06 refractive error

Refractive error
Prof Md Anisur Rahman
Head of the Department
(Ophthalmology). Dhaka Medical
College. Dhaka
9 Sept 2019 (LIONS) 1anjumk38dmc@gmail.com

Important topics of refractive error
• Hypermetropia
• Definition
• Types
9 Sept 2019 (LIONS) anjumk38dmc@gmail.com 2

Myopia
 Definition
 Treatment
 Types
 Diff between simple & pathological myopia
 Treatment
 Other myopia

Astigmatism
 Definition
 Symptoms
 Treatment
 Different types of astigmatism

Emmetropia
Emmetropia: (Optically normal eye, no refractive error
is at their) is defined as a state of refraction, when the
parallel rays of light coming from infinity are focused
at retina, when accommodation is at rest.

Ametropia
Ametropia: (Optically non normal eye, refractive error
is at their) is defined as a state of refraction, when the
parallel rays of light coming from infinity are focused
either in front or behind the retina, when
accommodation is at rest.

Types of ametropia
There are three types of ametropia:
1) Hypermetropia
2) Myopia and
3) Astigmatism

Hypermetropia

What is Hypermetropia (long sightedness)?
When parallel rays of light from infinity comes to a
focus behind the retina when accommodation is at
rest.

Why it is called long sightedness?
The alternative name of for hypermetropia, long
sightedness, is quite acceptable except in so far as it has
given rise to confusion in the layman’s mind. A patient
will often describe himself as very long sightedness when
what he intends to convey is that he sees well in the
distance and presumes himself to be optically normal; it
is, of course, true that early in life the hypermetrope sees
as well in the distance as the emmetrope.
9 Sept 2019 (LIONS) 10
DUKE ELDER 45

Some facts about hypermetropia
 It is the commonest refractive error
 At birth practically all eyes are hypermetropic to
the extent of 2.5 to 3.0 Diopter
 When adolescence is passed, the eye should
theoretically be emmetropic
 But about 50% doesn’t reached there and some
degree of hypermetropia is persists
 Some may be overshoot and become myopic
9 Sept 2019 (LIONS) Duke-Elders: 45 11

Etiological classification of Hypermetropia
1) Axial:
 This is the commonest of all types of ametropia.
One mm shortening of eyeball causes 3 D of
hypermetropia.

2) Index:
This type of hypermetropia may occur physiologically
in old age due to decrease in the refractivity of the
lens or pathologically in DM under treatment when
blood sugar level falls or in cortical cataract. The
outstand example of index hypermetropia is
APHAKIA.

3) Curvature:
This type of hypermetropia occurs due to decrease in
the curvature of any refracting surface. Usual site of
defect is in the cornea. 1 mm changes in the radius of
curvature of cornea causes 6 D of hypermetropia.

Nomenclature of Hypermetropia (components of hypermetropia)
Total Hypermetropia:
Is the total amount of refractive error, which is
estimated after complete cycloplegia with atropine. It
consists of Manifest and Latent Hypermetropia.

Latent Hypermetropia
Which is counteracted by the tone of the ciliary
muscle and can only be disclosed by abolition of the
tone of the ciliary muscle the latent hypermetropia is
disclosed when refraction is carried after abolishing
the tone with atropine.

Manifest Hypermetropia
Is that portion of hypermetropia which in normal
condition remains uncorrected, and not corrected by
ciliary tone. It consists of two components
 Facultative and
 Absolute hypermetropia

Facultative & Absolute hypermetropia
Facultative hypermetropia: Which can be corrected
by accommodation
Absolute hypermetropia: Which can’t be corrected by
accommodation

Latent Hypermetropia
Total hypermetropia
Manifest Hypermetropia
Facultative Absolute

Suppose a patient can read 6/9 without any aid. Now, if
with +1.00 D sphere he can just read 6/6, this is his
absolute hypermetropia.
Now, if with addition of another +0.50 D sphere he can
still read 6/6 this is his facultative hypermetropia.
These two combined together (+1.00+0.50) the manifest
hypermetropia.

 If this patient after full atropinization can read with
another addition of +1.00 D shpere, 6/6 is his latent
hypermetropia.
Then the total hypermetropia (Absolute +
Facultative + Latent ) = (1 + 0.5 + 1.0 = 2.5 ) of
this patient is +2.50 Dsh.

OSPE: 1
Your patient needs +2.00 D to see distance clearly.
However, he can tolerate up to +4.00D without
getting blurred distance vision. His cycloplegic
refraction is +6.00D sphere. What are the values in
diopter of his?

• Absolute hypermetropia?
• Manifest hypermetropia?
• Facultative hypermetropia?
• Latent hypermetropia?

