Cycloplegic refraction,spectacles and prescribing spectacles in children

Dr. Sidesh Hendavitharana(Registrar-
Ophthalmology)

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

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

.
Strabismic children
Amblyopic children
Suspected malingering and hysterical patients

Choice of cycloplegic agents
1. Atropine 1%
2. Cyclopentolate 1%drops
3. Homatropine 2-5%
4. Tropicamide 0.5-1.0%
5. Scopolamine 0.25%

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

.
 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.

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

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.

.
 If signs of systemic toxicity such as flushing,fever
or restlessness,immediate medical attention
needed.

Spectacle frame
• Parts of a spectacle frame
 Each frame has 2 main parts
1) Front
a. Rim
b. Bridge
c. Joint
d. Lug
2) Side piece

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

Spectacle frame materials
 Qualities of an ideal spectacle frame material
1. Non-allergic
2. Resistant to corrosion
3. Non-inflammable
4. Inexpensive
5. Durable
6. Adjustable

Spectacle frame materials
1) Natural material[tortoise-shell frames]
2) Plastic frames
3) Nylon supra frames
4) Metal frames
5) Combination frames
6) Rimless mounts

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.

Plastic frames
 Plastics are devided into two groups
1) Thermosetting(thermohardening)
2) Thermoplastic(thermosoftening)
 Can be heated and cooled without losing their plasticity

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

Nylon frames
 Rarely used nowadays and were used in spectacles for
children where chances of breaking were high.

Metallic frames
 They are non inflammable and inexpensive.
 Materials used are,
1) Stainless steel
2) Nickle silver
3) Anodized aluminium
4) Gold

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

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.

Abbe value of common lens materials.
 MATERIAL
Glass , crown
CR 39
Spectralite
High index 1.56 (resin)
Polycarbonate
High index glass
INDEX
 59
 58
 47
 39
 37
 32
 31
 25

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

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

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

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

Other shapes are,
 Perimetric shapes
 Upswept shapes
 Rimless or anular shapes
 Half eye shapes

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

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.

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.

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

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

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

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

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.

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

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

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.

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

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

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

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

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

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

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.

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

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

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.

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

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

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

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.

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Cycloplegic refraction,spectacles and prescribing spectacles in children