Table Of ContentContents
Preface to the Twenty-first Edition.........................................v 22. Diseases of the Optic Nerve...................................340
Preface to the Nineteenth Edition.........................................vii 23. Intraocular Tumours...................................................365
Acknowledgements to the Nineteenth Edition....................ix 24. Injuries to the Eye........................................................373
Section I: Anatomy and Physiology Section V: Disorders of Motility
1. Embryology and Anatomy..............................................3 25. Anatomy and Physiology of the Motor
2. Physiology of the Eye.....................................................18 Mechanism....................................................................393
3. The Physiology of Vision...............................................22 26. Comitant Strabismus..................................................405
4. The Neurology of Vision................................................29 27. Incomitant Strabismus...............................................424
Section VI: Diseases of the Adnexa
Section II: Ophthalmic Optics and Refraction
28. Diseases of the Lids..............................................439
5. Elementary Optics..........................................................41
29. Diseases of the Lacrimal Apparatus..................461
6. Elementary Physiological Optics..................................51
30. Diseases of the Orbit............................................470
7. Refraction.........................................................................61
8. Refractive Errors of the Eye...........................................72
Section VII: Systemic Ophthalmology
31. Diseases of the Nervous System with Ocular
Section III: Ocular Examination Techniques and
Manifestations..............................................................489
Ocular Therapeutics
32. Ocular Manifestations of Systemic
9. Ocular Symptomatology...............................................89
Disorders.......................................................................520
10. Assessment of Visual Function.....................................99
11. Examination of the Anterior Segment.......................115
Section VIII: Preventive Ophthalmology
12. Examination of the Posterior Segment and
33. Genetics in Ophthalmology................................529
Orbit...............................................................................129
34. The Causes and Prevention of Blindness..............539
13. Ocular Therapeutics.....................................................144
Section IX: Surgical Instruments in
Section IV: Diseases of the Eye
Ophthalmology
14. Diseases of the Conjunctiva.......................................161
35. Surgical Instruments in Ophthalmology...............555
15. Diseases of the Cornea...............................................187
16. Diseases of the Sclera..................................................218
Appendices
17. Diseases of the Uveal Tract........................................225
I. Local Anaesthesia in Ophthalmology....................581
18. The Lens ...................................................256
II. Lasers in Ophthalmology..........................................584
19. The Glaucomas..............................................................280
III. IOL Designs and Materials......................................585
20. Diseases of the Retina................................................301
21. Diseases of the Viterous............................................333 Index..........................................................................589
I
Section
Anatomy and Physiology
1 Embryology and Anatomy 3 3 The Physiology of Vision 22
2 Physiology of the Eye 18 4 The Neurology of Vision 29
A
1
Chapter
Embryology and Anatomy
Embryology 3
Anatomy 5
The Blood Supply of the Eye 13
Clinical Anatomy of the Eye 16
Summary 16
Suggested Reading 17
EMBRYOLOGY
The central nervous system is developed from the neural
groove which invaginates to form the neural tube running
longitudinally down the dorsal surface of the embryo. At
either side from the lateral aspect of the anterior portion
of this structure, which is the precursor of the forebrain, a
thickening appears at an early stage,(the optic plate) which
then grows outwards as a diverticulum towards the sur
face to form the primary optic vesicle (Tig. 1.1 A and B).
From this pair of diverticula from the sides of the fore
brain and the mesodermal and ectodermal structures in
contact with it, the two eyes develop.
After it meets the surface ectoderm, the primary optic
vesicle invaginates from below (the optic cup), the line of
invagination remaining open for some time as the embry
onic fissure (Fig. 1.1C). The inner layer of the cup forms
E F
the main structure of the retina, the nerve fibres from
which eventually grow backwards towards the brain. Its Fig. 1.1 The development of the eye. In each case the solid
outer layer remains as a single layer of pigment epithe black is the neural ectoderm, the hatched layer is the surface
ectoderm and its derivatives, the dotted area is the mesoderm: a,
lium; between the two lies a narrow space representing
cavity of the forebrain; b, cavity of the optic vesicle; c, cavity of
the original optic vesicle; and from its anterior border
the optic cup (or secondary optic vesicle) formed by invagination.
