Bovine Corneal Opacity and Permeability (BCOP, OECD 437) with Optional Histology

The BCOP (Bovine Corneal Opacity and Permeability) assay is an in vitro eye irritation test method developed by Gautheron et al. (1992), which uses living bovine corneal tissue, obtained as a by-product from abattoirs, to evaluate the potential ocular irritancy of a test article. Types of injury caused by exposure to the test article are quantitatively measured by changes in opacity and permeability to fluorescein.

The BCOP assay allows for the investigation of the mechanism of the damage caused. Corneal opacity can be caused by protein denaturation or the induction of stromal swelling, while corneal permeability reflects a loss in corneal barrier function and cell-to-cell membrane junctions of the corneal epithelium.

An additional histological endpoint can be added to assess the corneal swelling, hydration, or morphological alterations in the cornea. This assessment evaluates the type of observed lesions and the depth of injury into the corneas.

Quick Facts

Assay Model:

Organotypic, bovine corneas (obtained as a by-product from abattoirs)


  1. Opacity (determined by measuring the amount of light transmitted through the cornea).
  2. Permeability (determined by measuring the amount of fluorescein dye that penetrates through the cornea).

Each assay includes a positive and negative control. For more information about testing your materials using this assay, please see Applications. Specialized protocols may be prepared as requested through consultation with an IIVS Study Director.



BCOP is primarily used to evaluate test materials in the moderate to extreme irritancy/corrosive range. However, exposure protocol modifications can be made to increase the sensitivity of the assay system to resolve among milder ingredients and formulations.

Test Material Compatibility

The assay is compatible with both water soluble and insoluble formulations. Both solid and liquid test materials can be tested. Since test materials are topically applied, the test system is suitable for creams, pastes, highly viscous materials, and powders.

Alternate Endpoints

BCOP’s multiple endpoints allow the investigations of mechanism of action. An additional histological endpoint can be added to assess the types of observed lesions and the depth and degree of injury. Based upon the work of Maurer and Jester (2002), the depth and degree of injury may be used to predict the severity and outcome of the corneal injury.

Test article concentrations and exposure times may be adjusted as necessary to accommodate specific physical characteristics or client needs. Specialized protocols may be prepared as requested through consultation with the Study Director.


  • In the US and in Europe, the BCOP assay has been approved for identification of corrosive substances and those chemicals not requiring classification according to UN GHS.
  • OECD Test Guideline was adopted (TG437) in 2009 and revised in 2013.
  • The US EPA accepts the BCOP assay as part of a tiered strategy for the labeling of cleaning products with anti-microbial claims.

The results of a histological evaluation may be used in several ways depending on the study goals. It may be used to confirm the level of corneal irritation predicted by the opacity and permeability values. In other cases, it is helpful to understand the types of lesions and the depth of injury that a material might induce in the cornea.


For more information, please contact IIVS.