PorCORA - Porcine Cornea Reversibility Assay

Draize Rabbit Eye Replacement Assay for Ocular Corrosivity Screening

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The Missing Piece of the Puzzle

There are several alternative methods to characterize aspects of eye irritation and damage, but no established method can model recovery after injury as in a Draize test. PorCORA was specifically developed to fill this void by measuring corneal damage and recovery for extended periods in excised porcine corneas. When combined with other alternative assays, such as the HET-CAM or CAMVA for assessment of conjunctival injury and vascular damage and the BCOP for assessment of acute ocular irritation, PorCORA is the missing piece that allows evaluation of corneal healing.

What is PorCORA?

PorCORA is an ex vivo alternative assay for ocular corrision that evaluates similar mechanisms to those occurring in an in vivo Draize Rabbit Eye assay. In PorCORA, test substances are placed directly onto excised porcine corneal tissues kept in culture. The tissues are stained with fluorescent dye and damage to the corneal epithelia is visualized by the retention of fluorescent dye. The cultured corneal tissues can be repeatedly stained with fluorescent dye to assess changes in the area of damage over the course of 21 days and, the potential for recovery in ocular tissue is monitored using the percent of corneal area that retains fluorescent dye. Because corneal damage is generally the most persistent of ocular injuries, the time course measurements in the PorCORA are justifiable in modeling both reversible and non-reversible eye damage.

Background - PorCORA

For over five years, MB Research Scientists have been developing assay methods in order to create a cost-effective protocol to offer you a viable alternative to the Draize Rabbit Eye Test.

PorCORA is similar to the BCOP, but by culturing the excised corneas for up to 3 weeks, the reversal of damage to the cornea can be measured over time and the "Days to Clear" can be determined.

PorCORA - Time to Recover.

Assessment of Corneal Damage

Fluorescent dye stain retention by corneal epithelium has proven to be an effective tool in the assessment of ocular damage after exposure to irritants. This method is non-destructive and allows for re-staining of the same tissue over the course of the study. The area of damage is clearly defined and easily observed almost immediately after staining.

Initial ocular irritation and subsequent opacities are assessed and scored according to the PorCORA Fluorescent Dye Stain Retention Scoring System. Scoring of the area of damage is done by visually assessing the percentage of damage to the cornea shown by the retention of fluorescent dye and assigning a corresponding score.

PorCORA Fluorescent Dye Stain Retention Scoring System *

Ocular Irritation clearing after dosing.
  • 0 - No Stain Retention
  • 1 - One quarter (or less) but greater than zero.
  • 2 - Greater than one quarter but less than one half.
  • 3 - Greater than one half, but less than three quarters.
  • 4 - Greater than three quarters but less than 100%.
*Based upon Draize, J.H., et al., J. Pharm. Exp. Ther., 82:377-390, 1944.

Overview

  • PorCORA is an alternative test for eye irritancy and reversibility that does not use live animals.
  • Re-epithelialization of the corneal surface can be measured by fluorescent dye stain retention.
  • fluorescent dye stain retention is representative of actual tissue damage determined by a live/dead staining kit and observation by confocal microscopy.
  • PorCORA may fill the gap that is left by current alternative eye irritation assays since it has the potential to determine recovery after initial eye irritation.
  • Development of PorCORA was partially funded by a grant by the Society of Toxicology, sponsored by a Colgate-Palmolive Grant for Alternative Research.

Other Ocular Alternative Assays