Anatomy and physiology of the eye

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Anatomy and physiology of the eye


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Anatomy and physiology of the eye

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A 75-year-old man presents with drooping of the right eyelid and diplopia. Physical examination shows the right eye is pointing downwards and outwards. Which of the following nerves is most likely affected in this patient?  

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Our eyes allow us to visualize the world around us. They do this by converting light waves into neural signals so that our brains can process them.

The eye itself is shaped like a sphere that is elongated horizontally, as opposed to being perfectly round, and only the anterior one-sixth of the eye is visible. The rest of the eye is contained within the orbit, or eye socket, of the skull.

Now, the eye consists of three layers: the outermost fibrous layer, the middle vascular layer, and the inner neural layer.

The outer fibrous layer contains two main structures: the sclera and the cornea.

The sclera makes up the majority of the outer layer and is the white portion of the eye. It’s like a tough, fibrous covering that protects the more delicate structures within the eye and it also acts as an anchoring point for the extrinsic eye muscles to attach to.

The sclera is like a wall that’s built around the eye, that only has a tiny opening at the back to let the optic nerve through.

As the sclera approaches the anterior portion of the eye it reaches a transition point known as the corneal limbus where it becomes the cornea.

The cornea itself is a transparent, dome shaped clear layer that covers the iris and the pupil. It allows light to enter the eye, and its curved shape helps focus light on the retina in the back of the eye.

At the periphery of the cornea, there are stratified squamous epithelial cells which continually divide and regenerate the cornea, and they help to heal after a corneal injury or abrasion.

The cornea doesn’t contain blood vessels and therefore immune cells can't access the cornea. As a result, it’s one of the few parts of the body that is considered "immune privileged" since it can be transplanted without the fear of an immune response and organ rejection.


  1. "Medical Physiology" Elsevier (2016)
  2. "Physiology" Elsevier (2017)
  3. "Human Anatomy & Physiology" Pearson (2018)
  4. "Principles of Anatomy and Physiology" Wiley (2014)
  5. "Pupil shape as viewed along the horizontal visual field" Journal of Vision (2013)

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