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Eye CareAdults

Anatomy of the eyeDemonstrated by Lynn Ring, Ophthalmic Nurse Specialist,

Epsom & St Helier University Hospitals NHS Trust

©2015 Clinical Skills Limited. All rights reserved

Do not undertake or attempt any procedure unless you are, or have supervision from, a properly trained, experienced and competent person.Always first explain the procedure to the patient and obtain his/her consent, in line with the policies of your employer or educational institution

Structures of the anterior eye

A basic knowledge of anatomy is necessary to be able to examine the eyes effectively.

CorneaThe cornea is clear, to allow unobstructed passage of light, and convex, to bend and focus light rays on to the retina. It is highly sensitive, to protect the eye from intraocular invasion. The cornea has five layers. It is kept transparent by the sodium pump within the endothelial (inner) layer–when this pump breaks down, the stromal (middle) layer becomes waterlogged and loses transparency. The corneal epithelium is the only layer of the cornea to regenerate following damage. The cornea is only 0.6mm thick centrally, with 1.0mm thickness peripherally.

Crystalline lensThe lens sits in the posterior chamber, behind the iris and in front of the vitreous (posterior cavity). Like the cornea, it is a transparent structure which is biconvex and avascular. It is supported by suspensory ligaments called zonules that arise from the ciliary processes. The lens changes shape during ‘accommodation’—the action of viewing either near or distant objects. The ciliary muscles contract and relax, making the lens either spherical for near vision or elongated during distance vision. The lens grows more solid in people older than 45 years, gradually losing its ability to change shape, which affects near vision. This condition, called presbyopia, explains why spectacles are required for reading.

PupilThe iris controls the amount of light entering the eye through the pupil by causing a ring of smooth muscle fibres around the pupil to constrict in bright light; conversely, the pupil dilates in dim light by the contraction of the radial smooth muscle in the iris.

IrisThe iris is the coloured part of the eye. The iris is made up of muscle fibres that control the central aperture, which is known as the pupil.

ConjunctivaThe conjunctiva comprises: The palpebral conjunctiva, which lines the inner eyelids; The bulbar conjunctiva, which covers the entire sclera (the white of the eyeball) from the cornea back to the optic nerve; The superior and inferior fornices, where the palpebral conjunctiva gently folds back to form the bulbar conjunctiva. To allow for easy movement of the eyeball, the conjunctiva is loosely attached, especially within the fornices where it forms folds.

Anterior chamberBehind the cornea, and in front of the iris, is the anterior chamber which is filled with aqueous humour, a clear fluid produced by the ciliary body to nourish the cornea and maintain the intraocular pressure.

Sagittal section of the eye

Eye Care

Adults

Anatomy of the eye Page 2

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Do not undertake or attempt any procedure unless you are, or have supervision from, a properly trained, experienced and competent person.Always first explain the procedure to the patient and obtain his/her consent, in line with the policies of your employer or educational institution

Superior fornixThe conjunctiva folds in the fornices, forming pockets that allow for the movement of the eyeball.

ScleraAn opaque, tough outer coating of the eye that provides protection and an anchor for the external ocular muscles.

ChoroidThe vascular layer, which is responsible for most of the blood supply to the eye. This layer also assists with the drainage of aqueous humour via the uveoscleral route.

Inferior fornixThe conjunctiva folds in the fornices, forming pockets that allow for the movement of the eyeball.

Vitreous humour This is a gel-like substance that fills the posterior cavity of the eye. It is loosely attached to the retina at the ora serrata and the optic disc.

RetinaThis is the neural layer of the eye. It contains very sensitive photoreceptor cells that transmit light via the optic nerve to the visual cortex in the brain.

Suspensory ligamentsThese ligaments, called zonules, contract and relax to change the shape of the lens, to allow the eye to focus large or near objects onto the retina.

Ciliary processThe ciliary processes secrete aqueous humour which is responsible for the intraocular pressure of the eye.

Anterior chamber

Posterior chamber

There are six extraocular muscles: the lateral rectus, medial rectus, superior and inferior rectus and the superior and inferior oblique. Both eyes should work in a co-ordinated manner. In order to look right, for example, the right lateral rectus muscle contracts and the right medial rectus relaxes, while the left medial rectus contracts and lateral rectus relaxes. These muscles allow for movement that defines the limit of a person’s visual field.

Superior rectus

Inferior rectus

Superior rectus

Lateral rectus

Inferior rectus

Inferior oblique

Superior oblique

Superior oblique

Trochlea

Medial rectus

Eye movement

External appearance of the eye

Eye Care

Adults

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Do not undertake or attempt any procedure unless you are, or have supervision from, a properly trained, experienced and competent person.Always first explain the procedure to the patient and obtain his/her consent, in line with the policies of your employer or educational institution

Lower lacrimal punctumThe punctum at the medial aspect of the lower eyelid is the easiest to observe, having the appearance of a little hole, but there is also a punctum at the medial aspect of the upper lid. Through these openings, tears drain into the lacrimal duct and into the back of the throat

Upperpunctum

Plicasemilunaris

Medialcanthus

Lacrimalcaruncle

Bulbar conjunctiva

PupilIris