• 1)
• Absolute Hypermetropia:+ 2.00 D
• It is the minimum power which causes vision 6/6

2)
Manifest hypermetropia = + 4.00D
(Manifest hypermetropia is defined as without
cylcoplegia, the most plus correction that can be
tolerated without blurring of vision)

3)
Facultative hypermetropia = + 2.00D
(Facultative hypermetropia is defined as the
difference between absolute and manifest
hypermetropia + 4.00D - + 2.00D = + 2.00 D)

4)
Latent hypermetropia = + 2.00 D
(latent hypermetropia is defined as the
difference between manifest hypermetropia and
hypermetropia measured with cycloplegia +
6.00D - + 4.00D = + 2.00D)

Symptoms of Hypermetropia:
In patient with hypermetropia, the
symptoms vary depending upon the age of
the patient and the degree of refractive
error. These can be grouped as under:

1) Asymptomatic: A small amount of
refractive error in young patients is
usually corrected by mild accommodative
effort without producing any symptoms

2) Asthenopic symptoms: At times the hypermetropia
is fully corrected (thus vision is normal) but due to
sustained accommodative efforts patient develops
asthenopic symptoms. These include:
a) Tiredness of the eyes,
b) Frontal and frontotemporal headache,
c) Watering and
d) Mild photophobia

3) Defective vision with asthenopic symptoms:
When the amount of hypermetropia is such that it is
not fully corrected by the voluntary accommodative
efforts, then the patient complains of defective
vision more for near than distance associated with
asthenopic symptoms due to sustained
accommodative efforts.

4) Defective vision only:
When the amount of hypermetropia is high (more than
4D), the patients usually do not accommodate
(especially adults) and there occurs marked defective
vision for near and distance.

5) Crossed-eye sensation:
Some patients may feel that their eyes are
crossing without any diplopia. It also occurs
due to excessive accommodation

Factors to be consider prescribing spectacle
1) Age of patient: Younger patient have more
accommodative power, so under correct.
2) Symptom: No symptom, no treatment.
3) Accommodative state of the patient: If the Latent
Hypermetropia is more, under correct.
4) Muscle balance: In case of esophoria or esotropia
full correction is indicated to relieve extra
accommodation.
5) Consideration of general health
6) Profession.

Treatment: 1) Optical treatment
Basic principal of treatment is to prescribe convex
(plus) lenses, so that the light rays are brought to
focus on the retina
Fundamental rules for prescribing glasses in
hypermetropia include:
 Total amount of hypermetropia should always be
discovered by performing refraction under complete
cycloplegia

 If the total manifest refractive error is small, e,g, 1 D
or less, correction is given only if the patient is
symptomatic
 The spherical correction given should be comfortable
to the patient. However, the astigmatism should be
fully corrected.
 Gradually increase the spherical correction at 6
months interval till the patient accepts manifest
hypermetropia

 If there is associated exophoria, the hyperopia
should be under corrected by 1 to 2 D
 In the presence of accommodative convergent
squint, full correction should be given at the first
sitting
 If there is associated amblyopia, full correction with
occlusion therapy should be started.

 It is important to remember that in children
hypermetropia may diminish with the growth of the
child. So, refraction should be carried out every six
months and if necessary the correction should be
reduced.

Treatment: 2 Contact lenses
• Contact lens is the another option. When
there is high hypermetropia, the glass
becomes thick & heavy weight, in this case
contact lens is another option

Treatment: 3. LASIK
LASIK can correct up to 4 D (But some
latest instruments claim more correction)

Treatment: 4 Conductive keratoplasty (CK)
Conductive keratoplasty (CK) involves the application
of radiofrequency energy to the corneal stroma and
can correct low–moderate hypermetropia and
hypermetropic astigmatism.

Myopia or Short sightedness
1) Mild myopia includes powers up to -3.00 (D)
2) Moderate myopia, values of -3.00 to -6.00D
3) High myopia is usually myopia over -6.00D

What is Myopia?
When parallel rays of light from infinity comes
to a focus in front of the retina when
accommodation is at rest.

