JCRS, December 2006 www.besstformula.com Original formula derived - - PowerPoint PPT Presentation

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 – Corneal thickness

• IOLMaster / other device:

– Axial length No need of any pre-refractive surgery information.

Antr Post r

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)

• Myopia (N=34)
• Hyperopia (N=24)

58 eyes having Phaco after Laser Ref. Sx:

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

±0.81 ±0.78 ±1.02 ±1.14 * ±1.00 ±0.90 ±1.00 * ±0.89 ±0.95 ±1.12 *

Error From Target % ≤0.50 D 38% ≤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

±0.45 ±0.45 ±0.69 ±0.66 ±0.61 ±0.69 ±0.73 ±0.52 ±0.63 ±0.73