Optometry Notes

OPTOMETRY · SEMESTER 2 The Uveal Tract Ocular Anatomy and Physiology START READING NOTES Contents of This Topic The Uveal Tract THE IRIS The Uveal Tract CHAPTER 9. THE UVEAL TRACT THE FOLLOWING TOPICS WILL BE COVERED BY THE END OF THIS CHAPTER: DEFINITION AND STRUCTURE OF THE UVEA THE IRIS THE CILIARY BODY THE CHOROID SOME DISORDERS AFFECTING THE UVEA A RWONS 1. DEFINITION AND STRUCTURE. The uvea is the vascular middle layer of the eye ball. When the outer layer , the sclera ,is removed the eye ball appears like a black grape hanging on its stalk( the optic nerve), hence the name. The uvea is made up of three structures: The iris. The ciliary body. The choroid The is no clear demarcation between these three parts, they are continuous with each other , lining the sclera from the anterior opening to the posterior aperture for the optic nerve. 2. THE IRIS. This is the most anterior part of the uvea, measuring about 12mm in diameter.. The iris is a thin, circular structure located anterior to the lens, often compared to a diaphragm of an optical ‘system. The center aperture It is a thin, contractile, SdoUghnUt/shaped” structure that is found in the anterior segment of the eye between the cornea and the lens. It in turn divides the anterior segment into anterior and posterior chambers. The anterior chamber is the space between the cornea and the iris, while the posterior chamber is the space between the iris and the lens. This division of the anterior segment is important for the Cataract/surgeons!) 53 The central opening of the “doughnut” is called the pupil. By varying the size of the pupil, the iris muscles ( sphincter and dilator) , control the amount of light entering the eye. All light that enters the eye, passes through the pupil. The aqueous humour , formed by the ciliary processes in the posterior chamber , circulates through the pupil into the anterior chamber. The iris is made up of : connective'tissue;muscles)/pigmented|cells (melanocytes), nerves, blood vessels. The colour of the iris varies from one individual to another, depending on the amount of pigment contained by the melanocytes. 2.1. Surface anatomy of the iris. a. The anterior surface. The anterior surface of the iris contains crypts and crevices in contact with the aqueous in the anterior chamber. The aqueous humour thus has direct communication with the tissue spaces of the iris. The center is the pupil, a black aperture with a varying diameteffrom=8 mm. The pupil appears black because the interior of the eye is dark. The anterior surface is divided into: e acentral, pupillary zone and e aperipheral , ciliary zone. The iris is thickest at the demarcation zone between the pupillary and the ciliary zones called collarette, which lies about 2mm from the pupillary zone. At the pupillary margin , a darker zone is seen surrounding the pupil. This is the so called pupillary ruff, representing the posterior pigmented layer of the iris curving around the pupillary margin. 54 b. The posterior surface. The posterior surface of the iris is markedly pigmented and shows a number of contraction folds. 2.2. Microscopic anatomy of the iris. The iris consists of two layers: a. the stroma; b. the pigmented epithelial layers; a. The iris stroma. The stroma devoid of epithelium, represents the anterior border of the iris. Embryologically itforiginates frommesenchymey) It is composed of a highly vascular connective tissue containing collagen fibres, fibroblasts, melanocytes, nerve fibres and the smooth muscles that control the pupillary movements (the sphincter and the dilator pupillae) Blood vessels form the bulk of the iris stroma. Their course is mostly radial, arising from the major arterial circle passing towards the centre. The major arterial circle is located in the ciliary body, not the iris. At the level of the collarette , anastomoses occur between arteries and veins, to form the minor vascular circle , which is often incomplete. The sphincter pupillae muscle is an 1mm wide circular band of smooth muscle fibers, located in the posterior stroma near the pupillary margin. Its innervation is by parasympathetic fibres fromthe Edinger Westphal fiiclelis of cranial/nerve lll;ithese fibres synapse in the ciliary ganglion and are distributed via the short posterior ciliary nerves to the sphincter muscle. When the sphincter pupillae contracts , the pupil constricts ( miosis ). The dilator pupillae is made up by myorpithelial cells that extend from the iris root to the sphincter pupillae, lying parallel and anterior to the posterior pigmented epithelium. The nerve supply is from the sympathetic postganglionic fibres via the long ciliary nerves. When the dilator muscle contracts , the pupil enlarges ( mydriasis ). 