Eye –Anatomy, visual perception and prosthetic rehabilitation
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INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com
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The management of an anoptholmic socket requires the combined effort of ophthalmologist and maxillofacial Prosthodontist. The surgeon provide the basis for successful rehabilitation. The maxillofacial Prosthodontist provide prosthetic treatment to the best of his ability. A through knowledge of the anatomy is necessary for successful treatment. The goal of any prosthetic treatment is to return the patient to society with a normal appearance. www.indiandentalacademy.com
The orbits are pyramidal cavities, situated one on each side of the root of the nose. They provide sockets for rotatory movements of the eyeball. The long axis of the each orbit passes backwards and medially. The medial walls are parallel to each other. But the lateral walls are set at right angles to each other. The contents of the orbit are as follows
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1. Eyeball 2. Fascia: Orbital and bulbar. 3. Muscles: Extraocular muscles 4. Vessels: Ophthalmic artery, superior and inferior ophthalmic Veins and lymphatics. 5. Nerves: Optic, oculomotor, trochlear, abducent, branches of ophthalmic nerve and sympathetic nerves. 6. Lacrimal gland 7. Orbital fat. www.indiandentalacademy.com
A. ORBITAL FASCIA (PERIORBITA) It forms the periosteum of the bony orbit. Due to the loose connection to bone, it can be easily stripped. Posteriorly, it is continuous with the dura mater and with the sheath of the optic nerve. Anteriorly, it is continuous with the periosteum lining the bones around the orbital margin.
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Facial sheath of Eyeball (bulbar fascia) Tenon’s capsule: It forms a thin loose, membranous sheath around the eyeball, extending from the optic nerve to the sclerocorneal junction. The eye can freely move within this sheath The sheath is pierced: (a) extraocular muscles (b) by the ciliary vessels and nerves around the entrance of the optic nerve.
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The sheath gives off a number of expansions. (a) A tubular sheath covers each orbital muscle (b) The medial check ligament is a strong triangular expansion from the sheath of the medial rectus muscle: it is attached to the lacrimal bone (c) The lateral check ligament is a strong triangular expansion from the sheath of the lateral rectus muscle: It is attached to the zygomatic bone. www.indiandentalacademy.com
The lower part of the tenon’s capsule is thickened and is named the suspensory ligament of the eye or the suspensory ligament of Lockwood. It is slung like a hammock below the eyeÂball. It is formed by union of the margins of the sheaths of the inferior rectus and the inferior oblique muscles with the medial and lateral check ligaments. www.indiandentalacademy.com
EXTRAOCULAR MUSCLES Voluntary muscles 1. Four recti: (a) Superior rectus (b) Inferior rectus (c) Medial rectus (d) Lateral rectus. 2. Two obliqui: (a) Superior oblique and (b) Inferior oblique 3. Levator palpebrae superioris www.indiandentalacademy.com
Involuntary muscles 1. superior tarsal muscle 2. Inferior tarsal muscle 3. orbitalis
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RECTI origin The four recti arise from a common annular ring (tendinous ring). This ring is attached to the orbital surface of the apex of the orbit. It encloses the optic canal and the middle part of the superior orbital fissure. The lateral rectus has an additional small tendinous head which arises from the orbital surface of the greater wing of the sphenoid bone lateral to the tendinous ring. www.indiandentalacademy.com
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Insertion The recti are inserted into the sclera, a little posterior to the limbus. The average distances of the insertions from the cornea is : superior 足 7.7 mm inferior 足 6.5 mm medial 足 5.5 mm lateral 足 6.9 mm
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Nerve supply The lateral rectus is supplied by the 6th cranial (abducent) nerve. superior recti, inferior recti, and medial recti are supplied by 3th cranial (oculomotor) nerve Action Superior rectus: upward rotation, Medial rotation. www.indiandentalacademy.com
Inferior rectus: Downward rotation, Medial rotation. Medial rectus: Medial rotation. Lateral rectus: Lateral rotation
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OBLIQUE MUSCLE Origin The superior oblique arises from the body of the sphenoid, superomedial to the optic canal The inferior oblique arises from the orbital surface of the maxilla, lateral to the lacrimal groove. The muscle is situated near the anterior margin of the orbit.
