Introduction
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Primary function : to focus light on the retina.
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Cataract (lens opacification) : is the commonest cause of reversible visual disability in the world. Phacoemulsification with intra-ocular lens implantation is the commonest surgical procedure undertaken in the developed world.
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Presbyopia : is the gradual loss of the ability of the lens to focus on near objects. It is an inevitable ageing phenomenon and occurs as a consequence of a loss of accommodation secondary to reduced lens elasticity.
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Anatomy : (a) zonules hold the lens in position, (b) the capsule is an acellular membrane that encloses the lens material, (c) cuboid epithelial cells are located beneath the anterior capsule and extend to the lens equator; cells in the germinative area divide continuously and differentiate to form lens fibers, (d) the lens substance is made up of a central nucleus surrounded by corticular material.
Acquired cataract
Effect on vision
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Depends on : (a) extent of the cataract, (b) the position of the opacification, (c) the morphological appearance.
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Reduced visual acuity : which can initially be corrected with spectacles.
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Loss of contrast sensitivity .
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Change in colour perception : particularly an inability to accurately perceive blue colours.
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Glare : secondary to light scattering, causing difficulty with night driving.
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Monocular diplopia : especially when looking at a point source of light.
Age-related cataract
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Subcapsular : (a) anterior lies directly under the lens capsule, (b) posterior lies immediately in front of the posterior capsule and appears black on retroillumination. This type has a more profound effect on vision than a nuclear or cortical cataract and is often associated with glare and poor near vision ( Fig. 10.1A ).
Fig. 10.1
Age-related cataract: (A) posterior subcapsular, (B) nuclear sclerotic, (C) corticular, (D) Christmas tree.
(From Salmon JF, Kanski’s Clinical Ophthalmology: A Systematic Approach , 9th edition. Oxford, UK: Elsevier; 2020.)
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Nuclear : the most common; often associated with myopia due to an increase in the refractive index of the nucleus; when advanced, the nucleus appears brown ( Fig. 10.1B ).
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Cortical : starts as clefts and vacuoles between lens fibres due to hydration of the cortex and evolves into wedge-shaped or radial spoke-like opacities ( Fig. 10.1C ).
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Christmas tree : polychromatic opacities ( Fig. 10.1D ).
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Cataract maturity : (a) immature (lens is partially opaque), (b) mature (lens is completely opaque), (c) hypermature (shrunken and wrinkled capsule) ( Fig. 10.2A ), (d) Morgagnian cataract (inferior sinking of nucleus in a liquefied cortex) ( Fig. 10.2B ).
Fig. 10.2
Mature cataract: (A) shrunken and wrinkled capsule, (B) Morgagnian showing inferior sinking of nucleus in a liquefied cortex.
(From Salmon JF, Kanski’s Clinical Ophthalmology: A Systematic Approach , 9th edition. Oxford, UK: Elsevier; 2020.)
Cataract in systemic disease
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Diabetes mellitus : hyperglycaemia leads to the overaccumulation of metabolic products in the lens, initially leading to fluctuating refraction and later to cataract, particularly accelerated age-related nuclear.
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Myotonic dystrophy : fine cortical iridescent opacities that evolve into a visually disabling stellate posterior subcapsular cataract ( Fig. 10.3A ).
Fig. 10.3
Cataract in systemic disease: (A) myotonic dystrophy, (B) atopic dermatitis.
(From Salmon JF, Kanski’s Clinical Ophthalmology: A Systematic Approach , 9th edition. Oxford, UK: Elsevier; 2020.)
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Atopic dermatitis : dense anterior subcapsular plaque is characteristic ( Fig. 10.3B ).
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NF2 : cataract develops in approximately 60% of patients, often before the age of 30 years.
Causes of secondary cataract
A secondary (complicated) cataract develops as a result of other primary ocular disease such as the following:
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Chronic anterior uveitis : cataract may be caused both by inflammation and by steroids; progresses more rapidly in the presence of posterior synechiae ( Fig. 10.4A ).
Fig. 10.4
Secondary cataract: (A) chronic anterior uveitis, (B) glaukomflecken.
(From Salmon JF, Kanski’s Clinical Ophthalmology: A Systematic Approach , 9th edition. Oxford, UK: Elsevier; 2020.)
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Acute congestive angle closure : small, grey-white, anterior opacities within the pupillary area (glaukomflecken; Fig. 10.4B ).
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High (pathological) myopia : posterior subcapsular opacities and early onset nuclear sclerosis.
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Hereditary fundus dystrophies : retinitis pigmentosa, Leber congenital amaurosis, gyrate atrophy and Stickler syndrome (see Chapter 15 ).
Causes of traumatic cataract
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Penetrating trauma ( Fig. 10.5A )
Fig. 10.5
Traumatic cataract: (A) penetrating (arrows showing corneal and lens entry site), (B) blunt injury, showing typical flower-shaped opacity.
(From Salmon JF, Kanski’s Clinical Ophthalmology: A Systematic Approach , 9th edition. Oxford, UK: Elsevier; 2020.)
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Blunt trauma: may cause a characteristic flower-shaped opacity ( Fig. 10.5B ).
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Electric shock.
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Infrared radiation (e.g. occupational exposure).
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Ionizing radiation (e.g. for ocular tumours).
Management of age-related cataract
Preoperative considerations
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Indications for surgery : (a) visual improvement, (b) medical indications (e.g. phacomorphic glaucoma; see Chapter 11 ), (c) to facilitate management of fundus disease (e.g. diabetic retinopathy).
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Systemic preoperative assessment : general medical history; investigations are not usually performed for routine local anaesthesia.
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Ophthalmic preoperative assessment : (a) past ophthalmic history, (b) visual acuity (VA), (c) cover testing, (d) pupillary responses, (e) slit lamp biomicroscopy, (f) ocular adnexa (e.g. chronic dacryocystitis), (f) red reflex quality, (g) fundus examination (ultrasound if poor view), (h) refractive status (including postoperative result from the other eye).
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Biometry : facilitates calculation of the lens power for a planned refractive outcome by measuring corneal power (keratometry) and axial length (e.g. optical interferometry, US). Refractive outcome planning may need to take into account the refractive status of the fellow eye as well as the patient’s preferences and the effect of previous ocular surgery.
Intraocular lenses
The intraocular lens (IOL) is optimized for positioning within the intact capsular bag ( Fig. 10.6A ). Complicated surgery may necessitate alternative placement within the ciliary sulcus or in the anterior chamber.
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Flexible IOLs : made of silicone, acrylic, or Collamer; can be rolled or folded for introduction into the eye through a small incision.
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Rigid IOLs : still occasionally used.
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Sharp/square-edged optics : associated with a lower rate of posterior capsular opacification (PCO) compared with round-edged optics.
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Ultraviolet filter : routine in modern IOLs to reduce energy incident on the retina; blue light filters are also available.
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Aspheric IOL optics : counteract spherical aberration.
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Heparin coating : reduces the attraction and adhesion of inflammatory cells, which may have particular application in eyes with uveitis.
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Multifocal, accommodative and pseudo-accommodative IOLs : aim to provide clear vision over a range of focal distances ( Fig. 10.6B ).
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Toric IOLs : integral cylindrical refractive component to compensate for pre-existing corneal astigmatism.
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Adjustable IOLs : alteration of refractive power following implantation.
