The outer coat consists of the sclera and the cornea; their junction is called the limbus. SCLERA This is white, opaque, and constitutes the posterior ?ve-sixths of the outer coat. It is made of dense ?brous tissue. The sclera is visible anteriorly, between the eyelids, as the ‘white of the eye’. Posteriorly and anteriorly it is covered by Tenons capsule, which in turn is covered by transparent conjunctiva. There is a hole in the sclera through which nerve ?bres from the retina leave the eye in the optic nerve. Other smaller nerve ?bres and blood vessels also pass through the sclera at di?erent points. CORNEA This constitutes the transparent, colourless anterior one-sixth of the eye. It is transparent in order to allow light into the eye and is more steeply curved than the sclera. Viewed from in front, the cornea is roughly circular. Most of the focusing power of the eye is provided by the cornea (the lens acts as the ‘?ne adjustment’). It has an outer epithelium, a central stroma and an inner endothelium. The cornea is supplied with very ?ne nerve ?bres which make it exquisitely sensitive to pain. The central cornea has no blood supply – it relies mainly on aqueous humour for nutrition. Blood vessels and large nerve ?bres in the cornea would prevent light from entering the eye. LIMBUS is the junction between cornea and sclera. It contains the trabecular meshwork, a sieve-like structure through which aqueous humour leaves the eye.
The middle coat (uveal tract) consists of the choroid, ciliary body and iris. CHOROID A highly vascular sheet of tissue lining the posterior two-thirds of the sclera. The network of vessels provides the blood supply for the outer half of the retina. The blood supply of the choroid is derived from numerous ciliary vessels which pierce the sclera in front and behind. CILIARY BODY A ring of tissue extending 6 mm back from the anterior limitation of the sclera. The various muscles of the ciliary body by their contractions and relaxations are responsible for changing the shape of the lens during ACCOMMODATION. The ciliary body is lined by cells that secrete aqueous humour. Posteriorly, the ciliary body is continuous with the choroid; anteriorly it is continuous with the iris. IRIS A ?attened muscular diaphragm that is attached at its periphery to the ciliary body, and has a round central opening – the pupil. By contraction and relaxation of the muscles of the iris, the pupil can be dilated or constricted (dilated in the dark or when aroused; constricted in bright light and for close work). The iris forms a partial division between the anterior chamber and the posterior chamber of the eye. It lies in front of the lens and forms the back wall of the anterior chamber. The iris is visible from in front, through the transparent cornea, as the ‘coloured part of the eye’. The amount and distribution of iris pigment determine the colour of the iris. The pupil is merely a hole in the centre of the iris and appears black.
The inner layer The retina is a multilayered tissue (ten layers in all) which extends from the edges of the optic nerve to line the inner surface of the choroid up to the junction of ciliary body and choroid. Here the true retina ends at the ora serrata. The retina contains light-sensitive cells of two types: (i) cones – cells that operate at high and medium levels of illumination; they subserve ?ne discrimination of vision and colour vision; (ii) rods – cells that function best at low light intensity and subserve black-and-white vision.
The retina contains about 6 million cones and about 100 million rods. Information from them is conveyed by the nerve ?bres which are in the inner part of the retina, and leave the eye in the optic nerve. There are no photoreceptors at the optic disc (the point where the optic nerve leaves the eye) and therefore there is no light perception from this small area. The optic disc thus produces a physiological blind spot in the visual ?eld.
The retina can be subdivided into several areas: PERIPHERAL RETINA contains mainly rods and a few scattered cones. Visual acuity from this area is fairly coarse. MACULA LUTEA So-called because histologically it looks like a yellow spot. It occupies an area 4·5 mm in diameter lateral to the optic disc. This area of specialised retina can produce a high level of visual acuity. Cones are abundant here but there are few rods. FOVEA CENTRALIS A small central depression at the centre of the macula. Here the cones are tightly packed; rods are absent. It is responsible for the highest levels of visual acuity.