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Insertion superior oblique is inserted into the sclera behind the equator of the eyeball, between the superior rectus and lateral rectus Inferior oblique is inserted close to the superior oblique a little below and posterior to the superior oblique
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Nerve supply Superior oblique is supplied by the 4th cranial (trochlear) nerve Inferior oblique is supplied by the 3rd cranial (oculomotor) nerve Action Superior oblique: downward rotation, Lateral rotation. Inferior oblique: Upward rotation, Lateral rotation.
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LEVATOR PALPEBRAE SUPERIORIS Origin The levator palpebrae superioris arises from the orbital surface of the lesser wing of the sphenoid bone, anterosuperior to the optic canal and to the origin of the superior rectus Insertion it is inserted into superior tarsus and into the skin of the upper eyelid
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Nerve supply Supplied by the 3th cranial (oculomotor) nerve Action Elevation of the upper eyelid
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Movements are produced by combined actions of muscles. Similar actions get added together, while opposing actions cancel each other Normally, movements of the two eyes are harmoniously coordinated. Such coordinated movement of the both eye are called conjugate ocular movements. These are usually horizontal or vertical, but oblique movement also occur
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APPLIED ANATOMY SQUINT Weakness or paralysis of a muscle causes squint or strabismus. The two eyes appear to look in different direction. when the movement is attempted in a direction produced by the paralysed muscle, one eye moves normally, but the other eye is unable to keep up with it. Hence the two eyes are directed differently NYSTAGMUS –is characterized by involuntary rhythmical oscillatory movements of the eyes, due to in coordination of the ocular muscle www.indiandentalacademy.com
THE EYEBALL The eyeball is the origin of sight. It closely resembles a camera in its structure. It is almost spherical in shape and has a diameter of about 2.5cm.It is made up of three concentric coats. The outer or fibrous coat comprises the sclera and the cornea. The middle or vascular coat (also called the uveal tract) consists of the choroid, the ciliary body and the iris. The inner or nervous coat is the retina. Light entering the eyeball passes through several refracting media. From before backwards these are the cornea, the aqueous humour, the lens and the vitreous body www.indiandentalacademy.com
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The Sclera The sclera is opaque and forms the posterior five sixths of the eyeball. It is composed of dense fibrous tissue which is firm and maintains the shape of the eyeball. The outer surface of the sclera is white and smooth. Its anterior part is covered by conjunctiva through which it can be seen as the white of the eye. The sclera is continuous anteriorly with the cornea at the sclerocorneal junction or limbus. Posteriorly it is fused with the dural sheath of the optic nerve. The sclera is almost avascular ,however the loose connective tissue between the conjunctiva and sclera is vascular www.indiandentalacademy.com
CORNEA The cornea is transparent. It replaces the sclera over the anterior one sixth of the eyeball. Its junction with the sclera is called the sclerocorneal junction or limbus. The cornea is more convex, than the sclera, but the curvature diminishes with age. It is separated from the iris by a space called the anterior chamber of the eye. The cornea is avascular and is nourished by lymph which circulates in the numerous corneal, spaces. www.indiandentalacademy.com
CHOROID It is a thin pigmented layer which separates the posterior part of the sclera from the retina. Anteriorly it ends at the ora serrata by merging with the ciliary body. Posteriorly it is perforated by the optic nerve to which it is firmly attached. The attachment to the sclera is loose, so that it can be easily stripped. The inner layer is firmly united to the retina
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CILIARY BODY This is a thickened part of the vascular tract lying just posterior to the corneal limbus. It is continuous anteriorly with the iris and posteriorly with the choroid. It suspends the lens and helps it in accommodation for near vision. The ciliary body is triangular in cross section. It is thick in front and thin behind. The scleral surface of this body contains the ciliary muscle. www.indiandentalacademy.com
The ciliary muscle is a ring of (radial and circular muscle). The radial fibres arise from a projection of sclera (scleral spur) near the limbus. The circular fibres lie within the anterior part of the radial fibres. Their contraction relaxes the suspensory ligament so that the lens becomes more convex for near vision.
