Instrument for measuring near point of convergence and/or near point of accommodation

An instrument for measuring near point of convergence (NPC) and/or near point of accommodation (NPA), the instrument comprising:

• an instrument housing having a front face and a rear face disposed opposite to the front face;
• at least one visual target disposed on or in the front face of the instrument housing, the at least one visual target viewable by a subject that is facing the front face of the instrument housing;
• a distance measuring device disposed on or in the front face of the instrument housing, the distance measuring device configured to emit one or more output signals that are representative of a distance between a surface of the instrument and a body surface of the subject spaced apart from the surface of the instrument;
• at least one input device, the at least one input device configured to receive an input from a user and to output one or more input signals in response to the input from the user;
• a processing device disposed within the instrument housing, the processing device operatively coupled to the distance measuring device and the at least one user input device, the processing device configured to receive the one or more output signals that are output by the distance measuring device and to calculate the distance between the surface of the instrument and the body surface of the subject spaced apart from the surface of the instrument using the one or more output signals, the processing device further configured to receive the one or more input signals that are output by the at least one input device and to record the calculated distance in a memory of the processing device;
• and
• a visual display device disposed on or in the rear face of the instrument housing, the visual display device operatively coupled to the processing device, and the visual display device configured to display the distance calculated by the processing device to a user of the instrument that is facing the rear face of the instrument housing.

A method for measuring near point of convergence (NPC) and/or near point of accommodation (NPA) of a subject, the method comprising the steps of:

• providing an instrument that includes:
• an instrument housing having a front face and a rear face disposed opposite to the front face;
• at least one visual target disposed on or in the front face of the instrument housing, the at least one visual target viewable by a subject that is facing the front face of the instrument housing;
• a distance measuring device disposed on or in the front face of the instrument housing, the distance measuring device configured to emit one or more output signals that are representative of a distance between a surface of the instrument and a front of a head of a subject spaced apart from the surface of the instrument;
• and
• a processing device disposed within the instrument housing, the processing device operatively coupled to the distance measuring device, the processing device configured to receive the one or more output signals that are output by the distance measuring device and to calculate the distance between the surface of the instrument and the front of the head of the subject spaced apart from the surface of the instrument using the one or more output signals;
• positioning the instrument at an initial distance from the front of the head of the subject;
• displaying, by using the instrument, the at least one visual target to the subject so that the subject is able maintain his or her gaze on the at least one visual target;
• gradually advancing the instrument housing towards the front of the head of the subject while the distance between the surface of the instrument and the front of the head of the subject is calculated by the processing device of the instrument;
• stopping the advancement of the instrument housing towards the front of the head of the subject when a point is reached at which the subject either sees a double image of the visual target or the subject sees a blurry image of the visual target precluding an accurate identification of the visual target;
• and
• determining and recording, by using the instrument, either a diplopia distance which corresponds to the point at which the subject sees the double image of the visual target or an accommodation threshold distance at which the subject sees the blurry image of the visual target precluding the accurate identification of the visual target.