Fundamentals Of Glaucoma: A Guide For Ophthalmic Nurse Practitioners, Optometrists And Orthoptists. Группа авторов
and Midland Eye Centre, Birmingham, U.K.
Mr Michael Smith, Consultant Ophthalmologist, West of England Eye Unit, Exeter, U.K.
Mr Adam Booth, Consultant Ophthalmologist, Royal Eye Infirmary, Plymouth, U.K.
Mr Pierre Rautenbach, Consultant Ophthalmologist, Department of Ophthalmology, Royal Cornwall Hospitals NHS Trust, U.K.
Mrs Katie Smith, Specialist Optometrist, Bristol Eye Hospital, Bristol, U.K.
Mrs Pam Adams, Optometrist and LVA Clinic Supervisor, Department of Optometry and Vision Sciences, University of Plymouth, U.K.
Mr Abhijit A. Mohite, Glaucoma Fellow, Birmingham and Midland Eye Centre, Birmingham, U.K.
Mr Thomas Sherman, Specialist Registrar, South West Peninsula School of Ophthalmology, U.K.
Mr Neil Bowley, Specialist Registrar, South West Peninsula School of Ophthalmology, U.K.
Mr Andrew Swampillai, Specialist Registrar, South West Peninsula School of Ophthalmology, U.K.
ILLUSTRATIONS
Khadijah Azhar (www.khadijahazhar.com)
INTRODUCTION
Glaucoma is one of the commonest causes of visual impairment worldwide.
Ophthalmic Nurse Practitioners, Optometrists and Orthoptists are increasingly becoming invaluable team members for diagnosing, monitoring and treating glaucoma, particularly as the clinical demand increases.
This book has been written to assist our colleagues in such an endeavour, and it is hoped that it will provide concise but relevant information in a format that is easy to carry around and access. It is aimed primarily at nurse practitioners and allied health professionals, but we are confident that it will also be a useful reference for junior ophthalmic trainees learning about the condition.
We wish our readers all the best for their career as part of the glaucoma team!
1
ANATOMY
Pierre Rautenbach
In order to develop an understanding of the glaucomatous disease process and the treatment options available, it is imperative to have a good grasp of the basic anatomy and physiology of certain relevant parts of the eye.
The eye is an approximate sphere 2.5 cm in diameter (equivalent to an axial length of 25 mm) with a volume of 5 ml (it fills one-sixth of the orbit whose volume is 30 ml).
It is a highly specialised organ of photoreception. This is a process by which light energy from the environment produces changes in specialised nerve cells in the retina (rods and cones). These changes result in action potentials (the electrical voltage across a cell) that are subsequently relayed to the optic nerve and then to the brain where the information is processed and consciously appreciated as vision.
THE LAYERS OF THE EYE
The eye consists of 3 basic layers.
Fig. 1.1. The eye in cross section.
The Fibrous Corneoscleral Coat
It consists of the cornea and sclera.
•The Cornea
This is the anterior most transparent window of the eye. The cornea meets the sclera at the limbus, which is also where the conjunctiva ends. The conjunctiva covers the sclera but does not cover the cornea. The cornea is kept transparent by its avascularity and the innermost monolayer of cells (endothelium) which pumps fluid out of the corneal stroma. The cornea presents a tough barrier to trauma and infection and is responsible for about two-thirds of the eyes refractive power (the other one-third coming from the lens).
•The Sclera
This is an opaque white fibrous coat that also protects the eye and maintains its shape due to inherent structural integrity.
The Uvea (or Uveal Tract)
The middle vascular pigmented layer of the eye and consists of the iris, ciliary body and choroid.
•The Iris
This is a thin contractile circular disc, which is analogous to the diaphragm of a camera. The iris separates the anterior and posterior chambers, which are filled with aqueous humour and are in continuity through an opening, the pupil. The iris is attached by its root at the ‘angle’ (iridocorneal) of the anterior chamber where it merges with the ciliary body and trabecular meshwork. Aqueous humour drains mainly through the trabecular meshwork, which is visible using a mirror within a contact lens called a gonioscope.
•The Ciliary Body
This is approximately 6 mm in width and is responsible for the production of aqueous humour. It also contains muscles, which are attached to the zonular ligaments of the lens (changing its shape on contraction to focus or accommodate). It has two parts, the pars plicata and the pars plana. The pars plicata is the anterior part. It is 2 mm long (measured from the limbus) and contains about 70 ciliary processes which are the site of attachment for the aforementioned zonular ligaments. The pars plana is a posterior flat area which is 4 mm long. As the sclera and cornea are relatively rigid, excess production/reduced drainage of aqueous humour or injection of substances into the eye leads to raised intra-ocular pressure (normal is up to 21 mmHg). Intraocular pressure is high immediately after intravitreal injections (can be as high as 60 mmHg). Normalisation of the pressure usually occurs over 30 minutes after injection and is dependent on aqueous humour outflow through the trabecular meshwork.
•The Choroid
This highly pigmented and vascular posterior portion lies between the sclera and the retina and extends forward to the ciliary body. Its principal function is to nourish the outer layers of the retina and prevent unwanted light from reflecting back through the retina. It is composed of an outer layer of large calibre blood vessels, which divide into smaller diameter vessels and ultimately form the choriocapillaris (a network of capillaries). These drain into the vortex veins, which ultimately drain into the superior and inferior ophthalmic veins.
The Retina (Neural Layer)
This is where photoreception occurs and consists of two primary layers, the inner neurosensory retina and an outer layer called the retinal pigment epithelium. Anatomically the following regions are described:
•The Macula (Latin ‘patch’, same as macula lutea)
The area within the main vascular arcades and is 5–6 mm in diameter. Cone photoreceptors are mostly concentrated here for fine resolution (maximum density in the fovea).
•The Fovea (Latin: ‘pit’)
The central 1.5 mm diameter area of the macula. The foveola is the central 0.35 mm diameter area of the fovea.
•The Optic Disc
1.5 mm in diameter, it contains no normal retinal layers or photoreceptors (thus causing the blind spot) and is the area where nerve fibres of retinal ganglion cells pierce the sclera to enter the optic nerve. The central pale thinned area of the