Procedures 1 Spring 2010
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| What type of procedure is keratometry? | an objective refractive assessment technique in which refractive status is determined w/o input from the patient
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| Define Keratometry | it means literally "measurement of the eye"
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| What is an alternative name for keratometry? | Opthalmometry. It also means "measurement of the eye" but is less accurate and less commonly used
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| What does a keratometer measure? | The radius of curvature of the central cornea's anterior surface.
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| Name 4 types of instruments that can be used to perform keratometry | 1.Keratoscope (illuminated placido's disk) 2.2-position keratometers(the original manual models) 3.One-position keratometers(the most commonly used manual model & the ones that we use) 4.automated keratometers
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| How does (broadly) a keratometer work? | 1.cornea & tear film form a convex mirror 2.keratmr reflects obj of known size from known disnc off of cornea 3.size of relctd img is measured 4.estimtd refrctng pwr of crnea is calctd
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| What area of the cornea is measured in keratometry? | 1.the mire is NOT reflected of the exact center of cornea 2.reflctd from 2 small areas on either side of the axis of the instrument 3.reduem of curvature is measured from this small area about 3mm in diameter
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| How could one measure the periphery of the cornea? | Using a corneal topographer and unicorns
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| Define principle meridians | The 2 meridians of greatest & least curvature
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| Define regular astigmatism | the principle meridians are 90 degrees apart (note that this has no bearing on WTR or ATR classifications)
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| Define irregular astigmatism | The principle meridians are not 90 degrees apart (note that this has no bearing on WTR or ATR classifications)
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| Define WTR astigmatism | The principle meridian with the greatest curvature (and power) is vertical or x180
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| Define ATR astigmatism | The principle meridian with the greatest curvature (and power) is horizontal or X090
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| Define Oblique astigmatism | The principle meridian with the greatest curvature is greater than 30 degrees from either 180 or 090
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| Give four features of recordings of keratometry findings | 1.Horizontal meridian recorded first, vert second 2.recorded as power (not radius) found @ the measured meridian (not axis) 3.Recorded to the nearest .12D using three digits for the meridian 4.comment on mire quality if not clear and regular
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| How should measurements be gotten in the case of irregular astigmats? | For quantitative evaluation for irregular astigmatism corneal topography is used
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| Why is the dK not the same as total astigmatism? | 1.spectacle lens effectvty of 13mm is not considred 2.K's only measure the ant corneal surface 3.the back of the cornea can also be toric leading to internal astigmtsm 4.does not figure in lenticular astgmtsm due to natrl tlting of lens
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| What does the -0.50x090 used in Javal's rule account for? | The presence of lenticular astigmatism
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| How is posterior corneal curvature figured into Javal's rule? | It isn't. Posterior corneal curvature usually does not significantly contribute to total toricity.
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| What is Javal's formula for ETA? | 1.25dK + (-0.50X090)
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| What is the ETA of an oblique astigmat? | just: 1.25dK
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| What is the average K reading | 43.00 to 44.00
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| What is anisometropia? What is antimetropia? | 1.The two eyes have different refractive powers 2.One eye is myopic and the other is hyperopic
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| What are four clinical uses for keratometry? | 1.for refractive ETA & axis of astig 2.contact lens evaluations 3.assmsnt of opticl intgrty(qulty of cornea&tear flm) 4.diagnosis/eval of progressve optcl condtns (kertoconus)
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| When is using keratometry to find ETA particularly useful? | 1.when patnts not abl to prvide reliable sbjctv responses(eldrly&kids) 2.when ret is diffclt(lrg pupls, high ametropia) 3.for very high astigmats
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| How is keratometry used in contact lens evaluations? | 1.msrmnt of crvtr for fittng contcts 2.montring corneal damg secndry to contct wear 3.msrmnt of flexure of RGP's on eye 4.msrmnt of radius of crvtr of both soft & RGP's
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| When is keratomerty usually done (on which patients)? | New patients, all contact lens patients & when indicated by history/symptoms
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| What are 8 sources of error in keratometry | 1.imprpr calibration 2.imprprly focsed eye pc 3.faulty postning of patnt 4.lack of prpr fixatn by patnt 5.rdcd VA of examner 6.accmdtv fluctuation of examner 7.loclized corneal dstrtions 8.imprpr focusng of mires(espclly vertical)
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