Understanding Myopia: Causes, Symptoms and Treatment

Myopia, near sightedness or short sightedness is a refractive error where distant objects appear blurred while close objects can be seen clearly without visual aids.

This condition occurs when the eye is too long relative to the focusing power of the cornea and lens, causing light rays to focus in front of the retina rather than directly on it. The most frequent cause is lengthening of the eye, usually in childhood and the teens.

Myopia is increasingly recognised as a global health concern as the incidence of myopia is on the rise. By 2050, the World Health Organisation estimate that up to 50% of the world’s population will be myopic, with just under one tenth of the world’s population affected by high myopia (myopia > -5.00D).

Why is this a problem, if vision can be corrected with spectacles, contact lenses or by refractive surgery? Aside from the cost of visual correction, myopia is a risk to the health of the eye because the changes that cause myopia are accompanied by increasing risks of other medical conditions of the eye which can threaten sight including retinal detachment, glaucoma and macula degeneration.

High myopia is also associated with the early development of cataract and surgery in highly myopic eyes is associated with higher complication rates that surgery in non-myopic eyes.

What causes Myopia?

Factors contributing to myopia include genetics, environmental influences, and lifestyle factors such as prolonged near work and insufficient outdoor activities.

As far back as the 1970s, it was recognised that children who achieved higher educational attainments were more likely to become myopic by the age of 11 years and more recently, large clinical trials which analyse the results of large groups of studies have shown that increasing time spent outdoors is effective at preventing the onset of myopia.

Symptoms of myopia in adults include:

• Blurred vision when viewing distant visual objects e.g. schoolchildren unable to see a screen or blackboard at the front of a classroom.
• Difficulty in recognising faces of approaching people.
• Difficulty in reading road signs.
• Eyestrain or fatigue.

Symptoms of myopia in children include:

• Holding books or screens close toward them.
• Noticing blurred vision or sitting close to a television.
• Frequently rubbing their eyes or developing headaches.

But some symptoms in children may be far more subtle and include more behavioural changes. For example:

• Developing a shorter attention span or seemingly a reduced ability to concentrate.
• Losing interest in activities that they previously enjoyed because they can’t see well enough to perform the activity. This can be particularly important when it applies to outdoor pursuits or sports and more noticeable with sports that involve small balls e.g. tennis.

Treatment options for Myopia in children

There are three pillars of control when it comes to Myopia in children.

1. Mitigation

Mitigation involves strategies aimed at preventing or delaying the onset of myopia, particularly in children where even quite young children are now developing myopia. Starting the conversation early or with myopic parents or grandparents can be an effective way for Optometrists to inform and educate about lifestyle changes and opportunities for potential future treatments.

Lifestyle modification and spending time outside

There is clear evidence for time spent outdoors having a protective effect for the onset of myopia but less evidence for time outdoors slowing the progression of myopia. Factors influencing this effect may include:

• Higher illumination of the retina through increased light exposure.
• The chromatic spectrum of light outside compared with indoors.
• The spatial frequency of light outdoors compared with indoors.
• Peripheral defocus.
• Spending less time performing near work when outdoors
• Regulation of circadian rhythm and dopamine levels

A comprehensive review of these mechanisms has been published by Lingham G BJO 2020;104:593-599.

Spending more time outdoors often requires significant changes in behaviour and habits and is not easy to achieve, time outdoors may also present other risks e.g. increased sun exposure, and these should also be taken into consideration.

Reducing near work

Near work, and in particular, spending excessive time on near work is has been linked with the development of myopia although the evidence on how this might occur is less clear. Prolonged near work is likely to be linked with less outdoor activity, so environmental factors certainly play a role. In adults it is recognised that following the 20-20-20 rule can help reduce eyestrain and improve posture even if evidence for slowing myopia is less clear.

The 20-20-20 rule

Take a 20 second break every 20 minutes and look at something 20 feet away. This can be challenging when busy at work so try every hour or two to start with and combine this with standing up and rolling your shoulders back and forward a few times to reset your posture.