The chambers of the eye There are three: the anterior and posterior chambers, and the vitreous cavity. ANTERIOR CHAMBER Limited in front by the inner surface of the cornea, behind by the iris and pupil. It contains a transparent clear watery ?uid, the aqueous humour. This is constantly being produced by cells of the ciliary body and constantly drained away through the trabecular meshwork. The trabecular meshwork lies in the angle between the iris and inner surface of the cornea. POSTERIOR CHAMBER A narrow space between the iris and pupil in front and the lens behind. It too contains aqueous humour in transit from the ciliary epithelium to the anterior chamber, via the pupil. VITREOUS CAVITY The largest cavity of the eye. In front it is bounded by the lens and behind by the retina. It contains vitreous humour.
Lens Transparent, elastic and biconvex in cross-section, it lies behind the iris and in front of the vitreous cavity. Viewed from the front it is roughly circular and about 10 mm in diameter. The diameter and thickness of the lens vary with its accommodative state. The lens consists of: CAPSULE A thin transparent membrane surrounding the cortex and nucleus. CORTEX This comprises newly made lens ?bres that are relatively soft. It separates the capsule on the outside from the nucleus at the centre of the lens. NUCLEUS The dense central area of old lens ?bres that have become compacted by new lens ?bres laid down over them. ZONULE Numerous radially arranged ?bres attached between the ciliary body and the lens around its circumference. Tension in these zonular ?bres can be adjusted by the muscles of the ciliary body, thus changing the shape of the lens and altering its power of accommodation. VITREOUS HUMOUR A transparent jelly-like structure made up of a network of collagen ?bres suspended in a viscid ?uid. Its shape conforms to that of the vitreous cavity within which it is contained: that is, it is spherical except for a shallow concave depression on its anterior surface. The lens lies in this depression.
Eyelids These are multilayered curtains of tissue whose functions include spreading of the tear ?lm over the front of the eye to prevent desiccation; protection from injury or external irritation; and to some extent the control of light entering the eye. Each eye has an upper and lower lid which form an elliptical opening (the palpebral ?ssure) when the eyes are open. The lids meet at the medial canthus and lateral canthus respectively. The inner medial canthus is ?xed; the lateral canthus more mobile. An epicanthus is a fold of skin which covers the medial canthus in oriental races.
Each lid consists of several layers. From front to back they are: very thin skin; a sheet of muscle (orbicularis oculi, whose ?bres are concentric around the palpebral ?ssure and which produce closure of the eyelids); the orbital septum (modi?ed near the lid margin to form the tarsal plates); and ?nally, lining the back surface of the lid, the conjunctiva (known here as tarsal conjunctiva). At the free margin of each lid are the eyelashes, the openings of tear glands which lie within the lid, and the lacrimal punctum. Toward the medial edge of each lid is an elevation known as the papilla: the lacrimal punctum opens into this papilla. The punctum forms the open end of the cannaliculus, part of the tear-drainage mechanism.
Orbit The bony cavity within which the eye is held. The orbits lie one on either side of the nose, on the front of the skull. They a?ord considerable protection for the eye. Each is roughly pyramidal in shape, with the apex pointing backwards and the base forming the open anterior part of the orbit. The bone of the anterior orbital margin is thickened to protect the eye from injury. There are various openings into the posterior part of the orbit – namely the optic canal, which allows the optic nerve to leave the orbit en route for the brain, and the superior orbital and inferior orbital ?ssures, which allow passage of nerves and blood vessels to and from the orbit. The most important structures holding the eye within the orbit are the extra-ocular muscles, a suspensory ligament of connective tissue that forms a hammock on which the eye rests and which is slung between the medial and lateral walls of the orbit. Finally, the orbital septum, a sheet of connective tissue extending from the anterior margin of the orbit into the lids, helps keep the eye in place. A pad of fat ?lls in the orbit behind the eye and acts as a cushion for the eye.
