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Shape: Round or slightly oval (Fig. 5.22).
Colour: Pink with slight temporal pallor.
Physiological cup: a depression in the central part, is more pale than the surrounding disc and from it retinal vessels enter and leave the eye. It varies in depth and size but diameter should not exceed 50% of the disc.
Edge (margin) of the disc: Quite commonly, there is a surrounding white scleral ring, a dark pigmented ring or a stippled choroidal ring.
The retinal blood vessels: They radiate from the disc, dividing dichotomously into many branches as they pass towards the periphery. The arteries or arterioles have a smaller calibre than the veins, and have a bright red colour. Healthy vessel walls are not visible. Note the normal and abnormal pulsations.
Spontaneous venous pulsation is a normal finding;
while spontaneous retinal artery pulsations are abnormal and occurs in glaucoma and aortic regurgitation.
Macular region. It is a portion of the posterior retina containing xanthophilic pigment (hence, macula lutea) and two or more layers of ganglion cells. The fovea (5.5 mm in diameter) lies at the
Fig. 5.21: Ophthalmoscope
centre of macula and is devoid of blood vessels.
Macular involvement produces greater reduction of the vision than similar changes in any other part.
Periphery of the fundus. It is examined only when pupil is dilated with a mydriatic (tropicamide 0.5%
drops). Certain disease processes i.e. retinal tears and retinitis pigmentosa can be diagnosed.
B. The abnormalties of the fundus (Fig. 5.23 to 5.30) 1. Retinal atrophy
Old injuries and inflammation may result in atrophic scars. White patches of atrophic retina occur in congenital coloboma, high myopia and retinal degeneration.
2. Abnormal pigmentation
Macular degeneration (Fig. 5.23) occurs in old persons (age related process) in which retinal pigment epithelial changes cause
hypopigmenta-tion and pigment clumping at the macula. Central vision is poor.
Melanomas. Benign choroidal melanomas are flat dark lesions while malignant melanomas are raised, enlarge progressively and often metasta-size.
Retinitis pigmentosa is associated with pigment deposits like bony spicules, seen in Laurence-Moon-Biedle Syndrome.
3. Abnormal exudates (Table 5.7) 4. Optic atrophy
It is defined as atrophy or death of optic nerve fibres leading to reduction or loss of tiny blood vessels. In this condition, the disc is paler than normal, and may even be white (Fig. 5.24).
In optic atrophy, the number of capillaries that cross the disc margin is reduced from normal 10 to 7 or less (Kestenbaum's sign).
The classification of optic atrophy into primary (disc is flat, chalky-white in colour with clear cut margins), secondary (atrophy follows papilloe-dema) and consecutive (glucomatous) is confusing, hence, avoided.
Table 5.7: Abnormal deposits on the retina
Character Hard exudates (Fig. 5.29) Soft exudates (Fig. 5.28)
1. Site They are deep They are superficial.
2. Margins Well defined, deep seated (hence hard) Irregular or ill-defined, superficial (hence soft) 3. Arrangement They are often arranged in rings. At the macula, They look like deposits of cotton-wool
they may arrange in a star (macular star)
4. Pathogenesis They are caused by leakage of proteins though an They occur around areas of infarcted retina and may be abnormal permeable blood vessel. associated with other features of retinal ischaemia
(venous dilatation, haemorrhage, new blood vessels).
They are due to swelling of optic nerve fibre layer.
5. Causes They are seen in hypertension, diabetes, and They are seen in retinal artery ischaemia put it infarction following retinal vascular occlusions. due to hypertension or retinal vein occlusion
Fig. 5.23: Age related macular degeneration. Note the accumulation of drusen within macula. They appear as scattered yellow subretinal deposits
Fig. 5.22: Normal fundus
Fig. 5.25: Glaucomatous optic atrophy. The physiological cup is enlarged. The disc is pale. The retinal vessels are displaced nasally because of angulation of the optic cup
Fig. 5.26: Papilloedema. The fundus photograph was taken from a patient with raised intracranial pressure. Note the disc oedema, haemorrhage and cotton wool exudates
Clear focus here (periphery) Clear focus here (disc)
at –1 diopter at +2 diopters
Calculation of papilloedema +2 –(–1)=3, therefore disc
is elevated by 3 diopters, hence, popilloedema is 3D
(diopters) Fig. 5.24: Fundus photograph of a patient with optic atrophy.
Note the pallor of disc with arteriolar narrowing
Fig. 5.27: Calculation of papilloedema in diopters (read the text)
Causes: They are given in the Box 5.9.
