Transcript CLINICAL APPROACH TO REFRACTIVE ERRORS

CLINICAL APPROACH TO
REFRACTIVE ERRORS
Ayesha Abdullah
14.09.2012
Learning objectives
By the end of this lecture the students would be
able to;
• Correlate optics with the various types of
refractive errors & their correction with lenses
• Describe the clinical presentation of refractive
errors
• Describe the clinical protocol for the
assessment of refractive errors
To begin with
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Refraction ?
Refractive errors?
Main refractive surface of the eye?
How much is the refractive power of the cornea?
40-44 diopters
Why is it so?
So its mainly corneal refractive error!
How much is the role of lens in refraction?
What is the role of accommodation in refraction?
During accommodation in a youthful eye the lens can
change its refractive power from 19 D to 33 D
What determines the type and amount of
refractive error?
• Refractive power of the cornea and the lens
• Length of the eye (1m.m. changes represents
about 3 dioptres change in refraction)
• Refractive errors of up to 5 D are considered
to be biological variation
• Higher degrees of refractive errors are
associated with structural anomalies of the
ocular structures e.g. the cornea, lens,
choroid and the retina
What is emmetropia & ametropia?
• The state of having no refractive error is
emmetropia ; a balanced state of refractive
power of the cornea, lens and the length of
the eyeball.
• Parallel rays of light are brought to a focus on
the fovea
• The state of the eye when parallel rays of light
are not focused on the fovea is called
ametropia
Emmetropia
Axial length matches dioptric power of
the eye & parallel rays of light are
brought to a focus onto the retina
Ametropia
When parallel rays of light are NOT brought to
a focus onto the retina
Ametropia could be :
a. Axial (1m.m. changes represents about 3
dioptres change in refraction. )
b. Curvature (1m.m. change in radius of
curvature of cornea represents about 6 dioptres
of change in refraction. )
c. Index ; due to change in the refractive index
of the refractive media
Types of ametropia
• Myopia, common in young age group
• Hypermetropia/ hyperopia, common in very
young children & old age
• Astigmatism; common in young age group but
less common than myopia
Myopia (near-sightedness)
• Parallel rays brought to a focus in front of the retina.
The eye is stronger for the axial length of the eye
Simple myopia
Usual onset by adolescence but may begin as
late as 25 years of age.
Gradually increases until the eye is fully grown.
Seldom exceeds -6 dioptres.
Pathological myopia
Commonly begins as physiological but rather
than stabilizing when adult size of the eyeball is
achieved, the eye continues to enlarge.
It is associated with pathological changes in the
posterior segment that can be seen on
ophthalmoscopy
It can lead to complications like retinal breaks
and detachment
Can go upto over -20 diopters
Hyperopia/ Hypermetropia
Parallel rays brought to a focus BEHIND the retina.
The eye is weaker for the axial length of the eye.
What would happen if the person accommodates?
Hyperopia
• Manifest
• Latent – to measure this the accommodation
has to be knocked off through cycloplegic
agents like cyclopentolate and atropine
• At which age do you think the latent would
become manifest?
• Total
Hyperopia
At birth practically all eyes are hypermetropic to the
extent of +2.5 to +3.0 diopters.
Emmetropisation ensues as the eye grows.
Emmetropia may not be reached and hypermetropia
may persist.
May also occur pathologically due to orbital mass,
intraocular tumour, retinal oedema and RD.
Astigmatism
• The eye has different refractive power in
different meridians of the eye e.g.
• Vertical rays being focused in one position (in
front, behind or on the fovea) and horizontal
rays focused on another
• When the two meridians are at right angle to
each other its called regular astigmatism
otherwise its termed as irregular astigmatism
Astigmatism
May also be classified:
a. Simple – One axis ametropic either
myopic/hyperopic
b. Compound – both axes ametropic but either
myopic or hypermetropic.
c. Mixed – each axis of opposite power.
Simple Myopic astigmatism
Mixed astigmatism
How do refractive errors present?
• Asthenopia ,eyestrain & visual fatigue
• Blurring of vision
• Ocular discomfort with itching, burning of the
eyes and at times increased sensitivity to light etc
• Headache, rarely could be attributed to refractive
errors. Headache presenting after visual work
especially in those above 40 years could be
because of RE, however a headache presenting
early morning is extremely unlikely to be because
of RE
In children
• Can present in a variety of ways
• In preverbal children it can present as delayed
milestones of visual development; inability to
focus at visually stimulating objects, follow
light or bright object
• Squint
• Lazy eye or eyes
In school going children
• Lack of interest in visual tasks, class work
• Generally apathic or withdrawn behaviour
• Difficulty in reading or seeing the black/ white
board from distance
• Squint
• Lazy eye
Signs
• Decreased visual acuity that improves with
pinhole
• The eyeball may be obviously
small(hyperopia) or large (myopia)
• The cornea my be conical in shape (irregular
astigmatism (keratoconus)
• Pupils are normal
• Posterior segment may show abnormalities
Posterior segment signs
• In pathological myopia retinal degenerations (
myopic crescent, lattice) , breaks ( holes and
tears) etc
• In hyperopia psedupapilloedema ( blurring of
optic disc margins with hyperopia of greater
than 5 D)
• In high degrees of astigmatism the optic disc
may appear oval
Normal fundus
Treatment of RE
• Spectacles
• Contact lens
• Refractive surgery
Refractive assessment
1. Check VA with and without spectacles
2. Check with a pin hole
3. Pupillary examination
4. Ophthalmoscopy.
5. Cover test with and without correction
6.
Objective refraction/retinoscopy/refraction/
autorefraction (cycloplegic in children)
7. Subjective refraction
Subjective verification
Duochrome test.
Muscle balance – Maddox rod for distance.
Near vision correction
Maddox wing for near
Presbyopia
• What is presbyopia?
• How is it corrected?