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IRIS___________________ This is the anterior part of the vascular tract. It forms a circular curtain with an opening in the centre, called the pupil. By adjusting the size of the pupil it controls the amount of light entering the eye, and thus behaves like adjustable diaphragm. It isan placed vertically between the cornea and the lens, and divides the anterior segment of the eye into anterior and posterior chambers, both containing aqueous humour www.indiandentalacademy.com
Its peripheral margin is attached to the middle of the anterior surface of the ciliary body. The centre free margin rest against the lens. The colour of the iris determined by the number of pigment cells in its connective tissue. If the pigment cells are absent, the iris is blue in colour due to the diffusion of light in front of the black posterior surface. www.indiandentalacademy.com
Iris contains two sets of smooth muscles are seen: One set of well developed smooth muscles, called the constrictor pupillae is a circular band of smooth muscles surrounding the pupil. when contract, cause constriction of the pupil. The other set of smooth muscles, arranged radially are supplied by sympathetic fibers. When these muscles contract, dilatation of the pupil occurs and hence these fibers are called dilator pupillae www.indiandentalacademy.com
AQUEOUS HUMOUR This is a clear fluid which fills the space between the cornea in front and the lens behind (anterior segment). This space is divided by the iris into anterior and posterior chambers which freely communicate with each other through the pupil. Interference with the drainage of the aqueous humour results in an increase of intraocular pressure (glaucoma). This produces cupping of the optic disc and pressure atrophy of the retina causing blindness www.indiandentalacademy.com
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LENS The lens is a transparent bi足convex structure which is placed between the anterior and posterior segment of the eye. It is circular in outline and has a diameter of one cm. The central points of the anterior and posterior surfaces are called the anterior and posterior poles. The line connecting the pole constitutes the axis of the lens, while the marginal circumference is termed the equator www.indiandentalacademy.com
The posterior surface of the lens is more convex than the anterior. The anterior surface is kept flattened by the tension of the suspensory ligament. When the ligament is relaxed (by contraction of the ciliary muscle) the anterior surface becomes more convex due to elasticity of the lens substance. The suspensory ligament of the lens retains the lens In position and its tension keeps the anterior surface of the lens flattened. www.indiandentalacademy.com
VITREOUS BODY It is a colorless, jelly足like transparent mass which fills the posterior segment (posterior 4/5) of the eyeball. It is enclosed in a delicate homogeneous hyaloid membrane. The anterior surface of the vitreous body is indented by the lens and the ciliary processes www.indiandentalacademy.com
RETINA This is the thin, delicate inner layer of the eyeball. It is continuous posteriorly with the optic nerve. The outer surface of the retina is attached to the choroid, while the inner surface is in contact with the hyaloid membrane (of the vitreous). Opposite the entrance of the optic nerve there is a circular area known as the optic disc. It is 1.5 mm in diameter. The optic part of the retina contains nervous tissue and is sensitive to light. It extends from the optic disc to the posterior end of the ciliary body. The anterior margin of the optic part of the retina forms a wavy line called the ora serrata www.indiandentalacademy.com
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The depressed area of the optic disc is called the physiological cup. It contains no rods or cones and is therefore insensitive to light physiological blind spot. At the posterior pole of the eye (3 mm lateral to the optic disc) there is another depression of similar size, called the macula lutea. It is avascular and yellow in colour. The centre of the macula is further depressed to form the fovea centralis. This is the thinnest part of the retina. It contains cones only, and is the site of maximum acuity of vision. www.indiandentalacademy.com
LAYERS OF THE RETINA The functional components of the retina arranged in layers from the outside to the inside as follows:
1) Pigment layer 2) Layer of rods and cones projecting into the pigment 3) Outer limiting membrane 4) Outer nuclear layer containing the cell bodies of the rods and cones 5) Outer plexiform layer 6) Inner nuclear layer 7) Inner plexiform layer 8) Ganglionic layer 9) Layer of optic nerve fibers 10) Inner limiting membrane www.indiandentalacademy.com
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OPTICS OF THE EYE Refractive index Refractive index of a transparent substance is the ratio of the velocity of light in air to the velocity of light while traveling through the substance. The refractive index of air is presumed as 1.
