What is myopia?
Myopia is one of the common visual refractive errors, also known as nearsightedness or shortsightedness. In myopia, the patient can see near objects clearly, while far objects are usually hazy or blurred.
Shortsightedness is one of the common causes of visual impairment globally. In normal people (emmetropes), the light rays are centered on the surface of the retina, so they can see objects clearly. On the other hand, in patients with myopia, the light rays are centered just in front of the retinal surface; this causes the objects to be seen hazy.
What causes myopia?
Recent studies show that during early years of life, the newborn is hyperope, and the eye is changing out to reach normal stable vision at early childhood. The increase of the axial length of the eye during childhood rapid growth is balanced by decreasing in the optical power of the lens.
A study conducted by Mutti et al. showed that myopia is caused by a disturbance to the eye growth physiological balance with excessive lengthening or stretching of the eye, and a change to corneal optimum curvature and crystalline lens.
Myopia can occur at any age. It occurs in cases of:
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- The cornea has more curvature than expected
- The lens has excessive curvature than the eye lens in comparable emmetropes
- The longitudinal axis of the eye lens is longer than the usual length
The prevalence of myopia
Myopia is one of the leading causes of visual disability below 50 years old, and it is a cause of concern to the global health systems. A recent research fears that by the year 2050, half of the global population would be complaining of myopia.
Meanwhile, myopia affects more than 25% of the general populations in USA, Europe, and Australia. According to Vitale et al. there is approximately 66% increase in myopia prevalence in USA, and the new cases per year has been documented to be 2.6% of the general population.
The higher prevalence of myopia is in Asian ethnicity, In Asia the prevalence is as high as 90% of the young adults, while in Taiwan 84% of adults aged more than 24 years old have myopia.
In the United Kingdom, myopia prevalence reached 49% in adults aging 44 years old or older. In India, the adults aged 40 year or older have a myopia prevalence of 34.6%. in the Middle east, the myopia prevalence in adult males is 31.5%, and 31.9% in adult females.
Recent studies showed that the prevalence of myopia increases statistically with factors like:
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- Family history of refractive errors
- Family level of educations
- Overuse of eye in near work as in reading or using mobile phones excessively
Types of myopia
There are several types of myopia, with different degree and complications. Types of myopia include:
1- Simple myopia: It is the most common variant of myopia; the degree of simple myopia usually ranges from minus one to minus three (-1 to -3) diopters.
2- Moderate myopia: In moderate myopia,myopia degree ranges from minus three to minus six (-3 to -6) diopters. Patients in this category are more liable to develop conditions like glaucoma, and pigment dispersion disease.
3- High or degenerative myopia: It is a serious and rare type of myopia, andaffects 2% of populations. In this type, the myopia degree exceeds minus six (-6) diopters. In degenerative or pathological myopia, the concern comes from the substantial risk of developing different serious conditions such as: retinal detachment, glaucoma, cataract, macular degeneration, and even complete loss of vision could happen. In degenerative myopia, the patient’s visual acuity is deteriorated quickly, constantly, and do not stabilize in early adulthood as in simple myopia.
4- Night myopia: One of the common types of myopia, which causes decrease in the visual acuity at the night or any similar dim-light conditions. Unlike the previous types, night myopia can occur to a healthy individual with no refractive errors. This condition is thought to be because of the inability of the accommodation system of the eye to adapt from high light conditions to dim light conditions.
5- Pseudo myopia: A temporary condition due to excessive near work conditions like reading or working on computers; the excessive near work causes stress to the eye and its accommodation system. Taking rest every while can resolve this problem, but continuous stress on the eye increases the risk of developing a fixed myopia.
6- Instrumental myopia: Atemporary condition occurs when using instruments like microscope, vision would be blurry for a while after using the microscope for long time.
7- Induced myopia: Instrumental myopia is a type of myopia that can be results from use of specific medications, and diseases like diabetes mellitus and oxygen toxicity.
Symptoms of myopia
In myopia, the most important symptoms are seeing far objects blurry. Other associated symptoms may include:
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- Headache
- Eye fatigue
- Eye rubbing or squints especially in children
- Visual difficulties especially at night
In degenerative myopia beside the usual symptoms of myopia, the patient may complain of seeing eye floaters and flashes of light, and if the refractive error is extremely high, the patient may develop a retinal break or tear which may progress to a complete retinal detachment if not treated promptly.
Risk factors of myopia
There are multiple risk factors of myopia, which were linked to the incident of myopia and its progression.
Outdoor activity
Growing evidence suggest that outdoor activity plays significant role in protecting the eye from incidence of myopia and delaying its progression. A study by Sherwin et al. found that increasing outdoor activity have a protective role with myopia and can even lessen the risk of having myopia.
Activities that require excessive near work conditions like reading, and long hours of working on screens is considered important risk factors for developing myopia.
Ethnicity
One of the most risk factors for incident and progression of myopia, as in Asian ethnicity which show high prevalence of myopia in comparison to other ethnic groups. A study by Hyman et al. showed that in comparison to Asian ethnicity, African Americans have lower myopia progression rate.
