progressive addition lenses
TRANSCRIPT
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PROGRESSIVE ADDITION LENSES
BY, SANJANA CHOUHAN.S
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OBJECTIVES• Details of progressive lenses.• Types of progressive lenses.• Progressive markings.• Fitting error and alignment and also the
types of bi-focals
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INTRODUCTION • The very first Progressive lens was
invented by Bernard Maitenaz, from the French company Essel, in the year 1959 –known as Varilux lens .
• A progressive addition lens has more than one focal point or dioptric powers, without the need to switch lenses.
• Progressive lenses can be called progressive addition lenses (PAL), progressive power lenses (PPL).
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• Based on the number of focal points, ophthalmic lenses are divided into four types
Single vision lenses Bifocals Trifocals Progressive addition lens
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• SINGLE VISION LENSES - Corrects only one vision at a time . (Single focal point)
• BIFOCALS – Corrects two vision, Distance and near.(Two focal points)
• TRIFOCALS – Corrects three vision, distance, near and intermediate.(Three focal points)
• PROGESSIVE – Corrects different distances.(Many focal points)
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FEATURE OF A PROGRESSIVE LENS
• A progressive lens provides visual compensation at all distances namely Far, Distances and Near.
• It has a lens that changes its dioptric power continuously, starting at its geometric centre and gradually progressing its dioptre value.
• The progression of power occurs in an optically pure progression corridor.
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• By “Pure” it is meant that there are no astigmatic aberrations in the peripheral zones of the lens .
• The progression corridor starts few millimetre (mm) below the fitting cross and keeps progressing until it reaches the near visual field .
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• At the lateral zones the astigmatic aberration zones are present, where vision is not totally clear .
• The aspheric lens design is responsible for the power progression of PALS and has different radii of curvature.
• It is made up of multiple focal points due to change in its radius of curvature.
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PROGRESSIVE LENS DESIGNS
• Hard design • Soft design
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TEMPORARY MARKINGSDistance reference circle:• This is the identification circle used to
check the distance lens power. • It should be crossed checked with the
lensometer or focimetry. Fitting cross:• It should be located exactly at the center
of the patients pupil. • It is used to measure the MPD(monocular
pupillary distance) and fitting height.
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Prism reference circle:• This is the point which is used to check the
amount of prism in the lens.Near reference circle:• This marking is used to check the near
vision power. • It should be verified with the lensometer.
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Small horizontal locater:• This indicator should be level with the
prism reference point. • This mainly helps the surfacing lab
markers to mount the lenses and check the position of horizontality.
• The horizontality precision can even be spotted easily with the naked eye.
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TEMPORARY MARKINGS
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PERMANENT MARKINGS
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PERMANENT MARKING Lateral circles:• There are two small lateral circles that are used
to relocate the temporary markings and they are positioned exactly 34 mm apart one each on the nasal and temporal sides.
• Lens logo and material code:• The lens type is identified with the help of lens
logo.• The material coat helps us to identify the type of
lens material.
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• E.g: In case of 1.5 index the lens logo is followed by no.6 and in case of polycarbonate lens, a letter P is seen.
• This logo is nasally located. Addition power:• This is located below the temporal locator • We can read the addition power directly
from the lens by using the lensometer.
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DETAILS OF LENS MARKINGCentral fitting cross:• The central fitting cross is marked with the
ink• Mounted in the frame as per the center of
the customers pupil.• It is a temporary marking.• The marking can be wiped off with
isopropyl alcohol.
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RELOCATING THE FITTING CROSS
• A template is provided by the manufacturer for the progressive lenses.
• By placing the lens on the template marking sure to align the 2 lateral traces in the horizontal direction and mark the fitting cross.
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• The wearer should be looking straight ahead with the head in the straight up while the measurements are being taken.
• The fitting cross is placed exactly at the pupillary center.
• If these precautions are not taken it will lead to inaccurate measurements.
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ADVANTAGES • Improved appearance • Complete range of working distance• NO JUMP effect• Thinner and lighter• No need to switch lenses• No dividing line
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DISADVANTAGES• Peripheral aberrations• Adaptation problems• More critical fitting required• More expensive
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Guess the markings ???
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THANK YOU