Author(s): Miller PE, Stanz KM, Dubielzig RR, Murphy CJ. Mechanisms of acute intraocular pressure increases after phacoemulsification lens extraction in dogs. Am J Vet Res. 1997 Oct;58(10):1159-65.
Journal: American Journal Of Veterinary Research, Volume 58, Issue 10, Oct 1997
OBJECTIVE To investigate the mechanisms by which intraocular pressure (IOP) increases acutely after phacoemulsification (PE) lens extraction in clinically normal dogs.
ANIMALS 24 young adult dogs.
PROCEDURE Intraocular pressure was monitored for up to 24 hours after unilateral intercapsular PE in 17 clinically normal, adult dogs. In 8 of these dogs, use of 2% hydroxypropyl methylcellulose (HPMC) aided capsulorhexis. Mean volume of irrigation, PE time, and power were constant between groups. After surgery, dogs were randomized then euthanatized, and eyes were examined grossly and histologically at 0 (n = 4), 3 (n = 7), and 24 hours (n = 6) after PE. Seven additional dogs underwent anterior chamber decompression alone (n = 4) or served as morphologic controls (n = 3).
RESULTS Intraocular pressure peaked by postoperative hour 3 at 49.9 +/- 5.0 mm of Hg and normalized by 24 hours. Use of HPMC did not affect the peak or duration of IOP increase. Blood refluxed into the collecting channels and corneoscleral trabecular meshwork in operated eyes. Computer-aided morphologic analysis indicated significant (P < 0.001) reduction in ciliary cleft cross-sectional surface area and width immediately after PE, but not after anterior chamber decompression alone. Cleft collapse was significantly (P < 0.02) greater at 24 than at 3 hours, despite return of IOP to control values by 24 hours. Plasmoid aqueous also was found in the meshwork.
CONCLUSIONS AND CLINICAL RELEVANCE Sudden, large increases in IOP with few overt clinical signs may occur immediately after lens extraction in dogs. Such increases risk compromising the corneal incision and may damage the optic nerve, thereby complicating lens extraction. Structural alterations in the trabecular meshwork persist after IOP has normalized in 24 hours and may contribute to genesis of glaucoma in the late postoperative period.