55 b. The pigmented epithelial layers. There are 2 pigmented layers, the anterior and the posterior pigmented layer. Embryologically derived from the neuroectoderm of the optic cup, the cells of the two layers are apposed to each other apex to apex. Between lies a potential space that can, under certain circumstances, fill _ with fluid and become real space. The anterior epithelial layer , only slightly pigmented, lies in contact with the iris stroma and is closely associated with the myoepithelial cells of the dilator pupillae muscle. It is continuous withithejouten layer of the ciliary epithelium: The posterior epithelial layer , facing the posterior chamber, is made of cells densely packed with melanin. Anteriorly it extends to the pupillary ruff while posteriorly is continous with the inner layer of the ciliary epithelium. Anterior chamber angle Trabecular meshwork Ciliary zone Pupillary zone Schlemm's canal SOS Collarette [ — Pupil frill Pupillary 27 margin Anterior border Iris root layer Sphincter papillae __ Stroma with blood vessels and nerves Anterior epithelium— radial myopepithelial dilator papillae muscle Ciliary process Posterior epithelium pigmented epithelium Fig. 9.1. Diagram of iris and ciliary body anatomy. 56 2. THE CILIARY BODY. The ciliary body is aring shaped structuréthat bridges the iris'and! choroid. It is 6mm wide extending from the scleral spur (anteriorly ) to the ora serrata of the retina

OPTOMETRY · SEMESTER 2 The Crystalline Lens Ocular Anatomy and Physiology START READING NOTES Contents of This Topic The Crystalline Lens THE STRUCTURE OF THE CRYSTALLINE LENS Anterior Pole Bow Region The Crystalline Lens CHAPTER 10. THE CRYSTALLINE LENS BY THE END OF THIS CHAPTER YOU WILL HAVE COVERED THE FOLLOWING ASPECTS OF THE TOPIC: DEFINITION THE STRUCTURE OF THE CRYSTALLINE LENS BIOCHEMISTRY AND METABOLISM OF THE LENS THE FUNCTIONS OF THE LENS SOME DISORDERS OF THE CRYSTALLINE LENS ARWONS> 1. DEFINITION. The crystalline lens is a biconvex, transparent structure located directly behind the pupil. It lies posterior to the iris and anterior to the vitreous, Suspended in position by the The equatorial diameter of the adult lens is 9- 10mm. The anteroposterior length (approximately 4-5mm ), varies with accommodation. Fig. 10.1. Diagram of the anterior segment of the eye showing the lens held by the zonules to the ciliary body. 62 2. THE STRUCTURE OF THE CRYSTALLINE LENS. The lens is composed of : e capsule; e lens epithelium; ° cortex; e nucleus. 2.1. The capsule is a transparent elastic membrane . Anteriorly is considerably thicker than posteriorly. 2.2. The lens epithelium jis a single layer of metabolically active epithelial cells, situated under the anterior capsule. Continuously , new cell are formed The newly formed cells migrate posteriorly and differentiate into fibres. This change is associated with increase in protein content and loss of organelles (mitochondria, nucleus). The fibres are laid down in a concentric manner, their tips meeting to form sutures. The fibres crowd and compact the previously formed ones, with the oldest being the most central. 2.3. The cortex is made -up by the outermost fibres, most recently laid. The fibres have a high content of crystalline proteins which are responsible for the high refractive index of the crystalline lens. 2.4. The nucleus consists of all the fibres laid down before birth. There is no distinct morphologic differentiation between cortex and nucleus; rather, the transition between these regions is gradual. 63 Anterior Pole Surrounding Germinative Capsule ry, Zone Epithelial Cells . Equator a r Bow Region Cortical Fibers Nuclear Fibers Posterior Pole Fig. 10.2. Diagram showing the structure of the Crystalline Lens. 3. BIOCHEMISTRY AND METABOLISM OF THE CRYSTALLINE LENS. The human lens has a protein concentration of 33% , highest of any structure in the body; lens proteins can be divided in two groups based on their water solubility : a. Crystallins / water soluble (alpha, beta, gamma) & b. Water insoluble The crystallins are the major lens proteins. The crystalline lens lacks innervation and has no vascular system, it depends totally on the aqueous and vitreous for its nourishment. 4. THE FUNCTIONS OF THE CRYSTALLINE LENS. The functions of the lens are: e to maintain its own clarity (transparency); e torefract the light; e to provide accommodation. 64 4.1. The most important aspect of lens physiology is the maintenance of transparency. Lens transparency is highly dependent on cellular hydration; perturbation of cellular hydration can lead to lens opacification Responsible for the transparency is , also the homogenous structure of fibres , the small size of the extracellular space and the stable structure of the major lens proteins, the crystallins. As such, the lens is remarkable, unique, for its ability to preserve transparency throughout the human life span. 4.2. Refraction of light. The lens has a high refractive index (1.41 ) achieved by the high protein content of the fibres. The refractive power of the lens is 15 dioptres. 