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LENSOMETER

Md Nooruz zaman

Sankara College of Optometry

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Alternative and Old Method

• Hand Neutralization

 – ith Movement

 – Again!t Movement

 – O"li#ue Movement

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Other Name!

• $o%i Meter

• Len! Meter

• &erto Meter

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'rin%iple

• Len!ometer i! a A$OCAL Tele!%ope(

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'art! of Len! Meter

• Eyepie%e

• )rati%ule

•

Len! Stop• 'o*er +rum

• A,i! heel

•

-llumination Sour%e• A,i!. Center Marker

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/!e!

• Lo%ating and marking the len! Opti%al Center

• Orienting the a,i! of a !phero0%ylinder len!

• Lo%ating and 1!potting2 or 1marking2 the

'ri!m(

• &erifying len! 1add2 po*er in "ifo%al!.

trifo%al! and progre!!ive!

• Lo%ating area! of len! a"erration!

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A"out

•  The len!meter i! e!!entially a %entered

tele!%opi% opti%al !y!tem aligned *ith a

!tandard opti%al len! and a rotata"le

target illuminated "y a light !our%e(

• -t mea!ure! the fo%al length of a len! and

%onvert! it into diopter! on a %ir%ular

num"er line %alled a 'o*er +rum

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orking

• Len! "eing mea!ured i! pla%ed again!t a len!

!top

• Len! !top i! "et*een tele!%ope and !tandard

len!(

•  Target i! on other !ide of the !tandard len!(

• Len! !top i! po!itioned to get it! %entre at the

anterior fo%al point of the !tandard len!(

•  Thi! en!ure! the dioptri% !%ale i! linear and the

image !ize of the target i! not a3e%ted "y the

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orking

• 'o*er of the !tandard len! i! %on!tant "et*een

455+ and 456+(

• Ma,imum plu! of the len!ometer "eing !lightly

le!! than the !tandard len! po*er(

• $or 456+. target move! 7(86mm for every dioptre

of vergen%e(• $or 455+. target move! 5(9:mm for every dioptre

of vergen%e(

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orking

• 'o*er drum i! rotated until

the %lear image of the target

i! !een(

• Target i! rotated to ;nd the

prin%iple meridian of

%ylindri%al a,i!(

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Mire!

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Cali"ration

• Everyday "y Trial Len!(

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Sour%e of Error

• Eye pie%e fo%u!ing

• 'o!ition of the len! verte,

• avelength of light 6(:?

• -n!trumental error

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Projection Lensometer

•  Tele!%ope arrangement i! repla%ed *ith a

pro@e%tion devi%e

•  To over%ome the pro"lem of eye0pie%e(

• More than one operator %an vie* the

target at the !ame time(

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Advantage!

• Not re#uired any !u"@e%tive @udgement

• Automati% analy!i!

• +igital di!play

• Several mode!

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)eneva Len! Mea!ure

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$ormulae

• Radiu! of %urvature

r

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orking

• Simple me%hani%al in!trument u!ed to mea!ure

po*er and "a!e %urve of the !pe%ta%le len!(

• a!e %urve mea!urement *hi%h i! not po!!i"le "y

len!ometer(

• -n!trument *ith three leg!. outer t*o are ;,ed and

inner one %an !lide in and out to mea!ure the !ag(

• -nner leg i! atta%hed *ith !pring *hi%h e,ert! !mall

do*n*ard pre!!ure on the !urfa%e "eing mea!ured(

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A"out

• -na%%urate reading! due to improper leg

po!ition(

• Leg po!ition %an "e veri;ed "y pla%ing the

in!trument on Dat !urfa%e. inorder to get

zero value(

• +i!advantage not %onvenient to mea!ure

in tori% !urfa%e!(

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-n /!e