COMPREHENSIVE OPHTHALMOLOGY KHURANA PDF
Comprehensive OPHTHALMOLOGY This page intentionally left blank Comprehensive OPHTHALMOLOGY Fourth Edition A K Khurana Professor, Regional. Comprehensive. OPHTHALMOLOGY. Fourth tio. Edi n. A K Khurana. Professor,. Regional Institute of Ophthalmology,. Postgraduate Institute of Medical Sciences . Comprehensive Ophthalmology by Khurana, A. K. Ophthalmology' and different other aspects essential to the practical Review of Ophthalmology Compreh.
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Contraindications: DUREZOL® Emulsion, as with other ophthalmic corticosteroids, . ophthalmic corticosteroids, is contraindicated in most. The AK Khurana Comprehensive Ophthalmology 6th Edition is a book used by Medical students during their third year of MBBS. This is the 6th. AK Khurana Comprehensive Ophthalmology PDF Download [Direct Link].
Darkroom Procedures Ophthalmic Instruments and Operative Ophthalmology This page intentionally left blank 9. This page intentionally left blank The detailed anatomy of different structures is described in the relevant chapters. Although, generally referred to as a globe, the eyeball is not a sphere but an ablate spheroid. The central point on the maximal convexities of the anterior and posterior curvatures of the eyeball is called the anterior and posterior pole, respectively.
The equator of the eyeball lies at the mid plane between the two poles Fig. Dimensions of an adult eyeball Anteroposterior diameter 24mm Horizontal diameter Fibrous coat. It is a dense strong wall which protects the intraocular contents. Cornea is set into sclera like a watch glass. Junction of the cornea and sclera is called limbus.
Conjunctiva is firmly attached at the limbus. Vascular coat uveal tissue. It supplies nutrition to the various structures of the eyeball. It consists of three parts which from anterior to posterior are: Nervous coat retina. It is concerned with visual functions. Segments and chambers of the eyeball The eyeball can be divided into two segments: Anterior segment.
It includes crystalline lens which is suspended from the ciliary body by zonules , and structures anterior to it, viz. Gross anatomy of the eyeball. Poles and equators of the eyeball. Anterior chamber. It is bounded anteriorly by the back of cornea, and posteriorly by the iris and part of ciliary body.
The anterior chamber is about 2. It is shallower in hypermetropes and deeper in myopes, but is almost equal in the two eyes of the same individual. It contains about 0. Posterior chamber. It is a triangular space containing 0. It is bounded anteriorly by the posterior surface of iris and part of ciliary body, posteriorly by the crystalline lens and its zonules, and laterally by the ciliary body.
Posterior segment. It includes the structures posterior to lens, viz. Gross anatomy of the visual pathway. Each eyeball is located in the anterior orbit, nearer to the roof and lateral wall than to the floor and medial wall. Each eye is protected anteriorly by two shutters called the eyelids. The anterior part of the sclera and posterior surface of lids are lined by a thin membrane called conjunctiva. For smooth functioning, the cornea and conjunctiva are to be kept moist by tears which are produced by lacrimal gland and drained by the lacrimal passages.
The eyeball and its related structures are derived from the following primordia: Optic vesicle,an outgrowth from prosencephalon a neuroectodermal structure , Lens placode, a specialised area of surface ectoderm, and the surrounding surface ectoderm, Mesenchyme surrounding the optic vesicle, and Fig. Section of the orbital cavity to demonstrate eyeball and its accessory structures.
Visceral mesoderm of maxillary process. Before going into the development of individual structures, it will be helpful to understand the formation of optic vesicle, lens placode, optic cup and changes in the surrounding mesenchyme, which play a major role in the development of the eye and its related structures. Meanwhile the neural plate gets converted into prosencephalic vesicle. As the optic sulcus deepens, the walls of the prosencepholon overlying the sulcus bulge out to form the optic vesicle Figs.
The proximal part of the optic vesicle becomes constricted and elongated to form the optic stalk Figs. The surface ectoderm, overlying the optic vesicle becomes thickened to form the lens placode Fig.
