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.