Apparatus and method for determining angular orientation of eye

A method of determining the angular orientation of an eye of a subject fixating on a target, such method comprising the steps of:

• A. illuminating an eye of the subject with a collimated beam of a light source constrained for rotational motion about an axis coincident with a selected central axis of the eye;
• B. viewing first and fourth Purkinje images of the light in the eye of the subject;
• C. rotating the light source about the central axis while illuminating and viewing until the first and fourth Purkinje images determine a line parallel to the central axis, whereby the optical axis of the eye is determined to lie in a plane defined by the central axis and the light source;
• then
• D. covering the eye with a cover blocking the visual field of the eye but not blocking the illuminating and viewing of the eye;
• E. rotating the light source about the central axis while illuminating and viewing until the first and fourth Purkinje images determine a line parallel to the central axis;
• and
• F. taking as the measure of latent squint angle the difference between the angular orientation of the light source about the central axis after C and the angular orientation after step E.

A clinical apparatus for determining the angular orientation of a subject's eye, such apparatus having a stand with a headrest for supporting the head of a subject in a defined position, and further comprising

• light means for directing light at the subject's eye,
• pivotal frame means supporting said light means for pivoting about a horizontal or a vertical test axis,
• alignment means for aligning said pivotal frame means with respect to the stand so that the test axis coincides with a central axis of the eye of the subject,
• angle display means for indicating the angular position of said pivotal frame means as it pivots,
• said light means being supported by said frame means so as to direct light to the subject's eye at an illumination angle offset from the eye's optic axis so that the first and fourth Purkinje images of said light reflected from said eye are distinctly separate when viewed from a direction offset from the optic axis by said illumination angle on a side thereof opposite to the light means, and
• observation means on said frame means for observing the first and fourth Purkinje images from said direction offset by said illumination angle,
• whereby the angle display means displays the angular orientation of the optical axis of the subject's eye upon the pivoting of said pivotal frame means to locate the observed Purkinje images along said test axis.

A clinical apparatus for determining the angular orientation of a subject's eye, of the type for use with a stand and a headrest for supporting the head of a subject in a defined position, and further comprising

• light means for directing light at the subject's eye,
• pivotal frame means supporting said light means for pivoting about at least one of a horizontal or a vertical test axis,
• alignment means for aligning said pivotal frame means with respect to the stand so that the test axis coincides with a central axis of the eye of the subject,
• angle display means for indicating the angular position of said pivotal frame means as it pivots,
• said light means being supported by said frame means so as to direct light to the subject's eye at an illumination angle offset from the eye's optic axis so that the first and fourth Purkinje images of said light reflected from said eye are distinctly separate and form a visually determinable line when viewed from a direction offset from the optic axis by said illumination angle on a side thereof opposite to the light means,
• whereby by observing the first and fourth Purkinje images from said direction offset by said illumination angle, and pivoting said pivotal frame means to locate the observed Purkinje images along said test axis, the angle display means displays the angular orientation of the optical axis of the subject's eye.