Barr - Better Biometry notes
Contents
1. Reasons for Low Signal to Noise Ratio Dense medial opacity along the visual axis Restless patient Alignment of device to patient eye is not optimal Very high ammetropia 6 D Corneal scars Pathologic changes in the retina Slide 12 IOL Master e Troubleshooting e Adjust the joystick try scanning in all 4 quadrants of the circle Pull back or push forward de focus the reflecting light to fill the entire circle Observe sometimes you can see where the opacity is and try to scan around it Slide 13 Take matige eme ty Did you know You can take measurements with the patient wearing their glasses This can improve fixation in patients with high refractive errors and will not interfere with AL measurements Slide 14 IOL Master Key Points Don t be a button pusher Understand the information youre getting Read the manual nstruct the patient 80 9096 of patients can be scanned e What about the other 10 20 Slide 15 Ultrasound e Measured in hertz One hertz is one cycle per second The human ear hears sounds 20Hz 20 000Hz Ultrasound has a frequency of gt 20 000Hz Ophthalmic ultrasound uses a frequency of approximately 10 000 000 hertz 10Mhz Higher frequency means less penetration but greater resolution Slide 16 Slide 17 Slide 18 Slide 19 Ultrasound Contact Oops Slide 20 Ultrasound Contact Corneal compression This is2. 25D This is more significant in a short eye and less significant in a long eye Post op refractive errors e If eye measured too short then post op myopic error f eye measure too long then post op hyperopic error Slide 46 Standard Dimensions Average ACD 3 24mm Average lens thickness 4 6mm Will increase with progression of cataract K s 43 44D Should be within 1D of each other Slide 47 Slide 48 White to white 1 7mm 0 46mm Hyperopia Right eye e MR 43 50 1 25 X 025 Axial length 21 37mm K s 44 00 45 50 e MR 2 50 1 50 X 015 Axiallength 24 00mm K s 41 37 39 75 Myopia Right eye MR 6 00 1 00 X 135 Axial length 27 33mm K s 43 00 44 37 e MR 8 00 2 75 x 090 Axial length 23 30mm K s 48 25 50 00 Left eye e MR 43 75 1 75 X 130 Axial length 21 27mm K s 43 75 45 25 MR 42 75 1 00 x 165 Axial Length 23 85 Ks 41 62 40 12 Left eye e MR 5 75 0 75 X 045 e Axial length 27 47 K s 43 50 44 50 MR 8 50 2 25 x 090 Axiallength 23 50mm K s 48 12 49 75 Slide 49 Emmetropia Right eye Left eye MR plano 4 50 x 022 e MR 0 25 0 25 X 157 Axial length 22 24mm e Axial length 22 33mm K s 45 50 45 87 K S 45 37 45 25 e MRplano MR plano Axiallength 24 92 Axiallength 25 02 K s 42 00 41 87 K s 4175 4242 Slide 50 Slide 51 Resources The Ophthalmic Biometrist Fort Lauderdale 2008 Philadelphia 201
3. 0 Always check the gate placement incorrect placement means incorrect measurements Ultrasound Velocity Cornea 1 641 m s e Aqueous 1 532 m s Lens 1 641 m s Vitreous 1 532 m s Average 1 550 m s PMMA 2 78 m s Acrylic 2 120 m s Silicone 980 1100 m s Ultrasound Pseudophakia Find out what type of lens they had implanted Maybe the patient actually kept the lens card Maybe not e The various lens materials have unique spike patterns TN NN MN MAL M k ati A Scan Biometry Rhonda Waldron Slide 31 Ultrasound Gain When do you adjust the gain Turn the gain up for dense cataracts that are yielding a poorly rising retinal spike Turn the gain down for pseudophakic scans to reduce reverberating spikes Use CAUTION when adjusting the gain Only adjust as much as is needed to get the scan Slide 32 Ultrasound Gain Too high Erroneously short measurement Extra noise extraspikes incorrect gate placement Slide 33 Ultrasound Gain Too low Erroneously long measurement Lowamplitude spikes Slide 34 Ultrasound Pattern The most important thing about your A Scan eye length measurements is the PATTERN OF YOUR SCAN Standard deviation means nothing if you do you not have the correct pattern tis entirely possible to get multiple erroneous measurements with good standard deviation BUT the pattern is wr
