Method and apparatus for determining visual acuity in a human subject

Claim 3

A method according to claim 1, in which the step of changing a visually sensible parameter of the pattern of each presentation comprises the step of changing the position of the pattern in the image.

Claim 4

A method according to claim 1, in which the step of changing a visually sensible parameter of the pattern for each presentation comprises the step of changing the spatial frequency of the said variations.

Claim 5

A method according to claim 1, in which the said regular variations are variations between two different luminance levels.

Claim 6

A method according to claim 1, in which the said regular variations are variations between two different chromatic levels.

Claim 7

A method according to claim 1, in which the said regular variations are sine wave variations.

Claim 8

A method according to claim 1, in which the said regular variations are abrupt changes between the two said levels.

Claim 9

A method according to claim 7, in which each pattern is a chequer pattern having a predetermined chequer size.

Claim 10

A method according to claim 1, in which each pattern occupies at least part of a predetermined arc of a circle.

Claim 11

A method according to claim 1, in which the step of presenting a fixation mark to the subject comprises the step of presenting a fixation spot in the center of each image.

Claim 12

Apparatus for testing visual acuity in human subjects, comprising fixation means for presenting a continuous fixation mark to the subject for his visual field, presentation means for successively presenting, for respective brief and constant periods of time, respective visual images each including a pattern of regular variations between two visually contrasting levels which extends over a predetermined part only of the image, the said pattern being in a selected and randomised position relative to the fixation mark, and adjusting means for changing a visually sensible parameter of the pattern for each presentation while maintaining the mean luminance of each said pattern to be substantially identical with that of the remainder of the said image.

Claim 13

Apparatus for testing visual acuity in human subjects, comprising fixation means for presenting a continuous fixation mark to the subject for his visual field, presentation means for successively presenting, for respective brief and constant periods of time, respective visual images each including a pattern of regular variations between two visually contrasting levels which extends over a predetermined part only of the image, the said pattern being in a selected and randomised position relative to the fixation mark, and adjusting means for changing a visually sensible parameter of the pattern for each presentation while maintaining the mean luminance of each said pattern to be substantially identical with that of the remainder of the said image.

Claim 14

Apparatus according to claim 11, in which the presentation means comprises film means made up of a plurality of film sections respectively bearing said visual images each including a said pattern comprising distinctive edges extending over said predetermined part only of the image and arranged whereby for each image of the two visually sensible parameters consisting of the length of the said edges per unit area of the pattern and the poSition of the pattern relative to the image as a whole is different from the corresponding parameter for the other images, and means defining a predetermined light path capable of being illuminated for presenting for the brief and constant period of time an image corresponding to the image on the one of the film sections positioned in the light path, and the said adjusting means comprises means for positioning a different one of the film sections in the light path.

Claim 15

Apparatus according to claim 12, in which the film means comprises a film strip with each film section arranged on a different film frame, and the presentation means includes film transport means for supporting the film strip, and drive means for incrementally moving the film strip, frame by frame, past a datum area aligned with the light path.

Claim 16

Apparatus according to claim 13, in which the drive means includes a base, a rotatable drive member mounted on the base for engaging and driving the film strip, an electrical driving motor mounted on the base for rotating the rotatable drive member, switch means for controlling the energisation of the motor, a peripheral surface rotatable with the drive member and having a peripheral recess therein, a locking member resiliently biased into contact with the peripheral recess to lock the drive member against rotation, when the drive member is appropriately angularly spaced, and means for momentarily withdrawing the locking member against its resilient bias into a position in which it closes the said switch means to complete the energisation circuit for the motor, the consequent angular movement of the rotatable drive member preventing return of the withdrawn locking member and holding the switch means closed until the said surface has completed one revolution whereupon the locking member is biased back into the said recess and opens the switch means.

Claim 17

Apparatus according to claim 12, in which the film means comprises a plurality of film slides each forming one of the film sections.

Claim 18

Apparatus according to claim 11, in which the presentation means includes means bearing at least one visual image including a pattern of regular variations between two visually constrasting levels which extends over a predetermined part only of the image, defining a predetermined light path capable of being illuminated for presenting for the brief and constant period of time an image corresponding to the said one visual image, and the said adjusting means comprises optical means in the said light path and optically adjustable for changing the said visually sensible parameter.

Claim 19

Apparatus according to claim 16, in which the optical means includes a dove prism angularly movable for rotating the presented image into different angular positions.

Claim 20

Apparatus according to claim 16, in which the optical means includes means for altering the degree of magnification given to the present image.

Claim 21

Apparatus according to claim 11, in which the presentation means includes means for supporting an optical mask of predetermined pattern in the light path, whereby the presented image is dependent on the pattern of the mask.

Claim 22

Apparatus according to claim 11, in which each said pattern is a pattern of substantially sinusoidal variations between the two said levels.

Claim 23

Apparatus according to claim 11, in which each said pattern is a chequer pattern of predetermined chequer size.

Claim 24

Apparatus according to claim 11, in which each pattern occupies at least part of an arc of a circle.

Claim 25

Apparatus according to claim 11, in which the said two levels are levels of different luminance.

Claim 26

Apparatus according to claim 11, in which the said two levels are different chromatic levels.

Claim 27

Apparatus for testing visual acuity in human subjects, comprising means for continuously presenting a fixation mark for the subject for his visual field, film means made up of a plurality of film Sections each bearing a different visual image, each image being generally circular in shape and including a pattern of visually sensible edges between two contrasting levels which occupies part only of the circle, said patterns in some of the film sections occupying different parts of the circle as compared with the patterns in the others, and some of the film sections having a greater spatial frequency of edges than the others, but the mean visual intensity of each said pattern being substantially identical with that of the remainder of its said image, and means for successively presenting the visual images of the film sections in the subject''s visual field with a predetermined and randomised orientation relative to the fixation mark.

Claim 28

Apparatus for testing visual acuity in human subjects, comprising means for continuously presenting a fixation mark for the subject for his visual field, film means made up of a plurality of film Sections each bearing a different visual image, each image being generally circular in shape and including a pattern of visually sensible edges between two contrasting levels which occupies part only of the circle, said patterns in some of the film sections occupying different parts of the circle as compared with the patterns in the others, and some of the film sections having a greater spatial frequency of edges than the others, but the mean visual intensity of each said pattern being substantially identical with that of the remainder of its said image, and means for successively presenting the visual images of the film sections in the subject''s visual field with a predetermined and randomised orientation relative to the fixation mark.

Claim 29

Apparatus according to claim 25, in which the film means comprises a plurality of film slides each forming one of the film sections.

Claim 30

Apparatus according to claim 25, in which the film means comprises film strip having a series of frames each of which forms a respective one of the film sections.

Claim 33

Apparatus for testing visual acuity in human subjects comprising means for presenting a fixation mark to the subject for his visual field, and presentation means for successively presenting to the subject in his visual field, for respective brief and constants periods of time, respective visual images for detection of their spatial pattern by the subject, each image including a pattern of abrupt variations between two different colors of equal luminance, a visually sensible parameter of each pattern being different in a randomised manner from that for the other patterns.

Claim 34

Apparatus for testing visual acuity in human subjects comprising means for presenting a fixation mark to the subject for his visual field, and presentation means for successively presenting to the subject in his visual field, for respective brief and constants periods of time, respective visual images for detection of their spatial pattern by the subject, each image including a pattern of abrupt variations between two different colors of equal luminance, a visually sensible parameter of each pattern being different in a randomised manner from that for the other patterns.