Photorefraction ocular screening device and methods

1. A computer-implemented method of determining refractive error, said method comprising the steps of:

receiving a first image and a second image corresponding to an axis-conjugate meridian;

removing corneal glints present in pupil regions of said first image and said second image;

applying a low-pass filter to each of said pupil regions;

rotating said first image and said second image, after applying said low-pass filter to said pupil regions in each of said images, to align a stimulus angle in said axis-conjugate meridian associated with said first image and a stimulus angle in said axis-conjugate meridian associated with said second image with a horizontal meridian;

extracting a pixel strip of data from each of said pupil regions centered on a pupil center in said first image and in said second image;

computing a ratio of pixel intensity values using said pixel strips of data extracted from said first image and from said second image;

generating a refractive error correlate measure based on said ratio of pixel intensity values; and

converting said refractive error correlate measure to identify said refractive error.

2. The method of claim 1 , wherein said axis-conjugate meridian is one of three primary axis-conjugate meridians or one of two supplemental axis-conjugate meridians.

3. The method of claim 2 , wherein said three primary axis-conjugate meridians are located at a 0° meridian, a 60° meridian and a 120° meridian.

4. The method of claim 3 , wherein said 0° meridian includes an axis angle at 0° and a corresponding conjugate angle at 180°, wherein said 60° meridian includes an axis angle at 60° and a corresponding conjugate angle at 240°, and wherein said 120° meridian includes an axis angle at 120° and a corresponding conjugate angle at 300°.

5. The method of claim 4 , wherein said axis angle at 0°, said axis angle at 60°, and said axis angle at 120° each has three decentration positions along its axis angle, and

wherein said corresponding conjugate angle at 180°, said corresponding conjugate angle at 240°, and said corresponding conjugate angle at 300° each has three decentration positions along its conjugate angle.

6. The method of claim 4 , wherein said axis angle at 0°, said axis angle at 60°, or said axis angle at 120° is said stimulus angle associated with said first image.

7. The method of claim 4 , wherein said corresponding conjugate angle at 180°, said corresponding conjugate angle at 240°, or said corresponding conjugate angle at 300° is said stimulus angle associated with said second image.

8. The method of claim 2 , wherein said two supplemental axis-conjugate meridians are located at a 36.59° meridian and a 143.41° meridian.

9. The method of claim 8 , wherein said 36.59° meridian includes an axis angle at 36.59° and a corresponding conjugate angle at 216.59°, and wherein said 143.41° meridian includes an axis angle at 143.41° and a corresponding conjugate angle at 323.41°.

10. The method of claim 9 , wherein said axis angle at 36.59° or said axis angle at 143.41° is said stimulus angle associated with said first image.

11. The method of claim 9 , wherein said corresponding conjugate angle at 216.59° or said corresponding conjugate angle at 323.41° is said stimulus angle associated with said second image.

12. A system employing computer processing logic for determining refractive error, comprising:

a processor component coupled to at least one memory component, said processor component configured to:

receive a first image and a second image corresponding to an axis-conjugate meridian;

remove corneal glints present in pupil regions of said first image and said second image;

apply a low-pass filter to each of said pupil regions;

rotate said first image and said second image, after applying said low-pass filter to said pupil regions in each of said images, to align a stimulus angle in said axis-conjugate meridian associated with said first image and a stimulus angle in said axis-conjugate meridian associated with said second image with a horizontal meridian;

extract a pixel strip of data from each of said pupil regions centered on a pupil center in said first image and in said second image;

compute a ratio of pixel intensity values using said pixel strips of data extracted from said first image and from said second image;

generate a refractive error correlate measure based on said ratio of pixel intensity values; and

convert said refractive error correlate measure to identify said refractive error.

13. A non-transitory computer-readable storage medium programmed to include instructions that, when executed by a processor, cause the processor to perform a method for determining refractive error, said method comprising the steps of:

receiving a first image and a second image corresponding to an axis-conjugate meridian;

removing corneal glints present in pupil regions of said first image and said second image;

applying a low-pass filter to each of said pupil regions;

rotating said first image and said second image, after applying said low-pass filter to said pupil regions in each of said images, to align a stimulus angle in said axis-conjugate meridian associated with said first image and a stimulus angle in said axis-conjugate meridian associated with said second image with a horizontal meridian;

extracting a pixel strip of data from each of said pupil regions centered on a pupil center in said first image and in said second image;

computing a ratio of pixel intensity values using said pixel strips of data extracted from said first image and from said second image;

generating a refractive error correlate measure based on said ratio of pixel intensity values; and

converting said refractive error correlate measure to identify said refractive error.