Pathological Myopia

Description

Pathological myopia is a subgroup of myopia, and it is thought to affect approximately 3% of the population. Pathological myopia is of great clinical importance as it is progressive, irreversible, and affects individuals during the most productive years of their lives. High myopia (Severe nearsightedness) is defined as a refractive error of -6.00 OR an axial length of 26.5mm or more. Pathological myopia is defined as ‘high myopia with a posterior myopia-specific pathology, such as stretching and thinning of ocular layers including the retina, the choroid and the sclera’.

Symptoms

Individuals may not have any symptoms of pathological myopia during the slow progression of retinal and choroid stretching.  In some instances choroid neovascularisation (growth of new blood vessels in the choroid layer) (CNV) can result in specific areas of blurring in a persons’ visual field. Individuals might also notice that straight lines begin to appear wavy, such as window panes and street lamps, and there are noticeable blind spots in their field of view. Each of these symptoms can cause rapid decline in an individuals’ central vision.

Causes

Vision occurs when light rays are bent as the pass through the front window of the eye (cornea) and the lens. This light is then focused on the retina at the back of the eye where it is converted into messages that are delivered to the brain, and interpreted as images. With pathological myopia, light rays from nearby objects are not focused properly onto the retina, but instead they’re focused on a point in front of the retina. This is due to the eyeball being too long, having a lens which is not able to focus light onto the retina properly or having a cornea which is too curved. Pathological myopia generally begins in early childhood with an increased risk if both parents are also myopic. Unlike myopia, pathological myopia does not stabilise in early adulthood but instead continues to progress.

Diagnosis

Pathological myopia is diagnosed through a number of tests which are important for providing the correct diagnosis. This can include taking clinical tests, medical history and a family history. Pathological myopia is diagnosed based on fundus examination (examination of the components at the back of the eye including the retina, the optic disc, the macula and the fovea). The aim of this investigation is to identify characteristic features of pathological myopia and rule out other plausible cause for the degeneration associated with this condition. An imaging technique, fluorescein angiography, is used to assess the development of choroid neovascularisation (CNV) in patients. This technique is useful in identifying early stages of defects in areas of the retina at the macular or around the optic disc. CNV can be monitored over time using spectral domain OCT (SD-OCT). This is a non-invasive imaging technique which allows the doctor to obtain a cross –sectional image of the retina and other layers within the eye. This also allows for detection of macular hole formation. It is important that these assessments be carefully carried out as CNV is also present in age related macular degeneration (AMD) and correct diagnosis is key to providing the best possible treatment.

Treatment

There is currently no cure for pathological myopia. Individuals with stable high myopia will be followed up regularly for visual acuity, refraction, and general ophthalmic health. With glasses or contact lenses stable high myopathy can be corrected by altering the way in which light rays bend in the eye. In the instances where CNV develops or other associated complications, individuals will be followed more closely. There are no topical, local or systemic medications or surgery that is known to effectively alter the length of the eye or reduce the thinning of the sclera, choroid, and retina in pathological myopia. There are, however, treatments available for CNV which is a major complication of the condition. Anti-VEGF therapy is considered the first line intervention in patients with myopic CNV. VEGF, vascular endothelial growth factor, is naturally occurring in the body and supports the growth of new blood vessels. In certain disease states too much VEGF is stimulated resulting in the growth of unwanted, weak blood vessels.  Anti-VEGF therapy consists of rounds of anti-VEGF injections (usually 3) in to the back of eye. This is a significantly shorter regimen than that required for the treatment of CNV in age-related macular degeneration. Surgical options are also available in progressive pathological myopic cases whereby the risk of macular hole development is high. In these cases patients may benefit from a vitrectomy to alleviate the traction felt by the thinning retina. A vitrectomy requires the removal of the vitreous, a gel like substance in the eye, and instead replacing it with an air/gas bubble which helps to old the retina and other structures in place. No matter what level of vision a person may have, it is important to look after the eyes. To find out more about what can be done to take care of the eyes on a daily basis, please visit our Tips for Good Eye Health. For further information, please contact the Research Department on 01 6789004 or email research@fightingblindness.ie.

Research

Researchers and clinicians are continually seeking more effective approaches to treat and cure pathological myopia. Children who have myopic parents are statistically more likely to develop myopia than children with non-myopic parents. With this in mind researchers believe it is therefore possible that there is a genetic link to the development of this condition. Therefore it is possible to investigate a candidate target gene for myopia through a genomic study of pathological myopia. An active clinical trial in Taiwan is investigating potential disease causing genes of pathological myopia, with the hope of identifying a new therapeutic target (NCT00155753). Recently researchers have identified a gene, TNFRSF21, which may be related to the development of pathological myopia if mutations are present. Clinical trials are also on-going investigating the optimisation of conventional anti-VEGF therapies to address the key complication associated with pathological myopia. Information about clinical trials that are on-going and completed can be found on the clinical trials website and can be searched by both condition and location.

Support

Receiving a diagnosis can be overwhelming for anyone, but this is not a journey that you have to make alone. There are many groups and resources available to provide support for people living with Stargardt Disease. Fighting Blindness offers a free and confidential counselling service (Insight Counselling). For further information please contact insight@fightingblindness.ie or call 01 6746496. We also offer support groups for people with a visual impairment to share their feelings and experiences with others facing the same challenges. Please consult the support groups section of our website here to access the latest timings and days for the various support groups we offer. For further information please contact insightgroups@fightingblindness.ie or call 01 6746496.

Resources

Féach provides support for parents of children living with sight loss in Ireland. ChildVision is the national education centre for children with sight loss in Ireland. Vision Ireland, formerly NCBI (National Council for the Blind in Ireland) provides support and services for people living with sight loss in Ireland. Irish Guide Dogs for the blind helps individuals and their families to achieve improved mobility and independence.