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FOCAL LENGTH OF A LENS When light rays pass from one medium to another medium it bends or refracts. When parallel light rays passes through each point of a convex lens it will converge to a single point which is called the Focal Point. The distance beyond a convex lens at which parallel light ray converge to a common focal point is called the Focal Length of the Lens Focal Point
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ACCOMODATION If while looking at an object, situated at infinity, the gaze be transferred to an object near at hand, some readjustment of the power of the crystalline lens will have to occur, otherwise the image will fall behind the retina. This readjustment of the power of the crystalline lens are called accomodation. During accomodation, the ciliary muscles contract, this cause relaxation of the suspensory ligament and as a result of this relaxation, the anterior surface of the lens bulges and its power increases. By this mechanism, the image is focused nearer so that it is on the retina now. www.indiandentalacademy.com
FORMATION OF AN IMAGE When a light ray passes through the center of a convex lens, it will not be refracted in either direction. Any object in front of the lens is in reality a mosaic of point source of light. Each point source of light come to a point focus on the opposite side of the lens directly in line with point source and the center of the lens. This image is upside down with respect to the original object and the two lateral sides of the image are reversed. This is the method by which the lens focuses images on to the retina. www.indiandentalacademy.com
FOCAL POINTS
POINT SOURCE
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After light passes through the lens system of the eye and then through the vitreous humor, it enters the retina from the inside that is, it passes first through the ganglion cells and then through the plexiform layers, nuclear layer, and limiting membranes before it finally reaches the layer of rods and cones located all the way on the outer side of the retina. This distance is a thickness of several hundred micrometers. visual acuity is decreased by this passage through such nonhomogeneous tissue. However, in the central region of the retina, the inside layers are pulled aside for prevention of this loss of acuity. www.indiandentalacademy.com
RODS AND CONES There are about 120 million rods and 6 million cones in each eye. The rods and cones are the light receptors of the eye. The rods contain a pigment called visual purple. They can respond to dim light (scotopic vision). The periphery of the retina contains only rods, but the fovea has none at all. The cones respond only to bright light (photopic vision) and are sensitive to colour. The fovea centralis has only cones. Their number diminishes towards the periphery of the retina. www.indiandentalacademy.com
Functional segment of rods and cones (1) the outer segment, (2) the inner segment, (3) the nucleus; and (4) the synaptic body. In the outer segment, the light足sensitive photochemical is found. In the case of the rods, this is rhodopsin, and in the cones, it is one of three "color" photochemicals, usually called color pigments. In the cones, each of the discs is actually an infolded shelf of cell membrane. www.indiandentalacademy.com
Functional segment of rods and cones (1) the outer segment, (2) the inner segment, (3) the nucleus; and (4) the synaptic body.
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However, In the rod, the discs separate from the membrane and are flat sacs lying totally inside the cell. There are as many as 1000 discs in each rod or cone. Color pigments are incorporated into the membrane of the discs in the form of transmembrane proteins. The concentrations of these photosensitive pigments in the discs constitute about 40 per cent of the entire mass of the outer segment. The inner segment contains the cytoplasm of the cell with the cytoplasmic organelles and the mitochondria, which provide the energy for the function of the photoreceptors. The synaptic body is the portion of the rod or cone that connect with the neuronal cells www.indiandentalacademy.com
RHODOPSIN AND ITS DECOMPOSITION BY LIGHT ENERGY Rhodopsin is a combination of the protein scotopsin and the carotenoid pigment retinal . The retinal is a particular type called 11足cis retinal. This cis form of the retinal is important because only this form can bind with scotopsin to synthesize rhodopsin. When light energy is absorbed by rhodopsin, the rhodopsin begins within trillionths of a second to decompose to www.indiandentalacademy.com
bathorhodopsin, which is a partially split combination of the all足trans retinal and scotopsin. Bathorhodopsin itself is an extremely unstable compound and decays in nanoseconds to lumirhodopsin. This then decays in microseconds to metarhodopsin I, then in about a millisecond to metarhodopsin II, and finally, much more slowly (in seconds) into the completely split products: scotopsin and all足trans retinal. It is the metarhodopsin II, also called activated rhodopsin, that excites electrical changes in the rods that then transmit the visual image into the central nervous system www.indiandentalacademy.com