2. Measurement

One major advantage of Ophthalmology is that we can measure all sorts of things with incredible accuracy, both in terms of physical measurement e.g. the length of an eye, to optical measurement e.g. the aberrations in vision. Measurement in the field of myopia is an example of this, and accurate measurement is important in diagnosis, looking for signs of progression and accurately correcting vision.

Measurement in myopia takes two main forms:

• Regular eye check-ups, and
• Physical measurements of the eye
• Imaging of the retina

Regular eye examinations

Regular eye checks and sight testing with an Optometrist will pick up early signs of myopia and also quantify any progression. For further information on what the numbers in an Optometry report mean, see this link: https://www.andersoneyecare.co.uk/your-spectacle-prescription-explained/

The College of Optometry in the UK recommends 6-monthly eye exams under the age of 7 years if there is a refractive error but 6 monthly in the presence of progressing myopia according to clinical need.

Physical measurements of the eye

The axial length (AL) is the length of the eye from the front surface of the cornea to the macula area of the retina in the line of sight (see illustration). AL measurement is performed with a machine called a biometer. It involves looking into a machine for a minute or two, is painless and there is no contact with the eye (in particular, there is no puff of air!).

Imaging of the retina

These devices provide very detailed images of the retina ranging from a wide field view of the retina, almost all the way out to the edge (see DFA image), to detailed measurements of thickness where changes such as thinning or myopic maculopathy can be detected and quantified.

3. Managing or treating myopia

Myopia cannot be cured but treatment of myopia may slow or prevent progression in children. When the eye has fully developed and the refraction is stable, spectacles, contact lenses and refractive surgery are all methods to effectively correct refractive error.

For children, treatment can be medical or through the use of special glasses or contact lenses or a mixture of all of these.

Medical treatment for myopia

Medical treatment for myopia takes the form of Atropine eye drops. Atropine works by reducing accommodation which is the mechanism by which the eye lengthens causing myopia. Atropine must be prescribed by a Doctor and is prescribed in two strengths; 0.01% and 0.05% according to the rate of myopia progression. Children prescribed atropine typically require an eye examination at least every 6 months.

Orthokeratology (Ortho-K)

Ortho-K involves the prescription and wearing of specially designed contact lenses overnight. These lenses change the shape of the cornea, flattening it centrally and reducing the optical power of the eye. Ortho-K lenses can be used to treat myopia and also astigmatism and these lenses are managed by Optometrists.

Multifocal and Peripheral Defocus glasses and contact lenses

MiYOSMART® glasses

These are a specific type of spectacle lens which have been used here in the UK for the last 3 years and use a lens technology which simultaneously corrects the refractive error whilst also induces defocus to reduce myopic progression.

MiSight® contact lenses

These are single use contact lenses typically worn for around 10 hours a day, 6 days a week from the age of 8 years, shown to reduce progression of myopia when prescribed to children from 8 – 12 yrs.

Stellest® glasses

These are spectacle lenses with a central refractive correction surrounded by rings of tiny lenslets.

Treatment options for Myopia in adults

Whilst the eye is still changing in optical power, spectacles and contact lenses remain the mainstay of treatment.

Once the eye has reached stability, usually taken as not increasing in myopia by 0.5D each year, then depending on the age of the person, degree of myopia and the presence of other factors e.g. cataract, surgical intervention can be considered.

In younger adults, laser vision correction procedures e.g. PRK, SMILE and LASIK are highly effective and safe for treating low to high myopia up to -10.0D.

Laser vision correction can also be used to treat both myopia and presbyopia, the reduction in the ability to focus on near objects with age, with advanced laser protocols such as PRESBYOND® laser blended vision.

Implantable collamer lens (ICL) surgery can be considered for low to very high myopia as an alternative to laser vision correction either through personal choice or for reasons where laser vision correction may not be suitable e.g. thin or irregular corneas or very dry eyes.

Refractive lens exchange surgery may be considered in people when myopia is accompanied by loss of accommodation (or Presbyopia) typically in the age range of 50 to 65 years, whilst cataract surgery should be considered if the presence of cataract is detected at examination.

Lens surgery opens the possibility of using a replacement or intraocular lens that may be specified with additional functional properties e.g. multifocality.