GP Bifocal Fitting & Problem Solving
Richard Baker, OD
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GPLI CASE # 1
Initial Summary
The patient known as DA is a 58 –year-old GP Aspheric multifocal wearer. She presented with a complaint of poor vision when reading. She complains about the fact she needs to wear reading glasses over her contact lenses when reading for more than 10-15 minutes.
History
DA is a research scientist at the University of California at San Francisco. She is very active in sailing, running and other outdoor activities. Her expectations are clear close vision and unobstructed distance vision. She states her mid-range activities are not as demanding and is willing to supplement her vision with a computer spectacle if necessary.
Anterior Segment Evaluation
Lids, lashes corneas and conjunctivae were quiet and unremarkable. Her tear breakup time was greater than 12 seconds per eye. There were some signs of peripheral corneal staining related to a high riding rigid contact lens fit.
Presenting Gas Permeable Lens Design: Life Style Gas Permeable Contact lens
OD 7.60 EQ / -3.75 DS 9.50 Diam + 2.25 Add Dist VA 20/20 Near VA 20/40
Over refraction + 0.50 gave 20/20 @ Near
OS 7.90 EQ / -3.87 DS 9.50 Diam + 2.25 Add Dist VA 20/20 Near VA 20/40
Over refraction +0.50 gave 20/20 @ Near
Manifest Refraction
OD –3.25 -0.50 x 030 20/20 +2.00 Add 20/20
OS –3.00 –1.25 x 180 20/20 +2.00 Add 20/20
Keratometry
OD 44.75 / 45.50 @ 090 D/O
OS 43.87 / 45.37 @ 090 D/O
Corneal Topography
Maps for both eyes showed no signs of central or peripheral distortion and the sim K’s were similar to the manual Keratometry readings.
Ocular Measurements
- Pupil Sizes were 4.0+ Mesopic and 5.0 Scotopic OU
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Corneal Diameters are 12.0, OU
- Palpebral Fissures Size were 9.80, OU
- Dist from Lower Lid to Pupil 4.0
- Lower Lid Margin @ Lower Limbus
Considerations for Lens Design
DA needed a lens that would give crisp near vision and clear unobstructed distance vision. She did not have a demand for significant mid-range vision and was willing to use a supplemental computer range spectacle for occasional VDT use.
Treatment
When considering a lens multifocal that would meet the needs of DA, a translating design appeared to have the required features. An evaluation of available translating multifocal designs was considered. In the work-up, both a Tangent Streak flat top and a Natural Vision crescent segment lens was utilized. Both lenses contained a prism ballast and lower truncated area. The crescent segment designed performed best due to the fact that lens rotation was an issue.
Lens Design
The Natural Vision Crescent Segment design is a one piece, prism ballast bifocal with a controlled upsweep segment. The segment shape allows the reading area to rotate around the pupil when gazing at distance objects and does not bisect the pupil, eliminating the split image effect that is experienced with a straight top design. The enlarged reading are provides significant field of view in the near reading field. The lens is manufactured from F-60 material. The lens is moncentric and therefore does not cause any image jump that does occur with the fused design multifocal designed lenses.
Fitting Procedure
- Select Patient with normal upper lid position and lower lid within 1+ mm of corneal limbus.
- Always use a diagnostic lens to confirm riding characteristics. (9.0X9.4Diam) , Seg height (3.2-4.6mm), Prism (1.75-2.75D)
- Fit lens at least0.50 flatter than flattest “K” reading.
- Confirm segment height with trial lens – should be @ or below pupil margin in primary gaze w/normal room lighting.
- Determine add with trial lens over refraction ( +1.00 - +3.00).
First lens ordered is usually the final diagnostic lens.
Lens Parameters
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OD 7.67 BC -2.25 DS 9.60x9.10 Diam / 8.0 OZ 3.6 Seg/ 2.0 Dn / +2.25 Add
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OS 7.82 BC -2.25 DS 9.60x9.10 Diam/ 8.0 OZ 3.6 Seg/ 2.0 Dn / +2.25 Add
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Natural Vision Bifocal in Flouroperm 60 material
Visual Acuities
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Distance OD, OS, & OU 20,20
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Near OD, OS, & OU 20/20
Follow Up Visits
DA reported good comfort with 17 hrs / day of wearing her lenses. Slit lamp exam showed there was no peripheral staining. She was advised to use rewetting drops when performing extensive near point tasks. She reports only occasional use of supplemental +1.00 reading glasses for computer work.