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PHOTOCHEMISTRY OF CONES Cones have almost exactly the same chemical composition as that of rhodopsin in the rods. The only difference is that the protein portions, the opsins, called photopsins in the cones. The retinal portion of all the visual pigments is exactly the same in the cones as in the rods. The color足sensitive pigments of the cones, therefore, are combinations of retinal and photopsins. The color pigments are called blue足sensitive pigment, green足sensitive pigment, and red足 sensitive pigment. www.indiandentalacademy.com
COLOR VISION Color vision is possible because of the presence of cones, a normal person can see all wave lengths between violet to red. There are three types of cones, (i) red sensitive, (ii) green sensitive and (iii) blue sensitive cones. Proper admixture of the three primary colors can produce all varieties of color. When they are of equal proportion, the mixture has a white color. Black color means absence of color. www.indiandentalacademy.com
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An orange monochromatic light with a wavelength of 580 nanometers stimulates the red cones to a stimulus value of about 99 (99 per cent of the peak stimulation at optimum wavelength) It stimulates the green cones to a stimulus value of about 42 but the blue cones not at all. Thus, the ratios of stimulation of the three types of cones in this instance are 99: 42: O. The nervous system interprets this set of ratios as the sensation of orange. www.indiandentalacademy.com
Dark Adaptation When someone enters a dark room from a brightly lit outdoor, at first he sees almost nothing but gradually the person begins to see more, ie, he becomes adapted to the dark. This is dark adaptation . As soon as one enters a dark room from the bright outdoor visibility is very poor and the threshold of stimulation of the photoreceptors is very high. The low intensity light that is available in the dark room fails to stimulate the photo receptors. At around 40th minute, the dark adaptation is almost complete www.indiandentalacademy.com
Light Adaptation When someone is exposed to a very strong light then he, (specially if he was in dark room immediately before) cannot see anything. Thereafter, the ability to see increases and the person is stated to be developing light adaptation. Light adaptation is complete within about 5 minutes. During light adaptation the threshold rises rapidly.
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VISUAL PATHWAY___________________________ The impulses from the axons of the ganglion cells are collected by the optic nerve, and they make exit from the eye through the optic disc and continue to proceed to their destination as optic nerve. Fibers of the each optic nerve partially decussate at optic chiasm; the fibers from the nasal half of each retina cross to the opposite side but those of the temporal halves do not cross. After decussation, what is formed is called optic tract. Each optic tract contains fibers from nasal half of the opposite side and fibers from the temporal half of the same side. www.indiandentalacademy.com
The fibers of each optic tract synapse in the dorsal lateral geniculate nucleus, and from here, the geniculocalcarine fibers pass by way of the optic radiation (or geniculocalcarine tract) to the primary visual cortex in the calcarine area of the occipital lobe called (Brodmann's) area 17). The neighbouring areas, area 18 and area 19 are visual association areas. This area is concerned with understanding and interpreting what one is seeing www.indiandentalacademy.com
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Common Defects of the Image-Forming Mechanism Hyperopia In some individuals, the eyeball is shorter than normal and the parallel rays of light are brought to a focus behind the retina. This abnormality is called hyperopia or farsightedness. The defect can be corrected by using glasses with convex lenses, which aid the refractive power of the eye in shortening the focal distance.
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Myopia In myopia (nearsightedness), the anteroposterior diameter of the eyeball is too long. This defect can be corrected by glasses with biconcave lenses, which make parallel light rays diverge slightly before they strike the eye
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Astigmatism Astigmatism is a common condition in which the curvature of the cornea is not uniform. When the curvature in one meridian is different from that in others, light rays in that meridian are refracted to a different focus, so that part of the retinal image is blurred. Astigmatism can usually be corrected with cylindrical lenses placed in such a way that they equalize the refraction in all meridians. www.indiandentalacademy.com
Presbyopia Presbyopia is due to increasing hardness of the lens, with a resulting loss of accommodation. The nearest point to the eye at which an object can be brought into clear focus by accommodation is called the near point of vision. The near point recedes throughout life, slowly at first and then rapidly with advancing age, from approximately 9 cm at age 10 to approximately 83 cm at age 60. www.indiandentalacademy.com
CATARACTS A cataract is a cloudy or opaque area or areas in the lens. In cataract formation, the protein in some of the lens fibres become denatured. Later these proteins coagulate to form opaque areas in the place of normal transparent protein fibres. If there is complete impairment of vision, the condition can be corrected by surgical removal of lens. www.indiandentalacademy.com