4. Slide 1 pe LL nace 2 0m Lm a Adi als a i Ual i LN alas lana Serer eee PERSI nta naa ana La Jessica Barr COMT ROUB Clinical Supervisor The Children s Hospital of Philadelphia Division of Ophthalmology Co Director COT Program Camden County College Ophthalmic Science Slide 2 Discussion points Patient history Keratometry OL master Principles of ultrasound A Scan biometry Slide 3 Patient history Did the patient have prior surgery Lasik PRK Refractive procedures change keratometry measurements Retinal detachments scleral buckling procedures elongate the eye 0 5mm to 1 0 mm s the patient phakic Pseudophakic If so what lens materials Silicone PMMA Acrylic Aphakic You will need to adjust the settings on IOL M and or A scan Do they have a PK or corneal opacity If you can t see the retina a B Scan is always indicated and billable Slide 4 Patient history Key points for axial length measurements Myopic eyes are generally longer Hyperopic eyes are generally shorter Average eye is 23 5mm long Keratometry measurements can explain emmetropia in a patient with unusual AL Slide 5 Standardize your K readings Manual K s are the least reproducible amongst biometrists e Pick a method and stick with it Always use two methods for K s to verify the validity of the measurements Slide 6 Keratometry Manual Unco
5. e Rhonda G Waldron MMSc COMT CRA ROUB CDOS Diagnostic Echographer Senior Associate in Ophthalmology Emory Eye Center Atlanta GA Owner Eye Scan Consulting rhondawaldron comcast net Phone 404 286 9067 e A Scan Biometry Rhonda Waldron http emedicine medscape com article 1228447 overview Slide 52 Slide 53 Resources Warren E Hill MD FACS http doctor hill com Biometry OL master Formulas Optimization Post refractive calculations Great for techs and physicians References Devgan U September October 2011 Cataract Surgery in Small Eyes Premier Surgeon 10 11 Farrell T May 2009 Precision Biometry Ophthalmology Management Parkinson J April 2005 Sizing Up Your Biometry Options Ophthalmology Management Savini G Hoffer K J amp Zanini M April 2007 IOL Power Calculations After LASIK and PRK Cataract and Refractive Surgery Today Europe 37 44 Shammas H J 2004 Intraocular Lens Power Calculations Thorofare New Jersey SLACK Incorporated Tyson F August 2006 Choosing the Proper Formula for Accurate IOL Calculations Ophthalmology Management Zeiss IOL Master User Manual Software 5 xx
6. inaccurate even in the hands of the experienced biometrist Compression is UNAVOIDABLE Studies show the contact method compresses the cornea 0 144mm o 36mm Compression varies with IOP and corneal thickness Wecan t predict or control this Slide 21 Ultrasound Contact Fluid bridge measures the eye erroneously long Slide 22 Ultrasound Contact There is really scant defense for applanation anymore given the refractive demands of our cataract patients our refractive lens exchange patients and even more so the patients who have already had refractive surgery once Along with the immersion ultrasound technique partial coherence interferometry has rendered the applanation method obsolete when calculating a highly accurate IOL power is the goal Ophthalmology Management April 2005 Sizing Up Your Biometry Options Slide 23 Slide 24 Hansen shells Various sizes 16mm 18mm 20mm 22mm 24mm e Patient must be reclined Slide 25 Ultrasound Immersion Prager shell Not position dependent Probe locks in place Slide 26 Ultrasound Immersion 4 gates 5 6 spikes Cornea 2 anterior lens posterior lens retina sclera 9 I d i RE a re sal nn Poor screen resolution 7 Better screen resolution Slide 27 Ultrasound Gates Gates MUST be on the ascending edge of spike A Scan Biometry Rhonda Waldron Slide 28 Slide 29 Slide 3
