Se ha denunciado esta presentación.
Utilizamos tu perfil de LinkedIn y tus datos de actividad para personalizar los anuncios y mostrarte publicidad más relevante. Puedes cambiar tus preferencias de publicidad en cualquier momento.

IOL POWER CALCULATION IN DIFFICULT SITUATIONS

This ppt is prepared by referring recent articles and presented at a state conference 2018

  • Inicia sesión para ver los comentarios

IOL POWER CALCULATION IN DIFFICULT SITUATIONS

  1. 1. GANESH NETRALAYA “Caring Vision - Our Mission” IOL POWER CALCULATION IN DIFFICULT SITUATIONS – TIPS TO TACKLE DR VISHWANATH ANKAD CONSULTANT OPHTHALMOLOGIST CORNEAAND REFRACTIVE SERVICES GANESH NETRALAYA, SIRSI (UK)
  2. 2. GANESH NETRALAYA “Caring Vision - Our Mission” IOL POWER CALCULATION IN DIFFICULT SITUATIONS • POST REFRACTIVE SURGERY (LASIK /PRK /RK) • HIGH ASTIGMATISM CASES-KERATOCONUS, SCARRED CORNEAS • POST KERATOPLASTY CASES • PAEDIATRIC CASES • POST VITRECOMISED EYE • APHAKIA/ PSEUDOPHAKIA • PIGGYBACK LENSES • POSTERIOR STAPHYLOMA • MICRO CORNEA AND NANOPHTHALMOS
  3. 3. GANESH NETRALAYA “Caring Vision - Our Mission” IOL Power calculation in Post Refractive surgery After Laser visual correction (LASIK / PRK): A ) Refractive index error • LVC alters anterior corneal curvature and posterior curvature is un-altered • Standard keratometers and Topographers measure corneal power incorrectly • In myopic lasik-overestimates corneal power- under estimation of iol power – Postop hyperopic shift • Conversely in hyperopic lasik –over estimates iol power- myopic shift Trans Am Ophthalmol Soc 2013;111:34-45
  4. 4. GANESH NETRALAYA “Caring Vision - Our Mission” B ) Radius error : Ablations with smaller optic zone or decentred ablation C ) IOL Formula error / ELP Prediction error : • After myopic lasik flatter k leads to under estimation of ELP and under estimation of iol power • converlsy after hyperopic lasik –over estimation of ELP and over estimation of IOL power
  5. 5. GANESH NETRALAYA “Caring Vision - Our Mission” Methods to calculate iol power PRE LASIK DATA DEPENDENT Clinical history method : Post op corneal power estimation • Kc = Kpre – CRc (after a myopic correction) • Kc = Kpre + CRc (after a hyperopic correction) • CRc = Rc.post – Rc.pre • Rc = Rs / (1 – 0.012Rs) (vertex distance of 12 mm) Hoffer KJ. IOL Power (pp. 179-194).© 2011 SLACK Incorporated
  6. 6. GANESH NETRALAYA “Caring Vision - Our Mission” • Aramberri’s double k method: where the pre-LASIK Ks are used to calculate the correct ELP value, while the corrected post-LASIK Ks are only used as a measure of the corneal power. (SRK/T, Holladay 1 and Hoffer Q formulas ) Hoffer KJ. IOL Power (pp. 179-194).© 2011 SLACK Incorporated
  7. 7. GANESH NETRALAYA “Caring Vision - Our Mission” Online Barrett true k formula • Available for free on the websites www.apacrs.org and www.ascrs.org
  8. 8. GANESH NETRALAYA “Caring Vision - Our Mission” PRE LASIK DATA INDEPENDENT 1. Shammas Post LASIK Formula: • Post-LASIK K-readings Post myopic LASIK Kc = (1.14 X Kpost) - 6.8 Post Hyperopic LASIK Kc = (1:0457 X Kpost) −1:9538 • corrected K-value is used in the Shammas post-LASIK (Shammas-PL) formula Savini and Hoffer Eye and Vision (2018) 5:18
  9. 9. GANESH NETRALAYA “Caring Vision - Our Mission” 2. Haigis-L formula Available in IOL master As it predict the ELP from the AC depth r corr = 331.5 / ( -5.1625 X r meas + 82.2603 – 0.35 ) • Then enter it into the regular Haigis formula. 3. Barrett online calculator Absolute prediction error (APE) within +/-0.5D : Historical data available - 60-70% No historical data available - 50-60% TARGETING MYOPIA • When regular keratometry is performed after myopic refractive surgery, selective choice of an IOL to target myopia when other data are not available Savini and Hoffer Eye and Vision (2018) 5:18