Prosthetic rehabilitation The fabrication of eyes is not limited to this modern age. They have been used for centuries, with the earliest know examples found in mummies dating back to the fourth dynasty in Egypt (1613足2494 BC). Ambrose pare, a French dentist, is considered to be the pioneer of modern artificial eyes. He fabricated eye made of glasses and porcelain. Naval dental school (1940), tested the use of acrylic resin in fabricating a custom ocular prosthesis. Unlike a glass eye, an acrylic eye was easy to fit and adjust, unbreakable, inert to ocular fluids, esthetical good, longer lasting and easier to fabricate www.indiandentalacademy.com
Surgical procedures in the removal of an eye are classified into three categories Evisceration足 Removal of the contents of the globe, but leaving the sclera and sometimes the cornea in place. Because the extra足ocular muscles are left intact, good mobility of the prosthesis is usually possible Enucleation- Removal of the eyeball itself Exenteration- Removal of the entire contents of the orbit, including the extraocular muscles
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Ocular implants are classified as 1. Integrated 2. Semi 足 integrated 3. Non足integrated and 1. Buried or 2. Non足buried Integrated implants are designed to improve prosthesis motility by coupling to the overlying prosthesis. Implants is exposed through the conjunctiva to be directly coupled to the prosthesis with a peg, pin, screw or other method. www.indiandentalacademy.com
Semi-integrated ocular implants consist of an acrylic resin implant with 4 protruding mounds on the anterior surface. These acrylic resin mounds on the implant protrude against the encapsulating tissue. When an ocular prosthesis is made, a counter contour to the implant is formed on the posterior surface of the prosthesis. Nonintegrated implant This is done by placing a hollow or solid acrylic resin sphere ranging from 10 to 22mm in diameter. www.indiandentalacademy.com
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Stock tray impression technique An impression is made of the ocular defect using a disposable syringe, stock ocular trays and irreversible hydrocolloid. During the procedure ,the patient should be seated in an upright position with the head supported by the headrest. This position allows the natural positioning of the palpebrae and surrounding tissue relative to the force of gravity. The tray should be placed into the defect to determine the proper orientation and fit without overextension. The tray is then removed and the impression material is loaded in the syringe and sufficient material is ejected to fill the concavity of the tray. The tray is reinserted and sufficient www.indiandentalacademy.com
material is injected to elevate the lid contours similar to the normal side. once filled the patient is directed to move their eyes both up and done. After the impression sets the assembly is removed and examined for defects and voids.
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External tray impression technique Alginate impression material is expressed into the defect using a disposable syringe. Next a perforated acrylic resin tray is loaded and placed over the defect. The impression is first recovered from the lower, shallower sulcus first, then rotated out of the deeper, upper sulcus. The impression is boxed and poured in the dental stone up to the height of contour of the impression. A separating agent is placed and the reminder of the impression is poured www.indiandentalacademy.com
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Custom Ocular Prosthesis Fabrication wax pattern The melted wax is then poured through the funnel shaped hole and into the assembled mold. Soaking the mold in water for a few minutes prior to filling it with molten wax will prevent the wax from adhering to the stone. After the wax has cooled, the wax pattern is recovered. Once the wax pattern has been smoothed and polished, it is ready to be tried in the eye socket. To insert the wax pattern, the upper lid is lifted, and the superior edge of the pattern is placed behind the lid and gently pushed upward. While drawing the lower lid down, the inferior border of the pattern is seated in the inferior fornix, and then the lower lid is released. The eye contours are checked. www.indiandentalacademy.com
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Paper Iris Disk Technique When the wax pattern is determined to be appropriate, it is flasked and processed in scleral resin. The scleral blank is then finished, and it is polished using pumice and acrylic resin polish
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The scleral blank is tried in and the middle of the pupil is marked while the patient gazes directly at the clinician. The size of the iris is measured using a millimeter measurement gauge or optical scale. The outline of the iris is then marked on the scleral blank using Carmen red ink.
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This ink will transfer to the investing stone, facilitating the appropriate placement of the corneal prominence. The blank is tried in again to verify the location and size of the iris. The location of the iris will transfer to the investment and a scraper can then be used to create the corneal prominence of the prosthesis in the investment.