It is soon separated from the surface ectoderm at 33rd day of gestation Fig. It appears from Fig. In fact conversion of the optic vesicle to the optic cup is due to differential growth of the walls of the vesicle. The margins of optic cup grow over the upper and lateral sides of the lens to enclose it. However, such a growth does not take place over the inferior part of the lens, and therefore, the walls of the cup show deficiency in this part.
This deficiency extends to Fig. Formation of the optic vesicle and optic stalk. Formation of lens vesicle and optic cup. Developing optic cup surrounded by mesenchyme.
In the posterior part of optic cup the surrounding fibrous mesenchyme forms sclera and extraocular muscles, while the vascular layer forms the choroid and ciliary body. The inner wall of the optic cup is a single-layered epithelium. It divides into several layers of cells which differentiate into the following three layers as also occurs in neural tube: An extension of this mesenchyme also covers the optic vesicle.
Later, this mesenchyme differentiates to form a superficial fibrous layer corresponding to dura and a deeper vascular layer corresponding to pia-arachnoid Fig. With the formation of optic cup, part of the inner vascular layer of mesenchyme is carried into the cup through the choroidal fissure. With the closure of this fissure, the portion of mesenchyme which has made its way into the eye is cut off from the surrounding mesenchyme and gives rise to the hyaloid system of the vessels Fig.
The fibrous layer of mesenchyme surrounding the anterior part of optic cup forms the cornea. The corresponding vascular layer of mesenchyme becomes the iridopupillary membrane, which in the peripheral region attaches to the anterior part of the optic cup to form the iris. The central part of this lamina is pupillary membrane which also forms the tunica vasculosa lentis Fig.
Derivation of various structures of the eyeball. Lens placode and lens vesicle formation see page 5, 6 and Fig. Primary lens fibres. The cells of posterior wall of lens vesicle elongate rapidly to form the primary lens fibres which obliterate the cavity of lens vesicle. The primary lens fibres are formed upto 3rd month of gestation and are preserved as the compact core of lens, known as embryonic nucleus Fig. Secondary lens fibres are formed from equatorial cells of anterior epithelium which remain active through out life.
Since the secondary lens fibres are laid down concentrically, the lens on section has a laminated appearance. Depending upon the period of development, the secondary lens fibres are named as below: Fetal nucleus 3rd to 8th month , Infantile nucleus last weeks of fetal life to puberty , Adult nucleus after puberty , and Cortex superficial lens fibres of adult lens Lens capsule is a true basement membrane produced by the lens epithelium on its external aspect.
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Cornea Fig. Epithelium is formed from the surface ectoderm. Other layers viz. Sclera Sclera is developed from the fibrous layer of mesenchyme surrounding the optic cup corres- ponding to dura of CNS Fig. Choroid It is derived from the inner vascular layer of mesenchyme that surrounds the optic cup Fig. Ciliary body The two layers of epithelium of ciliary body develop from the anterior part of the two layers of optic cup neuroectodermal.
Stroma of ciliary body, ciliary muscle and blood vessels are developed from the vascular layer of mesenchyme surrounding the optic cup Fig. Matrix cell layer. Cells of this layer form the rods and cones. Mantle layer. Cells of this layer form the bipolar cells, ganglion cells, other neurons of retina and the supporting tissue.
Marginal layer. This layer forms the ganglion cells, axons of which form the nerve fibre layer. Cells of the outer wall of the optic cup become pigmented. Its posterior part forms the pigmented epithelium of retina and the anterior part continues forward in ciliary body and iris as their anterior pigmented epithelium.
Optic nerve It develops in the framework of optic stalk as below: Fibres from the nerve fibre layer of retina grow into optic stalk by passing through the choroidal fissure and form the optic nerve fibres. The neuroectodermal cells forming the walls of optic stalk develop into glial system of the nerve.
The fibrous septa of the optic nerve are developed from the vascular layer of mesenchyme which invades the nerve at 3rd fetal month. Sheaths of optic nerve are formed from the layers of mesenchyme like meninges of other parts of central nervous system. Myelination of nerve fibres takes place from brain distally and reaches the lamina cribrosa just before birth and stops there. In some cases, this extends up to around the optic disc and presents as congenital opaque nerve fibres.
