Convex-Apex Bi-Prism Tonometer for Post-LASIK IOP Accuracy
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Solution Overview
Problem
Current applanation tonometers, such as the Goldman tonometer, are unreliable for measuring intraocular pressure in myopic patients who have undergone LASIK or PRK surgery due to changes in corneal thickness, leading to inaccurate pressure readings.
Innovation Solution
An applanation tonometer with a transparent optical bi-prism featuring a convex-shaped apex, having a mean surface radius of 11.5 to 14 millimeters, which compensates for the thinner corneas post-surgery by providing a more accurate measurement of intraocular pressure, similar to pre-surgical readings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a flat apex Goldman tonometer is used, then IOP measurement is reliable in normal corneas, but measurement accuracy deteriorates in post-LASIK/PRK patients with thinner corneas
Solution Approach 1:
The invention modifies only the apex region of the bi-prism to have a convex curved shape, while the rest of the bi-prism structure remains unchanged. This localized modification allows the tonometer to adapt to post-surgical corneas without compromising the overall measurement mechanism, resolving the contradiction between maintaining measurement precision and expanding adaptability to different corneal conditions
Solution Approach 2:
The invention changes the geometric parameter of the apex from flat to convex curved, with a specific radius of curvature between 6-15 mm. This parameter change allows the applanation area to better match the actual contact area in post-LASIK/PRK patients, thereby improving measurement accuracy for this specific patient population while maintaining compatibility with the standard Goldman tonometer design
2Measurement precision
If the applanation area is fixed at 3.06 mm, then IOP measurement follows Imbert-Fick law, but measurement accuracy deteriorates when corneal thickness changes
Solution Approach 1:
The invention replaces the flat apex with a convex curved surface having a radius of curvature of 6-15 mm. This curvature allows the applanation area to dynamically adapt to variations in corneal thickness, ensuring that the measurement remains accurate across different corneal conditions including post-surgical thinning, thereby resolving the contradiction between fixed measurement parameters and variable corneal composition
3Reliability
If a standard Goldman tonometer is used, then the device structure is simple, but measurement reliability deteriorates in myopic post-surgical patients
Solution Approach 1:
The invention modifies only the apex region of the bi-prism to have a convex curved shape, while the rest of the bi-prism structure remains unchanged. This localized modification maintains device simplicity while improving measurement reliability for post-surgical patients, resolving the contradiction between reliability and complexity by concentrating the modification where it is most needed
Solution Approach 2:
The invention introduces a convex curved surface with radius of curvature 6-15 mm at the apex, which improves measurement reliability in post-LASIK/PRK patients. This geometric modification is minimal in scope but significant in effect, achieving improved reliability without substantially increasing device complexity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The convex-apex tonometer ensures reliable and reproducible IOP measurements in myopic patients by closely matching preoperative IOP values post-surgery, with a statistical power of over 90% correlation in experimental studies, and can be easily integrated into existing clinical setups with minimal additional cost.
Implementation Method 1
the objective measurement of IOP is based on the force required to flatten the cornea according to the Imbert-Fick law. This law postulates that the pressure inside a sphere (ideal, with dry and thin walls) is equal to the force necessary to flatten the surface divided by the area of flattening
Implementation Method 2
A transparent optical bi-prism with a distal apex intended to make contact with the anterior surface of the cornea
Data Source
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AI summary
Applanation tonometer for measuring intraocular pressure in patients who have undergone LASIK or PRK refractive surgery, said applanation tonometer comprising an optical, transparent bi-prism having a distal apex intended to come into contact with the eye of which the intraocular pressure is to be measured. The optical bi-prism has a curved distal apex with a convex shape viewed from outside the prism, which comes into contact with the anterior surface of the cornea.