What is Myopia (Nearsightedness)?
Myopia, also known as nearsightedness, is a common eye condition that affects children and young adults, making it difficult to see objects at a distance (refer to image: Myopia or Near Sightedness). Lately, myopia is becoming a greater concern as many parents are unaware of it and there are misconceptions surrounding the condition.
Moreover, the COVID-19 pandemic has contributed to the problem. The extended use of digital screens by children during the pandemic has led to more incidents of nearsightedness and resulted in the condition progressing faster. As a result, the number of people affected by myopia has significantly increased.
What Causes Myopia (Nearsightedness)?
Kids have shorter eye lengths than adults. The process of the eye adjusting its focus to see clearly, which scientists called “emmetropization,” starts around two years old. It often initially takes the form of nearsightedness (myopia) and typically settles into normal vision (emmetropia) by the time the child turns 14. Farsightedness (hyperopia) can occur when the eye length at birth is 18 millimeters. By the time a child is 14, it might grow to 23 millimeters, which would typically make a person nearsighted. However, changes in the shape of the cornea and thinning of the lens can offset this, resulting in normal vision.
On the other hand, some kids who have longer eye length at birth are more prone to nearsightedness. This can cause the eye to become nearsighted quickly during childhood. Even though the pace slows in young adulthood, the length can keep increasing until they’re about 18. For some people, this process might continue until they reach 25. After turning 25, any vision changes towards nearsightedness can be due to the lens in the eye becoming thicker.
Risk Factors and Frequency for Myopia (Nearsightedness)
Many children worldwide aged 5–17 suffer from myopia, also known as nearsightedness. It’s mostly observed in Asian children (18.5%), followed by Hispanic (13.2%), African American (6.6%), and Caucasian kids (4.4%). Specific studies show a prevalence of 20–30% among 6-7-year-old children in Taiwan and Singapore, and up to 84% among high school students in Taiwan.
In China, the issue is growing in younger ages, with the rate increasing from 5.7% in 5-year-olds to a worrying 78.1% in 15-year-olds. It’s worth mentioning that in Sweden and Greece, between the ages of 10 and 15, the rate of myopia stands at 49.7% and 37.2%, respectively.
For adults over 44 years old in the United Kingdom, the prevalence is 49%, this high rate has been linked to the presence of the lenticular component, a part of the eye related to the condition.
Signs and Symptoms of Myopia (Nearsightedness)
If your child is often holding books close to their face or making mistakes when writing down notes, they might have a vision problem called a refractive error. Other signs to look out for include trouble seeing the television from a standard sitting distance of 3 feet and recurrent headaches. Teenagers may complain about not being able to see clearly at a distance. Headaches are another common sign that could suggest a refractive error. Astigmatism, a specific type of refractive error, could result in symptoms like headaches, changes in vision throughout the day, occasional double vision, and neck pain. Frequent squinting, or a noticeable turn in the eye with a loss of near vision can also suggest the presence of a vision problem.
The patient’s medical history can provide useful hints about what might be causing their vision problems. A family history of nearsightedness (myopia), keratoconus (a corneal condition), or retinal complications, indicates a higher risk of these conditions. A patient with myopia along with a familial history of retinal complications and keratoconus require more in-depth eye examinations. If your child has been using steroid eye-drops for allergic conjunctivitis, it’s important to know that this could lead to certain types of myopia or muscle spasms around the eye due to high eye pressure.
A simple examination using a hand-held light (torchlight examination) can provide important information about your eye. By examining the reflection of light from the cornea, the eye’s front surface, we can detect abnormalities. The light reflex (Hirschberg reflex) is normally near the center of the cornea but moves to the side in abnormal conditions like outward turned eyes (exotropia). Strabismus, a deviation of the eyes, is frequent in patients with myopia. For instance, a study showed that 90% of patients with intermittent exotropia also had myopia.
In addition, there can be noticeable differences in the size of the two eyes in the condition anisometropia, which is a difference in the refractive error between the two eyes. In this condition, a larger globe size is common and can be detectable by looking at the visible white of the eye (scleral exposure). A technique called ‘diffuse torchlight examination’ can be used to detect keratoconus, a condition that changes the shape of the cornea. The lower lid’s impression or ‘dented’ appearance when looking down may suggest the presence of keratoconus.
Testing for Myopia (Nearsightedness)
Retinoscopy is a crucial tool used by doctors to measure refractive errors, which affect your eyes’ ability to focus. Two types of retinoscopy used are spot and streak. Streak retinoscopy uses a line of light, and is important to master for those in medical residences. The method works by shining a light onto your eye, which then reflects back. The movement of this reflected light can help reveal the eye’s refractive state, or how it focuses light.
During a retinoscopy, your doctor will aim to find the eye’s far point, which is the point farthest from the eye where light is still clearly focused. They’ll use the neutralization technique, which is when the movement of the projected light ceases to move. In patients with more nearsightedness (myopia), the reflected light moves in the opposite direction of the projected light stroke. To determine a patient’s refractive error, your doctor will add lens power until there’s no motion, and then subtract the working distance and cycloplegic correction (which is the adjustment made for your eye’s response to light).
For those with less severe myopia, the reflected light moves in the same direction as the streak light. This procedure needs to be done in multiple directions, and the results should be clearly documented for future reference.
Retinoscopy has been largely replaced for routine screening of myopia by autorefractometers, which are machines that objectively measure the degree of myopia with high accuracy. They do this by projecting light into your eye and using the reflected light to calculate any refractive error. These machines also employ the fogging method to relax accommodation, which is essential for obtaining an accurate assessment of refractive errors, particularly in children.
