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Five characteristics of "fogging"
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Sujective Refraction
Procedures 1 Spring 2010 Dr.Miller
| Question | Answer |
|---|---|
| purpose of subjective refraction | 1. determine the refractive state of the eye subjectively by combining lenses to place the farpoint of the eye at infinity. 2. Provide the best possible VA with accommodation maximally relaxed. |
| Five characteristics of "fogging" | 1. plus lenses are placed in front of the eye 2. image is converged prematurely in the vitreous 3. eye is made artificially myopic 4. even poorer vision would result if subject were to accommodate 5. no stimulus to accommodate is present |
| Results of inadequate fogging during subjective refraction | 1.Img formd could b behind retina 2.accomm. could b active as blur may be present 3.Subj. Refr. would then find insufficient + or excessive - 4.too much - can strain accomm. sys. 5.accomm. strain could cause symptoms of anesthopia w/ near wrk. |
| End point for sub. refraction | MPMA: Most plus for maximum acuity |
| When/ why are astigmatic charts used | 1.to determin cyl. comp. of refractive error 2. used when VA of 20/25 or better can't be gotten w/ Ret. or w/ spheres alone. 3.SUBJECTIVELY & MONOCULARLY |
| 2 Basic types of astigmatic charts & examples of each | 1. Fixed charts (clockdial & sunburst) 2. Rotating charts (Rotating T & paraboline) |
| When would you use an astigmatic chart | 1. When other methods get less than 20/25 VA & the problem is assumed refractive in nature 2. Other equipment such as autorefractor is not available. |
| What is the setup for using the clockdial astigmatic chart for finding cyl. comp. of correction | 1. Clockdial chart projected on wall for patient 2. patient is in phoropter, OS occluded 3. OD FOGGED to less than 20/40 |
| What is the process for correction using clockdial chart | 1.find axis of corcting cyl: patient ident's most distinct line. lower # x 30 is axis. this is dialed into phoropt. 2.find power by collapsing conoid. patient reports clarity of lines w/.25DC changes. -DCadd till lines=in clarity. extra- to brack |
| Other names for Jackson Cross Cylinder test | 1. JCC 2. Flip cylinder test 3. Cross cylinder test |
| Purpose of JCC test | 1. Subjly refine axis&power of cyl comp. of correctn 2.Refine prev detrmd obj astigmtic corrcts from Kerat & Ret. 3. Refine subjctvly detrmined astigmtc corrctions from astigmt charts |
| What is the setup prior to JCC | 1.best sphere in place to give best poss. VA 2.COLC on retina 3.COLC remains on retna whole time during JCC 4.JCC IS NEVER DONE FOGGED!!! |
| Process for refining Power during JCC | 1.JCC orinted so powers are parlel to princ.merids of crcting lens 2.JCC flipped & cyl comp. of corectn adjustd dep on patnt responce. COLC still on retna b/c sph eq is maintained 3.if 2 optns R=, endpt of pwr tst reachd 4.optns not= endpt not yet reac |
| Process for JCC axis refinement | 1.JCC positnd so pwrs are 45 from Princ Merids 2.once prop positnd JCC usd to refin cyl ax by flipng&makng adjstmnts accdng to SUBJCTV patnt respnce 3.endpt of test reached when choics r=clarity 4.choics not=, endpt not yet reached |
| Features of a JCC lens | 1.-cyl pwr on one side 2.+cyl pwr on other 3.cyl axis are 90 apart 4.pwrs of .25,.37 or .50 in most phorpts 5.hand held optns in various pwrs are available |
| Funtion of Subfective Refraction | 1.Analyss of oc motilty, accommdtn, binoc coordtn, basd on habit, inducd&unaided findngs 2.Diagnos of refract condts sch as anisomet, antimet, emmy, hyp, etc 3.Prognsis of condits sch as ambly, stabisms, etc 4.Teatmnt of ref er if appropriate |
| Note on Function of Subjective refraction | It is a measurment, not a prscptn. Treatmnt plan depends on the analysis&diagnosis which are dirctly&indirctly effectd by subj. refraction |
| Factors (9) that influence subjection refration [see your notes p14 of 25 for details] | Patnt's 1.case history 2.intelligence 3.discrimination 4.accommodative status 5.personality 6.health 7.age 8.past exp 9.interaction w/ doc |
| What are the 2 main phases of subjective refraction | 1.Monocular subjective phase 2.Binocular subjective phase |
| What is the purpose of the monocular phase of subj. refraction | 1.to determine monocular best sphere 2.to refine astigmatic axis and power |
| what are the three main steps of monocular subjective refraction? | -these 3 stps must b done sequntlly- 1.detrmine initial tentive monoc best sph or initl MPMA 2.refin ax&pwr of cyl cmpnt of crrctn w/ astig charts or JCC tst 3.determn 2nd monoc best sphere or 2nd MPMA if indicated |
| Initial MPMA setup/guidlines (some of this does not make a lot of sense to include under this heading, but was included in the notes) | 1.can b prfmd by diff methds depdng on prof jdgmnt 2.startd w/ net ret or autoref findings or habit crrtn in phopt 3.dont require Egger's Chart. gen rule is -.25sph incrses VA by 1 line 4.must encrg subj patnt resp. ask patnt to try to read line. |