develop parts of the ciliary body and iris (Fig. 1.1E). At (A) Transverse section through the anterior part of the forebrain
the point where the neural ectoderm meets the surface and optic vesicles of a 4mm human embryo. (B) The primary optic
ectoderm, the latter thickens to form the lens Dials, invagi vesicle. (C) The formation of the optic cup by invagination at the
embryonic fissure and invagination of the surface epithelium.
nates to form the lens vesicle (Fig. 1.1C) and then separates
(D) The optic cup and lens vesicle. (E) The formation of the ciliary
to form the lens (Fig 1.1D) The hyaloid artery enters the
region and iris, the anterior chamber, the hyaloid artery and the lid
optic cup through the embryonic fissure and grows for folds. The lens is formed from the posterior cells of the lens vesicle.
wards to meet the lens, bringing temporary nourishment (F) The complete eye.
Section I Anatomy and Physiology
Table 1.1 Summary of ocular embryogenesis
Period after conception Major milestone
3 weeks Optic groove appears
4th week Optic pit develops into optic vesicle
Lens plate forms
Embryonic fissure develops Fig. 1.1 A-D
1 st month Lens pit and then lens vesicle form
Hyaloid vessels develop
1Vi months Closure of embryonic fissure
Differentiation of retinal pigment epithelium
Proliferation of neural retinal cells
Appearance of eyelid folds and nasolacrimal duct
7th week Formation of embryonic nucleus of the lens
Sclera begins to form
Migration of waves of neural crest
First wave: formation of corneal and trabecular endothelium
Second wave: formation of corneal stroma
Third wave: formation of iris stroma Fig. 1.1E
3rd month Differentiation of precursors of rods and cones
Anterior chamber appears
Fetal nucleus starts to develop
Sclera condenses
Eyelid folds lengthen and fuse
4th month Formation of retinal vasculature begins
Hyaloid vessels begin to regress
Formation of physiological optic disc cup and lamina cribrosa
Canal of Schlemm appears
Bowman's membrane develops
Formation of major arterial circle and sphincter muscle of iris
5th month Photoreceptors differentiate
Eyelid separation begins
6th month Differentiation of dilator pupillae muscle
Nasolacrimal system becomes patent
Cones differentiate Fig. 1 .IF
7th month Rods differentiate
Myelination of optic nerve begins
Posterior movement of anterior chamber angle
Retinal vessels start reaching nasal periphery
8th month Completion of anterior chamber angle formation, hyaloid vessels disappear
9th month Retinal vessels reach temporal periphery, pupillary membrane disappears
After birth Macular region of the retina develops further
to the developing structures before it eventually atrophies the main structures of the cornea; while the surface
and disappears; as it does so, its place is taken by a clear ectoderm remains as the corneal and conjunctival epi
jelly (the vitreous) largely secreted by the surrounding thelium. In the surrounding region folds grow over in
neural ectoderm. front of the cornea, unite and separate again to form
While these ectodermal events are taking place, the lids (Fig. 1.1E and F). Summary of ocular embryo-
the mesoderm surrounding the optic cup differenti genesis is given in Table 1.1.
ates to form the coats of the eye and the orbital struc In summary, the eye is essentially formed from both
tures; that between the lens and the surface ectoderm ectoderm and mesoderm. The ectoderm is of two types:
becomes hollowed to form the anterior chamber, lined (i) the neural ectoderm derived from the neural tube
by mesodermal condensations which form the anterior and (ii) the surface ectoderm on the side of the head
layers of the iris, the angle of the anterior chamber and (Table 1.2).
4
1 Embryology and Anatomy
may be regarded as the continuation of the conjunc
Table 1.2 Primordial tissue and its derivatives
tiva over the cornea. Its basal cells lie on a lamina of
Precursor Derivatives the substantia propria, called Bowman's membrane. The
substantia propria may be regarded as the continuation
Neural ectoderm Smooth muscle of the iris
forwards of the sclera.