In a study conducted by the national health and nutrition foundation, founded that myopia prevalence were more in non-Hispanic whites with 35.2%, while in non-Hispanic blacks were (28.6%), and in Mexican Americans (25.1%).
Age
Diagnosing myopia refraction error on early age is a risk factor for developing a high myopia degree, and fast progression of myopia later in life.
Family history
Studies showed that if only one parent has myopia, this increases the risk of having myopia in early age, this risk jumps to six folds in case of both parents have a refractive error. Being a child of a myopic father is also a risk factor for developing degenerative or pathological myopia.
Gender
There is no confirmative data for specific sex predilection in myopia, but a survey by the national health and nutrition examination found that; men have lower prevalence than females in the general populations. Another study found that; females have more speed progression of myopia than males in the general populations.
Environmental risk factors
Recent studies suggest that environmental risk factors can be linked to the diagnosis of myopia, but these factors need more studies and investigations. From these factors:
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- Increasedmaternal age during pregnancy
- Excessive smoking during pregnancy
- Feeding the newborn artificial milk instead of breastfeeding
- Educational achievements are thought to be one of environmental risk factors positively associated with incident and progression of myopia
- Studies suggest that diet has a strong impact on eye health and has a role in the incident of refraction error
Diagnosis of myopia
To diagnose myopia, a full detailed history must be fulfilled first. The most key factors to focus while taking the history are age, ethnicity, gender, and if there is a family history of refraction error.
Your doctor will also ask you about specific diseases that may be associated with myopia such as down syndrome, marfan syndrome, Ehler-danlos syndrome, and diabetes mellitus.
“Examination of the eye”
The first steps in examination of the eye are to evaluate the structures of the eye with more detailed examination to
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- Eye length
- The corneal radius
- The crystalline lens powers
Measuring the axial length of the eye is valuable as it can give a clue about the rate of progression of myopia. Recent studies found that rate of eye axial elongation reaches the highest speed just before the onset of myopia.
Functional testing of the eye aims to
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- Measureof the refraction error
- Assessthe binocular vision
- Assessthe accommodation system of the eye
Retinal examination is crucial in the testing of the eye; as myopia can pose damaging impact on the retina, nearsightedness especially the degenerative type causes frequent stress on the retina that may lead to retinal tear and even detachment.
Treatment of myopia
The treatment of myopia focuses on correction of the refractive error, and there are multiple available options such as:
1- Eyeglasses
In most cases of myopia eyeglasses would be sufficient. Eyeglasses is the first choice of treatment for mild and moderate myopia types. For mild myopia, wearing the eyeglasses is usually enough for correction and may be needed in some situations like reading or driving only, while in cases of moderate or high myopia, the patient may need to wear his eyeglasses all day.
In eyeglasses, single vision lens is used to provide clear visual fields in all direction, and it is the most used corrective lens, while multifocal lens is prescribed to provide different powers above and below a certain line on the lens, it is usually used to treat patients with accommodation problems.
2- The contact lenses
Some patients may prefer contact lenses over eyeglasses for aesthetic reasons, and the contact lenses can give more unobstructed vision and a wider visual field. The contact lenses may have downsides such as:
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- Keratitis
- Recurrent infections
- Corneal ulcers
- Dry eye
- Decrease oxygenations of the eye
3- Orthokeratology
It is one of the available options of myopia treatment, this method is also known as corneal refractive therapy (CRT). In this treatment, a rigid lens is applied daily to slowly correct the corneal curvature.
Those lenses are typically applied overnight on a daily basis for a limited time to achieve the optimum results.
4- Laser therapy
In the recent years, laser therapy is used extensively and successfully to treat myopia in adults. There are multiple techniques using laser therapy in treating myopia. From these techniques:
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- LASIK: LASIK is laser in situ keratomileusis. It is a technique used to treat myopia. In this procedure, a thin flap is done on the outer surface of the cornea, then a thin layer of the cornea is removed, and the flap return to its place. This laser technique is preferable as it has rapid recovery and less patient discomfort and side effects. This technique may not be suitable for treating all degrees of myopia.
- LASEK:LASEK is laser assisted subepithelial keratectomy. In this procedure, a thin flap is made in the surface of cornea, then the laser tries to reshape the cornea and to decrease its curvature. After finishing, the epithelium is returned to its place.
- Photorefractive keratectomy (PRK): PRKis a technique that resembles LASIK technique, except that all the epithelium is excised completely, the epithelium heals and regrows.
Complications of myopia
As myopia is a common refractive error globally. Its complications increase the health burden on all the community. Regular follow up and screening is mandatory to prevent myopia complications. From these complications:
- Myopic macular degenerations (MMK): Itis one of the serious complications of myopia. The risk of MMK increases in association with the degree of myopia. A study by Haarmant et al. showed that prevalence of myopic macular degeneration is 1% to 7% in low myopia patients, while in degenerative myopia patients the prevalence ranges from 13% to 65%.
