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INTERNATIONAL
REVIEW
OF OPHTHALMIC
OPTICS
A perspective on the evolution and management of myopia
NAIDOO Kovin
,
WALLACE Diane
Refer this article as: Naidoo, K., Wallace, D., A perspective on the evolution and management of
myopia, Points de Vue, International Review of Ophthalmic Optics, N63, Autumn 2010
Publication date : 10/2010
Uncorrected myopia (short-sightedness) is a major public health challenge restricting employment
opportunities, affecting the learning ability of children and limiting the quality of life of affected
individuals. Further to this, high degrees of myopia create an increased risk of retinal detachment and
possibly, visual impairment and blindness. Recent reviews of the epidemiology of myopia reveal that
the prevalence and incidence of myopia have been increasing, especially in Asian populations where
myopia has reached epidemic proportions [1]. The number of myopes in the world is estimated to
grow from 1.6 billion currently to a staggering 2.5 billion by 2020 [2].
Development of Myopia
Myopia occurs when light is focussed in front of the retina [3] due to the eyeball being either too long
or the cornea having increased curvature as compared to the standard eye. Consequently, distant
objects appear blurred while near objects are visually clear. Infant eyes undergo a process of
emmetropization whereby both the average amount and the variance in the distribution of refractive
errors are reduced [4]. The refractive status shifts from hyperopia and astigmatism to emmetropia
(zero refractive error). Failure to achieve emmotropization results in myopia, which can be classified
into two groups according to the magnitude of myopia i.e. low to moderate degree of myopia
(referred to as simple myopia of the magnitude -0.5 to -6.0 dioptres) and high or pathological myopia
of the magnitude i.e. greater than 6.0 dioptres [5].
Causes of Myopia
In 1885, Fuchs stated that “acquired myopia is the result of several factors, among which prolonged
work requiring close vision takes the first place” [6]. More than a century later, we cannot fully
explain the cause of myopia, although the rapid increase in its prevalence in the past century
provides some clues about its aetiology [1]. Myopia has traditionally been considered to be a
genetically pre-determined refractive condition, though more recent indications are that
environmental factors such as excessive near work have an effect on the development and
progression of myopia [7].
Risk factors for the onset and progression of myopia include [10]:
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A perspective on the evolution and management of myopia | Points de Vue | International Review of Ophthalmic Optics
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Genetic predisposition or family history;
Premature and low birth weight individuals;
Cumulative effect of excessive near work.
Myopia can be broadly classified into 2 categories [10]:
1. Physiological - simple myopia not linked to any notable degenerative fundus changes;
2. Pathological - progressive or degenerative myopia usually leading to abnormal lengthening of the
eyeball and risk of retinal detachment [12].
Corrective options
Conventional methods of correcting myopia have been single vision spectacles and contact lenses
[14]. Increasingly, bifocal lenses and progressive lenses are being used in myopia control. In younger
patients, bifocal lenses are occasionally used to slow the progression of myopia [15].
Soft contact lenses have been used extensively to correct simple myopia, with rigid gas permeable
lenses used for high myopia [16]. While, patients desire comfort, clarity of vision, and prolonged
contact lens wear when contact lenses are used as a refractive correction, practitioners require
maintenance of the integrity of the eye with minimal complications that jeopardize vision or ocular
health [17]. For 30 years, contact lens research focused on the need for high oxygen-permeable (Dk)
soft lens materials as this was seen as necessary to maintaining corneal integrity over the long term.
High Dk silicone hydrogel contact lenses, made available in 1999, met this need, allowing as much as
seven times more oxygen to pass through to the cornea [18]. The availability of highly oxygen
permeable contact lenses has therefore increased the tolerance and safety of contact lens wear.
These improvements, together with those in lens design and maintenance products have reduced but
not eliminated the risks of infection, inflammation, other reactions associated with contact lens wear
[18].
Orthokeratology uses rigid lenses to reshape the cornea and thus alter the refractive error and is
enjoying a revival in popularity due to the advancements in lens design and the improvement in RGP
material. Ortho-k can have both a corrective and preventive/control effect in childhood myopia.
However, there are substantial variations in changes in eye length among children and there is no
way to predict the effect for individual subjects [19].
Increasingly refractive surgery has become an option for vision correction. In myopia the laser flattens
the central cornea and brings the focal point back on to the retina. Currently Laser in situ
keratomileusis (LASIK) is the most commonly performed refractive surgery. According to Andrew
Velazquez, “Of current refractive procedures, LASIK offers the least discomfort and the most rapid
postoperative healing and visual improvements. Epi-LASIK, photo refractive keratectomy [PRK], and
laser epithelial keratomileusis [LASEK] are usually reserved for patients whose corneas are too thin or
shaped in a way that rules out LASIK” [13].
Other surgical corrective options are clear lens extraction, implantable contact lens (between the iris
and lens) intracorneal lens implants (within the cornea) and intracorneal ring segments (plastic arcs in
the peripheral cornea) (Fig 1).
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A perspective on the evolution and management of myopia | Points de Vue | International Review of Ophthalmic Optics
Fig. 1: Intracorneal Rings - plastic inserts placed in the cornea which flatten the central cornea to
correct low degrees of myopia (sourced from www.isecmalaysia.com).
The use of pharmaceutical agents, as a result of costs and discomfort, has been limited.
Pharmaceutical agents such as atropine have been used with relative success in some parts of the
world in reducing the progression of myopia, though the bulk of evidence from wellconducted studies
shows that overall, most therapies for myopia have small treatment benefits that last for a relatively
short period of time or have significant side effects [14].
Future prospects: Contact Lenses
The solution to the reduction of infection from contact lenses and the development of more affordable
contact lenses remain elusive. Although the ocular health benefits of silicone hydrogel lenses have
increased the length of time lenses can be worn overnight, the risk of infection is similar to that found
with other soft lens types, and overnight wear remains a higher risk factor for infection than daily
wear, regardless of lens material [18]. Future contact lens research will focus on gaining a better
understanding of the way in which contact lenses interact with the corneal surface, upper eyelid, and
the tear film, and the lens-related factors contributing to infection and inflammatory responses [18].
Further the development of affordable and highly oxygen permeable contact lens materials that meet
the criteria for ocular health are critical to the growth of the contact lens market [21].
Corneal Onlay
The corneal onlay project of the Vision CRC in Australia is developing a permanent correction for
refractive errors with an implantable contact lens. A synthetic lens is surgically placed under the
superficial layer of corneal tissue (the epithelium), altering the corneal curvature. The lens is designed
to provide stable vision for at least five years, while being a reversible procedure in which no
permanent functional or structural damage is done to the eye.
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A perspective on the evolution and management of myopia | Points de Vue | International Review of Ophthalmic Optics
Anti-Myopia Products
That Arrest, Slow or Control the Progression Of Myopia The ability to focus images on the peripheral
retina may influence emmetropisation. A novel optical device that controls image formation in this
region may be a major breakthrough in eliminating or slowing the progression of myopia [21].
Conclusion
The elevation of uncorrected refractive error in the blindness prevention agenda has increased the
focus on myopia and the management thereof. Achieving greater access and efficiency in the
management of myopia is thus a critical challenge for eye care professionals.
Références
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