2. Principle of cycloplegic refraction
Determination of total refractive error during
temporary paralysis of ciliary muscles as an instillation
of cycloplegic drugs
Total hypermetropia
Latent hypermetropia
Manifest hypermetropia
Facultative hypermetropia
Absolute hypermetropia
3. Indication for cycloplegic
refraction
Accomodative esotropia
All children younger than 3yrs
Suspected latent hypermetropia
Suspected pseudomyopia
Uncooperative/noncommunicative patients
Variable and inconsistent end point of refraction
Visual acuity not corrected to a predicted level
6. Cyclopentolate 0.5-1.0%
Commonly used cycloplegic agent
Used in paediatric examinations
0.5%cyclopentolate-used <6 months of age,1%
thereafter.
Two main effects
Myadriasis-
max.effect 30-60min
Recovary time 1 day
Cycloplegia
Max effect 25-75 min
Recovary time 2-3 hrs
7. .
The adequacy of cycloplegia can be determined by
comparing retinoscopy finding with the patient fixing
for distance and then near.
If cycloplegia is adequate,there will be little or no
difference.
Topical anasthesia prior to instillation of
cyclopentolate is useful in preventing ocular irritation
and reflex tearing,thus increase in retention time.
8. Tropicamide 0.5-1.0%
Anti muscarinic drug with short-lasting effect on pupil
and on accomodation
For cyclo.ref,
Adults-one drop of 1% solution,repeat once in 5 min.
Children-one drop of 0.5% solution,repeat once in 5min
9. Atropine ,
Necessary in some patients with,
High hypermetropia
Heavily pigmented irides
0.5% atropine-used in iess than 12 months of age and
1% thereafter.
Dosage-1D bd for 3days before retinoscopy.
Max.effect of cycloplegia-3-6hrs
Recovery of accomodation starts at day 3 and complete
by 10 days.
10. .
If signs of systemic toxicity such as flushing,fever
or restlessness,immediate medical attention
needed.
14. Front part
1) Rim-may be complete or incomplete
2) Bridge-
connection between two rims
May be 3 basic types
1. Regular bridge-rest on the nose with full surface in
contact.
2. Inset bridge-project behind the frame plane
3. Saddle bridge-combinaton of regular and inset bridges
3) Lug-projections on the sides to which the side pieces
are attached
19. Natural material
In the past,natural materials like tortoise shell and
horn have been extensively used
Basically made from the shell of hawksbill turtle
These frames are durable,had attractive colours and
mottling and are easy to maintain.
20. Plastic frames
Plastics are devided into two groups
1) Thermosetting(thermohardening)
2) Thermoplastic(thermosoftening)
Can be heated and cooled without losing their plasticity
21. Materials used plastic frames are,
1. Cellulose nitrate-is hard,retain its shape even in hot
climates and is easy to work upon.only disadvantage
is that is inflammable
2. Cellulose acetate
3. Cellulose propionate
4. Perspex
5. Epoxy resins
22. Nylon frames
Rarely used nowadays and were used in spectacles for
children where chances of breaking were high.
23. Metallic frames
They are non inflammable and inexpensive.
Materials used are,
1) Stainless steel
2) Nickle silver
3) Anodized aluminium
4) Gold
24. Dimensions of spectacle frame
Systems of spectacle measurement are,
1) Datum system
Key wards used-datum line,datum centre,datum centre
distance
2) Other system-boxing system,GOMAC system
Front to bend length-distance between the back surface of
the front to the ear point
Pantoscopic tilt
lower end of frame is tilted backwards towards the face.
Reduces chromatic aberrations of a high-power lens and is
cosmetically more attractive
26. Abbe value
The abbe value (first describe by Ernest k. abbe a
German optical physicist) indicates the ability of a lens
material to purely refract white light without
chromatic aberration.