- Retinal detachment: In myopia especially degenerative or pathological myopia, there are elevated risk to develop retinal break or tear, which may progress later to complete retinal detachment. The same study by Haarmant et al. founded that all the types of myopia carry the risk of developing retinal detachment. Symptoms of retinal detachments include sudden blurry vision, sudden onset of eye floaters, or sudden increase of their numbers, and black curtain in the visual field that appear suddenly.
- Other complications: Myopia patients have a risk to be diagnosed with other conditions such as:
- Open angle glaucoma
- Cataract
How to cope with myopia in adults?
Myopia is an eye disease that can not be treated or prevented, but a lifestyle modification, and habits can help the myopia patient to adapt with his condition, and even delaying its progression such as:
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- Keep your eye protected from the ultraviolet rays of the sun. encourage wearing sunglasses.
- The myopic eye is weak, and vulnerable to injuries after a trauma so keeping the eye protected is a priority.
- Eating healthy balanced diet especially food rich in omega 3 like seafood has an extremely beneficial effect on eye health.
- Do not stress your eye with extended reading,especially in dim light conditions.
- Try to limit screen time, and abstain for two hours before sleep.
When to see your ophthalmologist for examination?
Patient with myopia must do a regular eye check on regular appointments. High myopia patients without complications should do an annual visit to check on their eye. If there are any complications, a more frequent visit is mandatory. If you see the following, you should visit your ophthalmologist as soon as possible:
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- Sudden onset of eye floaters or increase in their numbers
- Sudden onset of light flashes
- Sudden change in visual acuity
- Seeing a black curtain in your visual field
Myopia in children
Shortsightedness is a common refractive error in children. Pediatric ophthalmologists need to examine all school age children to diagnose the myopia in this age group early. They also need to assess myopia children for the rate of their myopia progression, and the possibilities to develop degenerative myopia, and other myopia complications.
The prevalence of myopia in children
Myopia is quite a common pediatric complaint in the world. A study in Australia found that 14.4% of 12-year-old children have myopia, and 29.6% of a 17- year- old children have myopia.
A meta-analysis and systemic reviews by Agarwal et al. found that 7.5% of Indian children have myopia, with a higher incidence in rural areas. Another study conducted in southern California found that between 60,780 children participated in the study, 41.4% had myopia, with higher incident in the Asian American children more than Whites, and African American.
In Saudi Arabia, the prevalence was 0.7%, and was 1.4% in South America. The highest prevalence of myopia in children was recorded in East Asia, China, and Singapore.
Risk factor of myopia in children
The drastic consequences of child myopia, and the health and socioeconomic burden of the myopia are important reasons to study myopia, its risk factors, and complications in children carefully to seek treatment, and even prevention of this disease in children. Studies showed that there are risk factors for myopia in this age group such as:
Family history of myopia
If one parent is diagnosed with myopia, the risk of myopia in his offspring increases in comparison to children with no parental myopia. A study by Handson et al. about offspring myopia showed that the children at the age of 14-year-old have a refraction error like their parent at the same age. A study called Sydney Adolescent Vascular and Eye Study (SAVES), found that parent’s myopia was a probable risk factor in developing myopia in 6-year-old children.
Day time exposure
It is one of the most important environmental factors in protecting against myopia and delaying the progression in children of myopia. SAVES study, which was evaluating the query risk factors in Australian children from five- to six-year-old, concluded that spending more time outdoor was associated with decrease the incident of myopia in the children involved in the study.
A recent study showed that outdoor time could decrease the progression of myopia in children. Their ages were between six- and seven-year-old, by approximately 30% in only one year.
A group of British researchers in a recent meta-analysis found that outdoor have an extremely good impact in decreasing incident and progression of myopia among 10,400 child and adolescents.
Near work
It is one of the associated causes of developing myopia in children. The SAVES study founded that near work can induce the onset of myopia in the younger children. Also, the same study founded that accelerating myopia progression was associated with higher myopia degree at diagnosis, and prolonged sessions of near work.
Sleep hours
Recently, many studies suggested that decrease sleeping hours could be associated with diagnosis of myopia. Gong et al. study showed that non-adequate daily sleep could be a risk factor for myopia in children aging between 12 to 15 years old, with the highest prevalence in the children who sleep less than seven hour or less daily.
Ethnicity
The ethnicity of the children has a significant impact on increasing the susceptibility of the children to have myopia, as in Asian ethnicity where it is associated with early onset of myopia, rapid progression, and late stabilization of his myopia degree. The yearly estimated progression of myopia in Singapore was minus 0.8 diopters in comparison to minus 0.5 diopters in European-Caucasian ethnicity.
Overcrowded neighborhoods
Overcrowded neighborhoods are of the controversial risk factors. Scientists claim that living in highly populated and crowded cities is associated with increasing in myopia diagnosis in children.
Can we prevent myopia in children?
There are multiple measures to decrease the incident of myopia or at least decrease its progression such as:
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- All children should be encouraged to spend more time outdoor daily
- Mobilephones, video games, and all screen times should be minimized
- An annual eye examshould be done for all children
- Close monitoring and regular checking for children diagnosed with myopia