Unexpected postoperative refractive surpriseClinical points
• Re-check IOL choice, A-constant, formula used, and target refraction.
• Re-measure AL and keratometry optically to exclude a biometry error.
Measure distance from anterior cornea to anterior surface of the IOL with either A or B scan (be careful not to measure to the posterior implant surface): too shallow or too deep will lead to myopic or hyperopic surprises, respectively (usually due to excess anterior or posterior vaulting of implant, often due to crimping of haptics).
• In cases of myopic surprise, also consider retained visco elastic behind the implant, distended bag may be visible on examination or with B-scan.
• Beware manufacturing/pack errors with mislabelled implant power (implant thickness can be measured in situ on B-scan and compared to a correctly labelled implant of the same model).
• Discuss treatment options with the patient.
• If the refractive outcome is tolerated, leave the IOL in situ and/or offer spectacle or CL correction.
• If not tolerated and no obvious biometry error, consider, IOL exchange, piggyback IOL or corneal refractive surgery.
• If the refractive outcome is not tolerated and if there is obvious biometry error, offer IOL exchange based on refraction or offer corneal refractive surgery. If the fellow eye has cataract consider equalizing refraction with second eye surgery or electing for anisometropic mono vision.
Unexpected postoperative refractive surprise power point presentations:
IOL power calculation FORMULAE
1. IOL power calculation FORMULAE
2. Generations! • First – SRK 1 & Binkhorst formula • Second – SRK2 • Third – SRK T , Hoffer Q , Holladay • Fourth – Holladay 2 , Haigis
3. • Theoretical formulae – based on mathematical principles revolving around the schematic eye • Regression formulae – working backwards on post operative outcomes • 3rd and 4th generation – mix of both.
4. A closer look 1. SRK formula • P = IOL Power • K = avg central corneal power in Diopters • L = axial length in mm. P = A – 0.9K – 2.5L Range – 22mm – 24.5mm
5. 2. SRK 2 formula – An attempt to OPTIMIZATION A1 =(A–0.5) for axial lengths greater than 24.5 A1 =A for axial lengths between 22 and 24.5 A1 =(A+1) for axial lengths between 21 and 22 A1 =(A+2) for axial lengths between 20 and 21 A1 =(A+3) for axial lengths less than 20
6. Why Optimize??
7. • All formulae work well within the range of 22.5-26 mm AL • A constant computed based on Avg AL 23.5mm • Assumption Reason?? AL α ACD K α ACD Dr Holladay
8. • SRK/T formula — uses “A-constant” • Holladay 1 formula — uses “Surgeon Factor” • Holladay 2 formula — uses “Anterior Chamber Depth” • Hoffer Q formula — uses “Pseudophakic Anterior Chamber Depth”
9. • Hoffer-Q formula • Dr Kenneth Hoffer – 1993 • P = f (A,K,Rx,pACD) • A = AL • K = avg corneal ref power • Rx = previous refraction
10. • pACD = The personalized ACD (pACD) is set equal to the manufacturer’s ACD-constant, if the calculation was selected to be based on the ACD-constant. In case the A-constant was chosen, pACD is derived from the A-constant [HOFFER, 1998] according to [HOLLADAY et al, 1988] pACD = ACD-const = 0.58357 * A-const – 63.896 .
11. Haigis formula • Gernet, Ostholt, Werner -1970 (GOW70 formula) • D = a0 + a1 ACD+ a2 AL • a0 constant moves the power prediction curve up or down • a1 constant is tied to the measured anterior chamber depth • a2 constant is tied to the measured axial length
12. Holladay 2 • Currently – most sophisticated formula ACCURACY PREDICTABILITY
13. 2 reasons for success
14. • 7 PARAMETERS Axial length White to white AC depth Previous refraction Age of pt Lens thickness Central corneal power
15. Effective lens position • Human eye – a dual lens system In any dual lens system, if the primary lens and the distance of the screen are fixed, then the effective power of the system will depend on the power and position of the second lens
16. Factors affecting ELPo • Anatomical factors 1. K value 2. AL 3. Limbal white to white dist 4. Pre-op AC depth 5. Lens thickness • IOL related factors 1. Shape 2. Length 3. Flexibility 4. Anterior angulation (if any) 5. Material of haptic 6. Shape, design material of optic
17. • Surgeon’s technique 1. CCC 2. Inadequate visco removal 3. Capsular fibrosis Bag to Sulcus shift
Unexpected postoperative refractive surprise Videos:
Refractive surprises after cataract surgery
Unexpected postoperative refractive surprise