27. Abbe value of common lens materials.
MATERIAL
Glass , crown
CR 39
Spectralite
High index 1.56 (resin)
High index 1.60 (resin)
High index 1.66 (resin)
Polycarbonate
High index glass
INDEX
59
58
47
39
37
32
31
25
28. Spectacle lenses
Properties of an ideal lens material
1) High degree of transparency
2) Good impact resistance
3) Low weight
4) Easy to manufacture and process
5) Good scratch resistane
6) Inexpensive
29. Commonly used lens materials are,
Glass lens- crown glass-R.I.-1.522 /Flintglass,R.I.-1.62
Plastic lenses
Materials used are,
I. Igard lenses-made using PMMA
II. CR-39 lenses
III. Zeiss duralet lenses
IV. Polycarbonate
V. Other-polyurethine/RLX-light
30. Lens forms
Flat verses curved lenses
Lenses are of two types-flat and curved
1) Flat lenses
Both surfaces have same types of curvature
Eg-biconcave or biconvex
One surface is flat and the power is ground on the other
surface
Eg-plano-convex,plano-concave
2) Curved lenses-2 types
Meniscus lens,toric lens
31. Lens shapes
Lens shape refers to outline of the lens periphary with
the nasal side and the horizontal indicated.
Geomatrical shape
Round lens-one of the most ancient lens shapes and
not much popular
Oval lens-one of the ancient lens shapes.elliptical in
shape and not much in use
Pantoscopic round oval(PRO)-lower half of a circle and
the upper half of an ellipse
32. Other shapes are,
Perimetric shapes
Upswept shapes
Rimless or anular shapes
Half eye shapes
33. Lens power
Vertex power and distance
Front and back vertex
Have got curved surfaces-front and back.
The points where these two surfaces intersect the optical
axis are termed front and back vertex
34. Vertex focal length
The distance between the secondary principle focus of
a lens and its vertex is called vertex focal lengths.
In a spectacle lens,there are front and back vertex focal
lengths.
35. Vertex power
Vertex power is reciprocal of vertex focal length.
Front vertex power[FVP]-not of much use.
Back vertex power[BVP]
Measured on lensmeter.
36. Vertex distance
Distance between back vertex and cornea.
Vertex distance should be specified for prescriptions of
more than 5.0D
Effectivity change=d×D2
d-change in vertex distance in metres
D-lens power in diopters
37. Single versus multiple power
lenses
Single vision lens
Refers to a lens having the same corrective power over
the entire surface
These are used to correct myopia ,hyperopia ,
astigmatism and presbyopia
38. Multifocal lenses
They may be bifocals,trifocals and varifocal.
Bifocals-different powers for upper and lower
segments
Trifocals-have 3 portions,upper,middle and lower
zones
Varifocals-many portions of different powers
39. Bifocal lenses
Invented by Benjamin Franklin.
Commonly used bifocals are the following
1. Cemented bifocals-made by grinding distance and
near segment seperately,then sticking the near
segment on anterior surface
2. Fused bifocals-
3. Solid bifocals-made up of single piece lens materials
41. Trifocal lens
As presbiopia increases,intermediate distances
become blurred.
Therefore,another segment is added between the
distance and the near segments to focus intermediate
zone.
43. Trifocals are unsuitable when,
There is anisometropia and prescription in the two
eyes differs by 1.5-2.0D in vertical meridian.
Rism is to be incorperated into reading addition
Larger distance segment and smaller near segment are
required as in outdoor workers,sports persons etc
44. Progressive power(addition)lens
Designed to simulate accomodation as far as possible.
Types of progressive lens are,
1) Sola’s percepta progressive lenses
2) Kodak progressive lenses
3) AO compact lenses
4) Essilor’s adaptor lenses
48. Dispensing of progressive lens
In progressive addition lenses,the change from
distance to near is spread over a 12mm-long channel.
In cases of large addition,this change will be rapid.
Eg-in case of +3.0D addition,1.0D change will be there
for every 4mm.
