1. Introduction

The SARS-CoV-2 is a new type of Coronavirus, first detected at the end of 2019 in China, which was responsible for the COVID-19 pandemic. The COVID-19 pandemic c caused by the SARS-CoV-2 virus has had a profound impact on all aspects of healthcare, including ophthalmology. As a highly infectious disease, COVID-19 has led to significant changes in the way ophthalmic care is provided, with an increased focus on infection control measures and minimizing patient contact. In addition, COVID-19 has also been found to have ophthalmic manifestations [1]. These include conjunctivitis, uveitis, retinal abnormalities, and other ocular manifestations ^[2][3][2,3]. Understanding the impact of COVID-19 on ophthalmology is crucial in providing safe and effective care to patients during this challenging time, which is the aim of this brief review.

Coronaviruses are a large family of viruses that can cause illness in animals and humans [4]. They are named for their crown-like spikes on their surface. Coronaviruses can cause a range of illnesses, from the common cold to more severe diseases such as severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and COVID-19 ^[5][6][5,6]. Coronaviruses are spread mainly through respiratory droplets when an infected person coughs, sneezes, talks, or breathes [7]. They can also be spread by touching a surface contaminated with the virus and then touching your mouth, nose, or eyes [8].

2. Ocular manifestations of COVID-19

There have been a limited number of reports on the ocular manifestations of COVID-19, and more research is needed to fully understand the relationship between the virus and the eyes. However, some examples of the reported ocular manifestations include the following:

Conjunctivitis and other inflammations of eyes’ outer layers: Considering all cases of COVID-19 disease, conjunctivitis was reported in 5-9% of cases, episcleritis in 2.2% of cases, keratitis in 0.5% of cases, and blepharitis or lid margin hyperemia in 5% of cases. Concerning the physiological mechanisms that occur during infection, these COVID-19-related ocular manifestations have been suggested to result from a direct impact of the virus on ocular tissues ^[9][10][38,39]. One study found that conjunctivitis was present in 1.1% of hospitalized COVID-19 patients ^[11][40]. Another study found that conjunctivitis was present in 3.6% of COVID-19 patients in China ^[12][41].

Epiphora (excessive tearing): A case report described a patient with COVID-19 who experienced epiphora in one eye, which resolved after treatment with antiviral medication. Another study by Scalinci and Trovato described epiphora as a manifestation of conjunctivitis in COVID-19 patients ^[13][42].

Dry Eye: Dry eye disease was reported in high rates among subjects affected by COVID-19 disease. School-based research revealed a preponderance of dry eye as measured with a validated paper-based instrument ^[14][43]. Female gender and being of an older age were indicated as exacerbating risk factors ^[15][44]. A theoretical explanation was proffered to be the increased screen time during the pandemic period. Diskmetas et al. also showed a correlation between mask use and reduced tear break-up time during the heat of the pandemic ^[16][45]. Researchers suggested that dry eye in itself was an epidemic during the COVID-19 pandemic ^[17][46].

Eye pain: COVID-19 sufferers may experience eye discomfort as a dull aching, soreness, or a sense of pressure. It is thought to be caused by viral infection-induced inflammation of the conjunctiva (conjunctivitis) or other ocular tissues. Several research and case reports have established the existence of ocular discomfort in COVID-19 instances. For example, Wu et al. discovered that roughly 12% of COVID-19 patients exhibited ocular symptoms such as eye discomfort ^[11][40]. Also, a case report described a patient with COVID-19 who experienced eye pain, which was relieved with topical steroids ^[18][47]. These findings imply that eye discomfort may be an additional manifestation of COVID-19, emphasizing the necessity of evaluating ocular symptoms in the disease’s diagnosis and therapy. More study is needed to thoroughly understand the underlying causes and incidence of ocular discomfort in COVID-19 individuals.

Photophobia: A few case reports have described COVID-19 patients who experienced photophobia ^[11][13][40,42].

Retinal changes: Retinal ganglion cells and plexiform layers were shown to have characteristic lesions when analyzed by ocular coherence tomography in a Brazilian study of 11 COVID-19 patients ^[19][48]. These findings mirrored animal model studies that reported similar changes ^[20][49].

It is worth noting that these ocular manifestations are relatively rare, and COVID-19 primarily affects the respiratory system. In most cases, the ocular symptoms linked to COVID-19 in children tend to have a mild course, and complete visual recovery is typical ^[21][50]. However, healthcare professionals should be aware of the potential ocular manifestations of the virus, particularly in patients who present with eye symptoms and have a history of exposure to COVID-19.

3. Confirmed ocular diseases in COVID-19

Dry eye diseases are the most common reported ocular complications of COVID-19 ^[22][51]. Krolo et al. reported that face mask use was related to higher ocular surface disease index (OSDI) scores ^[15][44]. Other possible reasons may include increased screen time occasioned by working from home and inability to obtained needed dry eye medications due to the lockdown ^[23][52].

Children with COVID-19 have been reported to present with a largely self-limiting vasculopathy akin to the Kawasaki disease ^[24][53]. The pathological and clinical manifestations of this disease include conjunctivitis, keratitis, intermediate uveitis, and inflammation of the optic nerve head [54].

Reyes-Bueno et al. detailed the post-COVID-19 Miller Fisher syndrome (MFS) reported in some patients which included complaints of blurred vision and extra-ocular muscle palsy ^[25][55]. Neophytou et al. published a systematic review of this syndrome in COVID-19 patients with a conclusion that the condition occurred more frequently after infection as compared to after vaccination ^[26][56]. The prognosis of MFS is spontaneous and very good even without administering intravenous immunoglobulin ^[26][56].

Generally, viral diseases are directly linked to reduction in CD4+ and CD8+ counts. This in turn has been implicated in the incidence and reoccurrence of diseases such as her-pes-zoster ophthalmicus, infection induced uveitis and infective cellulitis ^[27][57].