What is Myopia?
Myopia is among the many errors of refraction that affect the eyes. Also known as ‘near sightedness’ or ‘short sightedness,’ it hinders the ability of the eyes to see things which are placed far off.
Myopia today has acquired an ‘epidemic-like’ status, with an estimate of 2.5 billion people expected to be plagued by it till the year 2020. With people involved in more or less sedentary lifestyles and near-work most of the time, myopia has started increasing in terms of its incidence and prevalence over the years.
Most of us today are guilty of spending more and more time on our ‘screens’ such as smartphones, laptops and computers for abnormally large periods of time. Add to that our genetic tendencies and other environmental factors, we are in for a troubled vision which includes a spectrum of ocular diseases apart from myopia.
Types of Myopia
Near sightedness comes in different forms:
On the basis of clinical appearance –
- Simple Myopia – This problem is simply dependent on the anatomy and organization of ocular tissue. Problem lies in the axial length of the eye and optical power offered by the eye lens and cornea. According to the principles of optics, the optical power of the eye and its axial length are inversely related. Thus, longer the axial length, shorter will be its power. Simple myopia can be equal in both eyes or unequal for both eyes (anisometric myopia).
- Pseudomyopia – This type of near-sightedness happens only in the presence of certain stimuli, like those which require a high degree of concentration and near-work. Because of such stimulation, the ciliary muscles go into a temporary spasm, hence changing the accommodative capabilities of the eye. This can result in temporary blurring of far vision.
- Nocturnal Myopia – Like the name suggests, nocturnal myopia is a condition where the person is completely fine with his vision in adequate light conditions (as in day time) and the trouble sets in when its almost or completely dark. Darkness or low light conditions provoke the pupils to dilate at a higher capacity which allows more light to come in. When this happens, the focus depth decreases and there are changes in the accommodative powers of the eye lens.
- Induced Myopia – A reversible variety of myopia, this one is caused due to variations in biochemical factors in the body such as blood sugar levels, hardening of the eye lens or exposure to certain drugs/pharmaceutical factors.
- Degenerative Myopia – This variety is quite severe in its affect, since its complications include things like glaucoma and retinal detachment. This condition causes progressive degeneration in the posterior portion of eyes. Because of this, changes in visual acuity can happen with a lot of severity. Degenerative myopia is more inheritable than other types of near-sightedness.
On the basis of severity –
- Low Myopia – Refractive error measuring less than +3D
- Medium Myopia – Refractive error measuring between +3D to +6D
- High Myopia – Refractive error more than +6D
On the basis of the time of its onset –
- Congenital Myopia – This one is present at the time of birth and continues into infancy (the first year of life). Both boys and girls are equally prone to being affected by it. If detected at the right time, corrective lenses can be placed and the results are usually favorable.
- Youth Onset Myopia – Adolescents less than 20 years of age can be affected by it.
- Early Adult-onset Myopia – People in the age group of 20-40 years are troubled by this one.
- Late Adult-onset Myopia – People in the 4th and 5th decades of their lives are pretty vulnerable to it.
Symptoms of Myopia
The good thing about near-sightedness is that, it has an easy ‘alarm system’ that can warn a person about something amiss. Myopia often presents itself as:
- Trouble seeing while staring at far-away objects
- Driving does not seem comfortable anymore because staring in the night becomes difficult
- Excessive eye strain which leads to headaches
- Excessive blinking of eyes
- Rubbing of eyes with a more than normal frequency
- Unaware of objects placed at far away distances
- The need to squint eyes for seemingly normal task
- Kids needing to sit closer to blackboards in class or near the television
Mechanism of Myopia
Before we understand the causes behind short/near-sightedness, an understanding of the physics involved in myopia can be quite helpful.
The eye is a somewhat spherical shaped organ, also known as the globe. This globe has the unique ability to adjust its shape and size according to the things it has to view at near or far distances.
When we wish to see something nearby, our eyes reduce their focal length and assume a more spherical shape. This is what makes us see the pencil in our hand, the book we are reading or the computer screen right in front of us.
Now suppose we want to admire the beautiful scenery outside, or want to keep our eyes focused while driving on the road. Our eyes immediately assume a more flatter contour to increase the focal length. And voila! We have a clear view of what’s located far away.
The problem begins when the eye is unable to alter itself according to the visual needs of the person. If it has trouble to flatten itself when there is a need to view things placed far-off, what we get is a condition known as near-sightedness or myopia.
The images are formed in front of the retina rather than on it, so this causes the blurriness which one perceives while looking at things placed far away.
