INTRODUCTION
The latest pandemic, which started on December 31st, 2019, when cases of pneumonia of unknown etiology in Wuhan, Hubei province of China, were reported to the World Health Organization (WHO), has continued with the identification of a new coronavirus (2019-nCoV), and this new virus has spread rapidly and become a global problem. The new virus was named (SARS-CoV-2) due to its close similarity to severe acute respiratory syndrome coronavirus (SARS-CoV), and the disease caused by the virus was named COVID-19. In limited studies for SARS-CoV-2, the average incubation period has been determined as 5-6 days. Symptoms may occur within 2-14 days after contact and contamination may begin 1-2 days earlier. In the clinical presentation of COVID-19, fever, dry cough, and respiratory distress are considered as major findings (1,2). Although patients mostly present with an asymptomatic or mild clinical picture, it may progress to pneumonia or acute respiratory distress syndrome in patients with additional disease and those aged over 65 years (3)(4). Infection is transmitted from person to person by inhalation of droplets or contact with the eyes, nose, and mouth after touching surfaces contaminated by the virus (5).
Some respiratory system viruses such as adenovirus and H7 influenza virus can strongly stimulate the immune system in the cornea and conjunctiva, causing the inflammatory pathway to be activated and to consequently form conjunctivitis or keratoconjunctivitis (6).
Coronaviruses that can cause conjunctivitis in humans have also been reported. Human coronavirus NL 63 (HCoV-NL63) was first identified with bronchiolitis and conjunctivitis in an infant. Then, conjunctivitis was defined in 17% of 29 In pediatric patients with HCoV-NL63. No ocular involvement was reported in Middle East respiratory syndrome-related coronavirus (MERS-CoV) or SARS-CoV infections (7). However, in animal studies, ocular infection was observed as a result of direct inoculation of SARS-COV in the mouth, nose or eye (8)(9)(10). A tear film mostly covers the eye surface and prevents bacteria and viruses from adhering to the cornea and conjunctiva with antimicrobial agents and the immunoglobulins it contains (11).
It has been shown that SARS-CoV-2 infects host cells via angiotensin-converting enzyme 2 (ACE2) just like SARS-CoV and has similar receptor binding sites (12). ACE-2 receptor has been detected in the retina (13), choroid (14) and conjunctival epithelium (15) in the human eye. In previous studies, findings such as acute follicular conjunctivitis, conjunctival hyperemia, chemosis, epiphora, and increased secretion have been described in patients with COVID-19 (16). As with other viral infections, it is assumed that the ocular symptoms of COVID-19 are self-limited and can be managed with symptomatic treatment.
It is known that SARS-COV-2 can be found in tears and adhere to the ocular surface. Conjunctivitis in patients with COVID-19 has been reported at different rates in various studies. It is not clear whether it causes different findings or subclinical conditions on the ocular surface.
The aim of this study was to evaluate the frequency of ocular involvement in hospitalized patients with COVID-19 and to compare the demographic findings and various blood parameters of patients with and without ocular findings.