Abstract
Purpose :
Zone quick phenol red threads have previously been the gold standard for measuring aqueous tear volume in rodent studies of dry eye disease (DED). This product is no longer available outside of Japan due to changes in the supply chain after the COVID pandemic. A new method is necessary to measure tear volume in rodents. Even though the use of endodontic paper points (EPP) has been published before, the method has not been well validated. In this study we compare the efficacy and reliability of two brands and two sizes of EPP to measure tear volume in rodents, and a benzalkonium chloride (BAK) model of DED.
Methods :
Male C57BL/6J mice were used (n=5). Tears were measured unilaterally BID, 3x days a week for each brand and size. Animals were restrained by hand and EPP (Parallax 30, Parallax 35, IM3 30, IM3 35) was inserted into the nasal fornix of the eye for one minute. Tear volume was recorded in millimeters of paper. Reduced tear production was inducted with 2x / day topical 0.2% BAK for 14 days. Tear production was measured using IM3 35 EPP at Day 7, 10, and 14. Corneal fluorescein staining (CFS) was evaluated using the Oxford scores on Day 14.
Results :
There was a significant difference between the brands of EPP but no difference between sizes within either brand. For size 30, IM3 showed an average tear volume of 4.83±0.21 mm while Parallax was 3.78±0.24 mm. For size 35, IM3 brand showed an average 5.26±0.27 mm and Parallax, 4.08±0.24 mm. The IM3 35 size showed the greatest absorbance (higher tear collection) compared to other sizes and brands. Day 14 tear volume was not statistically significant however there was a downward trend of BAK treated mice (5.26±0.27 mm at Day 0; 4±0.46 mm). There was a significant difference between CFS Oxford scores at Day 14.
Conclusions :
IM3 EPP of both tested sizes captured a significantly greater volume of tears than Parallax EPP when used on C57BL/6J mice. Even though the 30 mm EPP is the most standardized size in dentistry and ophthalmic research, the 35 mm show better absorbance on the aqueous tear film collection. This method may be used to measure tear production in small rodents, with IM3 being the preferable brand. Future work should be done on validating the use of the EPP on different DED mice models.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.