Etiological Classification
1) Axial myopia.
2) Curvature myopia.
3) Index myopia.
 Simple or physiological myopia
 Pathological myopia

• There are some other myopia which is not
worldwide accepted but some books
discuss about it so you have to know some

Features School Myopia College myopia
Types of myopia Simple Simple
Age of onset First decade 2nd half of 2nd
decade
Increment of
power
-0.5 - -1.0
D/yearly
Not much
Stabilization -5.0 to -6.0 D -2.0 to -2.5 D
Astigmatism Less common Frequent
Stabilize by 17 – 18 year 22 – 25 year
Comparison between school myopia &
College myopia

Pathological myopia
• Pathological or degenerative myopia is characterized
by progressive anteroposterior elongation of the
scleral envelope associated with a range of secondary
ocular changes, principally thought to relate to
mechanical stretching of the involved tissues. It is
significant cause of legal blindness, with maculopathy
the most common cause of visual loss

Pathological myopia: Associations with Other Conditions
a) Down’s Syndrome, b) Ocular Albinism,
c) Infantile Glaucoma, d) Marfan’s Syndrome,
e) Retinopathy of Prematurity, f) Ehler’s-Danlos Syndrome,
g) low birth weight, and h) maternal alcoholism.
Patients with these diseases or conditions should be
considered “at risk” for pathological myopia and
carefully monitored.

Pathological myopia: Staphylomas
Pathological myopia causes the eye to elongate, which
in turn stretches and thins the retina and the sclera of
the eye. This leads to a bulging of the posterior
portion of the eyeball. This condition is called a
staphyloma.
By the age of sixty, 50% of patients with staphylomas in
both eyes will be legally blind.

Pathological myopia: Myopic Macular Degeneration
As the eyeball grows and stretches, it may also cause an
area of atrophy and/or cracks in the layers under the
retina. These cracks can serve as conduits for
abnormal blood vessels to grow under the retina.
These vessels can hemorrhage and scar and is called
Fuch’s spots.

Pathological myopia: Fuchs spot
What is Fuchs spot?
It is a raised, circular, pigmented lesion at the macula
developing after a subretinal hemorrhage has absorbed.
 Fuch’s spots, often occur in the 4th to 6th decades of
life. Approximately 5% of pathological myopia patients
develop Fuch’s spots, which lead to damage in the
macular region of the eye and a subsequent loss of central
vision.

Pathological myopia: Retinal Detachment
 The thinning of the layers of the eye may lead to
degenerative changes in the peripheral retina
including retinal holes and lattice degeneration which
puts one at high risk for a retinal detachment.
 If retinal breaks develop, fluid may leak behind the
retina causing it to detach.

Pathological myopia: Glaucoma
 The incidence of glaucoma may increase due to alterations of
the drainage angle of the eye causing which causes an increase
in the fluid pressure of the eye.
 Detection of glaucoma may be more difficult due to change of
CCT, The thickness of the patient’s eyeglass lenses may impair
visual fields testing, which is imperative in monitoring
glaucoma.

TIGROID FUNDUS As the eye enlarges, the retinal
pigment epithelium thins, resulting in a
tessellated (checkered) appearance of the fundus
and increased visibility of the choroidal
vasculature.

POSTERIOR STAPHYLOMA: Staphylomas are
localized ectasia (“enlargement”) of the sclera,
choroid, and RPE. It can be easily seen on a B-scan or
CT Scan. Staphylomas can eventually lead to atrophy
and loss of vision.

FUCHS SPOTS: Fuchs spots are dark spots due to RPE
hyperplasia. They can involve subretinal neovascular
membrane with an overlying retinal pigment epithelial
hyperplasia. The CNV can eventually cause disciform
scars on the macula in the 4th-6th decade of life.

LACQUER CRACKS: Lacquer cracks are spontaneous
ruptures of the elastic lamina of Bruch’s membrane
that appear yellowish-white and are usually located
in the posterior pole. They generally have linear or
stellate patters. IVFA will show hyperfluorescence as
the fluorescein leaks through Bruch’s membrane,
highlighting these cracks. These can lead to CNV in
the 4th-6th decade of life

Lattice with atrophic hole

LATTICE DEGENERATION: Lattice degeneration is a vitreo-
retinal degeneration that causes retinal atrophy (“thinning”). It
can be classified as pigmented or non pigmented. It takes on a
lattice formation (“crisscrossing”) because the retinal vessels
become sclerotic, and the collagen is laid down in this crisscross
pattern. Due to the retinal thinning, it is prone to causing retinal
breaks, tears, or holes, which could potentially lead to retinal
detachment. However, it is important to remember that retinal
breaks due to lattice degeneration rarely turn into retinal
detachments.

Treatment of pathological myopia: Spectacle
The lenses may be extremely thick and heavy.
Fortunately, we are able to use small eyeglass frames
combined with high index lenses to make the lenses
thinner, lighter and more cosmetic.

Treatment of pathological myopia: Contact Lenses
Contact lenses have been a good option for high myopes
for many years. It eliminates the weight and thickness
of the lenses in eyewear. It also eliminates the side
vision difficulties inherent in these thick lenses. Myopic
patients usually report having better vision when
wearing contact lenses, because of eliminating the
problems that the eyewear causes.