There are different reasons as to why myopia happens. Take a look.
Myopia – Causes & Risk Factors
- Premature Births:
Preterm babies are among the special breed of fighters who have to face things that a full term neonate can face in a better way. Having a preterm baby involves facing several challenges with respect to its health. Preterm babies have to deal with low birth weight for a start, which increases the risk of myopia in them. Add to that several other problems like neurological issues and increased chances of acquiring infections.
During the time spent by babies in the womb, they are well protected in an environment which has been specially designed to withstand several stresses and provide nutrition at all times. The sclera develops much earlier as compared to the cornea, lens, macula and the retina, meaning when you have a preterm child, more often than not you will have a cornea which is flattened as required. In fact, the crystalline lens do not become elongated till the foetus is full term. This contributes to myopia.
In this variant, the newborn baby is affected with myopia since the time of its birth. Because of certain problems in the development of a proper visual pathway, which makes the developing eye modify its structure in order to compensate for the disturbance caused. The white tissue of the eye (sclera) may be weak since birth, due to which its fibers can stretch and elongate the eyeball, causing myopia.
If the mother has suffered from some sort of illness during her pregnancy, there is a high probability of the kid suffering from myopia.
Sometimes myopia can happen in infants in combination with other diseases like albinism, Ehlers- Danlos syndrome, Fabry’s disease, Marfan syndrome and Pierre-Robin Syndrome among many others. This form of myopia can happen in association with several ocular diseases as well.
Research and studies over the years have shown that children whose parents have been affected by myopia of a higher degree, have strong chances that they too would be affected by it. Myopias often follow strong familial patterns, though that is not the case each time. It is still a matter of debate whether the hereditary factor is enhanced or unaffected by environmental triggers of myopia. Like other physical and mental traits, children may inherit the elongated eyeball design of their parents, hence the nearsightedness.
4. Faulty/Closeup Work Patterns:
These are the type of things which involve a more concentrated vision as compared to the type of eyesight one requires while performing routine tasks. Closeup work, such as working on a computer for long hours, needlework, reading, focusing with a microscope or any work that will require to utilize an increased power of accommodation. Over time, this work can put a lot of stress on the eyes which leads to an alteration in its ability to view far-off things properly.
5. Overuse of Eyes:
This can be more of a physiological trouble than any serious health condition.
The people doing ‘closeup type of work’ may be troubled by a happening known as ‘false or pseudo myopia.’ Because of over-concentrating their vision at a single place for long periods of time, it becomes difficult for such people to re-adjust their ability to view things at long distances. But this is nothing to worry about, since some amount of relaxation will refresh the eyes and make them normal again.
6. Decreased Sensitivity Towards Darkness:
Night myopia is a phenomenon when poor light conditions or darkness make it difficult for the eyes to focus themselves properly. The pupil dilates a lot in order to bring in more light and this results in a hazy gaze.
Young children are most prone to acquiring myopia. Genetics, heredity and environment play their roles in complicated ways to bring about the trouble of near-sin kids. In the initial phases of myopia, kids usually are unable to distinguish between a clear and a possibly blurry vision.
As age progresses, the juvenile form of myopia worsens with a progression rate of 0.3-0.5 D each year. Kids may complain of headache, trouble in focusing on far away things and frequent eyestrain. They may even move closer to things in order to see them properly. If you happen to notice any of these symptoms, you should rush immediately to your eye doctor for a thorough eye examination.
8. In Association With Other Medical Conditions:
Myopia is a type of eye disease which can happen on its own in a completely unrelated way or be a result of effects of other systemic, congenital or ocular diseases. It can also be a warning sign of cataract, which often precedes as blurriness of vision. Many patients suffering from diabetes mellitus have often complained of changes in vision, thus proving that myopia can happen because of changes in blood sugar levels. A temporary form of myopia has also been reportedly seen in cases of systemic tuberculosis.
Some medications like sulfonamides (acetazolamide, sulphasalazine, etc.), promethazine hydrochloride, insulin, tetracyclines, mefenamic acid, aspirin and recreational drugs like ecstasy and ephedrine can affect vision as well.
Medications can affect the eyes in the following 3 ways:
- Contraction of the ciliary muscle for a duration longer than expected
- Adsorption of water by the eyes which alters its refractive index
- Swelling of the ciliary processes of the eye, which in turn results in forward positioning of the lens.