These develop after birth. Development of the retina. Sphincter and dilator pupillae muscles are derived from the anterior epithelium neuro- ectodermal.
Stroma and blood vessels of the iris develop from the vascular mesenchyme present anterior to the optic cup. Development of the crystalline lens. Development of the eyelids, conjunctiva and lacrimal gland. Vitreous 1. Primary or primitive vitreous is mesenchymal in origin and is a vascular structure having the hyaloid system of vessels. Secondary or definitive or vitreous proper is secreted by neuroectoderm of optic cup. This is an avascular structure. When this vitreous fills the cavity, primitive vitreous with hyaloid vessels is pushed anteriorly and ultimately disappears.
Tertiary vitreous is developed from neuro- ectoderm in the ciliary region and is represented by the ciliary zonules. Eyelids Eyelids are formed by reduplication of surface ectoderm above and below the cornea Fig.
The folds enlarge and their margins meet and fuse with each other. The lids cut off a space called the conjunctival sac. The folds thus formed contain some mesoderm which would form the muscles of the lid and the tarsal plate. The lids separate after the seventh month of intra-uterine life.
Cilia develop as epithelial buds from lid margins. Conjunctiva Conjunctiva develops from the ectoderm lining the lids and covering the globe Fig. Conjunctival glands develop as growth of the basal cells of upper conjunctival fornix.
Fewer glands develop from the lower fornix. The lacrimal apparatus Lacrimal gland is formed from about 8 cuneiform epithelial buds which grow by the end of 2nd month of fetal life from the superolateral side of the conjunctival sac Fig. Lacrimal sac, nasolacrimal duct and canaliculi. These structures develop from the ectoderm of nasolacrimal furrow. It extends from the medial angle of eye to the region of developing mouth.
The ectoderm gets buried to form a solid cord. The cord is later canalised. The upper part forms the lacrimal sac. The nasolacrimal duct is derived from the lower part as it forms a secondary connection with the nasal cavity. Some ectodermal buds arise from the medial margins of eyelids. These buds later canalise to form the canaliculi. Extraocular muscles All the extraocular muscles develop in a closely associated manner by mesodermally derived mesenchymal condensation.
Surface ectoderm The crystalline lens Epithelium of the cornea Epithelium of the conjunctiva Lacrimal gland Epitheliumofeyelidsanditsderivativesviz. Epithelium lining the lacrimal apparatus. Neural ectoderm Retina with its pigment epithelium Epithelial layers of ciliary body Epithelial layers of iris Sphincter and dilator pupillae muscles Optic nerve neuroglia and nervous elements only Melanocytes Secondary vitreous Ciliary zonules tertiary vitreous 3.
Associated paraxial mesenchyme Blood vessels of choroid, iris, ciliary vessels, central retinal artery, other vessels. Primary vitreous Substantia propria, Descemet's membrane and endothelium of cornea The sclera Stroma of iris Ciliary muscle Sheaths of optic nerve Extraocular muscles Fat, ligaments and other connective tissue structures of the orbit Upper and medial walls of the orbit Connective tissue of the upper eyelid 4. Adult size Anterior chamber is shallow and angle is narrow.
Lens is spherical at birth. Infantile nucleus is present. Apart from macular area the retina is fully differentiated.
Macula differentiates months after birth. Myelination of optic nerve fibres has reached the lamina cribrosa. Lacrimal gland is still underdeveloped and tears are not secreted. Postnatal period Fixation starts developing in first month and is completed in 6 months. Macula is fully developed by months. Fusional reflexes, stereopsis and accommodation is well developed by months. Cornea attains normal adult diameter by 2 years of age.
Lens grows throughout life. Eye at birth Anteroposterior diameter of the eyeball is about The physiological activities involved in the normal functioning of the eyes are: Maintenance of clear ocular media, Maintenance of normal intraocular pressure, The image forming mechanism, Physiology of vision, Physiology of binocular vision, Physiology of pupil, and Physiology of ocular motility.
The major factor responsible for transparency of the ocular media is their avascularity. The structures forming refractive media of the eye from anterior to posterior are: The physiological apsects of the tears and tear film are described in the chapter on diseases of the lacrimal apparatus see page Physiological aspects in relation to cornea include: Transparency of cornea, Nutrition and metabolism of cornea, Permeability of cornea, and Corneal wound healing.
