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Contacts Test 2
Keratometer; Astigmatism; CL Parameters...
| Question | Answer |
|---|---|
| What is another name for the keratometer? | ophthalmometer |
| What is the keratometer used to measure? | The radius of curvature of the cornea. |
| What is the corneal cap? | The 3-5 mm in the center of the cornea that we measure with the keratometer; if measured off-center K's will be too flat. |
| What N is the keratometer calibrated for? | The N of tears = 1.3375 |
| What are the measurements from the keratometer called, and how are recorded? | K's or K-readings; recorded horizontal reading/vertical reading X axis |
| The axis always goes with the ________ meridian. | flattest (weakest) |
| What does the difference between the horizontal and vertical K-readings represent? | The amount of corneal astigmatism. |
| When using the keratometer, always start with the _____ eye? | right |
| Measure right eye, then left eye how many times? | Three |
| After you take all the measurements in both eyes, you then take an....? | average |
| If the mires are blurry and do not clear up after having the patient blink, what could be the causes? | keratoconus, corneal warpage; injury; surgery; over-wear of contact lenses |
| What is transient mire distortion? | When the mires are blurry, but clear up after the patient blinks a few times. |
| What is the average range of the power drum? | 36 to 52 D |
| What is the extended range of the power drum? | 30 to 61 D |
| Which lenses are used to extend the range of the power drum? | -1.00 and +1.25 |
| What are other uses for the keratometer? | check contact fit; check flexing of GP lens; follow up K's to see if contact changed shape of cornea; use conta-check to check the BC of a GP lens |
| What is a topogometer? | An attachment to the keratometer used to measure corneal curvature values across mutliple points on the cornea. |
| Who invented the topogometer? What else did he invent? | Joseph Soper; also invented lenses for keratoconus |
| What are other names for a corneal topographer? | Video Keratoscope; Photokeratoscope |
| What does a corneal topographer do? | Produces a color-coded map of the whole cornea to show where it is steepest and flattest. |
| What do the blue or cool colors represent on a topographer map? | Flat curves |
| What do the red or hot colors represent on a topographer map? | Steep curves |
| Corneal astigmatism is always represented with a plus or minus? | Minus |
| What is with-the-rule astigmatism? (WRA) | when the cornea has the flattest meridian horizontal and the steepest meridian vertical; has an axis between 0-30 or 150-180 degrees. |
| What is against-the-rule astigmatism? (ARA) | when the cornea has the flattest meridian vertically and the steepest meridian horizontally; has an axis between 60 and 120 degrees |
| What is oblique astigmatism? | the two principal meridians are located diagonally; Axis is between 31-59 and 121-149 degrees |
| What is irregular astigmatism? | the two principal meridians are not 90 degrees away from each other |
| Most patients have which type of astigmatism? | With the rule (WRA) |
| What is the sagittal depth? | The distance between the posterior surface of the central portion of the lens and a flat surface. |
| What are two other names for the Base Curve? | Posterior Central Curve (PCC); Central Posterior Curve (CPC) |
| Base curve is also known as the _______ curve. | fitting |
| What is base curve? | radius of curvature of the central posterior portion of the lens expressed in mm or diopter power |
| Steeper K's have a _______ radius? | shorter |
| Flatter K's have a _______ radius? | longer |
| What is the optical zone (OZ or POZ)? | The diameter over which the BC extends on the posterior surface of the lens; described in mm; contains the refractive power |
| Where is the Posterior Secondary Curve (Intermediate Curve) located? | between the base curve and the peripheral curve |
| Why is the Posterior Secondary Curve flatter than the base curve? | To align the flatter portion of the cornea. |
| What is the outermost curve? | Posterior Peripheral Curve |
| What is the function of the posterior peripheral curve? | to clear the flatter periphery of the cornea and to prevent impingement in the limbal area as the lens moves. |
| What is the average diameter of a GP lens? | 7.0 to 10.5 mm |
| What is the average diameter of a soft contact lens. | 12.5 to 16.0 |
