Is a modified version of the Gaussian Optics Formula (GOF) which allows to estimate Corneal power from corneal curvature measurements after laser refractive surgery. JCRS, December 2006 www.besstformula.com
Original formula derived from regression analysis on: • 170 eyes post laser refractive surgery • Wave Front LASIK-LASEK Myopia (123); Hyperopia (47) [Range: -10.00 to +4.50 D] BESSt formula in simple words: • Calculation of corneal power (CP) through adjusted GOF Software Development: • BESSt II IOL Power Calculator
Parameters needed (post-laser): • Oculus Pentacam: – Ant r – Post r Antr Post r – Corneal thickness • IOLMaster / other device: – Axial length No need of any pre-refractive surgery information.
Indications: • Laser refractive surgery for Myopia/Hyperopia • Unknown pre-refractive surgery information Contraindications: • Non-laser refractive surgery Caution (compare with other techniques): • Old laser ablations with small Optical Zones • Not tested: Myopia >-11.63 D; Hyperopia >+7.75 D
Improved Algorithm
* Area affected by the NEGATIVE SQUARE ROOT PHENOMENON ! = Inaccurate IOL power calculation using SRK/T formula *
Exporting data from Pentacam to BESSt:
Exporting data from Pentacam to BESSt:
(N=58) 58 eyes having Phaco after Laser Ref. Sx: • Myopia (N=34) • Hyperopia (N=24) SEQ (D) [- 11.63 to +7.75] Mean: -2.04 ±4.94 SD AL (mm) [ 19.71 to 30.36] Mean: 24.81±2.28 SD Ks (D) [ 35.38 to 50.91] Mean: 41.97±3.66 SD Ant r (mm) [ 6.45 to 9.66] Mean: 8.19±0.75 SD Post r (mm) [ 5.76 to 8.08] Mean: 6.52±0.37 SD A/P r ratio [ 1.00 to 1.48] Mean: 1.26±0.11 SD
±1.00 ±1.00 ±1.14 ±0.81 ±0.78 ±1.02 * * ±0.90 Error % From Target ±0.95 ±1.12 ≤ 0.50 D 38% ±0.89 * ≤ 0.75 D 59% ≤ 1.00 D 77% >1.50 D 11%
Mean error: 0.00 ±0.89 D Mean Abs Error: 0.71 ±0.52 D
±0.69 ±0.66 ±0.73 ±0.69 ±0.61 ±0.45 ±0.45 ±0.73 ±0.63 ±0.52
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