Its physiological aspects include: Lens transparency Metabolic activities of the lens Accommodation. In addition to its role in maintaining a proper intraocular pressure it also plays an important metabolic role by providing substrates and removing metabolities from the avascular cornea and the crystalline lens.
For details see page The main mechanisms involved in physiology of vision are: Initiation of vision Phototransduction , a function of photoreceptors rods and cones , Processing and transmission of visual sensation, a function of image processing cells of retina and visual pathway, and Visual perception, a function of visual cortex and related areas of cerebral cortex.
Light falling upon the retina causes photochemical changes which in turn trigger a cascade of biochemical reactions that result in generation of electrical changes. Photochemical changes occuring in the rods and cones are essentially similar but the changes in rod pigment rhodopsin or visual purple have been studied in more detail.
This whole phenomenon of conversion of light energy into nerve impulse is known as phototransduction. Photochemical changes The photochemical changes include: Rhodopsin bleaching.
Rhodopsin refers to the visual pigment present in the rods — the receptors for night scotopic vision. Its maximum absorption spectrum is around nm. Rhodopsin consists of a colourless protein called opsin coupled with a carotenoid called retinine VitaminAaldehyde or II-cis-retinal. Light falling on the rods converts cis-retinal component of rhodopsin into all-trans-retinal through various stages Fig. The all trans-retinal so formed is soon separated from the opsin.
This process of separation is called photodecomposition and the rhodopsin is said to be bleached by the action of light. Rhodopsin regeneration. The cis-retinal is regenerated from the all-trans-retinal separated from the opsin as described above and vitamin-A retinal supplied from the blood. The cis-retinal then reunits with opsin in the rod outer segment to form the rhodopsin.
This whole process is called rhodopsin regeneration Fig. Thus, the bleaching of the rhodopsin occurs under the influence of light, whereas the regeneration process is independent of light, proceeding equally well in light and darkness. Visual cycle. In the retina of living animals, under constant light stimulation, a steady state must exist under which the rate at which the photochemicals are bleached is equal to the rate at which they are regenerated.
This equilibrium between the photo- decomposition and regeneration of visual pigments is referred to as visual cycle Fig. Light induced changes in rhodopsin. Electrical changes The activated rhodopsin, following exposure to light, triggers a cascade of complex biochemical reactions which ultimately result in the generation of receptor potential in the photoreceptors.
In this way, the light energy is converted into electrical energy which is further processed and transmitted via visual pathway. However, the ganglion cells transmit the visual signals by means of action potential to the neurons of lateral geniculate body and the later to the primary visual cortex. The phenomenon of processing of visual impulse is very complicated.
It is now clear that visual image is deciphered and analyzed in both serial and parallel fashion. Serial processing. The successive cells in the visual pathway starting from the photoreceptors to the cells of lateral geniculate body are involved in increasingly complex analysis of image. This is called sequential or serial processing of visual information. Parallel processing. Two kinds of cells can be distinguished in the visual pathway starting from the ganglion cells of retina including neurons of the lateral geniculate body, striate cortex, and extrastriate cortex.
These are large cells magno or M cells and small cells parvo or P cells. There are strikinging differences between the sensitivity of M and P cells to stimulus features Table 2. Table 2. These can be compared to two-lanes of a road. The M pathway and P pathway are involved in the parallel processing of the image i. The receptive field organization of the retina and cortex are used to encode this information about a visual image.
The light sense It is awareness of the light. The minimum brightness required to evoke a sensation of light is called the light minimum. It should be measured when the eye is dark adapted for at least minutes. The human eye in its ordinary use throughout the day is capable of functioning normally over an exceedingly wide range of illumination by a highly complex phenomenon termed as the visual adaptation.
The process of visual adaptation primarily involves: Dark adaptation adjustment in dim illumination , and Light adaptation adjustment to bright illumination. Dark adaptation It is the ability of the eye to adapt itself to decreasing illumination. When one goes from bright sunshine into a dimly-lit room, one cannot perceive the objects in the room until some time has elapsed.