Conjunctiva A transparent mucous membrane that extends from the limbus over the anterior sclera or ‘white of the eye’. This is the bulbar conjunctiva. The conjunctiva does not cover the cornea. Conjunctiva passes from the eye on to the inner surface of the eyelid at the fornices and is continuous with the tarsal conjunctiva. The semilunar fold is the vertical crescent of conjunctiva at the medial aspect of the palpebral ?ssure. The caruncle is a piece of modi?ed skin just within the inner canthus.
Eye muscles The extra-ocular muscles. There are six in all, the four rectus muscles (superior, inferior, medial and lateral rectus muscles) and two oblique muscles (superior and inferior oblique muscles). The muscles are attached at various points between the bony orbit and the eyeball. By their combined action they move the eye in horizontal and vertical gaze. They also produce torsional movement of the eye (i.e. clockwise or anticlockwise movements when viewed from the front).
Lacrimal apparatus There are two components: a tear-production system, namely the lacrimal gland and accessory lacrimal glands; and a drainage system.
Tears keep the front of the eye moist; they also contain nutrients and various components to protect the eye from infection. Crying results from excess tear production. The drainage system cannot cope with the excess and therefore tears over?ow on to the face. Newborn babies do not produce tears for the ?rst three months of life. LACRIMAL GLAND Located below a small depression in the bony roof of the orbit. Numerous tear ducts open from it into predominantly the upper lid. Accessory lacrimal glands are found in the conjunctiva and within the eyelids: the former open directly on to the surface of the conjunctiva; the latter on to the eyelid margin. LACRIMAL DRAINAGE SYSTEM This consists of: PUNCTUM An elevated opening toward the medial aspect of each lid. Each punctum opens into a canaliculus. CANALICULUS A ?ne tube-like structure run-ning within the lid, parallel to the lid margin. The canaliculi from upper and lower lid join to form a common canaliculus which opens into the lacrimal sac. LACRIMAL SAC A small sac on the side of the nose which opens into the nasolacrimal duct. During blinking, the sac sucks tears into itself from the canaliculus. Tears then drain by gravity down the nasolacrimal duct. NASOLACRIMAL DUCT A tubular structure which runs down through the wall of the nose and opens into the nasal cavity.
Visual pathway Light stimulates the rods and cones of the retina. Electrochemical messages are then passed to nerve ?bres in the retina and then via the optic nerve to the optic chiasm. Here information from the temporal (outer) half of each retina continues to the same side of the brain. Information from the nasal (inner) half of each retina crosses to the other side within the optic chiasm. The rearranged nerve ?bres then pass through the optic tract to the lateral geniculate body, then the optic radiation to reach the visual cortex in the occipital lobe of the brain.... eye
For a diagnosis of PVS to be made, the state should have continued for more than a prede?ned period, usually one month. Half of patients die within 2–6 months, but some can survive for longer with arti?cial feeding. To assess a person’s level of consciousness, a numerical marking system rated according to various functions – eye opening, motor and verbal responses – has been established called the GLASGOW COMA SCALE.
The ETHICS of keeping patients alive with arti?cial support are controversial. In the UK, a legal ruling is usually needed for arti?cial support to be withdrawn after a diagnosis of PVS has been made. The chances of regaining consciousness after one year are slim and, even if patients do recover, they are usually left with severe neurological disability.
PVS must be distinguished from conditions which appear similar. These include the ‘LOCKED-IN SYNDROME’ which is the result of damage to the brain stem (see BRAIN). Patients with this syndrome are conscious but unable to speak or move except for certain eye movements and blinking. The psychiatric state of CATATONIA is another condition in which the patient retains consciousness and will usually recover.... persistent vegetative state (pvs)
Symptoms: blinking, watering, acute discomfort. Sensation of grit in the eye does not always imply foreign body, but symptoms of conjunctivitis or keratitis. Automatic blinking is sometimes enough to clear offending object.