Optic vesicle and cup
Iris epithelium The stroma, forming 90% of the total corneal thick
Ciliary epithelium ness, is composed of regularly arranged thin fibrils of
Part of the vitreous collagen ensheathed by acid mucopolysaccharides and
Retina
set in a ground substance. They form ribbon-like bun
Retinal pigment epithelium
dles and give the stroma a laminated appearance. The
Fibres of the optic nerve
collagen fibrils are circular on transverse section and are
Surface ectoderm Conjunctival epithelium
spaced equidistantly. They lie in staggered rows to form
Corneal epithelium
Lacrimal glands a hexagonal lattice.
Tarsal glands Transparency of the cornea is related to the regularity
Lens of the stromal components. The lattice theory proposes
Mesoderm Extraocular muscles that the stromal collagen fibrils are of regular diameter,
Corneal stroma arranged as a lattice with an interfibrillar spacing of less
Sclera
than a wavelength of light so that tangential rows of
Iris
Vascular endothelium of eye and orbit fibres act as a diffraction grating resulting in destructive
Choroid interference of scattered rays.
Part of the vitreous Descemet's membrane is a thin elastic membrane,
Neural crest* Corneal stroma, keratocytes and covered on its posterior surface by endothelium. The
endothelium primary mechanism controlling stromal hydration is a
Sclera
function of the corneal endothelium. Electrolytes are
Trabecular meshwork endothelium
removed and water flows passively. The endothelium
Iris stroma
Ciliary muscles may be examined by a specular microscope at a magnifi
Choroidal stroma cation of 500 x. Endothelial cells become less in number
Part of the vitreous with age and the residual individual cells may enlarge to
Uveal and conjunctival melanocytes
compensate.
Meningeal sheaths of the optic nerve
The cornea is set into the sclera like a watch glass so
Ciliary ganglion
Schwann cells of the that the latter overlaps the cornea all round the periph
Orbital bones ery; the junction of the two tissues is known as the lim-
Orbital connective tissue bus. The cornea is very richly supplied with nerve fibres
Connective tissue sheath and muscular layer
derived from the trigeminal nerve. It has no blood ves
of the ocular and orbital blood vessels
sels with the exception of minute arcades, extending
*During the folding of the neural tube, a ridge of cells comprising the about 1 mm into the cornea at the limbus, so that it is
neural crest develops from the tips of the converging edges and migrates
dependent for its nourishment upon diffusion of tissue
to the dorsolateral aspect of the tube. Neural crest cells from this region
subsequently migrate and give rise to various structures within the eye and fluid from the vessels at its periphery and the aqueous
the orbit. humour.
The structures are listed from anterior to posterior.
Lining the inner aspect of the sclera are two structures:
the highly vascular uveal tract concerned chiefly with the
nutrition of the eye, and within this a nervous layer, the
true visual nerve endings concerned with the reception
ANATOMY
and transformation of light stimuli, called the retina.
The uveal tract consists of three parts, of which the
The wall of the globe is composed of a dense, imperfectly two posterior, the choroid and ciliary body, line the sclera
elastic supporting membrane (Fig. 1.2). The anterior part of while the anterior forms a free circular diaphragm, the
the membrane is transparent—the cornea and the remain iris. The plane of the iris is approximately coronal; the
der is opaque—the sclera. The anterior part of the sclera is aperture of the diaphragm is the pupil. Situated behind
covered by a mucous membrane—the conjunctiva—which the iris and in contact with the pupillary margin is the
is reflected from its surface onto the lids. crystalline lens.
The cornea consists of three layers: the epithelium, the The anterior chamber is a space filled with fluid, the
substantia propria or stroma and Descemet's membrane aqueous humour; it is bounded in front by the cornea,
with its endothelium. The epithelium, which is stratified, behind by the iris and the part of the anterior surface
Section | Anatomy and Physiology
of the lens which is exposed in the pupil. Its periph (collagen and elastic components) and a fine framework
eral recess is known as the angle of the anterior chamber, (mucopolysaccharides) of extracellular materials, which
bounded posteriorly by the root of the iris and the cili form the probable site of greatest resistance to the flow
ary body and anteriorly by the corneosclera (Fig. 1.3). of aqueous.
