It is already known that contact of infectious body fluids with the mucosal membrane in the mouth, nose, and eye is the main route for the transmission of severe acute respiratory syndrome coronavirus (SARS-CoV) [19].
In February 2020, Lu et al. have commented that inhalation of droplets may not be the only pathway for the transmission of the pathogen of COVID-19 which is named as severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) [20]. The authors have drawn attention that direct or indirect contamination of the conjunctival epithelium with infectious droplets may be another route for the transmission of COVID-19. For this reason, it was advised people that touching eyes is a risky habit at this moment. Also, it was recommended to doctors, nurses, healthcare members, and other workers who are working in close contact with people that they should wear eye protection masks or face masks to protect themselves [21].
In March 2020, in the study of Wu et al., the authors have reported that 12 of 38 patients with clinically confirmed COVID-19 had ocular findings such as epiphora, increased secretions, conjunctivitis, chemosis, or conjunctival hyperemia [7]. But 2 of 12 COVID-19 patients with ocular findings had positive results for SARS-CoV-2 on RT-PCR from conjunctival swabs. In these patients, one patient had epiphora as the initial complaining of COVID-19. On these outcomes, they have concluded that COVID-19 may transmit via ocular surface but there is low evidence.
In April 2020, Daruich et al. have published a case report of a patient with conjunctivitis as the first sign of COVID-19 which was detected by telemedicine consultation [6]. The patient had no systemic symptoms but the general condition of the patient deteriorated in a short time following the detection of conjunctival hyperemia in his eye. The diagnosis of the COVID-19 was confirmed after positive RT-PCR for SARS-CoV-2, and ocular findings were regressed after eleven days of treatment. On the other hand, Chen et al. have reported a case report of a confirmed COVID-19 patient with bilateral redness in his eyes about 2 weeks after the onset of symptoms of sore throat and diarrhea in April 2020 [8]. Moreover, RT-PCR result of the conjunctival swab specimens was positive for SARS-CoV-2. The authors have commented that conjunctivitis as an ocular finding of COVID-19 may not occur only in the early period of the disease. Due to these similar publications, the place of the eye in COVID-19 was a matter of debate and eye immunity began to be questioned. [22, 23] Also, due to the news in the mass media, societies may have been attracted and awareness of the ocular signs of the COVID-19 may have been raised. [6, 8, 24,25,26] Therefore, the public interest of online searches on ocular signs of COVID-19 has increased.
Human-to-human transmission of SARS-CoV-2 has caused governments to give orders such as stay-at-home and social distancing. As well, lockdown has been carried out in many countries. Thus, outpatient visits have been reduced as much as possible and this unprecedented circumstance has caused people to search their complaints, symptoms, and get medical information mostly from internet search engines.
Moreover, many websites provide a wide range of opportunities for researchers to collect data on different topics and this new trend brought out infodemiology in the era of technology. Infodemiology is a new search field that includes analyzing internet data streams to inform about changes that can be foreseen in public health, especially during outbreaks [27]. In the last decade, there has been an increase in internet-based studies in the field of health information. The rate of internet searches has given researchers useful information about the course of the diseases, especially about infectious diseases. For instance, the association between influenza occurrence and influenza-related search terms has been investigated in the study of Polgreen et al. by using Yahoo! internet search engine and it was demonstrated that internet search activity for influenza predicted an increase in cultures positive for influenza 1–3 weeks before conventional reporting systems do [28].
Thus, evaluating internet-based information in unprecedented outbreaks may be a supplemental method to predict the course of infectious diseases. This kind of investigation may give clues for additional symptoms or may help to detect the changes in infectious disease activity. In this period, countless websites have given information about the COVID-19 pandemic. Mostly, people use internet search engines to get medical information. In addition, numerous medical journals have opened access publicly to supply updated information about the COVID-19 pandemic. For instance, the RSVs of the keyword of ‘conjunctivitis’ peaked on March 29–30, 2020, in Turkey [29]. At the same date, news drawing attention to the relation between conjunctivitis and COVID-19 was shared on the websites of three of the most widely read newspapers in Turkey [24,25,26]. This example may reflect the effect of mass media on the search activity of internet users. Indeed, there was a lot of traffic in the frequency of searching COVID-19-related keywords on the internet, globally. Presumably, this big data may reflect the COVID-19 activity. Internet sources such as GT provide free access to the data of users’ online activities and search queries. GT which is a very useful and free-to-access tool of Google supplies information about the search volumes of a particular subject or word in a certain region within a certain time interval. Thus, GT is a prominent internet data source for researchers during the COVID-19 pandemic. Several studies have recently been published to evaluate the relationship of different symptoms or diseases with COVID-19 using GT analysis [11,12,13,14,15].
Loss-of-smell-related and otolaryngology-related search volumes obtained by GT have been investigated during the COVID-19 pandemic in Italy, Spain, the United Kingdom, the United States, Germany, France, Iran, and The Netherlands and it was stated in these studies that there is a correlation between the RSVs of anosmia and COVID-19 in these countries [11,12,13]. As well, GT analyses of lung diseases and gastrointestinal symptoms related to the COVID-19 have also been evaluated in different countries and it was demonstrated that some search queries of associated keywords or terms have increased and some of them have decreased during the COVID-19 pandemic [14, 15].
To the best of our knowledge, the present study is a novel study in ophthalmology that aimed to investigate ocular-symptoms-related searches during the COVID-19 pandemic using GT. The preliminary outcomes of this study showed that the most RSVs of the investigated ocular-symptoms-related keywords were correlated with the COVID-19 new cases and new deaths in the United Kingdom, Spain, Italy, Germany, Turkey, and worldwide. We should state that the data obtained from GT does not contain the actual number of search activity. Instead, it represents the relative volume of the search terms rather than quantitative information. Due to this limitation, we could not compare the RSVs of the selected keywords among the countries. But, it has drawn our attention that the correlation of the investigated data was higher in Italy. In addition, one of the deeply affected countries in Europe at the beginning of the COVID-19 pandemic was Italy. Also, the present study has some other limitations. This infodemiological study contains the data of users who have access to the internet. Therefore, it may not be claimed that it represents the entire society in the aforementioned countries. In addition, users may have searched some keywords due to seasonal allergic ocular symptoms and the RSVs of these keywords may be part of our data. As well, users without ocular symptoms may have influenced by media news about ocular signs of COVID-19 and may have wanted to search some terms on the internet.