Box 5.9: CAUSESOFOPTICATROPHY
1. Inherited, e.g. Leber's optic atrophy
2. Toxic, e.g. ethambutol, methyl alcohol, carbon-monoxide and ethylene glycol (antifreeze)
3. Glaucoma (Fig. 5.25) 4. Extensive retinal disease 5. Ischaemic optic atrophy
6. Demyelinating disease, e.g. multiple sclerosis, Devic’s disease
7. Trauma, e.g. avulsion of optic nerve
8. Tumours, e.g. pituitary adenoma, craniopharyngioma 5. Papilloedema
It is bilateral optic disc swelling from raised intracranial pressure. All other forms of optic disc swelling, e.g. from inflammation of optic nerve (optic neuritis) or ischaemic optic neuropathy should be called "optic disc oedema" rather than papilloedema.
This convention is arbitrary but serves to avoid confusion. Disc changes in papilloedema are given in the Box 5.10 and Fig. 5.26.
Calculation of papilloedema in diopters: The elevated disc of papilloedema can be measured by noting the differences in diopters of the two lenses used to focus clearly on the disc and on univolved retina (Fig. 5.27).
neuritis in which neither the doctor sees any abnormality of the fundus nor the patient sees anything, i.e. vision is lost. The difference between optic neuritis and papilloedema are summarised in the Box 5.11. Optic neuritis is frequently followed by optic atrophy, with residual reduction in visual acuity and scotomas (central or peripheral). It may occur alone, bilaterally (Devic's disease) or during the course of multiple sclerosis.
Box 5.11: DIFFERENTIATIONBETWEENOPTICNEURITISANDPAPILLOEDEMA
Optic neuritis Papilloedema
• Eye movements are painful They are painless
• Ocular tenderness on No such tenderness compression
• In papillitis, there is hyper- Marked swelling of the aemia and some swelling of disc with loss of cup (e.g.
the disc cup is full)
• Severe visual loss Minimal visual impairment
• There may be signs of No signs of inflammation inflammation, e.g. hazy
vitreous and retinal exudates 7. Retinal haemorrhages
Superficial retinal haemorrhage are flame-shaped because of tracking of the blood along the horizontally arranged nerve fibres. They occur in hypertension.
Deep haemorrhages are round blotches and spots contained by vertically arranged deep retinal layers.
Microaneurysms also look very similar. Both occur in the dots (aneurysms) and blots (haemorrhage) of diabetic retinopathy.
Subhyloid haemorrhages, situated in front of retina, are occasionally very large round haemorrhage obscuring the underlying retina. They may occur following subarachnoid haemorrhage or follow bleeding from new retinal vessels in diabetic retinopathy.
Vitreous haemorrhage. The fundus is hidden by a dark haze of blood. The blood may be distributed diffusely through the vitreous gel or form clots which cause tadpole-like floaters. It is an important cause of sudden loss of vision.
Causes: They are given in the Box 5.12.
Box 5.12: CAUSESOFRETINALHAEMORRHAGES
• Hypertension
• Diabetes
• Trauma
• Blood disorders, e.g. anaemia, sickle cell disease, leukaemia, bleeding diathesis
• Anticoagulants
• Subarachnoid haemorrhage
• Retinal vein occlusion
• Age-related macular disease Fig. 5.28: Central retinal vein occlusion. The veins are tortuous and
enlarged, and haemorrhages of varying shapes are scattered throughout. The optic disk is obscured completely. A few cotton wool spots exudates can be seen on nasal side
Box 5.10: OPTICDISCINPAPILLOEDEMA (FIG. 5.26)
• The swollen disc is pink and hyperemic
• Disc vessels clearly visible, more numerous, curve over the borders of the disc. There is venous dilatation and loss of venous pulsations
• The margins are blurred
• The physiological cup is not visible, i.e. cup is lost and full.
Causes: They are given in the Table 5.8.
Table 5.8: Causes of papilloedema
1. Raised intracranial pressure due to tumours, abscesses, meningitis, obstructive hydrocephalus, subdural haematoma, subarachnoid haemorrhages, dural sinus thrombosis and idiopathic.
2. Cerebral oedema
3. Accelerated or malignant hypertension (hypertensive crisis) 4. Haematological disorders, e.g. anaemia, leukaemia
5. Respiratory diseases, e.g. emphysema, carbon dioxide narcosis 6. Vitamin A deficiency or excess
7. Hypoparathyroidism
8. Optic nerve tumour (Foster-Kennedy syndrome) in which there is ipsilateral optic atrophy and contralateral papilloedema 9. Pseudopapilloedema due to drusen (optic nerve drusen are refractile deposits within substance of the optic nerve head) 10. Papillitis
6. Optic neuritis
It results from inflammatory, demyelinating or vascular disease leading to marked loss of vision.
