"safetyVA" function. Difference between postoperative and preoperative corrected distance visual acuity

This is the most commonly used measure of safety because it answers the question, “If the refractive outcome is not totally acceptable, can the patient put glasses on again and see as well as they did before surgery?” A change of 1 Snellen line is within the range of normal biological variability for repeated measures, and therefore is not a meaningful change. A change of 2 or more Snellen lines has been generally adopted as the standard for safety.(1)

This function calculates the standardized Graph C detailed in the Journal of Refractive Surgery(2) from a two column matrix. First column should contain the preoperative visual acuity with correction (CDVA) and the second column the postoperative CDVA. The plot is only applicable to laser refractive surgery procedures.

Example:

  • [SI,CV]=safetyVA(VA,1,'en'). Computes the figure for 1 month after laser refractive surgery.

Two additional values are returned from the function, the Safety Index (SI) known as the ratio between postoperative and preoperative CDVA(3) and the percentage of eyes with CDVA worse than 20/40 for the subgroup of eyes with CDVA of 20/20 or better preoperatively.(4)

Below you have the help of the function. For more information about "refractiveAnalysis" Toolbox please Contact the author.

%   Computes the Safety in terms of loss of CDVA after laser refractive
%   surgery.
%
%   DESCRIPTION
%
%   Computes de Figure C from the standard of the JRS (Ref.1)
%
%   PARAMETERS
%
%   VA   Two columns matrix
%        In Laser Refractive Surgery [PreCDVA PostCDVA]
%
%   month       Number of months after surgery
%      
%   language    Language for the labels 'es' for Spanish or 'en' for English
%   
%   OUTCOMES
%
%   SI          Safety Index. Mean ratio from PostCDVA/PreCDVA.(Ref.2)
% 
%   CV          Critical Value. % of eyes with CDVA>=20/20 pre and <=20/40
%               post.(Ref.3)
%
%   EXAMPLE
%
%   [SI,CV]=safetyVA(VA,month,language)
%
%   VERSION
%   
%   1.0.0
%
%   demo data "safety.mat"
%
%   REFERENCES
%
%   1.- Reinstein DZ, Archer TJ, Randleman JB. JRS Standard for Reporting 
%   Astigmatism Outcomes of Refractive Surgery. J Refract Surg. 2014; 30: 654–9. 
%   2.- Koch DD, Kohnen T, Obstbaum SA, Rosen ES. Format for reporting 
%   refractive surgical data. J Cataract Refract Surg. 1998; 24: 285–7.  
%   3.- Eydelman MB, Drum B, Holladay J, et al. Standardized analyses of correction
%   of astigmatism by laser systems that reshape the cornea. J Refract Surg. 2006; 22: 81–95. 

REFERENCES

  1. Waring 3rd GO. Standard graphs for reporting refractive surgery. J Refract Surg. 2000; 16: 757–8.
  2. Reinstein DZ, Archer TJ, Randleman JB. JRS Standard for Reporting Astigmatism Outcomes of Refractive Surgery. J Refract Surg. 2014; 30: 654–9.
  3. Koch DD, Kohnen T, Obstbaum SA, Rosen ES. Format for reporting refractive surgical data. J Cataract Refract Surg. 1998; 24: 285–7.  
  4. Eydelman MB, Drum B, Holladay J, et al. Standardized analyses of correction of astigmatism by laser systems that reshape the cornea. J Refract Surg. 2006; 22: 81–95.