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A disk of ordinary artist's watercolor paper is punched out using a die. The size selected should be 1 mm smaller than the measured size of the iris. This will allow the iris to appear to be the appropriate size because the corneal prominence will cause a slight magnification of the iris disk. A good selection of colors for this purpose includes ultra足marine blue, yellow ochre, burnt sienna, burnt umber, yellow oxide, titanium white. Colors should be mixed and reapplied in a layering fashion to mimic the colored striations in the patient's iris. www.indiandentalacademy.com
IRIS ANATOMY
Pupil
Medial canthus
Limbus
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Begin by painting the darkest color, the area toward the outer edge of the iris ring (limbus). The color of the limbus varies from eye to eye, but it usually is a combination of gray and iris body color. In the natural eye, it can appear as a shadow from the overlapping sclera, covering the edge of the cornea. Next the collarette is painted. It is usually a lighter color than the body of the iris A black spot should be painted in the center of the disk to represent the pupil. www.indiandentalacademy.com
The diameter should mimic the natural pupil under indoor light conditions. This will make size appear relatively appropriate under most conditions. After the paint has dried, a drop of water is applied to create the magnification of the corneal prominence and the color matched
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Using a flat足end bur, a flat surface is prepared in the scleral blank for the iris painting. A sprue wax is luted to the prepared flat surface and tried in. The orientation of the surface is adjusted until the sprue points directly at the observer while the patient looks directly into the observer's eye. This will ensure that the prosthesis and the natural eye will have the same gaze
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Using a large abrasive stone, the entire anterior surface of the scleral blank is reduced at least 1 mm. The remainder of the prosthesis is then painted to match the sclera of the natural eye. Fine red embroidery threads are placed on the scleral painting to mimic the blood vessels of the patient's natural eye. The entire scleral portion is then coated with monomer polymer syrup to keep the blood足vessel fibers in place and allowed to set.
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Once the monomer足polymer syrup has set, the scleral blank is replaced into the flask, and the iris painting is placed on the flat section. Clear ocular acrylic resin is mixed and placed into the mold space and the flask trial packed. Once trial packed, the flash is removed and the location of the painting verified to ensure that it has not moved during trial packing.
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Black Iris Disk Technique The natural eye is observed closely and the diameter of the iris is estimated using a millimeter measurement gauge or optical scale. Ocular discs, which are used in the iris painting, are available in half足 mm sized increments, ranging from 11 mm to 13 mm. They come in black or clear, and either with or without pupil apertures. Clear corneal buttons are available in the same sizes as the discs. The buttons can also be purchased with pupils of various sizes already in place. www.indiandentalacademy.com
The technique employed in painting the disk produces a three足dimensional effect. oil pigments are employed in this technique but are mixed with a monomer足polymer syrup during the painting process. This mixing procedure provides some degree of translucency in the iris painting and permits rapid drying of the pigments. The basic eye color or background color is observed along with the limbus color. The background color is applied to the disk first, using brush strokes from the center toward the periphery. www.indiandentalacademy.com
After the background color is applied and dried, a coat of the clear syrup is applied and allowed to dry. Characteristic striations are applied over the clear layer and allowed to dry. A second clear layer is then applied and further characterization accomplished. After the second layer is dried, the limbus color is matched around the periphery of the disk and a third clear layer applied. The color around the pupil is applied over the last clear layer and the final color evaluated with the water interface. After a satisfactory color match has been obtained, a final clear layer is applied and allowed to stand for 15 minutes. www.indiandentalacademy.com
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A single droplet of the monomer足polymer syrup is then placed in the center of the iris disk and the lens button is gently placed and centered. The positioning of the iris足lens assembly on the wax scleral pattern is the most important phase in fabrication of the prosthesis. Fix the lens button to the scleral pattern in a manner such that the apparent gaze of both natural and artificial eyes is on the same object, or parallel to one another and in the same plane. www.indiandentalacademy.com
The size of the lens assembly selected should be large enough to include the limbus. The lens assembly is placed in a slight depression in the scleral pattern, and a thin layer of wax should be brought up over the curvature of the lens assembly. This thin layer of wax will allow the opaque white scleral acrylic resin to flow up over the edge curvature of the lens assembly during the packing procedure, forming a very thin, translucent layer. The finished pattern is then invested in a small two足piece brass flask. The resulting scleral blank is deflasked, trimmed, and polished www.indiandentalacademy.com
The position and gaze of the artificial eye is again observed. The sclera is slightly roughened using sandpaper disks in preparation for adding the simulated vasculature. Rayon足thread fibrils are placed onto the surface of the sclera using the monomer足 polymer syrup. The pattern and type of vessels ( tortuous, straight, branched) of the opposite eye are reproduced. The colors found in the sclera are usually yellow and blue, or combinations of these. Greens and browns can also be present. The scleral painting begins with the application of a wash of yellow comparable to that found on the patient's natural eye. www.indiandentalacademy.com
Next, blue is added, which is usually located inferior and superior to the iris. Finally, any characteristic details present in the natural eye are added. Once complete, a coat of monomer and polymer is applied to the sclera. The eye is now ready for the final processing, the application of a layer of clear acrylic resin
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The prosthesis is cleaned and placed in socket. The fit of the artificial eye are evaluated and adjustments are made as necessary.