| General procedure for initial monoc MPMA | 1.Occld OS, fog OD >20/40 2.Rduce fog in .25 stps to JR 20/20. ASK PATNT TO GUES OUT LOUD @ JR 20/20 3.Cont rducng fog to MPMA(no mor thn 3 past JR 20/20) 4.this endpt avoids over- & ensurs COLC on retna prior to JCC |
| What is done is resulting best sphere after initial monoc MPMA results in still less than 20/25 VA? | Astigmat charts or autoref used to better detrmn cyl comp of corrctn. If astig charts stil do not incrs VA bttr thn 20/25, astig is probably irreg or non refrctv in nature |
| How do you maintain COLC on retna during JCC? | For every -.50DC, add +.25DS For every +.50DC (taking out .5D of minus), add -.25DS * When you take out minus in meridian, you must add it in another. |
| What is true of JCC when the cyl component of the correction is large? | the greatr the cyl pwr, the greatr the need for accrt axis detrmntn. Easier for patnt to give defntve respncs when high cyl cmpt cmpard to weak one. |
| What must you consider regarding phoropter design when refining JCC axis | Though our clinic phorpts rotate JCC when axis of cyl is changed, some older models do not, & the JCC axis must be changed manually. |
| When can you omit the second monoc MPMA? | If no changes resulted from the JCC test findings. |
| What are the 2 basic steps of Binoc subjective Refraction phase (phase 3 of Subjective refraction proper) | -These 2 steps must be done sequentially- 1. Balance the accommodative stimulus/ effort 2. finalize sphere pwr binocularly |
| What is the purpose of Prism Dissociated Blur Balance Test? | 1.equalize stimls to acccommdtn for both eyes 2. relax accommdtn (this is a secndry purpose) |
| What is the set up for the Prism Dissociated Blur Balance Test (PDBBT)? | 1.ommttd if presbpc 2.done immdtly fllwing monoc subj ref 3.usd only if VA= in bth eyes fllwing monoc subj ref 4.this prcdre tries 2 prvnt unequl accmmdtve effrts b/t patnt's eyes whch wld hlp prvnt potntial asthenpia&reducd prfrmnce 5.OU, no acclded |
| What is the name of the lens used during PDBBT? | The MF'ing Risley Prism |
| Why would you omit doing PDBBT upon unequal monoc MPMA findings? | You would be adding plus to the better eye making it as good as the bad eye. |
| What do you do if the patient reports one a changing "most clear line" during PDBBT and no "equally blurry" point? | You present them with a forced choice. You ask them to chose which of the 2 options results in the lines being as close as possible to equally blurry |
| What is an alternative test to the PDBBT? How are the two tests similar? | The alternate occlusion test is an altrntive test to PDBBT. Both are VA dependent tests. |
| What the is general set up for the alternate occlusion test? | 1.same as PDBBT excpt no prsms are used 2.PDBBT is prfrrd b/c it's easier for patnts to make jdgmnts of clrty usng simultanuous comprsns vs successive comprsn |
| What is the general procedure for the alternate occlusion test? | 1.patnt is foggd& eyes are altrntly occlded w/covr pddle 2.patnt askd to compar views as each eye is altrntly occlded 3.A +.25added to eye seeing clrst till = acheved |
| What is done immediately following either the PDBBT or the alternate occlusion test? | The binoc MPMA |
| Give an example of a NON VA dependent test | The Bichrome test (or duochrome test) is a nonVA based sphricl endpoint determination test. |
| When/why is the Bichrome (or duochrome) test used? | 1.as monoc sph endpt or addnl/altrnt prcdre for monoc MPMA 2.as binoc balnc tst or add/alt prcdre for PDBBT 3.as binoc sph endpt tst or add/alt prcdre for bioc MPMA 4.to chck/retest rslts w/ acuty basd endpts 5.when acuty basd endpt tsts r unrlble/inv |
| How does the Bichrome test work? | 1.Unequl chrmtic refr rslts in green rfrctd most(shrtr wavlngth)&focsing in frnt of red(longr wavlngth) 2.chrmtc intvl creatd 3.retna most senstve to yllw (555nm) whch is b/t red&grn |
| How can the accuracy of bichrome tests be maximized | 1.all lghts off excpt for prjctr 2.prjctn systm must functn optmlly 3.appropriate prjctn scrn is ndeeded to MAXimze reflctn towrd patnt |
| What are the endpoints for: 1.Monocular Bichrome MPMA 2.Binoc Bichrome MPMA 3.Prism Diss Bichrome Balnce Test | 1.monoc-EQUAL 2.binoc-FIRST GREEN 3.PDBB-EQUAL For each eye |
| (A Bit of a repeat here) What is the purpose of each of the following tests? 1.Monocular Bichrome MPMA 2.Binoc Bichrome MPMA 3.Prism Diss Bichrome Balnce Test | 1.a monocular endpoint test 2.a binocular endpoint test 3.a binocular balancing test |
| Oder the tests for binocular balance from most to least accurate | 1. Prism Dissociated BLUR BT 2. Alt Occlusion Test 3. Prism Dissociated Bichrome Bal Test |
| Give the general procedure for Prism dissociated bichrome balance test | 1.drk rm, r/g fltr on, isltd 20/40 2.Rslys in 3BU OD, 3BDOS 3.Fog .75OU 4.Patnt looks at just top & reprts whch colr most clear 5.for reducd monocly till equal achievd 6.repeated OS |
Created by:
mm_coady