During this period, eye is adapting to low illumination.
The rods are much more sensitive to low illumination than the cones. Therefore, rods are used Dark adaptation curve Fig. Further, the dark adaptation curve consists of two parts: Dark adaptation curve plotted with illumination of test object in vertical axis and duration of dark adaptation along the horizontal axis.
When fully dark adapted, the retina is about one lakh times more sensitive to light than when bleached. Delayed dark adaptation occurs in diseases of rods e.
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Light adaptation When one passes suddenly from a dim to a brightly lighted environment, the light seems intensely and even uncomfortably bright until the eyes adapt to the increased illumination and the visual threshold rises. The process by means of which retina adapts itself to bright light is called light adaptation.
Unlike dark adaptation, the process of light adaptation is very quick and occurs over a period of 5 minutes. Strictly speaking, light adaptation is merely the disappearance of dark adaptation.
The form sense It is the ability to discriminate between the shapes of the objects. Cones play a major role in this faculty. Therefore, form sense is most acute at the fovea, where there are maximum number of cones and decreases very rapidly towards the periphery Fig.
Visual acuity recorded by Snellen's test chart is a measure of the form sense. Visual acuity form sense in relation to the regions of the retina: N, nasal retina; B, blind spot; F, foveal region; and T, temporal retina.
Components of visual acuity. In clinical practice, measurement of the threshold of discrimination of two spatially-separated targets a function of the fovea centralis is termed visual acuity. However, in theory, visual acuity is a highly complex function that consists of the following components: Minimum visible. It is the ability to determine whether an object is present or not.
Resolution ordinary visual acuity. Discrimination of two spatially separated targets is termed resolution. The minimum separation between the two points, which can be discriminated as two, is known as minimum resolvable.
Measurement of the threshold of discrimination is essentially an assessment of the function of the fovea centralis and is termed ordinary visual acuity. Histologically, the diameter of a cone in the foveal region is 0. It is reported that in order to produce an image of minimumsizeof0. It is called the minimum angle of resolution MAR.
The clinical tests determining visual acuity measure the form sense or reading ability of the eye. Thus, broadly, resolution refers to the ability to identify the spatial characteristics of a test figure. The test targets More complex targets include gratings and checker board patterns. It is that faculty by virtue of which an individual not only discriminates the spatial characteristics of the test pattern but also identifies the patterns with which he has had some experience.
Recognition is thus a task involving cognitive components in addition to spatial resolution. For recognition, the individual should be familiar with the set of test figures employed in addition to being able to resolve them.
The most common example of recognition phenomenon is identification of faces. The average adult can recognize thousands of faces. Thus, the form sense is not purely a retinal function, as, the perception of its composite form e. Minimum discriminable refers to spatial distinction by an observer when the threshold is much lower than the ordinary acuity.
The best example of minimum discriminable is vernier acuity, which refers to the ability to determine whether or not two parallel and straight lines are aligned in the frontal plane. Sense of contrast It is the ability of the eye to perceive slight changes in the luminance between regions which are not separated by definite borders.
Loss of contrast sensitivity results in mild fogginess of the vision. Contrast sensitivity is affected by various factors like age, refractive errors, glaucoma, amblyopia, diabetes, optic nerve diseases and lenticular changes. Further, contrast sensitivity may be impaired even in the presence of normal visual acuity. Colour sense It is the ability of the eye to discriminate between different colours excited by light of different wavelengths.
Colour vision is a function of the cones and thus better appreciated in photopic vision. In dim light scotopic vision , all colours are seen grey and this phenomenon is called Purkinje shift. Theories of colour vision The process of colour analysis begins in the retina and is not entirely a function of brain.
Many theories have been put forward to explain the colour perception, but two have been particularly influential: Trichromatic theory. The trichromacy of colour vision was originally suggested by Young and subsequently modified by Helmholtz.
Hence it is called Young-Helmholtz theory. It postulates the existence of three kinds of cones, each containing a different photopigment which is maximally sensitive to one of the three primary colours viz. The sensation of any given colour is determined by the relative frequency of the impulse from each of the three cone systems. In other words, a given colour consists of admixture of the three primary colours in different proportion.