4.3 Accommodation , the mechanism by which the eye changes focus from distant to near images, is produced by a change in the lens shape, resulting from the action of the ciliary muscle on the zonules. When the ciliary muscle contracts , the zonular fibres relax allowing the lens to become more spherical . Thus, the axial thickness of the lens increases , its diameter decreases, and its dioptric power increases , producing accomodation. Accommodation is controlled by the parasympathetic system, via cranial nerve Ill (oculomotor ). 5. CLINICAL CONSIDERATIONS. Accomodation diminishes with age; clinically evident loss of accommodation is called presbyopia. It can be corrected with spectacles. The opacification (loss of transparency )of the lens is called cataract. 65 Opaque lens Fig. 10.3. A. Slit lamp photograph of an eye with cataract. B. Diagrams of cataract. When the opacity of the lens interferes with the patient’s daily activities , the cataract can be surgically removed. The absence of the crystalline lens is called aphakia. The most common method of replacing the lost optical power after cataract removal, is the implantation of an intraocular lens. Correction with an intraocular lens is called pseudophakia. 66 Cataract is the leading cause of blindness in the world. 17 million people are blind from cataract. The most common type of cataract is the senile cataract. Cataracts may be congenital ( eg. rubella syndrome) ; can also result from injury or disease: secondary cataracts. In all cases , treatment consists of surgical removal of the opacified lens. 67 ← PREVIOUS TOPICNEXT TOPIC →VIEW MODULE NOTESVIEW SEMESTER NOTESALL OPTOMETRY NOTES Need These Notes as PDF? Request a formatted copy for offline study, printing or revision. GET PDF NOTES ON WHATSAPP

OPTOMETRY · SEMESTER 2 The Retina and Vitreous Ocular Anatomy and Physiology START READING NOTES Contents of This Topic The Retina and Vitreous ANATOMISTS CLINICIANS (HOW DOES THE EYE SEE?) The Retina and Vitreous CHAPTER 11. THE RETINA AND THE VITREOUS BY THE END OF THIS CHAPTER YOU WILL HAVE COVERED THE FOLLOWING TOPICS: 1. DEFINITION 2. GROSS ANATOMY 3. HISTOLOGY 4. THE RETINAL BLOOD SUPPLY 5. RETINAL BIOCHEMISTRY AND PHYSIOLOGY 6. COLOUR VISION 7. CLINICAL CONSIDERATIONS 8. THE VITREOUS. 1. DEFINITION. The BEEN is the inner neural layer or the nervous coat of the eye. It contains receptors that sense the light from the outer world and transmit it to the brain for higher processing. It is a thin transparent membrane with a purplish red colour in a living subject. Its thickness varies from 0.6mm near the optic disc to 0.1mm at its peripheral termination called the ora serrata. The outer surface is in contact with the choroid and the inner surface with the vitreous. The retina is firmly attached to the optic disc margin and at its peripheral a Externally, the peripheral termination of the retina corresponds with the site of insertion of the medial and lateral recti muscles. 2. GROSS ANATOMY. There are several prominent structures in the retina that can be identified with the help of an instrument called the ophthalmoscope. The procedure is called ophthalmoscopy or funduscopy , and the part of the eye visible on funduscpoy is called fundus. 68 2.1. The optic disc. This is most prominent structure of the retina and it is located nasally. It is a yellow-pink ,oval to round structure, also called papilla or optic nerve head . It represents the beginning of the optic nerve,( the second cranial nerve- the nerve that is responsible for vision ). The optic nerve head or the optic disc measures 1.75 mm vertically and 1.5mm horizontally in diameter. The centre of the disc has a circular depression that appears whiter than the rest of the disc. This is called the cup of the disc and is a location where the retinal arteries Fine vessels are seen to pass over the surface of the disc, which give it the pinkish appearance. The retina is firmly attached to the margins of the disc. There is no retinal tissue over the disc,thus it is insensitive to light and is referred to as the blind spot. 2.2. The area centralis. ‘Temporal to the disc is an area called the area centralis. This is the most posterior part of the globe and central part of the retina. Clinically, this area is called the posterior pole. It measures about 5-6 mm in diameter and is enclosed within the At the centre of the posterior pole is an area measuring about 1.5 mm called the macula lutea by the clinicians and fovea by the anatomists. It has a yellowish appearance when seen by an ophthalmoscope due a yellow pigment called the xanthophyll. The macula lutea or the fovea is located about 3mm temporal and 1mm inferior to the disc. The photoreceptor layer of the fovea contains only cones. The centre of the fovea is depressed and is called the fovea centralis by the clinicians and foveola by the anatomists. It measures about 0.35mm in diameter. 