Vertical Imbalance Flashcards
Vertical Imbalance
Difference in Total Power at 90 degrees x reading levelDivided by constant of 10 (Prentice’s Rule)
6 ways to correct VI
- Two pairs of glasses 2. Prism segments 3. Fresnel press-on prisms 4. Dissimilar segments 5. R-compensated segments 6. Slab-off prisms
Fresnel Principal
A series of small plastic prisms lying adjacent to each other on a thin platform of plastic Much thinner than a conventional ophthalmic prism 6 month life span Quarter increments 0.25, 0.50, 0.75 etc
What are the rules for Prism Segments?
Prism goes in both eyes Use increments of 0.5D, 1D, 1.5D Never see, rare, in glass only, ugly, expensive, long time to make Doesn’t matter which increment you use for each eye Goal is to cancel prism in chosen eye
When do you use Fresnel prisms?
Better for high diopters When you need quarter DioptersNot clearest vision, lose visual acuityAphakias, post cataract patients with no lenses
When do you use Slab - off prism?
When the vertical balance is present with antimetropia Meaning two different signs for each eye with a big difference between the powers
Slab off/ Bicentric Grinding
- Get the Vertical Prism 2. Most Minus BD / Least Plus BU 3. Prescribe Slab off Prism -MM BU in same eye to neutralize -LP BU in same eye to neutralize
How many choices are there for R-Compensated Segments?
7 choices One has to be R-4 R-4, R-5, R-6, R-7, R-8, R-9, R-104mm - 10mm
What are R-Compensated segs?
Round segs that have the bottom or top cut off in order to change where the OC ends up
When do you use R-Compensated Segs?
Only good for small amounts of vertical imbalance Can only separate the OCs by 6mm Glass durabilityBig in the Midwest
Do you know the BTS’s for doing dis-similar segs?
- TK/Kryptok/Round 22 = 11mm 2. Any fuses FT = 5mm 3. Ribbon Seg/Bar Seg 22 x 19 = 4.5mm // 22 x 14 = 7mm 4. Curve Top/Panoptik = 3.5mm 5. Round 22 = 11mm // Round 25 = 12.5 mm6. FT one piece = 5mm 7. Executive = 0 8. Ultex A and AA = 19mm 9. Blended/Seamless 22=11 mm 28=14 mm 10. Ultex B = 11 mm FT 45/ Welsh FT/ Thin Line 35 = 0
For which VI corrections do you use MMLP?
Dis-Similar Segs R-Compensated Segs Slab off Prism
Which lens has the VI?
Minus Lens has the imbalance in the strongest lens Plus lens has the imbalance in the most plus, always base up
Explain the need for intermediate vision.
Their is an inevitable loss of accommodation that results in the loss of clear vision at arm’s length, 20” to 30”. As presbyopia advances with age after 40, the add power becomes greater than the person’s accommodation. They get an intermediate blur at arm’s length. Bifocal is too strong to see further out than arm’s length and their accommodation is not strong enough to bring that area into focus.
What do we have to correct intermediate vision?
Progressives Trifocals Bifocals SV lenses for specific purpose like sheet music
What are examples of occupational progressives?
Zeiss Gradal RD, the Varilux Interview, Sola Access, Hoya Tact II, AO Technica, and the Shamir Office
Intermediate Vision definition
Distance will vary -16” to 24” SV - piano glasses Bifocal -top intermediate/bottom reading Trifocal -three focal lengths Usually prescribed after 2.00 add, not always Age dependent/use dependent
Donders
Ophthalmologist charted how much accommodation people had at various ages 60 yr old, +1 D left
11 Common Trifocal Types
- Executive 2. Flat Top 3. E.D. Trifocal 4. Progressives 5. Smart Seg 6. Occupational/Vocational Lenses 7. Double Flat Top 8. Double Round or Basketball Seg 9. Double Executive or E Line 10. Quadrifical 11. Rede-Rite
Executive Trifocal
Glass or plastic, one piece, 7mm intermediate segment height
Flat Top Trifocal
Glass or Plastic, fused or one piece Plastic Only =7x25 7x28 8x35Glass Only 9x35 7x35 1st measurement is distance btw first 2 lines
E.D. Trifocal
Plastic only, executive with a flat top segment Near Rx in FT segment Intermediate under executive line
Progressives
All one-piece, segment on the front Many different sizes and configurations Intermediate section small with distortion on each side Keyhole
Smart Seg
Made by SolaA FT design that incorporates an intermediate portion at the top of the segment30mm x 24 mm 30mm length of FT 24= 12 mm intermediate 12 mm near
Occupational/Vocational Lenses
Lenses designed for a specific function They often will fill a special need required for a hobby/employment
Double FT
22mm, 25mm, 28mm diameter only Glass or plasticThe upper segment may be for near vision or intermediate
Double Round or Baseball seg
Round 22mm or 25mm segments Glass or plastic Top round segment could be intermediate or near
Double Executive or E line
Glass or plastic Intermediate or Near Then Distance Then Near The Distance portion is 10-14mm long
Quadrifical
Vision Ease Glass only A double FT and smart seg on the bottom
Rede-Rite
Essentially, an upside down Ultex Looks like an OliveUpside down Ultex A
What type of intermediate lenses would you recommend for piano players who need to read sheet music?
Single Vision intermediate
Who would wear trifocals?
Progressive non-adapt
Who would wear occupational lenses?
Musicians, IT, laboratory personnel
Vertex distance
From the front surface of the cornea to the back of the lens
Ideal vertex distance
13.75mm
Reason for Vertex Distance Compensation
If a person with a +/-5.00 Diopter or greater lens is refracted at one distance and the glasses are fitted at a different distance, a disparity in visual acuity will exist
How do you determine the length that focused light rays hit inside the eye? Using your knowledge of vertex distance compensation, how far do focused light rays hit inside the eye if the optician fits the glasses at 14mm?
100mm-distance optician first glasses at = distance focused light rays hit the eye 100mm is the retina
Four rules of Vertex Distance Compensation?
A minus lens moved inward INCREASES it’s effective power A minus lens moved outward DECREASES its effective power A plus lens moved inward DECREASES its effective powerA plus lens moved outward INCREASES its effective power
What’s the relationship between focal length and lens power?
Shorter Focal Length = stronger lens power Longer Focal Length = weaker lens power
A high hyperope patient was examined at 8mm and fit at 13 mm, did you move inward or outward? Which rule?
Moved outwards/away Increases its effective power You need the opposite So you need a weaker lens
Vertex Compensation
When the frame does not sits at the same vertex distance as the phoropter/trial frame did during the examination Manipulating Focal Length
Four Rules Simplified
Plus Moved away gets stronger Plus Moved Closer gets weaker Minus moved away gets weaker Minus moved closer gets stronger
Shamir office
Shamir Computer™ is designed to provide patients with a wide field of near viewing with clear vision up to 5 feet, which is a far greater depth of field than that offered by conventional reading lenses. It is ideal for patients working at a computer or who are primarily stationary at their desk/workstation throughout the day. Professions that may benefit from Shamir Computer™ include architects, post office clerks, software engineers, data entry clerks, graphic designers, pianists and more.
Reverse Slab-off increments for Younger
1.5, 2, 2.5, 3, 3.5, 4, 5, 6
