Reducing errors of tonometric measurements by using a tonometer tip with a curved cornea-contacting surface

A device for determining intraocular pressure (IOP) of an eye with a use of contact tonometry, the device comprising:

• a first tonometer tip having
• a first axis;
• a front surface having a central portion that is non-planar and has a non-zero curvature, and that is configured to applanate the cornea of the eye to form an applanated portion of the cornea when pressed against the cornea while reducing a first error as compared with a second error,
• wherein the cornea has a corneal axis;
• wherein the first error is an error contributed to a first value of a determined IOP of the eye by adhesion between the front surface and the cornea,
• wherein the second error is an error contributed to a second value of the IOP measured with the use of a second tonometer tip that has a planar cornea-contacting surface, and
• wherein the adhesion is caused by a film of fluid present between the front surface and the cornea;
• and
• a back surface that is substantially transverse to the first axis.

A device for determining an intraocular pressure (IOP) of an eye with a use of contact tonometry, the device comprising:

• a first tonometer tip having a first axis and a front surface, the front surface including:
• a central portion that is non-planar, that has a non-zero curvature, and that is configured to applanate the cornea of the eye to form an applanated portion of the cornea when pressed against the cornea while having a first error reduced as compared with a second error, the cornea having a corneal axis,
• wherein the first error is an error contributed to a first value of the IOP of the eye by adhesion between the front surface and the cornea, the first value being a value of the IOP tonometrically determined with a use of said first tonometer tip,
• wherein the second error is an error contributed to a second value of the IOP measured with the use of a second tonometer tip that has a planar cornea-contacting surface, and
• wherein the adhesion is caused by a film of fluid present between the front surface and the cornea;
• wherein the central portion has a first curvature with a first sign, the cornea has a curvature of the cornea with a second sign, and the first sign is equal to the second sign.

A method for measurement of intraocular pressure (IOP) with a contact tonometer, the method comprising:

• applying a first force to the cornea of an eye by bringing an axial portion of a cornea-contacting curvilinear surface of a first tonometer tip in contact with the cornea
• i) to define a first surface of contact between the cornea-contacting curvilinear surface and the cornea, and
• ii) to cause first intra-corneal stress at a location of the cornea as a result of applanation of the cornea at the first surface,
• wherein the first tonometer tip has a first axis and the cornea has a corneal axis,
• forming a first image of the first surface of contact in light transmitted twice through the first tonometer tip and reflected from the cornea;
• and
• tonometrically measuring a first value of the IOP with a use of the first image,
• wherein the axial portion has a first curvature having a first sign of curvature that is equal to a sign of curvature of the cornea, and
• wherein a first value of the first intra-corneal stress is smaller than a second value of second intra-corneal stress that occurs at said location as a result of applanation of the cornea with a second tonometer tip having a flat cornea-contacting surface by applying the first force to the cornea with the flat cornea-contacting surface of the second tonometer tip.