5. Advanced Topography Selecting Premium IOLs and Complex Cases www.medsalesacademy.co.uk www.medsalesacademy.co.uk
Today we will learn Why K readings are important to IOL calculations ๏ How to take accurate measurements ๏ How to compare readings from di ff erent devices ๏ How to investigate irregular K readings ๏ Understanding di ff erent ways to measure corneal curvature ๏ Understanding Astigmatism front and back ๏ Using reports to screen out unsuitable patients ๏ www.medsalesacademy.co.uk
Topography & IOL IOL = A constant - 2.5 AL - 0.9K ๏ Axial Length specific location for measure ๏ A constant - Manufacturer or Optimised ๏ K readings ?????? ๏ 0.1 mm in K reading = 0.5 D change ๏ Today we will look at K readings and curvature ๏ www.medsalesacademy.co.uk
Curvature The cornea is not a uniform shape ๏ It varies depending on where we measure the K ๏ reading Auto Keratometer 3-3.3 mm - IOL Master 2.4mm - Pentacam 3mm - www.medsalesacademy.co.uk
Measuring Accurately Most readings are reflections of the tear film ๏ Make sure tear film is consistent across the surface ๏ Use Artificial Tears ๏ Haigis says don’t use ANY drops on cornea prior to ๏ measurement Use an instrument that measures cornea directly? ๏ www.medsalesacademy.co.uk
Pentacam Pentacam measures cornea not tear ๏ film, so should be una ff ected by artificial tears But … the cornea will change shape ๏ as it is lubricated 0.1 mm change in curvature equates ๏ to 0.5 D change in power www.medsalesacademy.co.uk
Solution The drier the eye the more it will be a ff ected by ๏ artificial tears Take measurements before and after drops ๏ Discuss with patient. If they are likely to keep ๏ with dry eye regime after surgery then use the lubricated reading If not use the pre drop reading ๏ www.medsalesacademy.co.uk
Comparing K Readings Check quality ๏ Review Images ๏ Were artificial tears used? ๏ www.medsalesacademy.co.uk
Comparing K Readings Choose Apex or Pupil. Choose Zone or Ring. Eg for IOL Master Eg for IOL Master choose pupil choose ring Set Zone to Diameter you wish to compare. Eg 2.4 for IOL master www.medsalesacademy.co.uk
Compare K Readings Compare eg Pentacam with IOL Master ๏ If the readings are close use the IOL master ๏ readings If the readings are di ff erent you may need to ๏ investigate further www.medsalesacademy.co.uk
Investigating K Readings Using Pentacam because ๏ Most popular - Images from and back surfaces of cornea - I have most experience with it - www.medsalesacademy.co.uk
Check Zone and Ring are Similar X XX/2=K1 X X XX/2=K2 X www.medsalesacademy.co.uk
If not - BAD www.medsalesacademy.co.uk
Tips Asymmetry is suspicious ๏ Check other reports like Belin Ambrosio ๏ Check for Artefacts ๏ Egg Shaped pupil suggests movement ๏ www.medsalesacademy.co.uk
Power Distribution www.medsalesacademy.co.uk
Corneal Curvature Sim Ks ๏ Anterior taken at 3mm (2.4 IOL Master) - True Net Power ๏ Add Anterior and Posterior power together - Thin Lens Formula - Total Corneal Refractive Power ๏ Ray trace through all surfaces - Thick lens formula - www.medsalesacademy.co.uk
True Net Power Cornea n=1.376 Air Aqueous n=1 n=1.336 + Power D = n-1 x1000 r mm www.medsalesacademy.co.uk
Total Corneal Refractive Power www.medsalesacademy.co.uk
Astigmatism WTR 60-120 OBL 30-160 O B L 1 2 0 - 1 5 0 ATR 150-180 ATR 0-30 www.medsalesacademy.co.uk
Astigmatism Anterior surface-based keratometry compared with Scheimpflug tomography- based total corneal astigmatism. Tonn B 1 , Klaproth OK 1 , Kohnen T 1 . www.medsalesacademy.co.uk https://www.ncbi.nlm.nih.gov/pubmed/25468887
Axis www.medsalesacademy.co.uk
Cataract Pre-Op www.medsalesacademy.co.uk
Also Chord Distance ๏ Di ff erence between Pupil Centre and ๏ Apex (where the patient is looking) Jack Holladay - over 0.5 mm not ๏ suitable for MF For more info www.gatinel.com ๏ www.medsalesacademy.co.uk
Example ๏ Lets review the topography www.medsalesacademy.co.uk
4 Maps Refractive www.medsalesacademy.co.uk
Power Distribution www.medsalesacademy.co.uk
BAD www.medsalesacademy.co.uk
Holladay Report - Chord www.medsalesacademy.co.uk
Refractive - Chord www.medsalesacademy.co.uk
Cataract Report www.medsalesacademy.co.uk
Today we have learnt Why K readings are important to IOL calculations ✓ How to take accurate measurements ✓ How to compare readings from di ff erent devices ✓ How to investigate irregular K readings ✓ Understanding di ff erent ways to measure corneal curvature ✓ Understanding Astigmatism front and back ✓ Using reports to screen out unsuitable patients ✓ www.medsalesacademy.co.uk
Thank you! We will email you some questions. ๏ Please send your questions and comments to ๏ emma@medsalesacademy.com We look forward to seeing you on the next course - ๏ A Constants and Formula www.medsalesacademy.co.uk
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