Variable Focal Length Lens Prism Reduction
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Solution Overview
Problem
Existing adjustable focal length lenses, such as Alvarez lenses, can cause discomfort due to excess vergence or divergence stimulation of the eye, particularly when the optical center of the lens moves towards the bridge, resulting in unwanted prism effects.
Innovation Solution
The ophthalmic apparatus splits the fixed corrective power of the lenses between the front and rear lens elements, reducing the amount of prism exhibited by the superposed lens elements as they are laterally displaced. This is achieved by configuring the front and rear lens elements with specific fixed powers, where the rear lens element's power (Φr) is adjusted to minimize prism, typically between 5% and 80% of the total prescription power (Φp).
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the optical center of the lens moves towards the bridge to provide variable focal length, then the lens can adjust focus for different viewing distances, but excess prism effects are generated causing eye discomfort
Solution Approach 1:
The lens is divided into two separate lens elements (front and rear) that can slide relative to each other. Each element has a portion of the total prescription power, with the rear element having power Φr between 5%-80% of Φp. This segmentation allows the variable focal length function to be achieved through relative displacement while distributing the prism effects across both elements, reducing overall discomfort.
Solution Approach 2:
The invention changes the power distribution parameter between the two lens elements, specifically setting the rear element power Φr to be between 5% and 80% of the total prescription power Φp. This parameter optimization minimizes the prism effects generated during lateral displacement while maintaining the desired variable focal length range from distance to near viewing.
2Adaptability or versatility
If the lens elements are laterally displaced to vary focal length, then focus adjustment is achieved, but lens thickness increases
Solution Approach 1:
By splitting the total prescription power Φp into two components (front element power and rear element power Φr), the patent enables more efficient thickness management. The rear element with optimized power contribution allows for reduced overall lens thickness compared to traditional single-element designs, particularly when the elements are in the aligned position for distance viewing.
3Adaptability or versatility
If the lens elements are laterally displaced to vary focal length, then focus adjustment is achieved, but aberrations and excess power contributions increase
Solution Approach 1:
The patent optimizes the power distribution parameter between lens elements, specifically setting the rear element power Φr to be between 5% and 80% of the total prescription power Φp. This parameter optimization minimizes aberrations and excess power contributions during lateral displacement, maintaining higher optical quality across the full range of focus adjustment from distance to near viewing.
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 reduces the amount of prism exhibited by the lenses, enhancing user comfort, reducing lens thickness, and allowing for a more aesthetically pleasing design by minimizing aberrations and excess power contributions.
Implementation Method 1
when rays of light pass through both lens elements in succession, the lens causes them to converge or diverge in a manner equivalent to a spherical lens
Data Source
AI summary
An ophthalmic apparatus comprising at least two corrective lenses (5, 5′) that are mounted to a support (113) for supporting the lenses in front of a user's eyes (1, 1′), thereby defining a viewing direction through each lens (5, 5′); at least one of the lenses being a variable focal length lens comprising front (131) and rear (141) superposed lens elements having cooperating optical surfaces that are shaped such that the focal length of the variable focal length lens is variable according to the relative lateral disposition (d) of the front (131) and rear (141) lens elements to provide a power, where d=0 is defined as the relative position of the front (131) and rear (141) lens elements at which the variable focal length lens provides an overall horizontal meridional power Φp corresponding to the intended user's prescription, and where the front lens element (131) has a fixed power Φr and a rear lens element (141) has a fixed power Φr, such that: ΦP=Φf+Φr+Φ° A wherein O° A is the power provided by the variable focal length lens at d=0, and wherein Φr has the same sign as Φp, is equal to between about 5% and about 80% of Φp.