UNIT SIX - Soft Lens Design And Selection Flashcards
What are some of the soft lens advantages?
Initial comfort Rapid adaption Intermittent wear Minimal lens loss Less flare Great cosmetic lens
What are some of the disadvantages with soft lenses ?
Spherical lenses provide no correction for corneal astigmatism Lack of durability Deposits Lens disinfection Less control of lens parameters
What does this image show ?
Soft lens deposits
What does this image show?
Discoloration of soft lenses
What does this image show?
Soft lens tear with fungus
What are the 6 soft lens performance factors ?
1) Oxygen transmission DK/L
2) Durability
3) Water content
4) Composition
5) Flexibility/Drape
6) Thickness
What does the acronym DK/L for oxygen transmission mean?
DK: Increases with water content
L: (Thickness) transmission doubles if thickness is reduced by 50%
What happens to durability if water content increases ?
It decreases
What happens to durability when thickness decreases?
It decreases
What is the water content range for soft lenses ?
25-85%
What are the high and low percentages of water content according to the FDA?
High: more than 50%
Low: less than 50%
What size are the pore on soft lenses when the water content is lowered?
They are smaller
Lower water content allows less or more enzyme absorption?
Less
What are some characteristics of higher water content lenses ?
Increased deposit problems and greater parameter changes.
What does ionic mean?
Negative surface charge attracts positively charged protein.
What does non-ionic mean?
Less reactive surface, less deposits
As water content increases, flexibility
Increases
As thickness decreases, flexibility
Increases
What are characteristics of thinner lenses ?
Increase oxygen thickness Contour to the eye Move less Fit tighter Increase initial comfort Dehydrate quicker in a dry environment Be more difficult to handle Not mask corneal astigmatism Damage more easily
What are some goals for soft lens design?
Full corneal coverage
Three point touch
Stable acuity
Comfort
What are three things apart of the initial lens selection process?
2mm greater than corneal diameter (HVID)
Lens power
Wearing and replacement schedule
What are the three steps to calculate the power of soft lenses?
1) transpose to - cyl
2) if cyl is 0.50D or greater, determine spherical equivalent. (1/2 cyl + sph)
3) compensate for vertex distance if the S.E. Power is greater than +/- 4.00D
What do we see in a well fit soft lens?
Good centralization/ full corneal coverage
0.5-1.0mm movement
Easy movement with glide or push up test
Stable keratometer mires, VA, and retinoscopy reflex
Good comfort
What do we see in a poor fit soft lens?
Poor centralization
Excessive movement with Glide or push up test
Keratometer mires, VA and retinoscopy reflex clear but blur immediately after blink
Poor comfort
Edge stand off