49. Important tips about dispensing
PALs,
1) Do not prescribe progressives till the pt is mortivated
and his or her profession demands visualization at
intermediatedistances
2) Pt selection-do not give good results in pts with
extra-broad nasal bridges and extra large
interpupillary distances
3) Selected pts must be explained aboutcommon
problems during adaptation period such as
peripheral distortion ,restricted near vision field
4) Frame selection
50. General guideline for prescription of
glasses in children
Why is it important to correct refractive error??
Uncorrected refractive error leads to,
a) Amblyopia
b) Delayed visual maturation
c) Deviation of the eye
51. When prescribing spectacles for
infants……!
1) Knowledge about the normal refractive error of
infants
2) Emmetropization process
3) The benefits and risks of prescribing spectacles
4) Any threat to normal visual development by the
prescription
52. Refractive error within the normal range
for the child’s age…….?
Most infants are hyperopic-+2.0 with the SD of 2.0.
First 3months-refractive status to be static or
decreasing.
Avarage is +2.16D
3-12 months-error decrease to 1.36D at 9 months
This is followed by a period of slower change until 2yrs
for hyperopes and 4-5yrs for myopes
53. How does emmetropization
begin?
Few children myopic at birth
The rate of emmetropization is generally
proportional to the initial error
Those who start off close to emmetropia or with a
low amount of hyperopia show little chance
Those who have higher ametropia generally show
greater and faster changes
54. In astigmatism
69% have astigmatism greater than 1.00D at birth
When aging,it reduces
8-30% in 1.2yrs
4-24% in 3-4yrs
2-17% in 6-7yrs
Higher the astigmatism,decrease more rapidly in
initial 3-4yrs
55. Anisometropia
Anisometropia is more common in infants than adults
It is transient in relatively lower level of refractive
error,eg-2.5D or less and may not lead to amblyopia
BUT,no way to predict with certainty whether a
particular child’s anisometropia is transient or will
remain into adulthood.
56. Following things should be taken
into account……….!
Monitor a child over a period of 4-6 months
Consider VA-if amblyopia present,requires treatment.
Higher level of anisometropia(5.0D or more)are less
likely to be transient.
Therefore,these children can be prescribed with the
main consideration being to optimize visual function
57. Prescribing for children…………….!
In adults,the correction of refractive errors has one
measurable endpoint-BCVA
For children,often has two goals,
1. Providing a focused retinal image
2. Achieving the optimal balance between
accomodation and convergence
58. Myopia,
Childhood myopia falls into 2 group
1) Congenital(usually high)
2) Developmental
Both forms of myopia are progressive, therefore
frequent refraction and periodic prescription changes
are necessary.
59. General guidelines for correction of
significant myopia,
Cycloplegic refraction are mandatory{infants,esotropic
children,children with very high myopia(>10D)}
In general,the full refractive error,including cylinder,should be
corrected
Intentional undercorrection of a child with myopic esotropia to
decrease the angle of deviation(rarely tolerate)
Intentional overcorrection of myopic error can be of some value
in controlling intermittent exodeviations
Contact lens may be desirable in older children to avoid the
problem of image minification found with high-minus lenses
Avoid overcorrection of myopia in orthophoric children
60. Hypermetropia
Insignificant hypermetropia,eg.up to +3.0,in the
absence of esotropia or reduced vision,can be left
uncorrected
If there is an esodeviation,full cycloplegic correction is
prescribed
In school going children,less than full cycloplegic
correction could be prescribed,to avoid distance
blur,even if there is esotropia
Hypermetropia may be corrected,even if
insignificant,if there is a strong family history of
accommodative esotropia
61. astigmatism
Visualy significant astigmatism should be fully
corrected
Insignificant astigmatism in very young children can
be left undercorrected
Refine the cylinder using jackson’s cross cylinder
wherever possible
62. Anisometropia
An anisometropic child is typically prescribed the full
refractive difference between the 2 eyes regardless of
age,amount of strabismus or degree of anisometropia
If presence of anisometropic amblyopia,correct
refractive differance and then occlusion therapy.