There may be retrobulbar involvement (retrobulbar
• Large flame-shaped haemorrhages and cotton-wool spots splashed over the fundus (Fig. 5.28)
• Swelling of the optic disc
• Gross venous dilatation.
10. Retinopathy. The two common types of retinopathy seen are hypertensive and diabetic. The fundus changes are given in the Box 5.13.
Box 5.13: FUNDUSCHANGESINTWOCOMMONRETINOPATHY
Hypertensive retinopathy Diabetic retinopathy
Fig. 5.29 Fig. 5.30
1. Diffuse or segmental 1.Microaneurysms.
narrowing of arterioles/ Capillary microane-arteries and thickening urysms are the earliest of their walls, venous abnormality detected in nipping. The thick background retinopathy walled arterioles
compress the veins at crossings giving "silver wiring"
appearance
2. Flame-shaped 2. Dots and blots
haemorrhages haemorrhage
3. Hard exudates. 3. Both hard and soft Sometimes star-shaped exudates (cotton-wool) exudates around the
macula (macular star)
4. Papilloedema may occur 5. Neovascularisation—new especially in malignant vessels extend into hypertension vitreous and may bleed,
are seen in proliferative diabetic retinopathy
• Pre-retinal and vitreous haemorrhage
• Fibrosis, retinitis proliferans and retinal detachment
Investigations for a case with eye disorder
1. Refraction test. It is done to ascertain the optical power of an eye. This is performed subjectively by placing neutralising lenses in front of the eye and simultane-ously assessing the visual acuity. An objective refraction is also performed in conjunction with a retinoscope.
2. Measurement of intraocular tension (see the method.
Fig. 5.5). It is measured by tonometry.
3. Ophthalmoscopy. It has already been discussed.
4. A slit lamp examination. It consists of a binocular microscope mounted on a table with an adjustable beam of light. This provides a magnified optical section of the various structures of the eye to be examined.
Fig. 5.29: Hypertensive retinopathy with macular star. Note the punctate hard exudates forming a macular star. Note also the flame-shaped haemorrhage and two small soft exudates
Fig. 5.30: Diabetic background retinopathy. Note the blot haemorrhages in different stages of resolution, microaneurysm (dots) and a few hard exudates in the lateral part of retina. This is a characteristic appearance as dot and blot appearance of fundus in diabetic background retinopathy
8. Occlusion of central artery of retina
It refers to sudden, and often total loss of vision. It is characterised by:
• Pale and swollen optic disc and surrounding retina
• A cherry-red spot at the macula
• The retinal arteries are narrow and thread-like.
It is due to embolic occlusion of retinal vessels from an atheromatous plaque.
9. Retinal vein occlusion. In central vein occlusion a little vision is retained. It is characterised by:
5. Fundus photography and fluorescein angiography.
They are useful adjunct to the diagnosis of retinal and choroidal disorder. The fluorescein angiography is superior to plain fundus photography because a detailed assessment of retinal and choroidal vasculature is possible after injection of sodium fluorescein—a dye. The blue filter of fundus camera excites fluorescence as the dye circulates.
6. Ultrasonography. It is used to detect retinal detachments and intraocular or orbital tumours.
7. Dacrocystography. A contrast study is used to identify the obstruction in lacrimal drainage system.
8. CT scan and MRI. They are also useful in the diagnosis of orbital disease.
9. Electrophysiological study:
• Visual evoked potential (VEP). If a stimulus is applied, for example, to the eye, it would normally be impossible to detect small EEG response evoked by it over the occipital cortex as the signal will be lost in background noise.
However, if EEG data from repeated stimuli
(100-1000) are averaged electronically and the noise is removed then an evoked potential can be recorded whose latency (time interval between stimulus onset and its maximum positive wave of the evoked potential, P100 wave) and amplitude can be measured.
The abnormalities in evoked potential occur in the form of either conduction delay (increased latency) or reduction in amplitude of the wave form or both.
It is useful for diagnosis of lesion of the visual pathways, usually demyelinating optic neuritis (retrobulbar neuritis) seen in multiple sclerosis, compressive lesion of the optic pathway, toxic and nutritional amblyopias, Leber's optic atrophy and heredofamilial ataxia.
VEP can be used to distinguish hysterical from cortical blindness.
Electroretinograms are used in assessing the patients with hereditary or acquired retinal degenerations.