COVID-19 May Temporarily Reduce Choroidal Thickness

Close up of a doctor doing an eye exam on his patient
Subfoveal choroidal thickness significantly decreased at the early postinfectious period compared with healthy patients, the study shows.

COVID-19 infections can reduce choroidal thickness in all choroidal layers, according to researchers. However, this damage appears to be reversible. These findings, published in the Canadian Journal of Ophthalmology, indicate global involvement of the choroid rather than just involvement of the choroidal stroma or blood vessels.

Although respiratory system involvement is the leading cause of mortality for patients with COVID-19, the hematological complications of the virus can cause severe morbidity or death. In addition to systemic complications, COVID-19 can also lead to retinal vascular occlusions and subsequent retinal damage, according to investigators.

SARS-CoV-2 enters human cells using the angiotensin-converting enzyme-2 receptor, and this receptor is expressed on some of the cells in the retina, ciliary body, and choroid. Certain antigens of the SARS-CoV-2 virus have molecular similarities with certain retinal structures and can cause thrombotic complications in ocular blood vessels.

To study the long-term changes in choroidal thickness and structure following COVID-19 infection, researchers conducted a prospective, longitudinal study that included 32 eyes of 16 COVID-19 patients and 34 eyes of 17 age-matched healthy control patients. Study participants underwent visual acuity assessments, slit lamp examinations, and indirect ophthalmoscopy. Enhanced depth optical coherence tomography imaging of the posterior pole and the peripapillary region was performed the early days after infection (days 15 to40) and 9 months postinfection.

None of the patient examinations revealed any ocular involvement of COVID-19. However, in COVID-19 patients, subfoveal choroidal thickness (SFCT) significantly decreased at the early postinfectious period compared with healthy patients (P =.045), according to researchers. SFCT significantly increased at the late postinfectious period compared with the early period (P =.002), and the difference between the patients and controls became statistically insignificant (P =.362). Investigators observed a similar trend regarding peripapillary choroidal thickness. Choroidal vascularity index (CVI) remained unchanged (P =.721) despite the significant decrease in SFCT and total choroidal area (P =.042), indicating that this decrease occurred both in the choroidal stroma and blood vessels. CVI remained unchanged in the late postinfectious period (P =.575) compared with the early period, indicating that recovery occurred in the entire choroidal tissue.

The limitations of this study include its sample size, lack of patients with severe COVID-19 infections, that all participants were healthcare workers, and that patients couldn’t be evaluated via indocyanine green angiography.


Hepokur M, Gunes M, Durmus E, et al. Long-term follow up of choroidal changes following COVID-19 infection: analysis of choroidal thickness and choroidal vascularity index. Can J Ophthalmol. Published online July 13, 2021. doi:10.1016/j.jcjo.2021.06.020