7. l spike AMD VMT ERM RD The prognosis and treatment plan may change Slide 42 Ultrasound Mac off RD FYI If a patient has an RD that will require scleral buckling along with CE IOL is it appropriate to add 0 75mm to the axial length since SB s will elongate an eye o 5mm 1 omm Slide 43 Slide 44 Slide 45 Ultrasound Sources of Error Byrne SF A Scan Axial Eye Length Measurements e Causes of a short measurement e Air bubble adherent to the transducer in a water filled probe Corneal compression contact method Sound velocity is too slow Corneal gate to the right of the corneal spike Retinal gate too far left of the retinal spike Gain set too high Lens measured too thin Misalignment of the sound beam e Ultrasound Sources of Error Byrne SF A Scan Axial Eye Length Measurements Causes of a long measurement Air bubble in the fluid bath immersion Fluid bridge contact method Sound velocity too fast Retinal gate to the right of the retinal spike Gain set too low Lens measure too thick Misalignment of the sound beam Standard Dimensions Axial Length Average eye ranges 22 0mm to 24 5mm Measurements for the same eye should be within o 2mm The two eyes should be within o 3mm of each other Any disparity needs to be explained BOTH eyes should ALWAYS be measured for comparative purposes o 1mm in an average eye is equal to approx 0
8. ong Do NOT be misled by reproducibility if you have any doubts about the pattern of your scan Ten bad scans with the same axial length are just ten bad scans Pattern trumps reproducibility Slide 35 Ultrasound Troubleshooting e Can t get a steeply rising retina spike Misalignment of the sound beam Localizing the macula Posterior staphyloma Macular pathology Slide 36 Ultrasound Troubleshooting You must be perpendicular to the visual axis Retina spike MUST BE 9o degrees angle from the baseline and steeply rising Slide 37 Ultrasound Misalignment A beautiful A Scan with no scleral spike is a bad measurement YOU ARE MEASURING TO THE OPTIC NERVE cum 29 04 m This eye is actually 22 72mm long when measured to the macula Slide 38 Ultrasound Localizing the Macula Pointthe probe nasally until you see the previous pattern without a scleral spike Now you know where you are Tilt the probe temporally until you see a sharply rising and clearly defined scleral spike F e Hello Macula i CN Slide 39 Ultrasound Posterior Staphyloma rregular contour of the staphyloma impairs reflectivity of sound Slide 40 Ultrasound Posterior Staphyloma OL Master measures these eyes most accurately Consider B biometry in conjunction with A Scan Slide 41 Ultrasound Macular Pathology An eye with a macular pathology may yield poor quality retina
9. rrected refractive error of the examiner WILL result in erroneous measurements ALWAYS focus your eye piece FIRST ALWAYS keep the fellow eye OPEN while measuring Focus the horizontal meridian mires first then measure You can re focus the mires now to take the vertical measurements Especially important for highly astigmatic patients Key point 1D error in keratometry reading will result in 1D post op refractive error Slide 7 Keratometry The two eyes should be with in 1D of each other Long eyes usually have flat K s Short eyes usually have steep K s Average K reading is 43 44D Slide 8 Keratometry Soft lenses should be out for about a week Gas perm lenses or hard lenses should be out until the K s are stable Slide 9 IOL Master Axial length Keratometry ACD White to white Formulas Haigis HofferQ Holladay SRK II SRK T Can be linked to Holladay II program and other network systems Slide 10 IOL Master Measuring Axial length tis useful to take all 20 measurements At least four of these measurements should be within o 02 mm of one another and should exhibit the characteristics of an Ideal Display An ideal axial length display is more important than a high signal to noise ratio SNR Coa ee puces o Tome bua maus uma n ramo pcm ph A lir oon ot TR mm ai rima perpe ore ananas b dei ar dcs incl i y cin t Slide 11 IOL Master
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