Myopia Treatment, Causes, Symptoms

Myopia or nearsightedness, is the most common human eye disorder in the world, and is a significant global public health concern. Along with cataract, macular degeneration, infectious disease, and vitamin A deficiency, myopia is one of the most important causes of visual impairment worldwide. Severe or high-grade myopia is a leading cause of blindness because of its associated ocular co-morbidities of retinal detachment, macular choroidal degeneration, premature cataract, and glaucoma.

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The Epidemiology of Myopia[rx]–[rx]

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Types of Myopia

Various forms of myopia have been described by their clinical appearance:^[rx][rx][rx]

• Simple myopia – Myopia in an otherwise normal eye, typically less than 4.00 to 6.00 diopters.^[rx]
• Degenerative myopia – also known as malignant?, pathological, or progressive myopia, is characterized by marked fundus changes, such as posterior staphyloma, and associated with a high refractive error and subnormal visual acuity after correction.^[rx] This form of myopia gets progressively worse over time. Degenerative myopia has been reported as one of the main causes of visual impairment.^[rx]
• Pseudomyopia – is the blurring of distance vision brought about by spasm? of the accommodation system.^[rx]
• Nocturnal myopia – Without adequate stimulus for accurate accommodation, the accommodation system partially engages, pushing distance objects out of focus.^[rx]
• Nearwork-induced transient myopia (NITM) – short-term myopic far point shift immediately following a sustained near visual task.^[rx] Some authors argue for a link between NITM and the development of permanent myopia.^[rx]
• Instrument myopia – over-accommodation when looking into an instrument such as a microscope.^[rx]

Induced myopia – also known as acquired myopia, results from exposure to various pharmaceutical drugs, increases in glucose levels, nuclear sclerosis?, oxygen toxicity (e.g., from diving or from oxygen and hyperbaric therapy) or other anomalous conditions.

• Sulphonamide therapy – can cause ciliary body edema?, resulting in anterior displacement of the lens, pushing the eye out of focus.^[rx]
• Elevation of blood-glucose levels –  can also cause edema? (swelling?) of the crystalline lens as a result of sorbitol accumulating in the lens. This edema often causes temporary myopia.
• Scleral buckles – used in the repair of retinal detachments may induce myopia by increasing the axial length of the eye.^[rx]
• Index myopia – is attributed to variation in the index of refraction of one or more of the ocular media.^[rx] Cataracts may lead to index myopia.^[rx]
• Form deprivation myopia occurs – when the eyesight is deprived by limited illumination and vision range,^[rx] or the eye is modified with artificial lenses^[rx] or deprived of clear form vision.^[rx][rx] In lower vertebrates, this kind of myopia seems to be reversible within short periods of time.^[rx] Myopia is often induced this way in various animal models to study the pathogenesis and mechanism of myopia development.^[rx]

Degree

The degree of myopia is described in terms of the power of the ideal correction, which is measured in diopters:^[rx]

• Low myopia – usually describes myopia of −3.00 diopters or less (i.e. closer to 0.00).^[rx]
• Moderate myopia – usually describes myopia between −3.00 and −6.00 diopters.^[rx] Those with moderate amounts of myopia are more likely to have pigment dispersion syndrome or pigmentary glaucoma.^[rx]
• High myopia – usually describes myopia of −6.00 or more.^[rx][rx] People with high myopia are more likely to have retinal detachments^[rx] and primary open angle glaucoma.^[rx] They are also more likely to experience floaters, shadow-like shapes which appear in the field of vision.^[rx]

Age at onset

Myopia is sometimes classified by the age at onset:^[rx]

• Congenital? myopia – also known as infantile myopia, is present at birth and persists through infancy.^[rx]
• Youth onset myopia – occurs in early childhood or teenage, and the ocular power can keep varying until the age of 21, before which any form of corrective surgery is usually not recommended by ophthalmic specialists around the world.^[rx]
• School myopia – appears during childhood, particularly the school-age years.^[rx] This form of myopia is attributed to the use of the eyes for close work during the school years.^[rx]

Adult onset myopia

• Early adult onset myopia occurs between ages 20 and 40.^[rx]
• Late adult onset myopia occurs after age 40.^[rx]

• Myopia is a refraction anomaly of the non-accommodated eye with a spherical equivalent of −0.5 dioptre (D) or lower.

