What happened to our third eyelid?
It’s actually the remnant of a third eyelid. In humans, it’s vestigial, meaning it no longer serves its original purpose. There are several other vestigial structures in the human body, quietly riding along from one of our ancestor species to the next.
What is the normal position of the third eyelid?
Figure 8-1 Diagram of the eye showing normal position of the third eyelid. (Modified from Evans HE [1993]: Miller’s Anatomy of the Dog, 3rd ed. Saunders, Philadelphia.)
What is the remnant of a third eyelid?
It’s actually the remnant of a third eyelid. In humans, it’s vestigial, meaning it no longer serves its original purpose. There are several other vestigial structures in the human body, quietly riding along from one of our ancestor species to the next.
When is it time to remove the third eyelid?
The third eyelid is a useful and important structure. The only indications for its removal are severe, irreparable trauma and histologically confirmed malignant neoplasia. The clinician can easily examine the palpebral surface of the third eyelid by digitally retropulsing the globe through the upper lid.
Are there any diseases of the third eyelid?
In general, the third eyelid is not prone to disease. “Cherry eye,” or protrusion of the tear gland normally found behind the nictitans, is the most common disorder of the third eyelid. Common in certain breeds of dogs and cats, the gland can easily be sutured back into place.
Why do we have a third eyelid in our eye?
You know that little pink thing nestled in the corner of your eye? It’s actually the remnant of a third eyelid. In humans, it’s vestigial, meaning it no longer serves its original purpose. There are several other vestigial structures in the human body, quietly riding along from one of our ancestor species to the next.
The third eyelid is a useful and important structure. The only indications for its removal are severe, irreparable trauma and histologically confirmed malignant neoplasia. The clinician can easily examine the palpebral surface of the third eyelid by digitally retropulsing the globe through the upper lid.
Is the third eyelid transparent in a bird?
In birds the third eyelid is almost transparent and is under voluntary control ( Figure 8-4 ). It sweeps over the globe in a ventromedial direction from the dorsolateral quadrant, although there is some species variation in direction of movement. The third eyelid in birds does not have a gland associated with it.
Where is the Harderian gland located in the third eyelid?
In the pig and many rodents a portion of the gland of the third eyelid or a separate gland (the Harderian gland) is found deeper within the orbit. The cartilage and gland are covered on both bulbar and palpebral surfaces by conjunctiva that is tightly adherent at the free margin of the third eyelid but looser over the base and gland.