9. Blunt Trauma:
Blunt trauma are usually closed wounds in nature. They do not show up as bleeding or any evident form of injury, but such a ‘hidden nature’ of these injuries is just as unfavorable. Blunt trauma can temporarily affect the ciliary body and crystalline lens. This results in the form of some swelling in the ciliary body and spasm of the ciliary muscles (muscles which control pupil opening), hence the subsequent visual disturbance.
How is Myopia Diagnosed?
The importance of checking patient history thoroughly and proper identification of signs and symptoms can never be underestimated. But there are a few diagnostic tests which are carried out in order to co-relate them with clinical findings and obtain a confirmed diagnosis.
A special device known as retinoscope is used to shine light inside the patient’s eyes. An ophthalmologist then examines the status of retina. Retinoscopy is very useful in order to determine the degree of refraction of both eyes. This procedure can be performed both with and without a cycloplegic agent (something that affects pupil dilation) for better visualization of the retina.
- Visual Acuity:
Visual acuity indicates the degree of eyesight clarity, something similar to resolution power of a camera lens. It is dependent on factors like the neurological status of the person, retinal health and the degree of retinal focus. Visual acuity should be measured with and without any aids (spectacles, lenses, etc.). For example, the Snellen chart is an useful indicator of visual clarity.
- General Ocular Health Assessment:
This test is used to assess the overall health of eyes. For this, tests like fundus biomicroscopy, ophthalmoscopy and slit lamp biomicroscopy are performed. These tests help to evaluate the status of retina, choroid and pupils. Intra ocular pressure can very well be determined using these tests. Differentiating between acquired or induced myopia becomes possible with the help of these diagnostic tools.
- Systemic Health Screening:
Since myopia can also happen in association with systemic diseases like diabetes, a proper routine health checkup in conjugation with ocular assessments can help the ophthalmologist to modify the treatment plan which addresses the individual needs of the patient.
- Ocular Parameters:
These parameters include ocular motility, accommodation and binocular vision. Different tests have been tailor made for appropriate evaluation of visual health parameters in both adults and children. The penlight test can be used to assess the motility of eye muscles. Similarly, the Cover test, Hirschberg test, Krimsky test, etc. can be used to evaluate the binocular status of children.
Treatment of Myopia
To correct myopia, a divergent lens is the treatment of choice. Also known as a concave lens, it helps light to focus images clearly on the retina instead of ahead or behind it.
Depending on the severity of near-sightedness, myopia can be managed in two ways:
- Conservatively – This method involves a variety of techniques aimed to correct myopia with simple tools and habits.
- Surgically – This approach is used only after the development of eyes has been completed. Earlier, this approach was taken only as a last resort procedure but now is performed electively on a routine basis.
Before we get to the treatment part, it is important to understand what it actually aims to do. Managing myopia intends to either slow down the progression of the disease or simply put a stop on the deteriorating condition once and for all. At the end of the day, the affected person should be able to have a comfortable, fully functional binocular vision which is not all troublesome or hazy at far off distances.
So here are a few treatment methods which are used to correct myopia:
These glassy and clear optical units have been found to be the first line approach for dealing with different varieties of myopia. Lenses can be available in the form of spectacles or contact lenses. Each of these has its own advantages and disadvantages. The preference for spectacles over contacts or vice versa is mostly dependent on patient compliance (how much the patient can adhere to the prescribed instructions), cosmetic needs and personal preferences.
Spectacles are advantageous in several ways. For starters, they are quite economical, come in a variety of shapes and sizes and provide some sort of protection to the eyes. They are flexible in the sense that these little contraptions can easily incorporate different types of glasses to suit different treatment needs like bifocals, prismatic lenses or others in order to provide treatment solutions to refractive errors co-existing with myopia. An additional bonus from a technical standpoint, these lenses require lesser accommodative powers than a contact lens.
Contact lenses on the other hand are very aesthetic and eliminate the need for carrying frames on the nose as in the case of spectacles. These lenses have an increased field of vision and provide better visual acuity to a myopic eye. Apart from this, contact lenses are effective in avoiding any sort of prismatic error unlike spectacles and are helpful in reducing the progression rate of myopia in the long run. The only trouble is that contact lenses need to be cared for very gently and do have the potential to irritate the eyes by causing allergies.
A special class of therapeutic agents had been suggested for managing the myopic eye known as cycloplegic agents. These agents include atropine, cyclopentolate, scopolamine, etc. Normally they are used by ophthalmologists in order to examine the retina in a detailed manner. It was advocated earlier to use these agents in the treatment of pseudomyopia by temporarily paralyzing the ciliary muscles. However, with time it became very clear that the benefits of cycloplegic agents were clearly outweighed by the ill effects caused by use of these drugs, such as systemic toxicity, too much of pupil dilations and retinal damage. Hence, this plan was discontinued as a line of treatment.
