Analysis of video-record of the action of the eye’s muscles of
Egyptian agama
The eye’s motion was monitored via video recording in the laboratory
(Fig. 8). Several video recordings were analyzed to identify movements,
such as the opening and closure of the palpebral fissure and the
elevation and depression of the upper and lower eyelids. However,
identifying eyeball movements like elevation, depression, and rotation
was challenging. The synchronization of eyelid movement with eyeball
movement helped to observe these movements more clearly. This
synchronization was particularly evident when the gaze was directed up
or down or when the eye was elevated or depressed, resulting in
significant movements of the eyelids\RL.
The elevation of the upper eyelid of T. mutabilis upward is
performed by the contraction of the dorsalis rectus muscle, cooperating
with the dorsalis oblique muscle, which elevates the eyeball.
Conversely, the depression of the lower eyelid downward is performed by
the contraction of the depressor palpebral inferioris muscle.
Simultaneous contraction of these upper and lower eyelid muscles expands
the eye-opening, opposing the action of the orbicularis oculi muscle
responsible for closing the eyelids.
Observations showed that when the pupil moves anteriorly with a decrease
in skin surface at the nasal canthus, it indicates rotation of the
eyeball towards the anterior direction, performed by the contraction of
the medialis rectus muscle. Conversely, when the eyeball abducts away
from the nasal canthus, it is performed by contraction of the lateralis
rectus muscle.
Depression of the eyeball is achieved by the contraction of the
ventralis rectus muscle and ventralis oblique muscle, while the
elevation of the eyeball is performed by the dorsalis rectus and
dorsalis oblique muscles.
A muscle never acts alone; in each antagonistic pair
(lateralis-medialis, dorsalis-ventralis, and obliques), one muscle
contracts while its companion relaxes. Most movements involve the
simultaneous action of these three pairs. Additionally, observations
indicated that the eyeball is retracted further into the eye socket by
the retractor bulbi and bursalis muscles.