To study the changes in the amount and isoform pattern of the myosin heavy chain (MyHC) in rabbit extraocular muscle (EOM) fibers after recession.

Sixteen New Zealand white rabbits were used. Recession surgery was performed on the right superior rectus (SR) muscle by 3 mm in eight rabbits, and performed by 8 mm in other eight rabbits. The left SR muscles were left intact as the control groups. The SR muscles in both eyes were harvested from two rabbits from each recession group at 3 days and 1, 2, and 4 weeks after surgery. The changes in MyHC amount and isoform pattern were analyzed by gel electrophoresis.

Total MyHC content decreased from 1 week after surgery in the 3-mm recessed group and from 3 days in the 8-mm group. The type IIb MyHC (MyHCIIb) plus EOM-specific MyHC (MyHCeom) showed similar proportional changes to the total MyHC at the different time points after surgery.

The fast MyHCIIb plus the superfast MyHCeom decreased after EOM recession, and these results appear to be related to the changes in the global layer rather than in the orbital one. This suggests that the global layer might be the fast and the superfast twitch portions of rabbit EOM, which perform the fast saccades in ocular movements.