Ophthalmology: Gradual loss of vision

Gradual loss of vision

Be suspicious of the presence of these common conditions:

• uncorrected refractive error
• cataract
• chronic simple glaucoma
• retinal disease
• tumour.

Aim

• Identify the common causes of gradual painless loss of vision in a white eye.
• Particularly consider the age of the patient when trying to figure out the cause.
  When a patient presents with a gradual painless loss of vision, the cause will often vary with age, as certain conditions can be more common in certain age groups (e.g. cataract and ageing maculopathy in the elderly).

Refractive error

• Undetected and uncorrected refractive error is a common cause of gradual visual loss in all age groups.
• Emmetropia means one can achieve 6/6 visual acuity unaided. In this situation, light rays are refracted (bent) by both the cornea and lens, and are in focus on the retina. Note that the cornea has two-thirds of the total refractive power of the eye.
• In myopia, light rays are refracted to a focal point anterior to the retina (somewhere in the vitreous) and so are blurred. Causes are:
  ○ Axial: when the eye is abnormally long.
  ○ Refractive: whereby the power of refraction is increased either due to the:
  ■ Cornea, such as in the condition keratoconus; or
  ■ Lens, particularly when nuclear sclerotic cataracts cause a so-called ‘myopic shift’.
• Traditionally, concave spectacles and/or contact lenses correct myopia. More recently, with higher patient expectations, refractive surgery has become more en vogue. In the United Kingdom, the most common procedure is LASIK (laser-assisted in situ keratomileusis), whereby a partial thickness (lamellar) circular flap and hinge are created by a femto-laser. An excimer laser is used to reshape the bared stroma and the flap replaced.
• In hypermetropia, the light rays are refracted to a focal point behind the retina. Again, the causes can be split into:
  ○ Axial: whereby the eye is short in length. This explains why children with their small developing eyes are hypermetropic.
  ○ Refractive: seen sometimes after complicated cataract surgery, if the patient is left without a lens (aphakic).
• As healthcare professionals, the most common refractive errors we encounter are:
  ○ Hypermetropia in young children.
  ○ Axial myopia in teenagers and young adults.
  ○ Refractive myopia in older patients.
  The young children group is the most important as they often don’t complain at all and amblyopia may have occurred prior to presentation.

Cataract

Vision depends on clear windows so that light can reach the retina: thus, opacities in cornea, lens and vitreous will impair VA. Most commonly, the opacity occurs in the lens (i.e. cataract).

• Cataract commonly causes gradual loss of vision in the elderly. They may notice nothing at all and the presence of an early cataract is detected by their optician, or they will have a gradual blurring of distant, then near, vision. If the cataract is placed posterior in the lens as a plaque (posterior sub-capsular lens opacity), they will notice glare and reduced vision in bright sunlight, with improved vision indoors.
• It may also occur in younger age groups who are at risk (e.g. patients with diabetes, on steroids, with chronic uveitis and/or with a family history of cataract).
• Cataract may also occur in young children (congenital cataract). It is very important to check the red reflex of any child who presents with reduced vision, and any baby who does not fix and follow, as they require urgent treatment with patching and glasses to prevent amblyopia. Some congenital cataracts do not significantly interfere with vision (e.g. blue dot cataract).
  Modern cataract surgery is performed through small incisions at the surgical limbus. The technique of choice is phacoemulsification and implanting a foldable intraocular lens. Throughout specialist training in the United Kingdom, we are exposed to increasingly difficult cataracts and are expected to have performed 350 operations at completion of training.

Glaucoma

Primary open-angle glaucoma (POAG)

• Causes slowly progressive glaucomatous optic neuropathy and painless visual field loss.
• Risk factors include Afro-Caribbean origin and family history of POAG.
• Patients are usually completely unaware that they have open-angle glaucoma, and it is detected by their optician finding raised intraocular pressure or noticing a cupped disc.
• By the time a patient with glaucoma presents with visual symptoms, 90% of the nerve fibre layer is destroyed.
• Glaucoma screening will often pick up POAG before any severe damage has occurred, and many patients are maintained on topical medication without significant progression or the need for drainage surgery.

Retinal disease

This should be considered in the patient with none of the above causes of reduced vision. It occurs particularly in patients at risk:

• Diabetics (diabetic retinopathy)
• Hypertensives (hypertensive retinopathy)
• The elderly (age-related macular degeneration (AMD)). This is the commonest cause of blindness in the elderly, in which their central vision for reading, colour and fine detail is affected.
• Children or young adults with neurometabolic diseases or a family history of retinal disease (e.g. retinitis pigmentosa).
• Previous history of an intraocular foreign body (IOFB) may cause the development of siderosis bulbi; this is a condition where iron from an IOFB that has not been removed can cause retinal toxicity. The patient presents years after the initial injury with gradual loss of vision.
  The iris in the affected eye of a blue-eyed individual may have a greenish hue.
• Individuals taking medications known to cause drug-induced macular disease (e.g. chloroquine, hydroxychloroquine, tamoxifen, chlorpromazine, thioridazine or vigabatrin).

Tumours

Any tumour that affects the visual pathway may cause symptoms of gradual, painless loss of vision by pressure on the optic nerve or eye.
Examples include:

• Intraocular tumour (e.g. choroidal malignant melanoma or choroidal metastases from the breast or prostate in adults, or retinoblastoma in children)
• Intraocular lymphoma, which may masquerade as bilateral intermediate uveitis
• Tumour of the optic nerve (e.g. meningioma or glioma)
• Tumour of the orbit or optic nerve (e.g. orbital lymphoma, sphenoidal wing meningioma or dysthyroid eye disease)
• Any brain tumour involving the visual pathways (e.g. pituitary tumour or occipital lobe tumour).
  These are not common and should always be considered when no other cause can be found.