? Photographs : Courtesy of
Kanski's Clinical Ophthalmology.
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3Learning Objectives
At the end of the class, students shall be able to
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? Understand what is refraction.
? Have basic knowledge of myopia and its management.
4
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Question
? You have gone fishing and see a fish in the water.
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You do not have a fishing rod. The onlyequipment that you have is a spear to catch the
fish. Where do you throw the spear?
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a. in front of the fish.
b. behind the fish.
c. directly at the fish.
d. It is not possible to hit the fish as it is a virtual
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image.
5
What is Refraction
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? When rays of light traveling through air enter a
denser transparent medium, the speed of light is
reduced and the light rays proceed at a different
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angle, i.e., they are refracted.? Except when the rays are normal
Refraction in Ophthalmology
? Methods for evaluating optical and refractive
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state of the eye
6
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Emmetropia? Parallel light rays, from an object more than 6 m away, are
focused at the plane of the retina when accomodation is at
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rest.? Clear image of a distant object formed without any
internal adjustment of the optics of the eye.
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? Absence of emmetropia = Ametropia
7
Progress of refractive state of eye
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? Birth : +2 to +3 D
? 90% of children at age 5 yrs are Hypermetropic
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? 50% of children at age 16 yrs are Hypermetropic? After the period of growth has passed , refractive state
tends to remain stationary, until in old age a further
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tendency of hypermetropia is evident.8
Refractive data in adult
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? Normal axial length 24 mm
? Change in axial length by 1mm = ?3D
? Refraction at corneal surface= +40 to 45(+43)D
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? Change in Corneal Curvature by 1mm = ?6D? Refraction by unaccomodated lens= +16 to
20(+17)D
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9
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Angle kappa ()
? M = Macula
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? D= Centre of pupil, on cornea? N = Nodal point
M
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Optic axis
D
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N(
B
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FD = Pupillary line
F
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FNM = Visual axis= "Between the visual axis and pupillary line, hence roughly corresponds to
angle ".
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10
Anisometropia
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? Anisometropia is a state in which there is a difference inthe refractive errors of the two eyes, i.e., one eye is
myopic and the other hyperopic, or both are hyperopic or
myopic but to different degrees.
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? This condition may be congenital or acquired due to
asymmetric age changes or disease.
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11
Refractive errors
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Anomalies of the optical state of the eye? Myopia
? Hypermetropia
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? Astigmatism
12
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What is Myopia ?? Diopteric condition of the eye
where parallel incident rays from
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optical infinity
focus anterior to light sensitive layers
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of retinawhen accomodation is at rest.
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13
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Myopia ? OpticsEmmetropia
Diverging lens
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14
Optics of Myopic eye
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? Far point is at a finite distance inversely proportional tothe degree of myopia
? Weakest concave lens that diverges rays just sufficiently
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to focus them at the retina is to be used
? Poor visual acuity is compensated to some extent by
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enlarged image size due to the nodal point being furtherfrom the retina
15
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Causes of Myopia
? The causes of myopia are not known.
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? Epidemiological correlation suggest...lengthy periods of close work are probably a
contributory factor
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there is some genetic predisposition to myopia and its
severity
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16Types of myopia
? Axial
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? Curvature
? Index
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? Positional17
Axial Myopia
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? AP diameter increased to 25.5 to 32.5 mm? 90-95% cases
? There may be...
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pseudoproptosis resulting from the abnormally large
anterior segment,
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a peripapillary myopic crescent from an exaggeratedscleral ring,
posterior staphyloma
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18
Curvature Myopia
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? Corneal curvature steeper than average, e.g.,keratoconus,
? Radius <7-8.5 mm (normal); 1 mm=6 D
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? Lens curvature is increased
? moderate to severe hyperglycemia (intumescence)
lenticonus (anterior/posterior)
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spasm of accomodation
spherophakia
19
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Index Myopia? Increased index of refraction in early to moderate
nuclear sclerotic cataracts in the elderly.
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? Many people find themselves ultimately able to read
without glasses or having gained "second sight."
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? Decrease in refractive index of cortex ? diabeticmyopia
20
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Positional Myopia
? Anterior movement of the lens is often seen after
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glaucoma surgery and will increase the myopic error inthe eye.
? Axial myopia of buphthalmos is countered to a large
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extent due to posterior displacement of lens-irisdiaphragm and flattening of the cornea
21
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Clinical course
?
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Simple?
Pathological
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22
Simple Myopia
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? Rarely present at birth, but often begins todevelop as the child grows.
? Usually detected by age 9 or 10 years in school
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vision tests
? May increase during years of growth, stabilizing
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around the mid-teens, usually at about 5 D orless.
23
Pathological Myopia
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? 2-3% population
? Increases by as much as 4 D/yr
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? Usually stabilizes at about age 20 years and frequentlyresults in myopia ? 10 to 20 D.
? If progress is rapid from age 15-20, likely to reach 20-30
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dioptres
? Commoner in women, Jews and Japanese
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24Pathological Myopia-Etiology
? Developmental defect affecting posterior segment
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? Retina grows extensively stretching sclera
? Adjuvants- growth influences during puberty and
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physical debility? Excessive convergence- stretching
25
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Pathological Myopia? Associated vitreous floaters, liquefaction, posterior
staphyloma and chorioretinal changes.