Treatment: Refractive Surgery / LASIK
LASIK or laser refractive surgery has not been as
effective in the highly myopic corrections, as it has in
the lower ranges of myopia.

Treatment: surgery
 “Bear Claw” intraocular lens implant. It is affixed in the
anterior chamber through a simple incision and can correct
extreme amounts of myopia.
 A clear lens extraction may be performed. The procedure is
identical to a cataract extraction. The patient’s lens is
removed, but an intraocular lens in not inserted. By
removing the lens, about fifteen diopters of myopia is
automatically corrected.

Low Vision Considerations
 Most patients respond well to low vision care and low
vision aids including magnifiers and CCTVs.
 These patients often present with mild photophobia and
benefit from sunglasses.
 Patients with retinal detachments, myopic macular
degeneration and staphylomas may have a poorer
prognosis depending upon the location of the problem.

Safety Issues – Physical Education
 Patients should not participate in any physical activities that
can lead to jostling or trauma to the eye.
 Contact sports and ball sports are too dangerous. Even
activities like jumping rope or volleyball can lead to a
retinal detachment.
 Children should not participate in physical education or
competitive sports without the prior review.

Knowing the Signs of Retinal Detachment
 Every patient with pathological myopia must know the
signs of a retinal detachment.
 These include the sudden appearance of flashes of
lights, like lighting flashes.
 Also floaters, little shadowy dots, and/or cobwebs,
shadowy strands could be the first sign of an impending
retinal detachment or a tear of the retina.

Difference between simple and pathological myopia
Simple myopia
 Relatively stationary
 Less than 6 D.
 No pathological
change present.
 No family history
present.
Pathological myopia
• Progressive in nature
• More than 6 D
• Pathological change
present
• Family history

Various Types of Myopia
Acquired Myopia
Pseudo-Myopia.
Space Myopia
Night or Twilight Myopia.

Acquired myopia
Acquired myopia can result from injury to the eye.
Concussion will sometimes cause a loss of the anterior
chamber.
Partial dislocation of the lens forward.
Induced myopia is seen after glaucoma operation.
Injury may also cause the lens to increase its water
volume producing myopia.

Pseudo-myopia
Spasm of the ciliary muscle and of accommodation
can occur in uncorrected hypermetropia or in early
presbyopia; myopia results and it is noticeable that in
this form of myopia there is poor accommodation and
usually severe eyeache and headache.

Space myopia
This condition is experienced when the individual has
no stimulation for distance fixation. The eyes tend to
choose a near fixation plane which can be very
variable. The degree of myopia due to this condition
is never more than -0.75 to -1.50 Dsph. It is
particularly troublesome to aviators when flying in
cloud or fog or at night.

Night or Twilight Myopia
Short sighted patients often complain that they cannot
see well in the distance at dusk or at night, especially
when driving, although their spectacles give them
good vision during daytime.

 There are 4 possible explanations;
1) Color shift: At night fall the blues & yellow are
clearly seen but red & green very badly; thus the
shorter wavelengths must be brought to a focus in
dim light.
2) Spherical aberration: The peripheral rays are more
refracted.

3) Depth of focus: This is the greatest with a
constricted pupil and it is much reduced with
pupillary dilation,
4) Accommodation will cause a spurious myopia,
especially in young nervous persons who peer into
darkness. This is noted in pilots who lack any
distance object on which to focus.

Treatment of Myopia: 1. Spectacle
For most people with myopia, eyeglasses are the
primary choice for correction. Depending on the
amount of myopia, one may only need to wear
glasses for certain activities, like watching a movie or
driving a car. Or, if very nearsighted, may need to
wear them all the time

Treatment of Myopia: 2. Contact lenses.
For some individuals, contact lenses offer clearer
vision and a wider field of view than eyeglasses.
However, since contact lenses are worn directly on
the eyes, they require proper care to safeguard eye
health.

Treatment of Myopia: 3. Ortho-k
Another option for treating myopia
is orthokeratology (ortho-k), also known as corneal
refractive therapy (CRT). In this nonsurgical
procedure, patient wear a series of specially
designed rigid contact lenses to gradually reshape
the curvature of cornea. The lenses place pressure
on the cornea to flatten it. Overnight, wear and then
remove. People with moderate myopia may be able
to temporarily obtain clear vision for most of their
daily activities.

