Myopia
Walter Huang, OD
Yuanpei University
Department of Optometry
Definition
The common name for this refractive error
is near-sightedness
Patients with myopia are known as
myopes
Definition
When parallel rays of light enter the eye
(with accommodation relaxed) and come
to a single point focus in front of the retina
Etiology
Axial length


The axial length of the eye is longer than
normal due to imperfect emmetropization
The most common cause of myopia for high
myopes
Etiology
Refractive power

The refractive power of the eye is too strong
Curvature myopia

Cornea or lens has a steep curvature (e.g., keratoconus)
Increased index of refraction (e.g., cornea, lens)
Anterior movement of the lens (e.g., nuclear
sclerosis)
Prevalence
Age






At birth: 24 to 50%
As birth weight decreases, the amount of myopia
increases in premature infants
The mean refractive error for full-term infants is +2.00
D
The prevalence of myopia decreases by 1 year old
due to the process of emmetropization
5 to 6 years old: 2% (>-0.50DS)
13 to 14 years old: 15%
Prevalence
Age

In Taiwan (1995)
7 years old: 12%
12 years old: 56%
15 years old: 76%
18 years old: 84%

In western countries
20 years old: 20%
Prevalence
Gender



In general, there are no significant differences
between males and females
Progression of myopia tends to begin and end
earlier in females
High myopia is more common in females
Prevalence
Ethnicity


Higher prevalence in Asians, Arabs, and Jews
Lower prevalence in Caucasians, Blacks, and
South Sea Islanders
Prevalence
Urban versus rural communities

Myopia is more common in urban
communities than in rural ones
Progression
Myopia tends to increase linearly until the
middle or late teenage years, at which
point, it levels off
The earlier a child becomes myopic, the
more rapidly the condition tends to
progress
Juvenile-Onset Myopia
Definition

Myopia in which the age of onset is 8 to 12
years
Juvenile-Onset Myopia
Etiology

Evidence for genetics influences
Greater similarity of refractive error and ocular
structures in identical twins than in fraternal twins
Juvenile-Onset Myopia
Etiology

Evidence for genetics influences
Increased prevalence of myopia in children of
myopic parents

Probability of a child being myopic is:
40% when both parents are myopic
20 to 30% when one parent is myopic
<10% when neither parent is myopic
Juvenile-Onset Myopia
Etiology

Evidence for environmental influences
Association between near work, education, and
myopia


Children who do a lot of near work, like reading, tend to
become myopic
Myopia is more common where occupations require
extensive near work
Myopia and Visual Acuity
Uncorrected VA
Refractive Error (D)
20/30
0.50
20/40
0.75
20/60
1.00
20/80
1.50
20/120
2.00
20/200
2.50
Symptoms
Blurry vision at distance
Clear vision at near
Squinting
Occasional headaches
Signs
Decreased visual acuities at distance
Clinical Tests
Visual acuity tests - distance
Retinoscopy
Subjective refraction
Management
Divergent or minus lenses in spectacles or
contact lenses
Cycloplegics
Surgery
Refractive surgery
Management
Spectacles


Single vision glasses
Bifocal glasses
More effective in children with near esophoria
Management
Contact lenses




Soft contact lenses
Rigid gas permeable contact lenses
Ortho-keratology contact lenses
Corneal reshaping therapy contact lenses
Management
Contact lenses

Ortho-keratology
Rigid gas permeable contact lenses are used to
flatten the cornea
Results are unpredictable (0 to 5.00 D of change)
Two eyes may respond differently in anisometropia
Procedure may induce astigmatism
Retainer lens is required; otherwise, the patient’s
prescription may return to normal
Management
Cycloplegics (e.g., atropine)


Reduce the ability to accommodate
May slow the progression of myopia
Management
Surgery

Radial keratotomy (RK)
Technique


Eight cuts with a blade in a radial pattern are made on
the surface of the cornea
The depth of each cut is through approximately 85 to
90% of the cornea
Management
Surgery

Radial keratotomy (RK)
Post-surgical complications




Hyperopic shift
Diurnal fluctuations of refractive error and visual acuity
Glare
Corneal scarring
Management
Refractive surgery

Photorefractive keratectomy (PRK)
Technique

High energy photons from an excimer laser are used to
photoablate a small amount of tissue from the anterior
corneal surface and sculpt the cornea
Management
Refractive surgery

Photorefractive keratectomy (PRK)
Post-surgical complications





Eye pain
Corneal disruption
Blurry vision
Prolonged duration of drug use
Greater time needed for eyesight recovery
Management
Refractive surgery

Laser in-situ keratomileusis (LASIK)
Technique




A microkeratome is used to cut a flap of superficial
corneal tissue
The flap is lifted back, exposing the underlying corneal
stroma
The excimer laser is used to perform tissue removal in
the corneal stroma
The flap is repositioned in its original position and
adheres to the underlying corneal stroma without the
need for sutures
Management
Refractive surgery

Laser in-situ keratomileusis (LASIK)
Post-surgical complications




Severe dry eye syndrome
Poor night vision
Reduced contrast sensitivity
Astigmatism
Management
Refractive surgery

Points to consider after the surgical procedure
Use eyedrops, as prescribed by the ophthalmologist
Be careful not to allow chlorinated water , shampoo, and
sweat to come into contact with the eyes
Wear sunglasses when outside to protect the eyes from
sunlight
Remember to go back to the hospital for regular follow up
visits with the ophthalmologist and to get eyedrops
Pathological Conditions Associated
with Myopia
Cataract

Nuclear cataract causes a myopic shift
Pathological Conditions Associated
with Myopia
Diabetes



High blood glucose levels cause increased
sorbital levels in the lens
Water rushes in and dilutes the sorbital in the
lens
Lens bulges and results in a myopic shift
Pathological Conditions Associated
with Myopia
Marfan’s syndrome


Suspensory ligaments break
Subluxation of lens occurs superiorly and
temporally and results in a very high increase
in myopia