Anatomy and physiology of eye

To understand the diseases and conditions that can affect the eye, it helps to understand basic eye anatomy. Here is a tour of the eye starting from the outside, going in through the front and working to the back. Eye Anatomy: Parts of the Eye Outside the Eyeball The eye sits in a protective bony socket called the orbit. Six The extraocular muscles are attached to the white part of the eye called the The layers of the tear film keep the front of the eye lubricated. The Front of the Eye Light is focused into the eye through the clear, dome-shaped front portion of the eye called the Behind the cornea is a fluid-filled space called the anterior chamber. The fluid is called Behind the anterior chamber is the eye’s Directly behind the pupil sits the By helping to focus light as it enters the eye, the cornea and the lens both play important roles in giving us clear vision. In fact, 70% of the eye's focusing power comes from the cornea and 30% from the lens. The Back of the Eye The vitreous cavity lies between the lens and the back of the eye. A jellylike substance called Light that is focused into the eye by the cornea and lens passes through the vitreous onto the A tiny but very specialized area of the retina called the The retina has special cells called The retina sends light as electrical impulses through the •

This chapter describes the anatomy of the eyeball, the visual pathway, and the ocular adnexae. It also provides a basic introduction to the physiology and functioning of the eye. Keywords • Optic Nerve • Retinal Pigment Epithelium • Lacrimal Gland • Ciliary Body • Central Retinal Artery These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves. Authors and Affiliations • Nottingham, UK Nicholas R. Galloway • Queen’s Medical Centre, Nottingham University and Hospital, Nottingham, UK Winfried M. K. Amoaku • St James University Hospital, Leeds, UK Peter H. Galloway • University Hospital, Royal Victoria Infirmary, Newcastle upon Tyne, UK Andrew C. Browning Cite this chapter Galloway, N.R., Amoaku, W.M.K., Galloway, P.H., Browning, A.C. (2016). Basic Anatomy and Physiology of the Eye. In: Common Eye Diseases and their Management. Springer, Cham. https://doi.org/10.1007/978-3-319-32869-0_2 Download citation • • • • DOI : https://doi.org/10.1007/978-3-319-32869-0_2 • Published : 15 July 2016 • Publisher Name : Springer, Cham • Print ISBN : 978-3-319-32867-6 • Online ISBN : 978-3-319-32869-0 • eBook Packages :

A number disorders can affect the iris; these can occur due to genetic abnormalities or other diseases. Notable among these are anisocoria (in which pupils are different sizes), impaired pupillary light reflex (where eyes are unable to adjust to light), as well as a range of other conditions, such as glaucoma, Horner syndrome, Holmes-Adie syndrome, as well as a number of others. Anatomy The iris is a circular, colored structure that sits in front of the lens within the coronal plane towards the front of the eye. Unbound in its middle to allow the pupil to change size, this structure is connected to the ciliary body—the part of the eye that produces the eye’s fluid (aqueous humor) and regulates contraction and constriction of the iris. It splits the space between the cornea and lens into anterior and posterior chambers. The former of these is bound by the cornea, while the latter connects with the ciliary bodies, zonules (a small anatomic band that holds the lens in place), and lens. Both chambers are filled with aqueous humor. Anatomical Variations The most common variation seen in iris anatomy is a condition called aniridia, in which the iris is incomplete or absent. Usually affecting both eyes at once, this congenital defect can be the result of either injury or mutations to the PAX6 gene. This then leads to a range of symptoms, including low visual acuity, degeneration of the macular and optic nerves (associated with processing visual information), cataracts (cloudy are...

Within the orbit, the eye is suspended by six extraocular muscles (four rectus muscles and two oblique muscles), suspensory ligaments, and surrounding orbital fat (Fig. 8-1). A tug-of-war exists between the rectus and oblique muscles. The four rectus muscles insert anterior to the equator, and pull the eye posteriorly, while the two oblique muscles insert posterior to the equator providing anterior counterforces. Posterior orbital fat also pushes the eye forward. If rectus muscle tension increases, the eye will be pulled back causing enophthalmos and lid fissure narrowing. Simultaneous cocontraction of the horizontal rectus muscles in Duane’s syndrome, for example, can cause significant lid fissure narrowing and enophthalmos. In contrast, decreased rectus muscle tone causes proptosis and lid fissure widening. Conditions such as muscle palsies or a detached rectus muscle allow the eye to move forward and result in lid fissure widening. Rectus muscle tightening procedures such as resections tend to cause lid fissure narrowing whereas loosening procedures such as rectus recessions induce lid fissure widening. When the eye is looking straight ahead with the visual axis parallel to the sagittal plane of the head, the eye is in primary position. The vertical rectus muscles follow the orbits and diverge from the central sagittal plane of the head by 23°. Thus, the visual axis in primary position is 23° nasal to the muscle axis of the vertical rectus muscles (Fig. 8-2). This discr...

The eye is a unique organ, from an anatomical and physiological point of view, in that it contains several highly different structures with specific physiological functions. This chapter provides a condensed general view of the anatomy and physiology of the eye much from the perspective of ocular drug delivery. The anterior segment of the eye comprises the cornea, conjunctiva, iris, ciliary body, the anterior and posterior chambers, and the lens. The cornea is the anteriormost transparent membrane of the eye continuing posteriorly as the sclera. The corneal epithelium contains large amounts of acetylcholine and choline esterases. The corneal endothelium is a single dell layer facing the anterior chamber. The conjunctiva can be regarded as a mucous membrane covering the inner surface of the eyelids and the visible part of the sclera. The eyelids consist of four main layers: the skin, the muscle layer, a layer of fibrous tissue or the tarsus, and the conjunctiva.