Saying that the SARS-CoV-19 virus is weird is a bit like saying water is wet, but we didn’t always have the information we’re privy to now. Even more than a year into the pandemic, plenty of questions regarding the virus remain unanswered. These questions ring true in the ophthalmic field as well, with plenty of blanks left to fill in. Surprising contradictions and eyebrow-raising surprises also appear when you dig a big past the surface. Anyone who says they fully understand this virus is either delusional or from the future.
The virus has disrupted the ophthalmic world particularly hard, but things are starting to get back to normal in some places. Compared to just over a year ago, in April and May of 2020, the situation is peachy — but that’s like comparing a gusty day to a hurricane, and it depends on which part of the world you’re in.
CAKE magazine has covered the topic of COVID-19 and the eye before, but we haven’t found the bottom of this rabbit hole yet. Our recent story about the current state of cornea banking sheds some light on possible transmission mechanisms of the virus, as well as safety protocols and procedures. But it just shed some more light down the tunnel.
To further plumb the depths of this tunnel, we turned to Dr. Rupesh Agrawal of Tan Tock Seng Hospital in Singapore. Dr. Agrawal made waves with a paper from March 2020 that currently sits at 402 citations as of this writing.¹ He was kind enough to share his research at the Association for Research in Vision and Ophthalmology (ARVO 2021) virtual meeting. So, without further ado, let’s dive back into this rabbit hole.
Ocular Manifestations of COVID-19
As has been noted in other parts of the body, COVID-19 can manifest in many ways in the eye. However, it’s difficult to pin down the specific cause of these adverse effects. Are they caused directly by the virus? Are they caused by systemic problems like CO2 retention related to the virus? We’re not entirely sure yet, but Dr. Agarwal helped us understand just what can happen.
Among the potential manifestations are:
- Conjunctivitis-like symptoms (hyperemia, epiphora, chemosis)
- Photophobia
- Blurring of vision
- Itching
- Dry eye
- Foreign body sensation
- Keratoconjunctivitis
Dr. Agrawal provided an example of one COVID-19 positive patient who suffered acute onset bilateral follicular conjunctivitis.
There are reported intraocular manifestations of COVID-19 as well. These can include:
- Transient refractive errors
- Uveitis and retinal necrosis
- Retinal microangiopathy
- Retinal vascular occlusion
- Retinal vascular changes
- Choroidal vascular changes
- Optic neuropathy/Optic neuritis
There you have a fairly expansive list of potential effects. But a lot of questions remain. Can COVID-19 be transmitted by tears and conjunctival secretions? And can COVID-19 itself cause localized eye disorders?
Can COVID-19 be transmitted via tears?
The short answer to the above questions is “we’re not sure.” Previous research² has suggested that while the virus can infect ocular tissue, it cannot replicate in ocular tissue. So, we’re left to discuss the mechanisms of potential transmission.
One somewhat obvious answer is that the virus can hitch a ride inside the body via the nasolacrimal duct. Alternatively, it could go the other way, and migrate upwards from the respiratory tract. Dr. Agrawal also suggested that it could occur via hematogenous infection of the lacrimal gland. This virus can get around — we know that.
So, how do you detect the virus in tears? A common method is the RT-PCR test conducted on conjunctival swabs, Schirmer’s test strips or glass capillary pipettes.
What researchers have found is that the virus is not commonly found in the tears of COVID-19 patients. In one paper Dr. Agrawal discussed, only 2 of 38 patients tested with conjunctival swabs were positive for the virus in their conjunctival fluid. That’s only 5.2% — quite low. Of those two, only one presented with conjunctivitis. Similar studies produced similar results. Effectively, the virus is rarely present in conjunctival fluid.
That’s great, but…
Dr. Agrawal had some surprising statistics to share about COVID-19’s ocular effects. For example, he noted a statistically significant increase in vein dilation; similarly, patients also exhibited an increase in choroidal thickness.
Yet there are still contradictions that present themselves. Dr. Agrawal pointed out that any conjunctivitis-like symptoms may be due to congestion, chemosis or systemic problems. If the virus could directly invade ocular tissue, there should be a more noticeable ocular inflammatory response.
However, unusually large cystoid bodies have been found in the retina of deceased COVID-19 patients. Similarly, some patients have displayed a decrease in vascular density and atrophy of several capillaries.
Where do we go from here?
The answer, as always, is that more research is needed. We can be reasonably sure that the virus doesn’t directly invade the eye, but it may be responsible for plenty of adverse ocular effects. Whether the virus itself or systemic problems caused by the virus lead to these effects is as of yet unknown.
We applaud Dr. Agrawal for his continued research and look forward to more information from the ophthalmic community. There’s few things more pressing at the moment than wrapping our heads around this virus, as it still plagues much of the world. Let’s figure it out and get rid of the damn thing.
References
- Seah I, Agrawal R. Can the Coronavirus Disease 2019 (COVID-19) Affect the Eyes? A Review of Coronaviruses and Ocular Implications in Humans and Animals. Ocul Immunol Inflamm. 2020;28(3):391-395.
- Bayyoud T, Iftner A, Iftner T, et al. Absence of Severe Acute Respiratory Syndrome-Coronavirus-2 RNA in Human Corneal Tissues. Cornea. 2021;40(3):342-347.