Discussion
This case demonstrates a long term Gas Permeable contact lens patient that was able to Successfully change from an Aspheric GP Multifocal that compromised her near vision, to a Crescent style Translating GP Bifocal. It demonstrates the importance of evaluating the patient’s expectations and evaluating alternative designs.
Discussion Topics
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Why this design?
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What alternative approaches could be considered?
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What about other multifocal designs?
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Other materials?
-- END OF CASE #1 --
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GPLI CASE # 2
Initial Summary
This patient DK is a 47-year-old female. She has worn gas permeable lenses for 25 years. She had previously worn single vision GP lenses. She wore a spherical base curve in her right eye and a bitoric lens in her left eye. She was experiencing difficulty with blurred vision when sewing and doing needlepoint crafts.
History
DK is an active mother of three children. Her activities include driving, arts and crafts in addition to many homemaker duties. She has difficulty using reading glasses when wearing contact lenses.
Anterior Segment
Lids, Lashes, corneas and conjunctivae were unremarkable. He tear break up time was greater than 13 seconds and no contact lens related NaFl
staining was observed.
Presenting Gas Permeable Design: Her current lens specification were:
OD 7.46 BC -4.37 DS 9.0 0 / 7.60 / 9.60/. 5 / .12Ct Boston ES
OS 771./7.26 -1.50/-3.50 9.00/7.60 / 9.70/.5/ .15Ct Boston ES
Manifest Refraction
OD -4.75-1.00x165 20/20 Add +1.50 20/20
OS -1.25-3.50x020 20/20 Add +1.50 20/20
Keratometry
OD 44.62 / 45.75 @ 92 Do
OS 43.87 / 47.50 @ 109 D1/2
Corneal Topography
Axial maps did not indicate any unusual corneal distortion. It did show a classic with the rule bow tie pattern in the left eye.
Ocular Measurements
- Pupil Size were 4.50 mm Mesopic and 6.0 Scotopic, OU
- Corneal Diameters were 12.5, OU
- Palpebral fissure size were 10.50, OU
- Lower Lid Position even with the lower limbus
Considerations for Lens Design
DK is a successful single vision Gas Pearmeable daily lens wearer. She needs good distance vision and a near effective+ 1.50 reading add. She was currently wearing a small thin lens design (9.0 diameter & .12 ct) . The lenses were well centered with just a slight superior riding position and the left lens had a toric base curve. In order to obtain a well centered left lens it was necessary to utilize a similar corneal alignment type design. Most of the successful designs require a well centered lens (Not Lid Attached) and must translate to give usable near vision.
Treatment
An evaluation was performed utilizing aspheric base curve lenses. The left eye fitting was unsuccessful with this design. A Mandell Seamless design was ordered for the final evaluation visit. There was still the challenge to adapt to a multifocal lens that needed to be larger (9.60) and thicker (.25 vs. .12ct).
Lens Design
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OD 7.50 BC –4.75DS 9.60Diam/8.0Oz +1.50 Add / 3.80mm Dist Zone
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OS 7.71/-1.25//7.30//-3.50 9.60 D/ 8.0Oz +1.50 Add / 3.80 mm Dist Zone
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Boston XO high Dk material
Visual Acuities
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Distance OD 20/20-1; OS 20/20-2 & OU 20/20-1
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Near OD 20/20-; 20/20-1 & OU 20/20-
Fitting Tips
- Select patients with average pupil size
- Lens must center well and translate when looking downward to see at near
- Fit the lens flat enough to allow good cent ration & avoid lid attached fit
- Smaller pupil use 3.0 Zone & larger pupils use 3.8 Zone
- Use largest distance zone that doesn’t compromise near vision
- Minimum lens diameter to use is 9.40
- Greater success with use of Diagnostic lenses
- Always evaluate vision for distance and near in straight ahead position
- Always use hand help trial lenses to test vision
Discussion Topics
- What other lens designs could be considered?
- What is the importance of material when designing a multifocal contact lens?
- How important are solutions to the success of a Presbyopic patient?
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