Red sensitive cone pigment, also known as erythrolabe or long wave length sensitive LWS cone pigment, absorbs maximally in a yellow portion with a peak at mm. But its spectrum extends far enough into the long wavelength to sense red.
Green sensitive cone pigment, also known as chlorolabe or medium wavelength sensitive MWS cone pigment, absorbs maximally in the green portion with a peak at nm. Blue sensitive cone pigment, also known as cyanolabe or short wavelength sensitive SWS conepigment,absorbsmaximallyintheblue-violet portionofthespectrumwithapeakatnm. Absorption spectrum of three cone pigments.
It has been studied that the gene for human rhodopsin is located on chromosome 3, and the gene for the blue-sensitive cone is located on chromosome 7.
The genes for the red and green sensitive cones are arranged in tandem array on the q arm of the X chromosomes. Opponent colour theory of Hering. In fact, it seems that both theories are useful in that: The colour vision is trichromatic at the level of photoreceptors, and Colour apponency occurs at ganglion cell onward.
According to apponent colour theory, there are two main types of colour opponent ganglion cells: Blue-yellow opponent colour cells obtain a yellow signal from the summed output of red and green cones, which is contrasted with the output from blue cones within the receptive field. Aray of light is the straight line path followed by light in going from one point to another. The ray- optics, therefore, uses the geometry of straight lines to account for the macroscopic phenomena like rectilinear propagation, reflection and refraction.
That is why the ray-optics is also called geometrical optics. The knowledge of geometrical optics is essential to understand the optics of eye, errors of refraction and their correction.
Therefore, some of its important aspects are described in the following text. Reflection of light Reflection of light is a phenomenon of change in the path of light rays without any change in the medium Fig. It lies between ultraviolet and infrared portions, from nm at the violet end of the spectrum to nm at the red end. Light ray is the term used to describe the radius of the concentric wave forms.
Agroup of parallel rays of light is called a beam of light. Important facts to remember about light rays are: The media of the eye are uniformally permeable to the visible rays between nm and nm. Cornea absorbs rays shorter than nm. Therefore, rays between nm and nm only can reach the lens. Lens absorbs rays shorter than nm. A line drawn at right angle to the surface is called the normal. Ocular Therapeutics, Lasers and Cryotherapy in Ophthalmology Systemic Ophthalmology Community Ophthalmology Clinical Methods in Ophthalmology Clinical Ophthalmic Cases Darkroom Procedures Ophthalmic Instruments and Operative Ophthalmology 4.
Kirk N. Gelatt, Brian C. Gilger, Thomas J. Kern Veterinary Ophthalmology: Two Volume Set 2 files Veterinary Ophthalmology, Fifth Edition is a fully updated version of the gold-standard reference for diseases and treatment of the animal eye in veterinary medicine. With an internationally renowned list of contributing authors, the book has been revised and expanded to incorporate the most up-to-date research and information.
New chapters cover ophthalmic genetics and DNA tests, microsurgery, photography, camelid ophthalmology, and rabbit ophthalmology, and existing chapters feature expanded coverage of noninvasive imaging techniques, feline ophthalmology, equine ophthalmology, and marine mammals and penguins. The book retains its classic structure, with sections on basic vision sciences, the foundations of clinical ophthalmology, canine ophthalmology, and special ophthalmology, which encompasses specific coverage of most commonly treated species and chapters on neuro-ophthalmology and systemic diseases.
A companion website offers the images from the book available for download in PowerPoint and the references linked to CrossRef. Veterinary Ophthalmology remains the most comprehensive resource for authoritative information on veterinary ophthalmology worldwide and is a key reference for anyone interested in veterinary or comparative ophthalmology.
David L. Williams Ophthalmology of Exotic Pets This quick reference handbook covers the diagnosis and treatment of eye disease in a range of exotic companion animal species, including rabbits, rodents, reptiles, birds, amphibians and fish. It clarifies when extrapolation from cat or dog eyes is appropriate, or when new information is needed to ensure that diagnoses and treatments are appropriate for the particular species. Ophthalmic Instruments and Operative Ophthalmology The detailed anatomy of different structures is described in the relevant chapters.
