| Anchoring bias165 | Clouding of judgments by placing inappropriate weight to pre-existing data that may in fact be limited. In medicine, anchoring may arise by overemphasising selected features of patient history and examination, leading to narrow differential diagnoses. | Definitive attribution of ocular congestion, chemosis, and production of secretions to COVID-19 conjunctivitis among the critically ill.15 Such conclusions overlook the many causes of ocular findings in hospitalised patients, including third spacing of fluid and exposure keratopathy. Anchoring conclusions of SARS-CoV-2 replicative potential on the basis of methods that only detect the presence of viral RNA (eg, RT-PCR).
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| Availability heuristic164 | Weighing evidence and drawing conclusions based primarily on how quickly and/or vividly a relevant experience is recalled. | Arguably present in the entire ophthalmic COVID-19 literature, given the prominence of the pandemic in the minds of physicians worldwide. The availability heuristic may explain the tendency to describe COVID-19 associations with ocular disease in causal terms, even though conditions for causal inference may not be met. Ascribing a possible causal association between COVID-19 and the progression from infectious keratitis to endophthalmitis, even though it is not mechanistically clear how such would occur.19
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| Confirmation bias162 163 | The tendency to accept study findings that are consistent with one’s own beliefs, while remaining inattentive to methodological constraints of the study. Confirmation bias may also lead to design of studies that induce spurious associations that are artefacts of invalid study methodology. | Attribution of retinal findings such as cotton wool spots and microhaemorrhages to COVID-19, using cross-sectional data that by design cannot establish whether exposure to SARS-CoV-2 truly preceded the outcomes of interest.76 172 Concluding that SARS-CoV-2 infects the epithelial layers of ocular surface cells, on the basis of localisation of viral antigens only in the conjunctival stroma.122 Concluding that prolonged eyeglass wear is associated with decreased risk of COVID-19 infection, on the basis of a case–control design limited by inherent selection bias, caused by enrolling historical controls that were not at risk of COVID-19.83
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| Insensitivity to small sample sizes167 | Generalisation of data from studies with small sample sizes to the underlying population in question, without consideration of the inherent statistical instability and variation of such data. | Overinterpretation of data from case reports and small case series16 as true frequency measures of ocular complications (eg, conjunctivitis) arising due to COVID-19, overlooking population-based cohort studies53 67 that have reported far lower prevalence figures.
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| Post hoc ergo propter hoc | Latin translation for, ‘after this event, therefore because of this event’. That is, establishing a causal association purely on the basis of two or more sequential events, even though a causal relationship may not truly exist. | |