Primary myopia –  due to elongation of the visual axis OR a combination of primary and secondary myopia OR unknown causes

• Simple myopia – myopia up to −7.75 D
• High myopia – refraction ≥−8.00 D or more negative

Secondary myopia – due to too strong refractive ocular media, among others

• Corneal curvature too steep
• Lens swelling?, higher refractive index or cataract
• Lens dislocation
• Medicine (eye drops) use
• Systemic? diseases including genetic syndromes involving the eye

Pseudomyopia

• Accommodation spasm?
• Night myopia

More than 2 SD of the statistical average according to age, sex and ethnicity.

In daily practice, it is often not possible or practical to determine axial length. When no signs of secondary myopia are present, and essentially the cause is unknown, it is also called primary myopia.

‡−8.00 is an arbitrary and often used cut-off point.

Causes of Myopia

Nearsightedness happens when your eye is longer than normal, or, less often, when your cornea is too curved. Objects focus in front of the retina instead of on the retina, causing it to be blurred. The exact cause of myopia is not known.

Research about myopia supports two key risk factors:

• Family history – If one or both parents are nearsighted, the chance of their children developing it increases.
• Working up close – Long hours of near work such as reading or computer work may be at increased risk for developing myopia.

Temporary nearsightedness can also occur due to visual stress and disease:

• Night Myopia – Some people experience blurred distance vision only at night. When it’s dark, the eye may simply not be receiving enough light to focus, or too much light from the sides may be entering the naturally dilated eye, making it hard to focus.
• False Myopia – Some people cannot focus far after long periods of near vision tasks. Usually the focusing ability of the eye will return after some rest.
• Myopia symptoms – could also be a sign of variations in blood sugar levels in people with insulin? is low or not working well. সহজ বাংলা: রক্তে চিনি বেশি থাকার রোগ।" data-rx-term="diabetes" data-rx-definition="Diabetes is a condition where blood sugar stays too high because insulin is low or not working well. সহজ বাংলা: রক্তে চিনি বেশি থাকার রোগ।">diabetes? or an early indication of a cataract.
• The retina’s center (macula) thins with age – While this does not affect side (peripheral) vision, the ability to focus on a particular object (like reading a sign) diminishes and is eventually lost.
• Retinal thinning – can also lead to tears and holes, which can cause the retina to detach.
• The retina can split – a condition called myopic retinoschisis (MRS).
• Layers of the eye under the retina can degenerate or crack – allowing new, faulty blood vessels to grow under the retina (a process called choroidal neovascularization, or CNV). The vessels can bleed and scar, with small scars causing minor macular damage and larger ones more significant problems.
• Myopia occurs – when the eyeball is too long, relative to the focusing power of the cornea and lens of the eye. This causes light rays to focus at a point in front of the retina, rather than directly on its surface.
• Nearsightedness – can also be caused by the cornea and/or lens being too curved for the length of the eyeball. In some cases, myopia occurs due to a combination of these factors.
• Myopia typically begins in childhood – and you may have a higher risk if your parents are nearsighted. In most cases, nearsightedness stabilizes in early adulthood but sometimes it continues to progress with age.
• Increased eye pressure – may lead to glaucoma.
• Cataracts – are more likely to develop.
• The eyes become more susceptible to injuries and other traumas, like surgery
• Your eye care professional can evaluate your eyes to determine the reason and severity of your myopia.

Symptoms of Myopia

Some of the signs and symptoms of myopia include:

• Eyestrain,
• Headaches
• Squinting to see properly, and
• Difficulty seeing objects far away, such as road signs or a blackboard at school.
• Recurrent headaches
• Incessant eye-rubbing
• Squint
• Eye tendon?. সহজ বাংলা: মাংসপেশি/টেনডনে টান।" data-rx-term="strain" data-rx-definition="A strain is injury to a muscle or tendon. সহজ বাংলা: মাংসপেশি/টেনডনে টান।">strain?
• Eye fatigue? when you try to see objects more than a few feet away
• Children with myopia often have trouble reading the blackboard at school.
• Squinting in an attempt to help vision
• Unexplained drop in school performance
• Blurry vision when looking at distant objects
• The need to squint or partially close the eyelids to see clearly
• Headaches caused by eyestrain
• Difficulty seeing while driving a vehicle, especially at night (night myopia)