In the inner layers of the sclera at this part there is a The endothelial cells of Schlemm's canal are con
circular venous sinus, sometimes broken up into more nected to each other by junctions which are not 'tight'
than one lumen, called the canal of Schlemm, which is but this intercellular pathway accounts for only 1%
of great importance for the drainage of the aqueous of the aqueous drainage. The major outflow pathway
humour. At the periphery of the angle between the canal appears to be a series of transendothelial pores, which
of Schlemm and the recess of the anterior chamber there are usually found in outpouchings of the endothelium
lies a loosely constructed meshwork of tissues, the tra called 'giant vacuoles' (Fig. 1.4A-C).
becular meshwork. This has a triangular shape, the apex The anterior chamber is about 2.5 mm deep in the
arising from the termination of Descemet's membrane centre in the normal adult; it is shallower in very young
and the subjacent fibres of the corneal stroma and its children and in old people.
base merging into the tissues of the ciliary body and The iris is thinnest at its attachment to the ciliary
the root of the iris. It is made up of circumferentially body, so that if torn it tends to give way in this region
disposed flattened bands, each perforated by numer (Fig. 1.3). It is composed of a stroma containing
ous oval stomata through which tortuous passages exist branched connective tissue cells, usually pigmented but
between the anterior chamber and Schlemm's canal. The largely unpigmented in blue irides, with a rich supply
extracellular spaces contain both a coarse framework of blood vessels which run in a general radial direction.
Chapter 1 Embryology and Anatomy
Fig. 1.3 The region of the angle of the anterior chamber.
The tissue spaces communicate directly with the ante sclera and related to the trabecular mesh work. The
rior chamber through crypts found mainly near the cili greater part of the muscle is composed of meridional
ary border; this allows the easy transfer of fluid between fibres running anteroposteriorly on the inner aspect of
the iris and the anterior chamber. The stroma is covered the sclera to find a diffuse insertion into the suprachor
on its posterior surface by two layers of pigmented epi oid. Most of the remainder of the fibres run obliquely
thelium, which developmentally are derived from the in interdigitating V-shaped bundles so as to give the
retina and are continuous with each other at the pupil impression of running in a circle round the ciliary body,
lary margin. The anterior layer consists of flattened cells concentrically with the base of the iris. The third por
and the posterior of cuboidal cells. From the epithelial tion of the muscle is composed of a few tenuous iridic
cells of the former, two unstriped muscles are developed fibres arising most internally from the common origin
which control the movements of the pupil, the sphincter and finding insertion in the root of the iris just anterior
pupillae, a circular bundle running round the pupillary to the pigmentary epithelium in close relation to the
margin, and the dilator pupillae, arranged radially near dilator muscle.
the root of the iris. The inner surface of the ciliary body is divided into
The anterior surface of the iris is covered with a single two regions; the anterior part is corrugated with a num
layer of endothelium, except at some minute depressions ber of folds running in an antero-posterior direction
or crypts which are found mainly at the ciliary border; it while the posterior part is smooth. The anterior part
usually atrophies in adult life. is, therefore, called the pars plicata, the posterior, the
The iris is richly supplied by sensory nerve fibres pars plana. About 70 plications are visible around the
derived from the trigeminal nerve. The sphincter pupil circumference macroscopically, but if microscopic sec
lae is supplied by parasympathetic autonomous secreto- tions are examined, many smaller folds, the ciliary pro
motor nerve fibres derived from the oculomotor nerve, cesses, will be seen between them. These contain no part
while the motor fibres of the dilator muscle are derived of the ciliary muscle, but consist essentially of tufts of
from the cervical sympathetic chain. blood vessels, not unlike the glomeruli of the kidney.