69 It is thus apparent that anatomists and clinicians differ in their terminologies as follows: ANATOMISTS CLINICIANS Area centralis Posterior pole Fovea Macula lutea (or just the macula) Foveola Fovea centralis ( or just the fovea) As clinicians, we will stick to the clinical terminologies henceforth to avoid confusion. The macula is responsible for central and colour vision. The sharpest central vision is achieved at the fovea 2.3. The peripheral retina. The remainder of the retina outside the posterior pole is termed peripheral retina, although further subdivision exists but that is beyond the scope of this work. The peripheral termination of the retina shows teeth like projections called the ora serrata. The retinal cells at the ora serrata continue over the ciliary body to form the non- pigmented epithelial layer of the pars plana. In the peripheral retina the predominant photoreceptors are the rods. The retina is divided into temporal and nasal halves by an imaginary line that runs vertically through the fovea. _ The centre of the optic disc is used to divide the retina into 4 quadrants: e Supero- nasal; ° supero-temporal; e infero-nasal; e infero-temporal. This division helps the clinician locate and document the position of lesions on the surface of the retina. With this division in mind one can visualise the retinal vessel's distribution on the surface of the retina. 70 The retinal artery emerges as a single vessel called the Central Retinal Artery , which then divides in to 2 branches the superior and inferior retinal arteries Each of these then further divides into 2 branches, one for the temporal and the other for the nasal quadrants of the retina. The same applies with the distribution of the Central Retinal Vein. Fig. 11.1. Anatomical landmarks of the left eye fundus. A- anatomical macula / clinical posterior pole; B- anatomical fovea / clinical macula; C- anatomical foveola / clinical fovea; D- optic disc; E- optic cup. 71 GD ait with wes offic 3. HISTOLOGY. The retina, the layer which develops from the inner and outer layers of the embryological optic cup, is divided into two major portions: e The Retinal Pigment Epithelial layer ( RPE); e The Neurosensory layer. 3.1. The Retinal Pigment Epithelium (RPE ). a. Anatomical features. The RPE is a GifigléllayerOnicellS deriving embryologically from the outer — layer of the optic cup. It is located between the choroid and the neurosensory retina, the apices of the cells pointing towards the vitreous while the base rests on its basement membrane towards the choroid. The RPE is a continuous monolayer of cuboidal / columnar cells which extend from the optic disc margin to the ora serrata. From ora serrata it continues over the ciliary body as the pigmented

OPTOMETRY · SEMESTER 2 Neuro-ophthalmic Anatomy and Physiology Ocular Anatomy and Physiology START READING NOTES Contents of This Topic Neuro-ophthalmic Anatomy and Physiology THE PHYSIOLOGY OF VISION Pituitary Chiasma Edinger Westphal Neuro-ophthalmic Anatomy and Physiology CHAPTER 12. NEURO-OPHTHALMIC_ ANATOMY AND PHYSIOLOGY BY THE END OF THIS CHAPTER YOU WILL HAVE COVERED THE FOLLOWING ASPECTS OF THE TOPIC: THE ANATOMY OF VISUAL PATHWAYS THE PHYSIOLOGY OF VISION COMMON SYMPTOMS IN NEURO-OPHTHALMOLOGY OCULAR MOTOR NERVES ANATOMY AND PATHOLOGY ASPECTS PUPILLARY PATHWAYS AND REFLEXES ARWONS> 1. THE ANATOMY OF THE VISUAL PATHWAYS. The route taken by the light-generated impulses the eye is called the visual pathway. The visual pathway is effectively a tract within the central nervous system and it is made up of the: optic nerves; optic chiasm; optic tracts; lateral geniculate bodies; optic radiations; visual cortex. Disorders affecting different parts of the visual pathway produce characteristic changes in the field of vision. The nature of visual field disturbances , therefore, can help in determining which part of the visual pathway is affected. 84 Temporal retina Optic tract Lateral ‘eniculate ody Optic radiations Visual cortex Fig. 12.1. Diagramatic representation of the visual pathways. 1.1. The Optic Nerve ( Cranial_Nerve II ). The optic nerve is made up by the axons of the retinal ganglion cells . It may be divided anatomically, into four portions: intraocular (1mm); intraorbital (25mm); intracanalicular (9mm); intracranial (16mm). 