Nearsightedness is often first detected during childhood and is commonly diagnosed between the early school years through the teens. A child with nearsightedness may:

• Persistently squint
• Need to sit closer to the television, movie screen or the front of the classroom
• Seem to be unaware of distant objects
• Blink excessively
• Rub his or her eyes frequently

Diagnosis? of Myopia

• Short-sightedness is simple to diagnose – An optometrist or ophthalmologist usually asks you to read a special chart (Snellen chart) that has large letters at the top and smaller letters at the bottom. If you can see all the letters clearly you have 6/6 vision. If you have 6/12 vision, it means that you can read letters at 6 m that a person with normal vision can read from a distance of 12 m.
• In everyday language – people still talk about 20/20 vision, which is a throwback to when Australia, like the USA, used imperial measurements and so 20/20 is the same as 6/6 vision.
• Doctors diagnose – most cases of high myopia by age 13. Patients then get regular eye exams to check the retina for further problems. We may use a special test called fluorescein angiography to look for new blood vessels, with doctors injecting dye and then taking photographs.

Treatment of Myopia

Single Vision Lenses

• An active emmetropization mechanism regulated by optical defocus is supported by results of numerous studies (reviewed in ^[rx]). Strong evidence is provided by compensatory ocular growth seen in response to lens-induced defocus in animal models. ^[rx] Based on these results, it has been suggested that spectacle intervention in myopic children with the commonly prescribed single vision lenses (SVLs) might lead to increased progression and axial elongation.

Bifocals and Progressive Addition Lenses

• The use of bifocals or progressive addition lenses (PALs), sometimes called no-line bifocals, for slowing the progression of myopia has produced relatively small treatment effects overall, on the order of 0.15 to 0.50 D over 1.5 to 3 years, ^[rx–rx]
• The use of bifocals or progressive addition lenses (PALs), sometimes called no-line bifocals, for slowing the progression of myopia has produced relatively small treatment effects overall, on the order of 0.15 to 0.50 D over 1.5 to 3 years, although treatment effects are reported to be larger in certain subgroups of myopic children, as described below[rx].
• The largest of the treatment trials with this type of lens was the Correction of Myopia Evaluation Trial (COMET), a multi-center, randomized, double-masked clinical trial to evaluate whether PALs slow the rate of progression of myopia compared to conventional SVLs[rx],[rx].

Contact Lenses

• Many early investigations of rigid gas permeable contact lenses (RGP) for myopia control suffered from lack of randomization and a high drop out rate from the contact lens group[rx]–[rx].
• In an attempt to eliminate the high loss to follow-up found in previous studies, a recent randomized clinical trial, the Contact Lens and Myopia Progression (CLAMP) study, implemented a run-in period to ensure good compliance with rigid contact lens wear.

Prism bifocal spectacle lenses

• Prism bifocal spectacle lenses are bifocal spectacles with 3-Δ base-in prism in near addition of + 1.50D. With this device, the effort for convergence and accommodation during near work can be attenuated. It appears to work best for myopic children with low lags of accommodation. In these patients, 0.99D/year of myopia retardation as compared with control was observed.[^rx]

Medication

Atropine

• Recent well-designed studies using topical atropine, a non-selective muscarinic antagonist, have demonstrated statistically and clinically significant reductions in the progression of myopia.^[rx,rx] Shih et al ^[rx] reported that myopia progression was significantly slowed (p<0.0001)over 18 months in 6-13 year old children randomized to 0.5% atropine with multi-focal glasses (0.41 D) compared to multi-focal glasses alone (1.19 D) or SVLs alone (1.40 D). Chua et al^[rx] reported similar results in a two-year study of 400 6-12 year-old myopic children in Singapore, although this study used a different experimental paradigm.

Pirenzepine

• Pirenzepine, like atropine, is a muscarinic antagonist but it is less likely to produce mydriasis and cycloplegia. Two clinical trials of pirenzepine have been conducted, one in Singapore, Hong Kong, and Thailand^[rx] and the other in the United States.^[rx–rx] In the Singapore study, myopia in children increased over a one-year period by 0.47 D for those using pirenzepine ophthalmic gel twice a day, 0.70 D for those using it once a day, and 0.84 D for the control group.^[rx]

References