 pandemic has become a new challenge for ophthalmologists, and SARS-Cov-2-related conjunctivitis has emerged.

Many pathogen microorganisms can access the eye through different routes, including invasion of the intact or damaged ocular surface, direct intraocular inoculation during surgery, penetrating trauma, or via hematogenous spread. The broad clinical spectrum produced by the different infective capabilities and tissue damage of extended genera of pathogen agents, including bacteria, fungi, viruses, and parasites, makes diagnosis a real challenge. Many ocular infectious diseases also represent a therapeutic challenge due to the microorganism's virulence, its capacity to become resistant to anti-microbial therapy, and its complex immune system interaction, characterized by an adaptive immune response to destroy the pathogen with inflammatory consequences to the infected tissue and innocent bystanders surrounding the site of infection. Another important therapeutic consideration is the potential for drug toxicity to delicate and susceptible tissues like the cornea and the retina.

This book provides the most recent advances in diagnostic methodologies and therapeutic alternatives for different infectious eye diseases. It is divided into four sections. The first section includes recent diagnostic techniques and novel treatment modalities for challenging corneal infections, from contact lens-related infectious keratitis due to a broad pathogen spectrum including bacteria, fungi, and *Acanthamoeba* spp. to herpetic and fungal corneal infections, commonly seen in general ophthalmology clinics. In the second section, an update on multimodal imaging technology for diagnosing ocular toxoplasmosis, the most common form of posterior infectious uveitis seen worldwide, is nicely illustrated with representative clinical and optical coherence tomography images at the different stages of the disease. The third section thoroughly discusses the two most important types of infectious endophthalmitis—postoperative and endogenous—from the most recent diagnostic technologic methodologies to novel therapeutic alternatives. Advanced polymerase chain reaction (PCR) techniques and another molecular sequencing, Matrix-Assisted Laser Desorption Ionization–Time of Flight Mass Spectrometry

(MALDI-TOF MS), and magneto-DNA nanoparticle systems are emerging as useful for the accurate diagnosis of infectious endophthalmitis, increasing the sensitivity and specificity of detecting pathogens. Finally, the fourth section is devoted to eye infections related to the current COVID-19 pandemic. One chapter discusses in detail the potential infectious capacity of the SARS-CoV-2 coronavirus in the ocular tissues. In another chapter, the authors bring us up to date on the most common ocular manifestation seen so far during the COVID-19 pandemic: viral conjunctivitis.

We want to congratulate all the chapter authors for their devotion in bringing us an excellent update on the most common and challenging causes of ocular infectious diseases. This book will appeal to ophthalmologists from any subspecialty since none of us are exempt from seeing and taking care of patients with such devastating sight-threatening diseases.

> **Alejandro Rodriguez-Garcia, M.D. and Julio C. Hernandez-Camarena, M.D., Ph.D.** Tecnologico de Monterrey, School of Medicine and Health Sciences, Institute of Ophthalmology and Visual Sciences, Monterrey, Mexico

Section 1 Infectious Keratitis
