SARS-CoV-2 and the ocular surface: test accuracy and viral load.

Area of Science:

• Ophthalmology
• Infectious Diseases
• Molecular Diagnostics

Background:

• Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) can cause coronavirus disease 2019 (COVID-19).
• Ocular surface involvement in COVID-19 is of clinical interest for diagnostic and transmission perspectives.

Purpose of the Study:

• To evaluate SARS-CoV-2 RNA presence on the ocular surface of individuals with suspected COVID-19.
• To determine the accuracy of ocular surface molecular testing compared to nasopharyngeal swabs.
• To assess different tear film collection techniques for SARS-CoV-2 detection.

Main Methods:

• 152 individuals with suspected COVID-19 underwent simultaneous nasopharyngeal and ocular surface sampling.
• Tear film was collected using the Schirmer test filter strip and conjunctival swab/cytology.
• Quantitative reverse-transcriptase polymerase chain reaction (RT-qPCR) was performed on all samples.

Main Results:

• 86 out of 152 patients (56.6%) tested positive for COVID-19 via nasopharyngeal PCR.
• Both Schirmer (16.3%) and conjunctival swab (17.4%) tests detected SARS-CoV-2 RNA, with no significant difference between them.
• No ocular tests were positive in patients with negative nasopharyngeal PCR results.
• Ocular viral load (mean Ct 35.6-36.4) was significantly lower than nasopharyngeal viral load (mean Ct 18.2).

Conclusions:

• Schirmer and conjunctival swab tests are comparably accurate for detecting SARS-CoV-2 RNA on the ocular surface.
• Ocular surface viral load is substantially lower than in nasopharyngeal samples.
• Ocular manifestations observed via slit lamp biomicroscopy were not linked to ocular RT-PCR positivity.