Lenses and Magnification

8/3/2019 Lenses and Magnification

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Lenses and Magnification

Ocular Prosthesis |

Group 3


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MICROPTHALMIA also referred to as microphthalmos, nanophthalmia

or nanophthalmos, is a developmental disorder of

the eye that literally means small eye (micros = small;

ophthalmos = eye).

One (Unilateral Microphthalmia) or both (Bilateral

Microphthalmia) eyes may be involved.

grossly visible, but small malformed globe


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Causes

Idiopathic/sporadic

Inherited as dominant, recessive, or sex-linked

Chromosome deletion in band

Maternal infections or teratogenic exposure

75% associated with syndromes

Microphthalmia in newborns is sometimes associated with

fetal alcohol syndrome or infections during pregnancy,

particularly herpes simplex virus, rubella and cytomegalvirus

(CMV), but the evidence is inconclusive.


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Pathophysiology

Development problem with optic disc in week 4 or

later

Morbidity Outgrowth of the globe drives growth and

development of the bony orbit .

Prevents fitting of prosthesis

Unilateral anophthalmos hemifacial hypoplasia

Bilateral anophthalmos central hypoplasia


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Rare Condition S

panishS

tudy of 1.1 million births: 36/100,000 with eye malformations

23/100,000 with

anophthalmia/microphthalmia

No racial predilection |No sex predilection

Microphthalmia and Coloboma occur in around

1 in 10,000 births.

Clusters of anophthalmia and microphthalmiain England have been alleged in the media,

with hypothesized links to environmental

exposure such as pesticides


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Associated Ocular Findings

Orbital findings Small orbital rim and entrance

Reduced size of bony orbital cavity

Extraocular muscles usually absent

Lacrimal gland may be absent Small and maldeveloped optic foramen

Eyelid findings Foreshortening of the lids in all directions

Absent or decreased levator function with decreased lidfolds

Contraction of orbicularis oculi muscle

Shallow conjunctival fornix, especially inferiorly


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3D CT Reconstruction


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Treatment Options

Progressive conformers i.e. artificial eyes or contact lenses

Easily extruded

Balloon expanders i.e. skin flaps/ grafts for tissue skin

expansion

Easily extruded and require cooperation

Progressive orbital implants

Require multiple surgeries

Hydrogel tissue expander implant (self-inflating)

Good early results

Late complications in scleral buckling


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Procedure

Children can be fitted for a prosthetic(artificial) eye for cosmetic purposes and to

promote socket growth.

Every few weeks a child will progress to alarger size conformer until about two years of

age.

The average child will need three to four newpainted prostheses before the age of 10.


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The specialist in prosthetic diseases for the eye will

make conformers, plastic structures that helpsupport the face and encourage the eye socket to

grow.

Children with microphthalmia may have some

residual vision (limited sight). In these cases, thegood eye can be patched to strengthen vision in the

microphthalmic eye. A prosthesis can be made to cap

the microphthalmic eye to help with cosmetic

appearance, while preserving the remaining sight.


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Complications

Significant cosmetic deformities if not

treated early

Fitted prostheses are completelyimmobile.

Shortened and immobile eyelids

Even with treatment, results often arecosmetically disappointing.


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Patient Education

Treatment will be long and complicated

Multiple surgical treatments throughout

a patients lifetime

Consider genetic counseling in familial

cases


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The Formation of Images by Lenses

IMAGE FORMATION BYA CONVERGING LENS

In this example, when the object is placed further than

twice the focal length from the lens, the real image isinverted and smaller than the object.


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A diverging lens always forms an upright, virtual, diminished image.

The Formation of Images by Lenses

IMAGE FORMATION BYA DIVERGING LENS


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Angular Magnification.

d1

h1 NE U

h5U

Optical Device

e.g. Telescope


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Angular Magnification

M = angle subtended at the eye by instrument imageangle subtended at the eye by object

This is generally refers to the magnification provided

by optical instruments (e.g. telescopes).

Versatile means of magnification as it does not involve

changing object or viewing distance.


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d1

h4

NEU

U h4

Real Image or Transverse Magnification

h1


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Real Image or Transverse Magnification

M = tan U = h4

x d1 =

h4

U d1 x h1 h1

M = size of real image

size of object

This is typical of the situation used with a CCTV device

where a magnified image of the object is created on a

TV screen.

This real image is created in approximately the samelocation as the object.


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Magnification is NOT aboutmaking objects clearer it is

simply about making them

bigger.


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Type of

Magnification

Field of

View

Working

Space

Distance of

Task

Increase size

Decrease distance

(by +ve lens magnifiers)

Real image

Angular

(Telescope)

No change

No change

Decreased

Decreased

Decreased

No change

Decreased

Decreased

No change

No change

Usually N only

D, I or N

Near only

Usually N only

D, I or N


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Thank you!

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Lenses and Magnification