Method for evaluating an individual's astigmatism

A method for evaluating an astigmatism value of an individual's eye implemented subsequently to evaluating visual acuity of the individual's eye and to determining a sphere value for the individual's eye, the sphere value determined being non-zero, the method being performed from a previous optical correction of the individual comprising a prescribed cylinder value and a prescribed axis value for the individual's eye, the method comprising:

• placing at least one optotype at a fixed distance from the individual's eyes;
• placing, between the individual's eye and the optotype, an initial lens having a value equal to the sphere value determined;
• if if the prescribed cylinder value is zero:
• if if the visual acuity evaluated is greater than or equal to a first predefined visual acuity threshold:
• placing, between the individual's eye and the initial lens, a first cylinder having a minimum value along a first axis having a minimum value;
• receiving information relating to an improvement in vision for the individual resulting from placing the first cylinder compared with an absence of the first cylinder:
• if the information received does not reflect an improvement with the first cylinder, assigning an astigmatism value comprising a zero cylinder value to the individual's eye;
• if the information received reflects an improvement with the first cylinder, removing the first cylinder and determining a cylinder value via a twirling cross-cylinder test starting from the value of the first cylinder and the value of the first axis:
• if the cylinder value determined is greater than the value of the first cylinder. determining an axis value via a twirling cross-cylinder test starting from the cylinder value determined and the value of the first axis and assigning an astigmatism value comprising the cylinder value determined and the axis value determined to the individual's eye;
• otherwise, assigning an astigmatism value comprising the cylinder value determined and the first axis value determined to the individual's eye;
• if the visual acuity evaluated is less than a first predefined visual acuity threshold:
• placing, between the individual's eye and the initial lens, a second cylinder along a second axis, then along a third axis, then along a fourth axis, then along a fifth axis, the value of the second cylinder depending on the visual acuity evaluated;
• receiving information relating to an improvement in vision for the individual resulting from placing the second cylinder for one of the axes from among the second axis, the third axis, the fourth axis and the fifth axis;
• if the information reflects an improvement in vision for one of the axes, referred to as the preferred axis, from among the second axis, the third axis, the fourth axis and the fifth axis, removing the second cylinder, determining an axis value via a twirling cross-cylinder test starting from the value of the second cylinder and the value of the preferred axis, determining a cylinder value via a twirling cross-cylinder test starting from the second cylinder value and the axis value determined, and assigning an astigmatism value comprising the cylinder value determined and the axis value determined to the individual's eye;
• otherwise, assigning an astigmatism value comprising a zero cylinder value to the individual's eye;
• if the prescribed cylinder value is non-zero:
• placing, between the individual's eye and the optotype, an initial cylinder with a value equal to the prescribed cylinder value according to the prescribed axis value;
• if the prescribed axis value is between a first axis value and a second axis value or between a third axis value and a fourth axis value, or if the prescribed cylinder value is less than a first cylinder value and the prescribed axis value is between a fifth axis value and a sixth axis value, and the visual acuity evaluated is greater than or equal to a second predefined visual acuity threshold, determining a cylinder value via a twirling cross-cylinder test starting from the prescribed cylinder value and the prescribed axis value, and assigning an astigmatism value comprising the cylinder value determined and the prescribed axis value;
• if the prescribed cylinder value is between a second cylinder value and a third cylinder value and the prescribed axis value is between a seventh axis value and an eighth axis value:
• placing, between the individual's eye and the initial lens, a first lens with a value equal to the spherical equivalent of the prescribed cylinder value;
• removing the first lens and placing, between the individual's eye and the initial lens, a third cylinder with a value equal to the prescribed cylinder value according to the prescribed axis value;
• receiving information relating to an improvement in vision for the individual resulting from placing the third cylinder relative to the first lens:
• if the information does not reflect an improvement in vision for the individual with the third cylinder relative to the first lens, assigning an astigmatism value comprising a zero cylinder value to the individual's eye;
• otherwise, removing the third cylinder, determining an axis value via a twirling cross-cylinder test starting from the third cylinder value and the prescribed axis value, determining a cylinder value via a twirling cross-cylinder test starting from the third cylinder value and the axis value determined, and assigning an astigmatism value comprising the cylinder value determined and the axis value determined to the individual's eye;
• otherwise, determining an axis value via a twirling cross-cylinder test starting from the prescribed cylinder value and the prescribed axis value, determining a cylinder value via a twirling cross-cylinder test starting from the prescribed cylinder value and the axis value determined, and assigning an astigmatism value comprising the cylinder value determined and the axis value determined to the individual's eye.