| What is a juncture? | Where the posterior radii meet, between the BC, PIC, and PPC. |
| What are blends? | contour modification to the posterior side to smooth out the junctures between the radii. |
| What is center thickness? | measured in mm at the GC from posterior to anterior; varies depending on the lens power |
| What is the anterior optical zone also known as? | Refractive Power; Power Curve; Lenticular Curve |
| What is the difference between the radii of the anterior and posterior lens surface. | Lens power |
| What is the lenticular flange? | The increase or decrease in anterior edge thickness to change the lens mass and aid in lens positioning. |
| What type of flange decreases edge thickness? | hyperflange |
| What type of flange increases edge thickness? | myoflange |
| What is the portion of the CL in contact with the upper lid when blinking? | anterior zone |
| What is the function of the anterior zone? | minimize lid irritation during the blink |
| What is the posterior zone? | The small reverse curve on the posterior lens surface to flare the edge away from the cornea. |
| What is the function of the posterior zone? | To allow free movement of the lens across the cornea. |
| What is the junction between the anterior and posterior zones? | Edge Apex |
| Why does the edge apex have to be smooth? | to mininmize lid awareness during the blink |
| What is the SAG a combination of? | The base curve and diameter |
| Magic number for converting diopter power to radius of curvature.... | 337.5 |
| All PMMA lenses have what type of replacement schedule? | Conventional |
| What type of contact lenses can never be slept in and are only daily wear (DW)? | PMMA |
| Who invented the PMMA lens? | Kevin Touhy |
| What are advantages of PMMA lenses? | durable and good optical quality |
| What are disadvantages of PMMA lenses? | hypoxia which leads to edema |
| Which type of lens is not offered with a disposable replacement schedule. | GP |
| What was the first GP lens? | CAB - cellulose acetate butyrate; was not successful and is no longer used |
| What are GP lenses made of today? | SA - silicone acrylate; FSA - fluoro-silicone acrylate |
| Why was silicone added to GP lenses? | Allow more oxygen to the cornea |
| Why was fluoro added to GP lenses? | to improve wetability |
| What are advantages of GP lenses? | oxygen permeability; less chance of edema; excellent optical quality; corrects regular and irregular astigmatism; easier to care for than soft conventional; parameters verifiable; polish and modify; use fluorescein to evaluate lens; last longer |
| What are disadvantages of GP lenses? | initial comfort; harder to fit; more chair-time; more follow-ups; cost more initially; can pop-out easier |
| What is the lacrimal lens? | Tears formed by the back of a GP lens and the front of the cornea that is used to help correct astigmatism. |
| Who created soft hydrogel lenses? | Otto Wichterle |
| Who gained FDA approval to distribute soft hydrogel and when? | Bausch and Lomb in 1971 |
| What are other names for soft hydrogel lenses? | hydrogel; HEMA; gel lens; hydrophilic |
| When was the first silicone hydrogel lens available? | late 90s |
| What was the first silicone hydrogel lens? | Ciba Focus Night and Day |
| What type of disposable lenses are available in silicone hydrogel? | 1 day; 1 week; and 30 days |
| What type of planned replacement lenses are available in silicone hydrogel? | 2 weeks and 1 month |
| Are there conventional lenses available in silicone hydrogel? | No |
| What was the second silcone hydrogel lens available? | Bausch and Lomb Purevision |
| What are advantages of soft lenses (hydrogel and silicone hydrogel)? | initial comfort; best for occasional wear; good for sports (stay on better); less sensitivity to light; less edge reflections; available in single use; available in 2 week and 2 month planned replacement |
| What are soft hydrogel advantages? | available in color enhancement and opaque; higher water content (more oxygen); and thinner lens |
| What are silicone hydrogel advantages? | allows more oxygen due to the silicone |
| What are problems with silicone? | makes the lens stiffer, so while it may be easier to handle it is less comfortable |
| What are soft lens disadvantages? | spherical lenses do not correct astigmatism; cannot use fluorescein; cannot easily verify parameters; conventional need more lens care; cannot polish or modify |
Created by:
griffiskr
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