The lamina papyracea is a smooth bone plate shaped like a leaf that is commonly known for being situated close to the ethmoid bone in the musculoskeletal system. The ethmoid bone forms the area of the skull at the roof of the nose, where it sets the nasal cavity apart from the brain. Thus the ethmoid is right between the two orbits, which contain the eyes. By extension, the lamina papyracea is also part of the orbit, which is why it is sometimes referred to as the orbital lamina.
The main purpose of this bone is to cover the middle and posterior cells of the ethmoid bone. Its location particularly provides a lateral surface for the ethmodial labyrinth, which is one of the three parts that constitute the ethmoid bone. This function is the reason why it is known by the alternate term orbital plate. Overall, the lamina papyracea forms a huge portion of the orbit's medial wall, which is the structure's middle bone.
The lamina papyracea extends to three out of the seven bones that articulate the orbit. The ethmoid bone is one of these structures. It also touches the frontal bone, which forms the forehead; and the sphenoid, a small structure that sits underneath the frontal bone and behind the ethmoid bone. This is named after its manner of construction. "Lamina" is a term used in anatomy for a thin plate or layer. "Papyracea" originates from "papyrus," a type of paper produced from the Cyperus papyrus plant.
Due to its thin nature, the lamina papyracea can easily fracture. This can be achieved during a fight, with a blow delivered to the eye. Such violent pressure causes the thin layer to push into the ethmoid bone or the maxillary sinus, which is an air-filled space in the upper jaw anatomically known as the maxilla. In fact, the lamina papyracea is the weakest part of the orbit.
When the maxillary sinus is adversely affected by such destruction, it can increase the chance of infection entering and spreading throughout the orbit, which can result in orbital cellulitis. This is a medical condition that involves acute infection of the eye's tissues, with Haemophilus influenzae, Staphylococcus aureus or Streptococcus being the main bacterial culprits. Symptoms include eyelid swelling and redness, fever, limited eye movement, and the eye bulging out of the orbit. If left untreated by antibiotics or surgery, this condition can lead to double vision and a steady decrease in visual perception.