- Vision Therapy:
This one is also known as vision training. Vision therapy has been used for harnessing the forces of the eye movements & muscle coordination in order to bring about a change in visual acuity of the patient. A set of exercises designed for effective eye training are performed by the patient under the observation of an ophthalmologist. The exercises can vary from simple eye movements to reading different sets of cards.
Vision therapy has proven to be more useful for treating pseudomyopia instead of myopia. It was not much effective for curing myopia in the long run.
This is an interesting treatment modality. This therapy involves the component of graduated exposure, where a series of contact lenses of different powers are given to the patient to wear over a stipulated period of time. Mostly, the ophthalmologist asks the patient to wear these lenses overnight and sleep.
The contact lenses used in this technique are rigid and permeable to gases in nature. These contact lenses are proven to reduce the degree of myopia by as much as 3D, with an average of 0.75-1D. With time, these lenses gradually flatten the cornea in the center and bring about changes in the steepness of the peripheral cornea.
Orthokeratology is indicated for use in adults only because of better tolerance and good compliance. If proper follow up care has been performed, this technique is among the safest therapeutic modalities for the treatment of myopia. However, a small degree of refractive error has been noted in patients who stop wearing the designated contact lenses completely.
- Refractive Surgery:
Refractive surgery covers several minimally invasive procedures, most of which have produced good clinical outcomes and long term results.
Some techniques of refractive surgery include:
1. Radial Keratotomy – Here, tiny incisions are made on the corneal region in a radial like pattern. The rationale behind this technique being that the incisions which have been given in the para central part of the cornea will weaken, which will in turn steepen it and make the central cornea flatter and reduce myopia. Though this technique worked well initially, it was later replaced by more modified techniques which are mentioned below.
2. Laser Assisted In-situ Keratomileusis (LASIK) – This technique is among the most popular surgical procedures performed to correct refractive errors like myopia, astigmatism and presbyopia. With the help of LASIK, many people have been very satisfied with the quality of their new vision and its longevity.
The eyes are numbed using anesthesia and are stabilized in place using special instruments. A tiny flap is made in the cornea. Now, with the help of an excimer laser, the cornea is reshaped according to the degree of correction required. Being a computer operated system, the excimer laser is programmed in advance for easy and efficient work. This information can be later on retrieved by the eye surgeon as and when he/she pleases.
At most, a LASIK procedure takes 15-20 minutes to perform (it’s so fast!) and your total stay at the doctor’s office will last for hardly 2 hours!
3. Photorefractive Keratectomy (PRK) – It is a surgical procedure very similar to LASIK, with the difference that in PRK, the epithelial cells of the cornea are removed first with mechanical means. After this, the excimer laser is used to remove the tissue located on the cornea. Once this is complete, a bandage contact lens is kept on the operated part for a few days till the new epithelium grows back into place. The bandage is removed after complete healing of the cornea and you are ready to move!
PRK is a procedure which has shown good results, but a little less in comparison to LASIK. It takes a few months for the new vision to stabilize, following which, an enhancement procedure may be required in some cases. Unlike patients treated with LASIK, PRK treated patients have also complained of some degree of irritation after surgery.
4. Intra Ocular Lens Implant (IOL) – When it comes to patients troubled with high myopia, Phakic IOLS are the answer. These unique pieces of vision are placed in the eye over the original eye lens. Made of flexible plastic, Phakic IOLs have proven to be very useful in correcting distance vision. Mostly, monofocal lenses are employed in this procedure, but multifocals are useful if the myopia is co-existing with another refractive error such as astigmatism.
An IOL implantation procedure has many benefits in the long run, but the ones having it should take extra care to maintain it properly by religiously attending the follow-up appointments.
5. Laser Assisted Subepithelial Keratectomy (LASEK) – A surgical procedure which can somewhat be called as a ‘win-win’ situation. A LASEK procedure combines the benefits of PRK and LASIK and minimizes the complications associated with them.
LASEK is performed using a variety of approaches & methods and is performed usually in cases where LASIK and PRK cannot be done.
The only catch with LASEK is that it has a relatively longer recovery period and can cost you more than LASIK or PRK.
Myopia is among the commonest refractive errors which affect the eyes. It sometimes appears as a warning sign associated with other clinical conditions. Today, with advanced surgical techniques, myopia can be treated with very good success rates.
Timely recognition and immediate intervention – All it needs is a good eye.