The ciliary body in anteroposterior section is shaped They are covered upon the inner surface by two layers
roughly like an isosceles triangle, with the base for of epithelium, which belong properly to the retina, and
wards. The iris is attached about the middle of the base, are continuous with similar layers in the iris; the outer
so that a small portion of the ciliary body enters into layer, corresponding to the anterior in the iris, consists
the posterior boundary of the anterior chamber at the of flattened cells, the inner of cuboidal cells, but only the
angle (Fig. 1.3). The chief mass of the ciliary body is outer layer in the ciliary body is pigmented.
composed of unstriped muscle fibres, the ciliary muscle. The ciliary body extends backward as far as the ora
This consists of three parts with a common origin in serrata, at which point the retina proper begins abruptly;
the ciliary tendon, a structure which runs circumferen- the transition from the ciliary body to the choroid, on the
tially round the globe blending with the 'spur' of the other hand, is gradual, although this line is conveniently
Section Anatomy and Physiology
Fig, 1.4 (A) Electron micrograph of a typical macrovacuoiar configuration as seen normally in the endothelial cells lining the trabecular
wall of Schlemm's canal. The vacuole (V), bound by a smooth unit membrane, is in fact formed by a basal invagination of the cell
surface and eventually opens on the luminal aspect, thus constituting a transient transcellular channel that allows the bulk outflow of the
aqueous humour. Owing to the vacuolar configuration of the channel, which has small basal and apical openings, these openings are rarely
encountered together in a single plane of section. The nucleus (N) is displaced to one side to accommodate the macrovacuole that contains
aqueous humour. For comparison of the size of the macrovacuole, a micropinocytotic vesicle (100nm) is denoted with p. J, junctional
complex of lining endothelial cells; BM, patchy basal lamina seen beneath the endothelial lining of Schlemm's canal; PT, loosely organized
pericanalicular tissue of the trabecular wall of Schlemm's canal (SC) (x18720).
Fig. 1.4 (B) Diagrammatic representation of the cyclical sequence of events in the formation of vacuolar transcellular channels that constitute
a dynamic system of pores, and the mechanism of the bulk outflow of the aqueous humour across the endothelial barrier of Schlemm's
canal. Initially, the vacuolar configuration is formed by a membranous depression or infolding on the basal aspect of the cell surface
(Stage 2). A progressive enlargement of this infolding leads to the formation of a macrovacuoiar structure (Stages 3 and 4) which eventually
opens on the luminal aspect of the cell's surface (Stage 5), thus forming a temporary vacuolar transcellular channel (continuous arrow). The
bulk outflow of aqueous humour takes place down a pressure gradient (i.e. from the trabecular meshwork into the lumen of the canal of
Schlemm) via such vacuolar transendothelial channels which also act as one-way valves. After a certain time interval, the basal infolding is
occluded and the cell returns to its non-vacuolated state (Stage 1).
Chapter 1 Embryology and Anatomy
Fig. 1.4 (C) Semidiagrammatic representation of the walls of Schlemm's canal (SC) and adjacent trabecular meshwork (TM) in a
composite sectional and three-dimensional view. The endothelial lining of the trabecular wall of Schlemm's canal is very irregular
and normally the cells show luminal bulges corresponding to cell nuclei (N) and macrovacuoiar configuration (V), the latter representing
cellular invaginations beginning from the basal aspect and eventually opening on the apical aspect of the cell to form transcellular
channels (arrows) through which aqueous humour flows down a pressure gradient. The sequence of events in this process is illustrated
in Fig 1.4 (B). A diverticulum (D) on the inner wall of Schlemm's canal is seen with its endothelial lining being continuous with that of the
canal and contains macrovacuoiar configurations. Such blind, tortuous diverticula course for a variable distance into the trabecular
meshwork but remain separated from the open spaces of the meshwork by their continuous endothelial lining. The endothelial lining of the
trabecular wall is supported by an interrupted, irregular basement membrane and a zone of pericanalicular connective tissue (PT) of variable
thickness; the cellular element predominates in this zone and the fibrous elements, especially elastic fibres, are irregularly arranged in a
net-like fashion, and the open spaces are narrower than the trabecular meshwork. The corneoscleral trabecular sheets show frequent
branching and the endothelial covering (asterisk) may be shared between adjacent trabecular sheets. The corneoscleral wall (CW) of
Schlemm's canal is more compact than the trabecular wall, with a predominance of lamellar arrangement of collagen and elastic tissue.
