Refractometer Visual Axis Alignment Using Purkinje Images
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Solution Overview
Problem
Current methods for determining the refraction of an eye during surgery, especially under general or retrobulbar anesthesia, are prone to errors due to the inability to accurately align the visual axis, and the internal eye pressure fluctuations during surgery affect refraction measurements.
Innovation Solution
A method and system that utilize Purkinje images to align the refractometer with the visual axis of the eye, allowing for accurate refraction measurement and adjustment of internal eye pressure by establishing a relationship between Purkinje image positions and eye properties using empirical reference measurements or mathematical models.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the patient is under general anesthesia or retrobulbar anesthesia, then the patient cannot actively move or fixate the eye, but the alignment of the visual axis becomes arbitrary and measurement errors increase
Solution Approach 1:
The system uses Purkinje images, which are naturally generated by the eye's optical surfaces when illuminated, to automatically determine visual axis orientation. The eye itself provides the reference markers (Purkinje images) needed for alignment, eliminating the need for patient cooperation or external fixation markings.
Solution Approach 2:
The patent replaces manual alignment methods (requiring patient fixation and surgeon adjustment) with an optical-based automated system. The refractometer is equipped with imaging means that detect Purkinje images and calculate visual axis orientation through image processing, substituting mechanical alignment with optical detection and computational analysis.
2Measurement precision
If Purkinje images are used to establish visual axis alignment, then accurate refraction measurement is achieved, but the system complexity increases
Solution Approach 1:
The refractometer is designed with multi-functionality by integrating imaging means (camera or sensor) that serve dual purposes: capturing the Purkinje images for visual axis alignment and potentially assisting in other surgical visualization tasks. This reduces overall system complexity by combining functions rather than adding separate dedicated devices.
Solution Approach 2:
The system introduces an image processing unit as an intermediary that automatically calculates visual axis orientation from Purkinje image positions. This intermediary component handles the complex computational tasks, keeping the optical hardware relatively simple while achieving high measurement precision through software-based analysis.
3Stress or pressure
If internal eye pressure changes during surgery, then the radius of curvature of the cornea changes, but refraction measurements become inaccurate
Solution Approach 1:
The system performs visual axis alignment using Purkinje images before the refraction measurement is taken. By establishing the correct alignment beforehand, the system ensures that subsequent measurements are taken along the accurate visual axis even if pressure changes occur during the measurement process, thereby maintaining measurement precision.
Solution Approach 2:
The system uses Purkinje image positions as feedback to continuously monitor and confirm proper alignment during the measurement process. The image processing unit analyzes the positions of multiple Purkinje images to verify that the visual axis is correctly aligned, providing real-time feedback that compensates for pressure-induced corneal shape changes.
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
Enables precise intraoperative refraction measurement and adjustment of internal eye pressure, ensuring accurate measurements even under anesthesia, by aligning the refractometer with the visual axis and maintaining normal eye parameters for reliable surgical outcomes.
Implementation Method 1
The first Purkinje image is the reflection on the outer surface of the cornea
Data Source
AI summary
A method for establishing the refraction of an eye (9) by means of a refractometer (3) is provided, in which the current visual axis (S) of the eye (9) is established before establishing the refraction, the refractometer (3) is aligned with respect to the visual axis (S) of the eye (9) and the refraction is established after the alignment. The visual axis (S) of the eye (9) is established on the basis of the position of a Purkinje image of at least one light source (41, 50) used to illuminate the eye and a relationship between the position of the Purkinje image and the visual axis (S).