Quantification of Tear Volume in an Autoimmune Dry Eye Rat Model using the Phenol Red Thread

Overview

This video demonstrates the phenol red thread test to determine tear volume in an autoimmune dry eye rat model. The pH-sensitive acidic phenol red thread changes color when it comes in contact with the alkaline tears. The shorter length of color change in the phenol red thread corresponds to reduced tear volume.

Protocol

All procedures involving animal models have been reviewed by the local institutional animal care committee and the JoVE veterinary review board.

1. Assessment of Dry Eye Features

NOTE: The anesthetized rats should be held gently by a gloved hand in an upright position on a flat surface to avoid movement.

1. Measure the tear volume with phenol red thread.

1. Use one pair of forceps to hold the thread and another to pull the lower eyelid of the rat. Place the thread at the proximal corner of the lower fornix for 1 minute and then remove the thread.
   NOTE: Tears make the wetted part of the thread red in color.
2. Take an image of the length of the wetted part of the thread next to a ruler with millimeter markings. Measure the wetted length to the tenth of a millimeter using an image software (e.g., ImageJ).

Materials

Name	Company	Catalog Number	Comments
Phenol red thread	Tianjin Jingming New Technological development Co. LTD.