  10. 10. GANESH NETRALAYA “Caring Vision - Our Mission” IOL POWER CALCULATION IN POST RK • Changes in both anterior and posterior corneal curvatures • Keratometric refractive index error • Formula error • Radius error • Mechanical instability of the cornea following incisional surgery may temporarily reopen the keratorefractive incisions ,may result in stromal edema and hyperopic shift. • This instability may exacerbate central flattening and peripheral bulging Savini and Hoffer Eye and Vision (2018) 5:18
  11. 11. GANESH NETRALAYA “Caring Vision - Our Mission” IOL CALULATION METHOD • Clinical history method • Double-K formulas and Holladay 2 formulae to avoid an erroneous ELP prediction • Barrett online calculator
  12. 12. GANESH NETRALAYA “Caring Vision - Our Mission” HIGH CORNEAL ASTIGMATISM Regular astigmatism : • Ideal candidates for toric iol • Optical biometer • Barrett Online toric calculator Irregular astigmatism : Keratoconus, post surgical and other scarred irregular corneas • Optical biometers is preffered, as visual axis is off centered. • In keratoconus keratometers overestimate the k values and ELP prediction error toward hyperopia CRST EUROPE Editorial Spotlight | Mar 2017
  13. 13. GANESH NETRALAYA “Caring Vision - Our Mission” Methods of corneal power estimation : Contact lens over refraction: Plano hard contact lens of known base curve K = BC + D+ (OR - MR) Topography method : Orbscan – Total optical power /total axial power of central 3mm Pentacam –EKR / TCRP @ 4.5mm zone These k values are used in 3rd / 4th generation formulae Barret online toric calculator : • Mild to moderate keratoconus if central 3 mm zone shows regular astigmatism Toric iols can be considered • Toric IOLs will be debulking the astigmatism but not canceling it 100% • Multifocal lenses are not recommended due to the high amount of higher order aberrations
  14. 14. GANESH NETRALAYA “Caring Vision - Our Mission” POST KERATOPLASTY IOL implantation can be as a part of - TRIPLE PROCEDURE or in - PRIOR GRAFTED eyes • In triple procedure better keep aphakic , 4-8 months later can plan secondary iol provided all sutures removed • Biometry from fellow eye • Central corneal power values input from topography • Optical biometer preferred • 3rd and 4th generation formulae suggested • Toric IOLs can also preferred to correct high astigmatism provided stable refraction after complete suture removal • Piggybacking toric sulcus fixated lenses can also be considered Indian J Ophthalmol. 2010 Mar-Apr; 58(2):115-8
  15. 15. GANESH NETRALAYA “Caring Vision - Our Mission” IOL POWER CALCULATION IN PAEDIATRIC PATIENTS Factors affecting : • Low ocular rigidity , prone for corneal compression easily • Shorter axial length, steeper cornea with higher keratometry values and smaller ACD DOS Times - Vol. 19, No. 8 February, 2014 Parametrs Birth Adult Axial length 16.8mm 23.6mm Natural lens power 34.4D 18.8D Mean keratometry 51.2D 43.5D
  16. 16. GANESH NETRALAYA “Caring Vision - Our Mission” IOL CALCULATION METHOD : • Very young age -Biometry done under sedation - A scan – immersion technique, - Hand held keratometry - No eye speculum IOL Formula: • It is preferable to use the theoretical formulas (e.g., SRK-T, Holladay I and Hollday II, Hoffer I and II, Hoffer Q and Haigis) because they are generally more accurate for small eyes Kerala Journal of Ophthalmology, Rupal H. Trivedi et al sept 2006. Vol. XVIII, No. 3
  17. 17. GANESH NETRALAYA “Caring Vision - Our Mission” IOL POWER SELECTION : • IOL power should balance between addressing amblyopia and minimal refractive error in adulthood • Minimum age of IOL implantation is 1–2 years. • 6 months -1 year can also plan iol implantation • Less than 6 months of age is still controversial • Immediate near emmetropia and later refractive correction in adult age • <2yrs- 20% undercorrection • 2-8 yr – 10% undercorrection • 8yrs and above Full correction Saudi Journal of Ophthalmology (2012) 26, 271–275
  18. 18. GANESH NETRALAYA “Caring Vision - Our Mission” Validation of guidelines for undercorrection of IOL power in children Age Post operative refractive goal 1 year + 6D 2 year + 5D 3 year + 4D 4 year + 3D 5 year + 2D 6 year + 1D 7 year Plano 8 year -1 to -2 D American Journal of Ophthalmology , Volume 174 – Feb 1, 2017
