When the vitreous gel shrinks as part of the normal ageing process, it tugs on the retina (rods and cones), causing flashing lights. When the gel separates from the retina, floaters (which may appear as dots, spots or cobwebs) are seen. Floaters are more commonly seen with age, but are also more common in people who are myopic or who have had eye surgery such as removal of cataracts. It is important to consider retinal detachment but if floaters remain constant there is little cause for concern. The appearance of a fresh onset of flashes or floaters is of concern.
Indistinct or blurred vision is most commonly caused by errors of refraction—the commonest being myopia.
In the normal eye (emmetropia) light rays from infinity are brought to a focus on the retina by the cornea (contributing about two-thirds of the eye’s refractive power) and the lens (one-third). Thus, the cornea is very important in refraction and abnormalities such as keratoconus may cause severe refractive problems.6
The process of accommodation is required for focusing closer objects. This process, which relies on the action of ciliary muscles and lens elasticity, is usually affected by ageing, so that from the age of 45 close work becomes gradually more difficult (presbyopia).6
The important clinical feature is that the use of a simple ‘pinhole’ in a card will usually improve blurred vision or reduced acuity where there is a refractive error only.1
Close objects appear clearly but far objects are blurred. This is usually progressive in the teens. Highly myopic eyes may develop retinal detachment, macular degeneration or glaucoma.
This condition is more susceptible to closed angle glaucoma. In early childhood it may be associated with convergent strabismus (squint). The spectacle correction alone may straighten the eyes. It is mostly overcome by the accommodative power of the eye, though it may cause reading difficulty. Typically, the long-sighted person needs reading glasses at about 30 years. A convex lens is used for correction.
There is a need for near correction with loss of accommodative power of the eye in the 40s.
There is non-spherical (variable) curvature of the lens or cornea. This creates the need for a corrective lens that is more curved in one meridian than another because the cornea does not have even curvature. If uncorrected, this may cause headaches of ocular origin. Conical cornea is one cause of astigmatism.
Keratoconus is a bulging, slowly progressive thinning and distortion of the cornea, leading to loss of visual acuity—commonly irregular astigmatism. It usually appears between the ages of 10 and 25 and seems to be genetically determined. Frequent changes of glasses is a feature and contact lenses may help. If not, corneal transplant surgery may be necessary.
The pinhole reduces the size of the blur circle on the retina in the uncorrected eye. A pinhole acts as a universal correcting lens. If visual acuity is not normalised by looking through a card with a 1 mm pinhole, then the defective vision is not solely due to a refractive error. The pinhole test may actually help to improve visual acuity with some cataracts. Further investigation is mandatory.
The term ‘cataract’ describes any lens opacity. The symptoms depend on the degree and the site of opacity. Cataract causes gradual visual loss with normal direct pupillary light reflex.
The prevalence of cataracts increases with age: 65% at age 50–59, and all people aged over 80 have opacities.3 Significant causes of cataracts are presented in TABLE 77.2 and causes of progressive visual loss in TABLE 77.3.
Table 77.2Causes of cataracts ||Download (.pdf) Table 77.2 Causes of cataracts
Steroids (topical or oral)
Radiation: long exposure to UV light
TORCH organisms ➜ congenital cataracts
Table 77.3Progressive bilateral visual loss ||Download (.pdf) Table 77.3 Progressive bilateral visual loss
|Globe || |
|Retina || |
|Optic nerve || |
Optic nerve compression (e.g. aneurysm, glioma)
Toxic damage to optic nerves
|Optic chiasma ||Chiasmal compression: pituitary adenoma, craniopharyngioma, etc. |
|Occipital cortex || |
difficulty in recognising faces
problems with driving, especially at night
difficulty with television viewing
reduced ability to see in bright light
may see haloes around lights
The type of visual distortion seen by patients is illustrated in FIGURE 77.2.
Blurred vision: appearance of a subject through the eyes of a person with cataracts.
Photo courtesy Allergan Pharmaceuticals
Reduced visual acuity (sometimes improved with pinhole)
Diminished red reflex on ophthalmoscopy
A change in the appearance of the lens
The red reflex and ophthalmoscopy
The ‘red reflex’ is a reflection of the fundus when the eye is viewed from a distance of about 60 cm (2 feet) with the ophthalmoscope using a zero lens. This reflex is easier to see if the pupil is dilated. Commencing with the plus 15 or 20 lens, reduce the power gradually and, at plus 12, lens opacities will be seen against the red reflex, which may be totally obscured by a very dense cataract. The setting up of the ophthalmoscope to examine intraocular structures is illustrated in FIGURE 77.3.
Settings of the ophthalmoscope used to examine intraocular structures
Advise extraction of the cataract when the patient cannot cope. Contraindications for extraction include intraocular inflammation and severe diabetic retinopathy. There is no effective medical treatment for established cataracts. The removal of the cataractous lens requires optical correction to restore vision and this is usually performed with an intraocular lens implant. Full visual recovery may take 2–3 months. Complications are uncommon yet many patients may require YAG laser capsulotomy to clear any opacities that may develop behind the lens implant.
Postoperative advice to the patient
Avoid bending for a few weeks.
Avoid strenuous exercise.
The following drops may be prescribed:
— steroids (to reduce inflammation)
— antibiotics (to avoid infection)
— dilators (to prevent adhesions)
Sunglasses, particularly those that wrap around and filter UV light, may offer protection against cataract formation.
Glaucoma, which is caused by raised intraocular pressure, is categorised as open-angle or closed-angle and further as primary or secondary and acute or chronic. Open-angle glaucoma, also known as chronic simple glaucoma is the commonest cause of irreversible blindness in middle age.1 At a very late stage, it presents as difficulty in seeing because of loss of the outer fields of vision due to optic atrophy (see FIG. 77.4). Acute glaucoma, on the other hand, has a relatively rapid onset over a few days.
Typical visual field loss for chronic simple glaucoma; a similar pattern occurs with retinitis pigmentosa and hysteria
Clinical features (chronic glaucoma)
No early signs or symptoms
Central vision usually normal
Insidious progressive restriction of visual field resulting in ‘tunnel vision’
Adults 40 years and over: 2–5 yearly (at least 2 yearly over 60)
Start about 30 years, then 2 yearly if family history
Treatment can prevent visual field loss
Medication (for life) usually selected from:7
— timolol or betaxolol drops bd
Note: These beta blockers can cause systemic complications, e.g. asthma
— latanoprost (or other prostaglandin analogue) drops, once daily
— pilocarpine drops qid
— dipivefrine drops bd
— brimonidine drops bd
— acetazolamide (oral diuretics)
Surgery or laser therapy for failed medication
Primary degeneration of the retina is a hereditary condition characterised by a degeneration of rods and cones associated with displacement of melanin-containing cells from the pigment epithelium into the more superficial parts of the retina.
Begins as night blindness in childhood
Visual fields become concentrically narrowed (periphery to centre)
Blind by adolescence (sometimes up to middle age)
Irreversible course—may be delayed by vitamin A