Although, generally referred to as a globe, the eyeball is not a sphere but an ablate spheroid. The central point on the maximal convexities of the anterior and posterior curvatures of the eyeball is called the anterior and posterior pole, respectively.
The equator of the eyeball lies at the mid plane between the two poles Fig. Coats of the eyeball The eyeball comprises three coats: Fibrous coat. It is a dense strong wall which protects the intraocular contents.
Cornea is set into sclera like a watch glass. Junction of the cornea and sclera is called limbus. Conjunctiva is firmly attached at the limbus.
Vascular coat uveal tissue. It supplies nutrition to the various structures of the eyeball. It consists of three parts which from anterior to posterior are: Nervous coat retina. It is concerned with visual functions. Segments and chambers of the eyeball Dimensions of an adult eyeball Anteroposterior diameter Horizontal diameter Vertical diameter Circumference Volume Weight z Formation of lens vesicle Formation of optic cup Changes in the associated mesoderm Development of various ocular structures Structures derived from the embryonic layers Important milestones in the development of the eye 24 mm Anterior segment.
It includes crystalline lens which is suspended from the ciliary body by zonules , and structures anterior to it, viz. Gross anatomy of the eyeball. It is bounded anteriorly by the back of cornea, and posteriorly by the iris and part of ciliary body.
The anterior chamber is about 2.
It is shallower in hypermetropes and deeper in myopes, but is almost equal in the two eyes of the same individual. It contains about 0. Posterior chamber. It is a triangular space containing 0. It is bounded anteriorly by the posterior surface of iris and part of ciliary body, posteriorly by the crystalline lens and its zonules, and laterally by the ciliary body. Posterior segment. It includes the structures posterior to lens, viz.
Poles and equators of the eyeball. Each eyeball is located in the anterior orbit, nearer to the roof and lateral wall than to the floor and medial wall. Each eye is protected anteriorly by two shutters called the eyelids. The anterior part of the sclera and posterior surface of lids are lined by a thin membrane called conjunctiva. For smooth functioning, the cornea and conjunctiva are to be kept moist by tears which are produced by lacrimal gland and drained by the lacrimal passages.
Visceral mesoderm of maxillary process.
Before going into the development of individual structures, it will be helpful to understand the formation of optic vesicle, lens placode, optic cup and changes in the surrounding mesenchyme, which play a major role in the development of the eye and its related structures. The eyeball and its related structures are derived from the following primordia: Gross anatomy of the visual pathway. Section of the orbital cavity to demonstrate eyeball and its accessory structures.
Meanwhile the neural plate gets converted into prosencephalic vesicle. As the optic sulcus deepens, the walls of the prosencepholon overlying the sulcus bulge out to form the optic vesicle Figs.
The proximal part of the optic vesicle becomes constricted and elongated to form the optic stalk Figs. The surface ectoderm, overlying the optic vesicle becomes thickened to form the lens placode Fig.
It is soon separated from the surface ectoderm at 33rd day of gestation Fig. It appears from Fig. In fact conversion of the optic vesicle to the optic cup is due to differential growth of the walls of the vesicle.
AK Khurana Comprehensive Ophthalmology PDF Download [Direct Link]
The margins of optic cup grow over the upper and lateral sides of the lens to enclose it. However, such a growth does not take place over the inferior part of the lens, and therefore, the walls of the cup show deficiency in this part. This deficiency extends to Fig. Formation of the optic vesicle and optic stalk. Formation of lens vesicle and optic cup. In the posterior part of optic cup the surrounding fibrous mesenchyme forms sclera and extraocular muscles, while the vascular layer forms the choroid and ciliary body.
The inner wall of the optic cup is a single-layered epithelium.The proximal part of the optic vesicle becomes constricted and elongated to form the optic stalk Figs. Modes of prescribing concave lenses are spectacles and contact lenses. Clinical Ophthalmic Cases Images formed by cylindrical lenses. Components of visual acuity. It is the commonest form.
It is called the minimum angle of resolution MAR. Keratometry and computerized corneal topotograpy reveal different corneal curvature in two different meridia in corneal astigmatism see page 3. At the end of the book, there are instruments and surgical procedures given beautifully.
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