Fundus photographic technique to determine eye refraction for optic disc size calculations

A method of determining the true dimensions of an optic nerve head and nerve tissue of a patient's eye, the method comprising the steps of:

• positioning a patient's eye before a fundus imaging apparatus;
• adjusting a focus mechanism of said imaging apparatus to bring a retina of said eye into focus;
• recording a setting parameter value of said focus mechanism as adjusted in the previous step;
• acquiring an image using said fundus imaging apparatus;
• determining a glass refraction of said patient's eye using said setting parameter value and a calibration function established for said focus mechanism;
• determining a scale of said image using said glass refraction of said patient's eye;
• and
• measuring true dimensions of an optic nerve head and nerve tissue of said eye using said image and said scale.

A fundus camera comprising:

• a focus mechanism for focusing a fundus camera to image a retina;
• measuring means associated with said focus mechanism for measuring a position setting parameter of said focus mechanism and providing a position setting parameter signal;
• and
• means for automatically determining the glass refraction of patient's eye of said image using said signal and a calibration function for said focus mechanism.

A method of calculating the glass refraction of a patient's eye, the method comprising the steps of:

• positioning a patient's eye before a fundus imaging apparatus;
• recording the separation distance between said patient's eye and said imaging apparatus;
• adjusting a focus mechanism of said imaging apparatus to bring an image of a retina of said eye into focus;
• recording a position setting parameter value of said focus mechanism as adjusted in the previous step;
• and
• calculating the glass refraction of said patient's eye using said separation distance and said position setting parameter value;
• displaying said image.