Myopia (high, pathological)

Overview

Pathological myopia, also known as high or degenerative myopia, represents a more severe form of short-sightedness than common myopia. Individuals with this condition have a very high refractive error, meaning their eyes cannot focus light correctly. This often results from the eyeball growing too long from front to back [PMID:33671408]. Unlike typical short-sightedness which usually stabilises in adulthood, pathological myopia can progressively worsen over time and is associated with structural changes within the eye. These changes can significantly impact vision and lead to serious complications.

Symptoms & clinical features

The primary symptom of pathological myopia is extremely blurred vision when looking at distant objects. This typically requires strong corrective lenses, such as glasses or contact lenses, to achieve clear vision. Beyond blurred distance vision, individuals may also experience 'floaters' - small specks or cobweb-like images that drift across the field of vision - or flashes of light, particularly if the retina is affected [PMID:33671408]. In more advanced stages, vision can become distorted or patchy due to complications affecting the back of the eye.

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Affected organs

Pathological myopia primarily affects the eye, specifically the retina, choroid, and sclera (the white outer layer of the eyeball). The excessive elongation of the eyeball stretches and thins these delicate structures. The retina, which is responsible for detecting light and sending signals to the brain, is particularly vulnerable to damage. The choroid, a layer of blood vessels beneath the retina, can also be affected, impacting the retina's blood supply. These changes can lead to vision-threatening complications.

Multiple body systems

Systemic involvement

Cellular impact

Mechanism at cellular level

Risks & severity

The severity of pathological myopia can vary, but it carries a higher risk of serious eye complications compared to common myopia. These include retinal detachment, where the retina pulls away from its underlying support tissue; myopic macular degeneration, affecting central vision; glaucoma, a condition that damages the optic nerve; and cataracts, a clouding of the eye's lens [PMID:33671408]. The risk of these complications generally increases with the degree of short-sightedness and the extent of eye elongation. While the exact prevalence is not well established, some estimates suggest it affects around 5% of the general population. The condition can manifest at various ages, from childhood into adulthood, and progression can continue over many years.

Genetic causes

Pathological myopia is understood to have a complex genetic basis, meaning it is influenced by a combination of multiple genes and environmental factors [PMID:33671408]. Unlike conditions caused by changes in a single gene, there isn't one specific gene identified as the sole cause of pathological myopia in all cases. Instead, research suggests that various genetic predispositions, alongside environmental influences such as extensive near-work activities and limited outdoor time, contribute to the development and progression of the condition [PMID:33671408]. The exact mechanisms by which these genetic and environmental factors interact are still being investigated.

Inheritance pattern

Pathological myopia follows a polygenic or complex inheritance pattern. This means that multiple genes contribute to an individual's susceptibility, rather than a single gene being responsible. It also suggests that environmental factors play a significant role alongside genetic predisposition. Therefore, while a family history of pathological myopia may increase an individual's risk, the condition does not typically follow a straightforward inheritance pattern like autosomal dominant or recessive traits. Predicting the likelihood of developing the condition in relatives can be challenging due to this complex interplay.

Diagnosis & testing

Diagnosis of pathological myopia typically involves a comprehensive eye examination by an optometrist or ophthalmologist. This includes measuring visual acuity, assessing refractive error, and examining the internal structures of the eye, particularly the retina, using specialised equipment. Imaging techniques such as optical coherence tomography (OCT) may be used to assess the thickness and health of the retina and choroid [PMID:33671408]. If pathological myopia is suspected or diagnosed, individuals are usually referred to an ophthalmologist for further assessment and ongoing management. In the NHS, such referrals are typically managed through routine ophthalmology pathways, and a specific R-code for genetic testing for this complex condition is not usually required.

Management & lifestyle

Managing pathological myopia primarily focuses on correcting vision and monitoring for, and treating, potential complications. Corrective lenses (glasses or contact lenses) are essential for improving vision. Regular eye examinations are crucial to detect early signs of complications such as retinal detachment or myopic macular degeneration. Treatment for complications may include laser therapy or surgery, depending on the specific issue [PMID:33671408]. There are no specific genetic therapies available for pathological myopia, given its complex genetic architecture. Individuals should discuss their specific management plan with their ophthalmologist. Lifestyle considerations, such as spending time outdoors and reducing prolonged near-work, may also be discussed as part of a broader management strategy for myopia progression, though their impact on established pathological myopia is less clear.

UK care pathway

In the UK, individuals with suspected or diagnosed pathological myopia would typically enter the NHS ophthalmology care pathway. Initial assessment often occurs through a local optometrist, who can then refer to an NHS ophthalmologist for specialist opinion and ongoing care. Genetic counselling is not routinely offered for pathological myopia due to its polygenic nature, but individuals with concerns about family history or specific genetic conditions should discuss this with their GP for a potential referral to clinical genetics services.

Related conditions

While pathological myopia is a distinct condition, it falls under the broader category of myopia (short-sightedness). Some genetic conditions can also present with severe myopia as part of a wider set of symptoms, such as Stickler syndrome or Marfan syndrome. However, in these cases, the myopia is usually one feature among many, and other characteristic signs and symptoms would typically be present, guiding towards a different diagnosis. Pathological myopia, in contrast, primarily involves severe vision impairment and associated eye complications without these other systemic features.

Frequently asked questions