(By courtesy of RC Tripathi)
accepted as the limit of the two structures. The ora ser- large vessels, the whole being held together by a stroma
rata thus circles the globe, but is slightly more anterior consisting of branched pigmented connective tissue cells
on the nasal than on the temporal side. (Fig. 1.5). The choroid is supplied with sensory nerve
The ciliary body is richly supplied with sensory nerve fibres from the trigeminal as well as autonomic nerves,
fibres derived from the trigeminal nerve. The ciliary presumably of vasomotor function.
muscle is supplied with motor fibres from the oculomo The retina corresponds in extent to the choroid, which
tor and sympathetic nerves. it lines, although the same embryological structure is
The choroid is an extremely vascular membrane in con continued forwards as a double layer of epithelium as
tact everywhere with the sclera, although not firmly adher far as the pupillary margin. If the two layers of epithe
ent to it, so that there is a potential space between the two lium are traced backwards, the anterior layer in the iris is
structures—the epichoroidal or suprachoroidal space (Fig. 1.5). found to be continuous with the outer layer in the ciliary
On the inner side, the choroid is covered by a thin elastic body, and this again is continued into the pigment epi
membrane, the lamina vitrea or membrane of Bruch. thelium of the retina as a single layer of hexagonal cells
The blood vessels of the choroid increase in size from lying immediately adjacent to the membrane of Bruch.
within outwards, so that immediately beneath the mem Similarly the posterior layer in the iris, although pig
brane of Bruch there is a capillary plexus of fenestrated mented, passes into the inner unpigmented layer of the
vessels, the choriocaptilaris (Fig. 1.6). Upon this is the layer ciliary body, and this suddenly changes at the ora serrata
of medium-sized vessels, while most externally are the into the highly complex visual retina.
9
I5BI | Anatomy and Physiology
Fig. 1.5 Normal choroid: R, rods and cones; P, pigment epithelium; B, Bruch's membrane; C, choriocapillaris; S, small vessels; and L, large
vessels. (By courtesy of Garner)
Most externally, in contact with the pigment epithe
lium, is a neural epithelium, the rods and cones, which
are the end-organs of vision (Fig. 1.8). The microanat
omy of the rods and cones reveals the transductive
region (outer segment), a region for the maintenance of
cellular homoeostasis (inner segment), a nuclear region
(outer nuclear layers) and a transmissive region (the
outer plexiform or synaptic layer).
When the outer segments of the rods are sectioned
parallel to their long axes, they are seen by the electron
microscope to consist of a boundary or cell membrane,
which encloses a stack of membrane systems. The discs
in the rods of many species are continuously renewed
throughout life. New discs are formed in the region
of the inner segment and are progressively displaced
towards the pigment epithelium. Rod discs have a
limited life and are eventually lost to the pigment
epithelium.
At the junction of the inner and outer segments, the
cell body of both rods and cones constricts. The electron
microscope reveals a connecting cilium which is always
eccentric and provides the only link between the inner
and outer segments.
Fig. 1.6 Freeze-fractioned replica of endothelial cell membrane
from the choriocapillaris of the rabbit to show groups of The pigment epithelium consists of a single layer of
fenestrations separated by smooth cytoplasmic areas. (By courtesy hexagonal cells lying between the photoreceptor outer
of S Melamed) segment and Bruch's membrane. They assist the metab
olism of the retina by transporting selected substances
The retina consists of a number of layers (Fig. 1.7A to the receptor cells. Products of metabolism are freely
and B) formed by three strata of cells and their exchanged between the receptor cells and the pigment
synapses—the visual cells (lying externally), a relay layer epithelium.
of bipolar cells (lying intermedially) and a layer of gan The most striking inclusions in the pigment epithe
glion cells (lying internally), the axons of which run into lium are the organelles responsible for its colour, the
the central nervous system. melanin granules. Most of the light which passes through
10