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COMPLICATIONS IN FITTNG ANOPHTHALMIC SOCKET Ptosis: Superior eyelid ptosis is a frequent problem in the restoration of an anophthalmic patient. Pseudoptosis is due to the loss of volume between the implant and the lids after removal of the eye. If the physiological function of the eyelids is intact, correction of Pseudoptosis is achieved by increasing the volume of the prosthesis in the socket. This condition usually occurs whenever a small, poorly fitted prostheses is used. A simple technique of correcting Pseudoptosis is to make a larger prosthesis that will thrust forward and separate the eyelids www.indiandentalacademy.com
Persistent ptosis requires modification of the ocular prosthesis to correct for a deficient levator muscle, which causes the upper eyelid to droop. Attempts aimed at increasing the size of the ocular prosthesis, as seen in Pseudoptosis, will not correct the problem in persistent ptosis. The tension on the superior lid forces the larger prosthesis downward, thus depressing the lower eyelid, deflecting the gaze downward and creating patient discomfort. www.indiandentalacademy.com
A thin transparent shelf can be made across the front surface of the eye to hold the upper eyelid at the desired open position. The shelf is 3 to 4 mm wide and is placed along the upper limbus. This modification of the prosthesis works well for ptosis caused by a superiorly migrated, large, spherical implant with limited socket space between the implant and the upper eyelid.The major drawback to the shelf is that eye cannot blink or close. The weight of the upper eyelid and the action of the orbicularis muscle may press the eye downward. www.indiandentalacademy.com
This may be corrected by adding material to the inferior tissue surface of the prosthesis to contour it backward and upward. The surface above the shelf can be reduced to decrease the weight of the prosthesis and to create space for a tight upper eyelid.
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Ectropion: 足 Inferior displacement of the implant can lead to the loss of the inferior fornix and cause ectropion of the lower lid. Patients have difficulty with retention of the prosthesis, since it has a tendency to slip down and out over the everted lower lid. This is rectified by extending a thin lower edge that will press downward upon the tarsus, and rotate it into a more vertical plane, thus creating a lower fornix. The lower edge should be rounded and at least 1 mm in thickness so it will not cut into the socket. The lower fornix will deepen within minutes of modification, and insertion of the prosthesis and retention will improve www.indiandentalacademy.com
Sagging lower eyelid: The weight of the prosthesis, and the contraction force of the upper eyelid on the prosthesis can cause a downward displacement of the lower eyelid, causing it to droop. www.indiandentalacademy.com
Degenerative disease may also weaken the lower eyelid, causing it to droop. By removing resin from the mid inferior margin of the prosthesis, downward pressure against the middle of the lower fornix is relieved. Wax is added to extend the nasal and temporal aspects of the inferior margin to create pressure in the medial and lateral areas of the lid. This directs the weight of the prosthesis where the lower eyelid is strongest, near the palpebral ligaments. These modifications tilt the tarsus of the lower eyelid favorably so that the eyelid margin is elevated.
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conclusion The goal of any prosthetic treatment is to return the patient to society with a normal appearance and reasonable motility of the prosthetic eye. The disfigurement resulting from loss of eye can cause significant psychological, as well as social consequences. However with the advancement in ophthalmic surgery and ocular prosthesis, patient can be rehabilitated very effectively. The maxillofacial Prosthodontist should provide prosthetic treatment to the best of his ability and should also consider psychological aspects and if necessary the help of other specialist should be taken into consideration. www.indiandentalacademy.com
1. Textbook of Medical Physiology – GUYTON AND HALL 2. Review of Medical Physiology WILLAM F. GANONG 3. Medical Physiology – CHAUDHARY 4. Clinical Maxillofacial Prosthetics THOMAS D. TAYLOR 5. Maxillo Facial Rehabilitation – Prosthodontic and surgical consideration JOHN BEUMER www.indiandentalacademy.com
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