85 a. The intraocular portion. This part includes the optic disc and the portion of the optic nerve that lies re The optic disc lies in the nasal retina, medial to the macula. Also called the optic nerve-head or papilla, it represents the confluence of approximately 1.2 million ganglion cell axons. It's pale pink in colour, slightly oval vertically . It has a central cup and a peripheral rim of neural tissue The central retinal vessels emerge at the centre of the optic disk, pass over the rim, and radiate out to supply the retina. The optic disk derives its blood supply via the short ciliary arteries from the ophthalmic artery, while the retina is fed by the central retinal artery. The nerve fibres of the intraocular portion are not myelinated. They traverse the sclera through the lamina cribrosa . Just posterior to the sclera, the fibres acquire a myelin coating. b. The intraorbital portion. The orbital portion of the nerve extends from the globe to the optic canal. It is 3-4mm thick, double the diameter of the intraocular portion as a result of the acquisition of myelin and meningeal sheath. Posteriorly , the meningeal sheath is continuous with the meningeal sheath around the brain. Thus, a rise in the intracranial pressure will be communicated to the subarachnoid space around the optic nerve, and may result in papilloedema. The length of the intraorbital portion of the optic nerve is longer than the anteroposterior dimensions of the orbit. The extra length of the intraorbital optic nerve allows unimpeded globe rotation as well as axial shifts within the orbit. c. The intracanalicular portion. 86 In addition to the optic nerve , the canal contains the ophthalmic artery and sympathetic fibres of the sympathetic carotid plexus. In the canal the nerve is firmly anchored (the dura and the periosteum are fused). As aresult, a small lesion in the optic canal can produce a compressive optic neuropathy even before it becomes easily visible upon neuroimagining. d. The intracranial portion. The optic nerve exits the posterior opening of the optic canal , enters the middle cranial fossa and continues posteriorly ascending to join the optic chiasma. Above the optic nerve lie the inferior surface of the frontal lobe, the olfactory tract , and the anterior cerebral and anterior communicating arteries. The lateral aspect of the optic nerve if often immediately adjacent to the internal carotid artery . Inferiorly and medially , the posterior ethmoid and sphenoid sinuses are adjacent to the nerve. The blood supply of the optic nerve is through the pial network of vessels. Arterial branches feeding the pial network originate from the ophthalmic artery . The venous drainage of the optic nerve is chiefly by the central retinal vein and to a lesser extent via the pial venous system. Both systems drain into the ophthalmic venous system ( superior and/or inferior ophthalmic veins ) in the orbit and less commonly directly into the cavernous sinus. 1.2. The Optic Chiasm. Fibres from the two optic nerves merge to form the optic chiasm. The chiasm is located anterior to the hypothalamus and above the sella turcica. 87 Fig. 12.2. Relation between the optic nerve and chiasm, the sellar structures and the third ventricle (III ). The chiasm overlies the sella turcica with the pituitary gland below, being The relatively large space between the chiasm and the pituitary explains the fact that only large tumours of the pituitary gland will compress on the chiasm and cause visual field defects. The chiasm forms the floor the third ventricle and carotid arteries bound it at either side. The circle of Willis surrounds the chiasm. 88 Anterior cerebral artery | Internal j carotid / artery I Posterior communicating Basilar artery artery Fig. 12.3. Relationship between the Optic Chiasm and the Circle of Willis. Fibres from each nasal retina cross in the optic chiasm , whereas fibres from each temporal retina do not cross. Slightly more than half of the fibres (65% ) decussate , because the nasal retina contains more ganglion cells than the temporal retina. Lesions of the chiasm characteristically involve crossing nasal fibres. As such , they cause bilateral temporal visual field defects, that respect the vertical line. 1.3. The Optic Tracts. The optic tracts begin at the posterior aspect of the optic chiasm , diverge laterally , and continue posteriorly to terminate primarily in the lateral geniculate bodies. A group of fibres leave the optic tract just before the lateral geniculate body for the pretectal area; the pretectal pathway controls light-mediated pupillary constriction. 89 Each optic tract contains crossed nasal fibres from the contralateral