Late opening of eyelids in newborn rabbits
Esther van Praag, Ph.D.
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Newborn rabbits are nidicole and, as a consequence, born immature, naked, deaf and blind. Their eyelids are closed. It is only after their opening, around the age of 10 days, that the consequences of a late opening or deformations of the eyelids become visible.
Rabbits are born with the lower and upper eyelids stuck shut to protect the eye - an entity that includes the optic nerve and the eye globe. Indeed, the development of the eye is not complete in newborn rabbits; it is in no way a miniature version of the adult vision organ. The size, shape, but also the proportions of the different parts of the eye change during the first weeks of life of the newborn rabbit. The proportions between the anterior chamber and the posterior chamber of the eye are very different from those of the adult. The surface of the retina - the organ that is sensitive to vision at the back of the eye, increases and becomes more and more innervated. The cornea and the conjunctiva, respectively the transparent layer covering the eyeball and the transparent mucous membrane lining the inside of the eyelids, are also immature and will continue their development after the birth of the rabbit.
Anatomy of the eye of a healthy rabbit
Opening of the eyelids
The opening of the eyelids happens usually on the 10th day after birth. A small split appears in the inner corner of the eye that progresses slowly from the outer cutaneous portion of the eyelid to the conjunctival inner surface. Ligaments and muscles of the eyelids also participate in the appearance of the split. Once the eyelids are separated, the free edges gradually harden. Eyelashes grow. The sebaceous glands located on the inner edge of the eyelids become functional and release secretions to lubricate the eyelids. The full opening of the split may take a few days. When completed, the upper and lower eyelids protect the cornea against foreign objects, trauma, light or wind. They help maintain a proper hydration of the cornea by distributing the tear fluid - secreted by the various lacrimal glands via the lacrimal duct, over its surface. The opening of the tear duct is visible inside the lower eyelid, when it is delicately pulled forward.
Rabbits have a third eyelid or nictitating membrane. Its active or passive movements protect the cornea and the conjunctiva. The nictitating membrane has an accessory lacrimal gland which contributes to the aqueous portion of the tear film. Rabbits beat their eyelids only 10 to 12 times per hour.
Cornea and lens
The organization of corneal tissue begins during the development of the embryo, with a very precise organization of collagen fibrils. This phase is critical as it ensures the transparency of the cornea in adult rabbits. At birth, the cornea is opaque. Its development is linked to the opening of the eyelids. At this time, the state of hydration and vascularization differs from that of adult rabbit and important changes will take place. The thickness of the cornea will decrease after the opening of eyelids. This process continues for a few weeks, then the membrane thickens and becomes similar to that observed in adults. These changes are accompanied by a decrease in the density of cells in the cornea. The lens of the eye also changes. During the first two weeks of life of the rabbit, the lens shows a spectacular growth and reaches 50% of the size of the adult rabbit. During this period, the lens accumulates cholesterol molecules and gradually becomes transparent. In young rabbits with a late opening of the eyelids, irreversible opacity of the cornea and/or lens is often observed. It is assumed that a delay of eyelid opening disorganizes the development of these tissues and disturbs their transformation, which leads to an opacity of the cornea and/or the lens. Very little information is available on this topic.
C. Wayne Wright
Closed eyelid et secretion of a thick fluid is often a sign of conjunctivitis
Late opening of the eyelids and possible infection
The eyes of the newborn rabbits are very sensitive organs and the risk of bacterial infection is high during the first weeks of life. If the opening of the eyelids is late, beyond the 10th day of life, there is a high risk of developing a neonatal infection of the conjunctiva and the outer layer of the cornea . Any suspicious inflammation, protuberance or presence of pus must be taken seriously. Bacteria such as Staphylococcus spp. or Streptococcus spp. are often responsible for these infections. The newborn comes into contact with these pathogens during parturition, when passing through the urogenital system of the doe, but also in the nest, especially in the colder season. Characteristic signs of such infections are eyelids pointing outwards because of inflammation or accumulation of pus in the inner eye corner, and the presence of crusts or thick, yellowish-colored secretions between the eyelids. The conjunctiva may become inflamed, reddish and the cornea is opaque. In severe cases, the structures of the eye may be affected. A superficial lesion of the cornea may develop into a painful ulcer; it may be accompanied by opacification of the surface of the cornea and lens. This opacity is often temporary and regresses slowly with appropriate treatment.
Opaque cornea after a late opening of the eye in a 3 weeks old rabbit
A retraction of the eyeball inside the eye-socket is sometimes observed after a late opening of the eyelids.
Retracted eye in a lop rabbit
Treatment of non-opened eyelids
If a treatment is started quickly, the chances of total healing are good. When the eyelids are not showing any sign of opening (split near in the inner corner), or remain closed beyond the 10th day, it is necessary to open them manually. The eyelids are moistened with sterile saline solution and separated. Very gently to avoid damaging or tearing the eyelids. Once open, the eyelids and the eye are washed with a sterile saline solution to eliminate any cellular waste or foreign body. In case of infection, it is necessary to remove the infectious waste material at regular intervals and to administrate antibiotic eye drops. Warm compresses placed on the eyelids will prevent them from closing together again. It is important to keep the cornea moist, especially if the infection prevents the twitching of eyelids. This can be ensured by the administration of "artificial tears" drops for human use that do not contain preservatives. If the surface of the cornea is damaged, scarring may lead to the formation of a whitish veil. Even if it is unsightly, the adult rabbit suffers at most from a small non-painful visual discomfort.
It is important to examine the other members of a litter as a newborn rabbit is rarely affected alone.
Scar on the cornea of an adult rabbit, after a traumatic lesion of the cornea when she was a few weeks old
Huge thanks to Michel Gruaz (Suisse) and C. Wayne Wright (USA) for their pictures and their permission to use them in MediRabbit.