Treatment of Myopia: 4. Radial Keratotomy

Treatment of Myopia: 5. Laser procedures.
Laser procedures such as
1) LASIK (laser in situ keratomileusis)
2) PRK (photorefractive keratectomy) are also possible
treatment options for myopia in adults.
• PRK was the first kind of corrective eye surgery
to use a laser rather than a blade to remove corneal
tissue.
• PRK became less and less popular following the
development of LASIK

ASTIGMATISM

ASTIGMATISM: DEFINITION
When parallel rays of light from infinity comes to focus at
different meridian of retina when accommodation is at rest.

ASTIGMATISM: CLASSIFICATION
1) Regular astigmatism
2) Irregular astigmatism

ASTIGMATISM: Classification
Regular Astigmatism:
 When two meridians are at right angles to each
other and the astigmatism can be fully corrected
by spectacles. When the meridians are not at 900,
it is often called oblique astigmatism although
two axes are at right angles to each other.

 Irregular astigmatism:
 In Irregular astigmatism, there are irregularities
in the curvature so that no geometrical figure is
adhered to. It does not tend itself to adequate
correction by spectacles.
 Example: Keratoconus, corneal opacity
 RX : It can’t be corrected with spectacle so RGP Contact lens
is the treatment of choice

Regular astigmatism can be classified in various
way:
a) According to steepness of vertical meridian
 With the rule astigmatism
 Against the rule astigmatism

b) According to relation of the two axes:
 At right angles to each other: Oblique astigmatism
 Not at right angles to each other:

At right angles to each
other: Oblique
astigmatism

 c) According to type of error of refraction:
• Myopic
• Hypermetropic
• Combination
 (P.K Mukherjee: p 94)
(But this classification is not widely accepted)

d) According to position of image in relation to the
retina:
i. Simple.
ii. Compound
iii. Mixed.
(This is the most widely and well-accepted classification)

• Simple myopic astigmatism
• Simple hypermetropic astigmatism
• Compound myopic astigmatism
• Compound hypermetropic astigmatism
• Mixed astigmatism

Simple regular astigmatism
Where one of the foci falls upon the retina, the other
focus falls in front or behind the retina, so that while
one meridian is emmetropic, the other meridian is
hypermetropic or myopic. These are respectively
designated as:
• a. Simple hypermetropic astigmatism.
• b. Simple myopic astigmatism.

Simple hypermetropic astigmatism & Simple myopic astigmatism.

Compound hypermetropic astigmatism.
& Compound myopic astigmatism.
Neither of the two foci lies upon the retina but are
placed both in front or behind it. The state of the
refraction is then entirely hypermetropic or myopic.
Thus they are:
• a. Compound hypermetropic astigmatism.
• b. Compound myopic astigmatism.

Compound hypermetropic astigmatism.
& Compound myopic astigmatism.

Mixed astigmatism
Where one focuses in front and the other behind the
retina, so that the refraction is hypermetropic in one
direction and the myopic in other

OSPE: 2
 A girl of 18 years-old came to you with -15.0
Dsph/-4.50 Dcyl 1700 (R/E) and -17.0 Dsph/-5.0
Dcyl 1800 (L/E) for LASIK surgery. Her BCVA is
6/18 and 6/36 respectively
• Now you have to counsel him about her desire,
life style and future plan.

Guideline of OSPE: 2
a) Ask why LASIK is important to her?
b) Contraindication of LASIK in this case
c) Can try contact lens but not regular (RGP)
d) Surgical option at there but mention the side
effects
e) Discuss safety profile of her life style
f) Discuss warning sign of RD
g) Discuss LVA (may need in future)
h) If unmarried, not to marry other myopic

OSPE: 3
 Calculate the spherical equivalent, do the simple
transposition & mention type of astigmatism of
the following prescriptions:
a) +2.00 /―3.00 X 800
b) ―3.00 / + 2.00 X 900
c) +1.50 /―3.00 X 450
d) Plano/―1.50 x 900

Spherical equivalent:
a) +2.00 /―3.00 X 800
+0.50
b) ―3.00 / + 2.00 X 900
-2.00
c) +1.50 /―3.00 X 450
Plano
d) Plano/―1.50 x 900
-0.75

Simple transposition
a)+2.00 /―3.00 X 80
ANS: -1.00/+ 3.00 X 170
b) ―3.00 / + 2.00 X 90
ANS: -1.00/-2.00 X 180

Simple transposition
c) +1.50 /―3.00 X 45
ANS: -1.50/+3.00 X 135
d) Plano/―1.50 x 90
-1.50 /+ 1.50 x 180

Type of astigmatism
a)+2.00 /―3.00 X 800

Type of astigmatism
b) ―3.00 / + 2.00 X 900

Type of astigmatism
c) +1.50 /―3.00 X 450

Type of astigmatism
• Plano/―1.50 x 900

06 refractive error

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