1. PRCTICAL DIFFICULTIES OF PROGRESSIVE LENS FITTING

2. BRANDS AND DESIGN
Progressive lenses are by far one of the most complex lenses on the market. This often leaves the patient begging to know what the difference is between brands and designs.

3. Adapting To Progressive Lenses
The strength of the lens prescription can make a difference to the ease of adaptation to progressive lenses.
When the lens prescription is fairly weak, it is usually easier to adapt to progressive lenses than when the lens prescription is strong.
A strong lens prescription is required for people whose fields of view are narrow, and these people should be prepared to take some time adapting to their new progressive lenses.

4. Characteristics Of Progressive Lenses
To see objects clearly whether they are far away, at a medium
distance or close up.
This is done by blending varying lens powers so that the eye glass wearer can look through the glasses at different angles, depending on the type of vision required.
The distance section is at the top of the progressive lenses, and the close-up section for actions such as reading is at the bottom. The intermediate vision area, usually suited to tasks about an arm’s length away such as computer work, is in the centre.

5. Advantages Of Progressive Lenses
Progressive lenses have no visible dividing lines to indicate that the lens prescription has taken different levels of vision into consideration.
The glasses appear to have clear, unlined lenses but they are actually constructed with a number of curves through which the progression from one area of focus to the next is achieved.
The progression is gradual, meaning that the progressive lenses enable the person wearing the glasses to adjust focus smoothly from one area of vision to the next. The absence of visible dividing lines on the surface of the lenses also makes progressive lenses more aesthetically appealing to many eyeglass wearers.

6. Another advantage of progressive lenses is the variety of choice they offer to people who need to wear glasses. Depending on different and individual requirements, progressive lenses can be customized to take those requirements into consideration. Progressive lenses can, for example, be customized to suit a person whose day includes a predominance of computer work and needs glasses with lenses that make it as easy as possible to carry out this work.

7. When some people begin wearing progressive lenses in their glasses they may experience some temporary side effects such as dizziness and headaches.
These symptoms are often particularly noticeable in people who tend to suffer from motion sickness. They indicate that the brain is working to adapt to the progressive lenses, and usually disappear in the first couple of weeks. People getting used to new progressive lenses may also find their perceptions of depth and distance are altered to some extent initially, but this usually improves during the adjustment time.

8. Disadvantages
Distortion: Progressive lenses suffer the disadvantage that the power progression creates regions of aberration away from the optic axis,
Yielding poor visual resolution (blur). As the lenses combine a range of powers in a single surface there are also geometric distortions to the visual field, which increase with the addition power while the prescribed addition powers are low.
The wearer can then adapt to the increases in a series of steps in addition power over a number of years as their presbyopia progresses.

9. Higher Order Aberrations consists of a variety of aberrations that have increasing levels;
Coma
Trefoil
Spherical aberration

10. Lower Order Aberrations consist of sphere and cylinder powers
Myopia
Hyperopia
Astigmatism

11. The fitting of individual progressive lens needs the measurement of individual data of the face and frames in situ. 

12. Pupillary distance and hight of the gaze

13. Lens - Face tilt Working or reading distance

14. HARD AND SOFT
Hard lenses have a much higher concentration of blending in these zones. This allows for a much clearer distance and reading but can give the wearer an intense 'swimming' feeling

15. Later lens designers reduced the harshness of hard lens designs by creating the soft lens.
These lenses increase the blending zones. This spreads them out into the distance and reading portion of the lens.
People who tend to be very active in their lenses can appreciate the reduced swimming feeling.

16. Common difficulties Double vision Blurriness Ghost images Halos
Starbursts and bright light
A reduction in visual contrast
Poor night vision

17. Main Reasons and faults
Frame selection
Face measurements
Poor handling of lab technicians
Quality and material of the lens
Visible field of area
Ocular physiological problems
Customer satisfaction

18. conclusion Precise eye sight measurement Careful manufacture
Perfect fitting by lab technician
To train the patient with his full satisfaction

19. Thickness and Refractive index

20. WISH YOU ALL ON THIS ALL INDIA OPTOMETRY CONFERENCE DAY.
S PALANIAPPAN,HONORARY OPTOMETRIST AT MILITARY HOSPITAL,
CHENNAI