Eye Refractive Power Measurement Apparatus with Hole Mirror
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Solution Overview
Problem
Conventional eye refractive power measurement apparatuses face challenges in maintaining measurement accuracy due to noise light interference and decreased signal-to-noise ratio, especially when dealing with refractive errors and wide measurement ranges, as the shared objective lens causes measurement light to enter the photodetector as noise, and moving components to maintain optical conjugacy complicates noise prevention.
Innovation Solution
The apparatus employs a measurement optical system with a hole mirror and concave mirror, where the measurement target is projected onto the eye's fundus via the hole mirror and concave mirror, and the photodetector is positioned to receive light via the concave and hole mirrors, with movement units ensuring optical conjugacy between the measurement target, image-forming member, and photodetector, allowing for accurate refractive power calculation without noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the measurement target is arranged at a decentered position from the optical axis to dissipate reflected measurement light off-axis, then noise light entering the photodetector is reduced, but the image of the measurement target formed on the fundus becomes blurred and measurement accuracy decreases when the examinee's eye has refractive errors
Solution Approach 1:
The patent divides the optical system into separate projection and photo-receiving optical systems with different optical paths. The projection optical system projects measurement light through the objective lens onto the fundus, while the photo-receiving optical system captures reflected light through a different path using a beam splitter, preventing noise light from entering the photodetector while maintaining clear imaging for refractive error measurement
Solution Approach 2:
The patent extracts the photo-receiving function from the projection path by using a beam splitter to separate the reflected measurement light from the direct path to the photodetector. This extraction allows the system to capture the reflected light signal while blocking the direct reflected light that would otherwise enter as noise, resolving the contradiction between noise reduction and measurement accuracy
2Measurement precision
If the measurement target and photodetector are moved in the optical axis direction to maintain optical conjugacy with the fundus, then measurement accuracy is improved for eyes with refractive errors, but the reflection angle of measurement light changes making it difficult to prevent noise light from entering the photodetector over a wide measurement range
Solution Approach 1:
The patent segments the optical paths so that the projection and photo-receiving systems operate independently with fixed relative positions. The beam splitter creates separate optical channels that remain geometrically stable even when components move along the optical axis to maintain conjugacy, allowing accurate measurement while preventing noise light entry through the separated paths
Solution Approach 2:
The beam splitter acts as an intermediary element that mediates between the projection and photo-receiving optical systems. It allows the systems to move independently to maintain optical conjugacy while the beam splitter itself maintains a fixed geometric relationship with both systems, preventing noise light from coupling into the photodetector path regardless of position 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
This configuration effectively prevents noise light from entering the photodetector, maintaining high measurement accuracy even with refractive errors and wide measurement ranges, by ensuring the measurement target and photodetector remain optically conjugate with the fundus, enhancing the signal-to-noise ratio and resolution.
Implementation Method 1
a hole mirror having an aperture through which the optical axis passes and a reflective surface around the aperture, a concave mirror arranged on the optical axis, a projection optical system having a measurement target arranged on the optical axis, which projects measurement light from the measurement target onto a fundus of the examinee's eye via the aperture of the hole mirror and the concave mirror
Implementation Method 2
a concave mirror arranged on the optical axis, a projection optical system having a measurement target arranged on the optical axis, which projects measurement light from the measurement target onto a fundus of the examinee's eye
Implementation Method 3
a photo-receiving optical system having an image-forming member and a photodetector which are arranged on the optical axis, which photo-receives the measurement light reflected from the fundus via the concave mirror, the reflective surface of the hole mirror and the image-forming member by using the photodetector
Data Source
AI summary
An eye refractive power measurement apparatus capable of accurate measurement while preventing noise light from entering a photodetector even a measurement target is moved in an optical-axis direction, has a measurement optical system including an optical axis, a hole mirror having an aperture and a reflective surface, a concave mirror, an optical system projecting measurement light from the target onto a fundus via the aperture and the concave mirror, and an optical system having an image-forming member and the photodetector photo-receiving the light reflected from the fundus via the concave mirror, the reflective surface and the image-forming member, a unit moving the target and the image-forming member or photodetector in the direction to have a positional relationship optically conjugate with the fundus, and a calculation part obtaining eye refractive power based on a travel position or amount of the image-forming member or photodetector and an output from the photodetector.