Fitting Guides > Buckley Bifocal
Fitting Guides
The Buckley Bifocal
Fitting Guide
- Valley Contax offers the best choice among Bifocal lenses for today's presbyopic population.
- The Buckley Bifocal is a crescent shaped translating design.
- Manufactured in any material of your choice.
The Buckley Bifocal has a crescent segment for add. The lens is a one piece translating bifocal, which uses prism ballast as a means of controlling the lens position. Generally the lens is manufactured with a .02 to .04 truncation for optimum positioning. The truncation also aids in the lens resting on the lower lid as the patient looks into a downward gaze.
The fitting for the Buckley Bifocal is simple and sure.
Ask for the use of a diagnostic set to fit the Buckley. Select a slightly flatter base curve than a single vision lens.
The Buckley Bifocal is the preferred bifocal exclusively from Valley Contax.
That means Valley Contax has complete and ultimate parameter control for quality and reproducibility. Purchase the Buckley Bifocal with the Valley Contax Failsafe Warranty.
The Buckley Bifocal is available exclusively from Valley Contax in a wide range of parameters:
Base Curves: Any base curve radius
Powers: Made to order
Diameters: Suggested sizes, 9.0 through 10.0
Truncation: .2 to .4
Edge Lift: Standard
Parameter Selection:
Base Curve
We recommend that a slightly flatter base curve than a single vision GP lens is used to ensure translation and allows for a larger optic zone providing a large vertical distance field.
| Corneal Astigmatism | Base Curve |
| 0.00D | 1.00 D flatter than K |
| 0.50D | 0.50 D flatter than K |
| 1.00D | Use the flat K |
| < 1.00D | Steeper than flat K by a 1/4 of the amount of corneal astigmatism |
Distance Power
The distance power is calculated by adding plus or minus to the sperical power of the manifest refraction depending on whether the base curve selection is flatter or steeper than the flattest K reading. For best results over refract with hand held lenses in normal lighting over the best fitting diagnostic lens.
Add Power
Use the spectacle add or for best results, use hand held trial lenses to over refract in adequate room illumination while patient is in the reading position.
Diameter
Choose a 9.9/9.5 when vertical fissure/cornea is a large size.
Choose a 9.5/9.1 when vertical fissure/cornea is a medium size.
Choose a 9.1/8.8 when vertical fissure/cornea is a small size.
For every .30 mm increase in horizontal diameter, flatten base curve 0.25D
For every .30 mm decrease in horizontal diameter, steepen base curve 0.25D
Seg Height
When visible white exists (< 1.00 mm) between inferior limbus and lower eyelid, choose a 4.4 mm.
When inferior limbus and lower lid are tangent, choose a 3.9 mm.
When inferior limbus is above lower eyelid (not > 0.75 mm above), choose 3.5 mm.
Lens Fitting
| A good fit exhibits the following: | |
1. |
Intrapapebral fit |
2. |
In distance gaze, the lens rests on the lower lid. |
3. |
In near gaze, the lens has good upward translation. |
4. |
The seg height is located at the lower pupil margin. |
5. |
The edge lift is adequate. |
6. |
The seg height is positioned at 180°. |
7. |
The seg height drop is <1.0 second. |
| A flat fit is determined by the following objective findings: | |
1. |
The lens decenters laterally following the blink. |
2. |
There is excessive edge lift. |
3. |
The lens rotates... and rocks on the blink. |
4. |
There is an absence of tears centrally. |
5. |
The segment height angle fluctuates. |
6. |
The lens drops extremely fast. |
7. |
The lens decenters temporally. |
| A steep fit is determined by the following objective findings: | |
1. |
There is an excessive amount of pooling centrally. |
2. |
The lens is bearing mid-peripherally. |
3. |
There is no or very little edge lift. |
4. |
The lens is decentering either inferiorly or nasally. |
5. |
The segment drop is slow or not at all. |
6. |
There is little or no translation. |
7. |
Vertical movement is limited. |
7. |
The segment has > 15° nasal rotation. |
| Problem solving techniques | |
1. |
A superior positioning lens with normal edge lift may require a steeper base curve and/or an increase of prism by .50D. |
2. |
A lens that is not positioning laterally may require a larger diameter. |
3. |
If the lens doesn't drop quickly enough, the base curve may need to be adjusted either flat or steep (depending on your fluorescien pattern). Also consider increasing the prism by .50. |
4. |
The patient holds their chin to the chest for distance; Check the distance of the seg height in relationship to the pupil with the aid of the ophthalmoscope in primary gaze. It should be within the lower pupil measure. The seg height may need to be lowered. |
5. |
If the patient holds their reading material to their chest, raise the seg height. |
6. |
The lens is rotating more than 15° nasal. Flatten the base curve by a .50D or/add .50D prism. |
7. |
The lens is rotating more than 10° temporal, steepen the base curve by a .50D and/or add .50D prism. |
8. |
If the lens pops out, steepen the base curve. |
9. |
If superior flare to observed by the patient, a larger diameter is needed. |
10. |
If the lens slips underneath the lower lid, increase the prism by .50D. |
Steve
President
"Valley Contax feels proud to be one of the select laboratories who have earned this prestigious award..."
"...as a reflection of the importance we place on quality."
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