  19. 19. GANESH NETRALAYA “Caring Vision - Our Mission” SILICON OIL FILLED EYE • Low sound velocity and difficulty in identifying Retinal spike • Error in AL measurement occurs as ultrasound travels longer time to reach the probe which is interpreted as longer measurement – post op hyperopia IOL calculation method • Optical biometer with silicone oil mode is preferred • Ultra sonic measurement : Measure axial length in sitting position • Usually, IOL required is 2 – 3 D stronger than indicated by standard power calculation.
  20. 20. GANESH NETRALAYA “Caring Vision - Our Mission” Formula: • True Vitreous Length= 980/1532 X Apparent Vitreous Length Corrected axial length = True vitreous length + ACD + Lens thickness • Corrected AL = Correction factor (0.71) x Measured AL • When silicone oil removal is performed 2-5 D of induced myopia should be expected • Silicone IOLs should be avoided • Plano convex configuration of the implanted IOL with the plano surface facing posteriorly IC-29: Phacoemulsification (PE) in Eyes with Co-existing Vitreoretinal Pathologies ESCRS 2011
  21. 21. GANESH NETRALAYA “Caring Vision - Our Mission” APHAKIA • Two lens spike – replaced by a single spike from anterior vitreous face and posterior lens capsule • Uniform sound velocity of 1532m/s, slower speed than phakic eye. • Optical biometers with aphakic mode • Immersion technique is also preferred • In ACIOL or Scleral fixated IOL, the appropriate A constant is used
  22. 22. GANESH NETRALAYA “Caring Vision - Our Mission” POWER AT CAPSULAR BAG BAG/SULCUS POWER DIFFERENCE +30.0 D -1.45 D +22.0 D -1.0 D +12.0 D -0.50 D +5.0 D -0.20 D Am J Ophthalmol.2003;136:426–32.
  23. 23. GANESH NETRALAYA “Caring Vision - Our Mission” PSEUDOPHAKIA • Important for IOL exchange or for comparison with other eye • Optical Biometry is preferred • Immersion A-scan with correction of AL by correction factor (CF) according to lens type and thickness. • True axial length (TAL) = Apperent axial length (AAL) 1532 + ( Correction factor (CF) x Lens thickness( T)) Am J Ophthalmol 1993; 115(4): 536 - 537
  24. 24. GANESH NETRALAYA “Caring Vision - Our Mission” POSTERIOR STAPHYLOMA • Significant error in AL because the anatomic axial length (the distance from the corneal vertex to the posterior pole) may differ from the refractive axial length (the distance from the corneal vertex to the fovea) • B-scan can be used to demonstrate the shape of posterior ocular wall and the relationship of macula to the staphyloma • Probes with fixation light are preferable • Optical biometer Preferred • Barret universal ll formula used • Optimised axial length/ or optimised iol Constants minimises error J Cataract Refract Surg 2011; 37:2018–2027 Q 2011 ASCRS and ESCRS
  25. 25. GANESH NETRALAYA “Caring Vision - Our Mission” PIGGYBACK LENSES Primary piggyback • Haigis or Hoffer Q • IOLs of two different materials, or two silicone IOLs, may be preferable in order to prevent interlenticular opacification • Usually single piece in the bag and 3 piece in the sulcus • Divide the power between the IOL and reduce 1 D for sulcus placed IOL Secondary piggyback IOL for pseudophakia • Patients with refractive error following the primary IOL implantation. • Calculated based on refractive error. • Holladay IOL Consultant (R Formula) • No knowledge of primary implant or the AL is required.
  26. 26. GANESH NETRALAYA “Caring Vision - Our Mission” MICROPHTHALMOS / NANOPHTHALMOS (a) Simple microphthalmos: Short axial length (>2 SD smaller than age- based normative) and no other ocular malformations (b) Relative anterior microphthalmos: Normal axial length with disproportionately small anterior segment (c) Nanophthalmos: Short axial length (<20.5 mm), Optical biometry / Immersion biometry preferred over ultrasound biometry Hoffer-Q / Holladay 2 are preferred Piggyback IOLs may be better than large powered single IOL , cause less spherical aberration Sci J Med & Vis Res Foun February 2017 | volume XXXV |
  27. 27. GANESH NETRALAYA “Caring Vision - Our Mission” THANK YOU

×