SINGLE VISION LENSES &

BIFOCAL ZOHRA RASOOL

ISRA SCHOOL OF OPTOMETRY

Single vision lenses

SINGLE VISION LENSES

• - Single vision prescription lenses have one single prescription across their entire surface:

• Distance to see far away. Ex: Driving, Watching Television, sports

• Intermediate to see arms length. Ex: Computer viewing.

• Reading to see close up. Ex: Reading a Book, magazine, newspaper etc.

BIFOCAL

BIFOCAL

DEFINATION The lenses having two discrete

portion of different focal power, using usually for distance and near

REASON FOR PRESCRIBING PresbyopiaHigh AC/A ratio & accommodative

esotropiaPseudophakia

TYPE OF BIFOCAL ACCORDING TO MANUFACTURING STRATEDIES

SPILT BIFOCALFUSED BIFOCALCEMENTED BIFOCALONE PIECE BIFOCAL

• SPILT BIFOCAL The spilt bifocal is the Franklin type bifocal with a lens above

and below cut along a straight line and joined in a frame

• CEMENTED BIFOCAL the second class of bifocal is the cemented bifocal in which a

small plus segment is glue to back side of the main lens with glue like canada balsam

• FUSED BIFOCAL Fused bifocal is a glass bifocal in which a small button of high

refractive index is fused at high temperature in to a concavity at front surface of low refractive index of the main lens

• ONE PICEC BIFOCAL This kind of bifocal is obtained by grinding a different curved

on the front of back part of the lens .

ACCORDING TO SHAPE

• FLATE TOP D segment bifocal Width rang from 25mm to 45mm Nearly invisible Relatively light Good size field of view Relatively little amount of image jump

• CFR (CROMA FREE ROUND) Segment width range 22, 24, 25,30,38mm Phase out Round top (lesser near task, suitable who are used to) Image jump Cosmetically attracting Light weight

• Curved top C style segment Width 28, 35,and 45mm Phased out Round corner enhance peripheral vision Little image jump Good size of field view Relatively light Cosmetically light

• Curved top C style segment Width 28, 35,and 45mm Phased out Round corner enhance peripheral vision Little image jump Good size of field view Relatively light Cosmetically light

• Executive bifocal Occupational lens ( lot of near work) Negligible image jump Heavy Ugly Dirty in that long, deep crevice

• Ultex bifocal Segment width 38mm Occupational (vast reading range) Round segment allow peripheral vision Plus cylinder Significant image jump

• Blended bifocal Irvin rips 1955 Invisible bifocal Segment width 28mm Cosmetically good Non adaptive PALs