Treatment. External. Evert lid and remove. Swab out with dilute Witch Hazel on cotton wool. Inject one drop Castor oil, (also good for scratched cornea), Aloe Vera gel or juice. Fenugreek seed puree. Juice of Houseleek and dairy cream.
Difficult case. Removal of particles of iron or dust, apply mucilage of Slippery Elm powder to eye – patient lying on his back, a second person injecting it into corner of eye, the patient moving eye in opposite direction. Safe and healing. Clean eye and bathe with warm milk.
Referral to consultant ophthalmologist. ... eyes – foreign body
Added to the above are:– muscular rigidity, loss of reflexes, drooling – escape of saliva from the mouth. Muscles of the face are stiff giving a fixed expression, the back presents a bowed posture. The skin is excessively greasy and the patient is unable to express emotional feelings. Loss of blinking. Pin- rolling movement of thumb and forefinger.
Causes: degeneration of groups of nerve cells deep within the brain which causes a lack of neurotransmitting chemical, dopamine. Chemicals such as sulphur used by agriculture, drugs and the food industry are suspected. Researchers have found an increase in the disease in patients born during influenza pandemics.
Treatment. While cure is not possible, a patient may be better able to combat the condition with the help of agents that strengthen the brain and nervous system.
Tea. Equal parts: Valerian, Passion flower, Mistletoe. 1 heaped teaspoon to each cup water; bring to boil; simmer 1 minute; dose: half-1 cup 2-3 times daily.
Gotu Kola tea. (CNS stimulant).
Tablets/capsules. Black Cohosh, Cramp bark, Ginseng, Prickly Ash, Valerian.
Formula. Ginkgo 2; Black Cohosh 1; Motherwort 2; Ginger 1. Mix. Dose. Powders: 500mg (two 00 capsules or one-third teaspoon). Liquid extracts: 1 teaspoon. Tinctures: 1-3 teaspoons in water or honey. Fava Bean Tea.
Case report. Two patients unresponsive to Levodopa treatment reported improvement following meals of fresh broad beans. (Vicia faba) The beans contain levodopa in large amounts. (Parkinson Disease Update Vol 8, No 66, p186, Medical Publications, PO Box 24622-H, Philadelphia, USA) See also: BROAD BEANS. L-DOPA.
Nacuna Pruriens. Appropriate. Essential active constituent: L-dopa. (Medicinal plants and Traditional Medicine in Africa, by Abayomi Sofowora, Pub: John Wiley)
Practitioner. To reduce tremor: Tincture Hyoscyamus BP. To reduce spasm: Tincture Belladonna BP. To arrest drooling: Tincture Stramonium BP.
Diet. It is known that people who work in manganese factories in Chile may develop Parkinson’s disease after the age of 30. Progress of the disease is arrested on leaving the factory. Two items of diet highest in manganese are wheat and liver which should be avoided, carbohydrates in place of wheat taking the form of rice and potatoes.
Supplements. Daily: B-complex, B2, B6, niacin. C 200mg to reduce side-effects of Levodopa. Vitamin E 400iu to possibly reduce rigidity, tremors and loss of balance.
Treatment of severe nerve conditions should be supervised by neurologists and practitioners whose training prepares them to recognise serious illness and to integrate herbal and supplementary intervention safely into the treatment plan.
Antioxidants. Evidence has been advanced showing how nutritional antioxidants, high doses of Vitamin C and E, can retard onset of the disease, delaying the use of Levodopa for an average of 2 and a half years. (Fahn S., High Dose Alpha-tocopherol and ascorbate in Early Parkinson’s Disease – Annals of Neurology, 32-S pp128-132 1992)
For support and advice: The Parkinson’s Disease Society, 22 Upper Woburn Place, London WC1H 0RA, UK. Send SAE. ... parkinson’s disease
Health Encyclopedia