Another important tool in the diagnosis and treatment of myopia is corneal topography. This test maps out your cornea (the front surface of your eye) in order to spot any irregularities, like corneal disorders commonly related to myopia. For instance, it can detect keratoconus, which is when your cornea bulges out in a cone shape. This method can be particularly important when planning for corrective laser surgery. The machines involved in topography use a variety of technologies, the most common ones being Orbscan and Pentacam.
The Orbscan machine uses light slit technology to take detailed images of your cornea and provide comprehensive data about it. This information helps doctors plan for suture-free vision correction procedures. More recently, devices using Schiempflug technology have become popular. These more advanced devices rotate light in a particular manner to provide more detailed information about the structure and health of your eye.
Apart from these high-tech methods, slit-lamp examinations provides a more straightforward evaluation of your eye, examining things like corneal thickness, anterior chamber depth, lenticular thickness, optic disc, and the macula. This can be useful for identifying any potential issues, such as thinning of the cornea or astigmatism.
Treatment Options for Myopia (Nearsightedness)
Myopia, or nearsightedness, can be managed in different ways, including non-surgical methods and surgical procedures.
Non-surgical Management
The most common way to correct myopia is by using glasses with concave lenses which help to focus light properly onto the retina, the sensory layer of the eye. It’s important that the lenses are prescribed accurately and fitted correctly in the frame to ensure clear vision and to avoid eye strain. Lenses are now made of advanced materials like polycarbonate which are lighter and thinner. However, some users can experience problems like glare, ghost images, and reduced light transmission. As a result, coatings are applied to lenses to reduce these issues. Modern lenses may also have a blue-light filter to protect the eyes from harmful blue light, reducing potentially harmful effects such as digital eye strain.
Contact lenses also play a significant role in managing myopia. They are made of highly flexible materials which allow good oxygen flow to the eyes, making them comfortable to wear. If prescribed accurately, they can give clear vision and are especially popular with adolescents and young adults. However, they can cause complications like eye inflammation or hypoxia (a condition where not enough oxygen reaches tissues) if not used properly or if hygiene is not well maintained.
Surgical Management
In the last two decades, surgical treatments for myopia have greatly advanced. There are two main types, those that work on the cornea (the clear front layer of the eye) and those that work on the clear lens inside the eye.
Laser vision correction works by reshaping the cornea to alter the way light is focused onto the retina. This is typically done using an excimer laser which doesn’t penetrate deeply into the eye. This procedure can be done with a flap created on the cornea (laparoscopic surgery), or without a flap (photorefractive keratectomy). Femtosecond lasers, which cut the corneal tissue very precisely, have been recently employed for myopia treatment.
Laser correction surgery, however, can lead to a weakening of the cornea, creating issues for eyes that already have weak corneas. Other potential associated issues include blister-like infiltrates in the cornea, increased intraocular pressure, and a possible increase in the steepness of the cornea leading to poor vision.
A different surgical approach to treating myopia involves placing an artificial lens either in the front chamber of the eye (anterior) or the back chamber (posterior) to adjust how light is focused onto the retina. Placing the lens in the anterior chamber is an older method, and it often leads to complications like an increase in intraocular pressure and damage to endothelial cells. Modern approaches usually place the artificial lens in the posterior chamber which has been proven safer and more effective.
Alternatively, the eye’s natural lens can be replaced with an artificial one. This procedure is generally considered for patients who have a more complex case, and it can help provide spectacle-free vision. However, the removal of the natural lens can lead to serious complications like retinal detachment, which can lead to permanent vision loss if not promptly treated.
It’s crucial to remember that while these procedures can correct myopia, each comes with potential risks and complications. Therefore, it’s essential to consult with your healthcare provider to discuss the best treatment option for your particular case.
What else can Myopia (Nearsightedness) be?
Pseudomyopia is a specific type of nearsightedness. It’s triggered by spasms in the ciliary muscle (a ring of muscles in the eye) which prevent the relaxation needed to allow the lens in the eye to flatten when looking at distant objects.
Possible Complications When Diagnosed with Myopia (Nearsightedness)
The back part of the eye plays a crucial role in managing vision. The injuries that affect this part can be classified as either affecting the central or peripheral part of the retina, the innermost, light-sensitive layer of the eye. The main aim of identifying these injuries is to avoid a sudden vision loss, which can occur due to the detachment of the retina.
People with a high number of vision errors and a longer eye size are primarily at risk for these injuries. In patients with short-sightedness (myopia), the retina stretches towards the back of the eye, causing it to become thin and possibly lead to damage.
To prevent retinal detachment, specific conditions need to be monitored and treated. Tears and holes in the peripheral retina are important to monitor in short-sighted patients. A particular type of tear and small holes should be treated with retinal lasers to prevent any complications. While smaller holes can be observed and monitored during the early stages of retinal detachment.
Some damages are common in short-sighted patients, like thinning and discoloration of the retina, and do not require treatment unless there are holes or tears.
The central part of the retina is vital for clear vision. In patients with extreme myopia, irregularities are observed which affect the vision. The three critical conditions observed are posterior staphyloma, the growth of new blood vessels in the choroid (the layer between the retina and the sclera), and the splitting of the retina’s inner layers. These conditions need to be monitored, with some needing further treatment in case they progress.
A hole developing in the macula (central part of the retina used for precise vision) is a rare complication following minor trauma, it is often due to the traction of a structure inside the eye (posterior hyaloid) over the macula.
Other conditions like a dome-shaped macula and tears in parts of the retina are observed but do not require aggressive treatment.
For the effective treatment of myopia, a condition called amblyopia, characterized by abnormal development of vision in one or both eyes, needs to be addressed. Patients with different vision errors in each eye are more likely to have amblyopia in the eye with a higher vision error. Patients’ vision does not improve to normal, even after the best visual correction, in a condition known as ametropic amblyopia.