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? Degeneration is not necessarily comparable with degree
of myopia
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? Genetic predisposition in offspring as per laws ofrecessive Mendelian inheritance ? if both parents
affected, close supervision needed
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26School/ Physiologic/Pseudo-Myopia
? 2D
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? Excessive near work causing accomodativespasm
? Inherited predisposition-more in Orientals and
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Jews
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Clinical features of Myopia
28
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Symptoms1. Blurred distance vision.
2. Squinting to sharpen distance vision by
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attempting a pinhole effect through narrowing of
palpebral fissures.
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3. Eye strain seen in patients with uncorrected lowmyopic errors
29
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Symptoms4. Closer working distance at near that typically
gets closer and closer as the person sustains
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working at near.
5. Delayed dark adaptation
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6. Floaters, photopsiae7. Visual deterioration
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Clinical Signs ?
Apparent convergent squint
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? The problem begins at near and spreads to distanceleading to a cascade of changes in the findings over time
? Results usually in apparent convergent squint due
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to excess convergence
31
Clinical Signs ?
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True divergent squint
? Excess convergence for near work disorients
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accommodation which may increase causing ciliaryspasm or
? more frequently, attempt at convergence is given up, its
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latent insufficiency causing muscular imbalance till
? advantage of binocular vision is given up, one eye is
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relied upon for vision while the other deviates outwardscausing true divergent squint
32
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Clinical Signs
? Eye appears large and prominent ? pseudoproptosis
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? Deep anterior chamber? Large, sluggish pupil
? Post segment sclera is thinned up to 25% of normal
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? Post vitreous detachment ? Weiss ring
? Liquefaction ? muscae volitantes, large floaters
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33
Fundus
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? Atrophy of retina and choroid ?depigmentation
? Tigroid fundus with prominent
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choroidal vessels
? Patches of choroidal atrophy
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surrounded by pigment associatedwith haemorrhages
? Atrophic patch at macula
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associated with loss of central
vision
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34Fundus
? Appearance of dark pigmented area at macula-Foster-
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Fuch's fleck ? rare, sudden, proliferation of pigmentary
epithelium with intra-choroidal haemorrhage or
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thrombosis? Macular bunches of dilated capillaries or aneurysms
? Myopic crescent ? temporal or annular
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? Nasal supertraction crescent
35
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Macular haemorrhage
36
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Posterior staphyloma? Herniation of posterior pole
? Crescentric shadow 2-3 DD temporal to disc,
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? Sudden kinking of retinal vessels as they dip over the edges,
? Gross atrophy
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37
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PeripheralDegenerations
Not requiring
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prophylaxis:
Paving stone
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38Predisposing Degenerations
Lattice, snailtrack, retinoschisis, white without
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pressure
Snailtrack
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Retinoschisis39
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Lattice degenerationFigure:
40
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Complications
? Atrophy ? scotomata
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? macular most incapacitatingHorseshoe Tear
? Vitreous degeneration + floaters
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? Tears + haemorrhages? Detachment ? post traumatic or spontaneous
associated with peripheral degenerations due to
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vitreous adhesion? Lenticular opacities, esp. posterior cortical
? Open angle glaucoma
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41
Night myopia
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?Manifest in reduced illumination
?
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~ 0.5 D
?
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Cone-rod shift in retina, pupillary dilatation,ciliary muscle activity
?
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If night vision appears seriously impaired,
appropriate correction may be given
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42Treatment
1. Optical correction after subjective and objective
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refraction
Spectacles
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Contact lens (including Orthokeratology)2. Visual hygiene
3. Refractive surgery
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LASIKo
LASEK
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Wavefront Lasik
o
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Clear lens ExtractionPhakic IOL
o
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ICRS
4. Pharmacological intervention
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43
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Optical correction
44
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Myopia ? OpticsDiverging lens
45
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Cycloplegic Refraction? Cycloplegia is the employment of pharmaceutical
agents to paralyze the ciliary muscle temporarily
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to stabilize the accommodative reflex of the eye
so that a definitive end point may be measured.
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? Benefit of relaxing the accommodative tone isespecially important in young individuals.
? Cycloplegic + Mydriatic = Relaxes accomodation
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+ dilates pupil for better reflex
46
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Cycloplegic RefractionDrug
Actions
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Onset
Duration
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RemarksAtropine
Strong
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6 ? 24 hr
10 ? 15 days
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Slow,Prolonged
Homatropine
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Weak
1 hr
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1 ? 2 daysWeak,
Prolonged
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Phenylephrine
Mydriatic
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TropicamideWeak
20 ? 30 min
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4 ? 10 hr
Fast, Short
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CyclopentolateWeak
10 ? 30 min
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12 ? 24 hr
Fast,
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intermediate47
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Visual Hygiene? Proper illumination
? Proper posture
? Clear print
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? Better contrast48
Visual Hygiene
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? Avoid ocular fatigue
? Proper occupation in case of degenerative
myopia
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? May need special institutions if low vision
dictates
49
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Summary
? Refraction is a method for evaluating optical and
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refractive state of the eye.? Myopia is a diopteric condition of the eye
where parallel incident rays from optical infinity
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focus anterior to light sensitive layers of retinawhen accomodation is at rest.
? Myopia is corrected by concave lenses prescribed
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after cycloplegic refraction.50
Question
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? Which of the following drugs can cause acquired
myopia?
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? a. chloroquine.? b. sulfonamides.
? c. phenothiazines.
? d. benzodiazepines.
51
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Question
? Which of the following is a cause of acquired
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myopia?? a. orbital tumor.
? b. central serous chorioretinopathy.
? c. intravitreal silicone oil.
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? d. childhood glaucoma.52
Thank you
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