How to Avoid Common Mistakes in Measuring Medical Optics

The partnership between optics and medical devices dates back to the invention of the microscope in the late 1500s to mid-1600s. Over time, the desire to visualize the human body to diagnose and treat illnesses has increased.

Image Credit: Zygo Corporation

In modern medical devices, optics are primarily used in two categories: for diagnosing illness and for therapeutic purposes in various treatments.

Such devices include endoscopy, optical coherence tomography (a non-invasive imaging test), surgical guidance cameras, intraoral cameras, ophthalmological imaging equipment, 3D dental scanners, and short-pulse laser surgical systems.

What Differentiates Optics Used in Medical Devices from Other Industries?

What sets optical medical devices apart from other photonic products is not necessarily their use of extreme tolerances or unique manufacturing processes but rather a unique mindset that prioritizes the functional requirements of medical devices before the design process begins.

There are several considerations to remember, such as whether the device will come into contact with the patient, if it needs to be autoclavable, and whether it will be reliable and perform consistently in a medical environment. The materials used in the manufacturing process must be compatible with medical use and be clean.

High-quality materials, such as non-leaded glasses, medically qualified epoxies, and stainless steel, are some of the best materials for these devices.

Governmental regulations and strict health and safety standards heavily influence the development process for optical medical devices from start to finish.

Unlike in other industries where design flaws can be corrected after the prototype phase, in the medical device industry, there is often only one opportunity to design a product correctly, as changes made post-prototype phase can be expensive and time-consuming.

This is due, in part, to the costly medical qualification process that prototypes must go through. Changes made to the product after it has been qualified will require it to be requalified, which can negatively impact the project's schedule and costs.

Planning the End Result from the Beginning

Defining an optical device involves creating design specifications, developing a budget, avoiding mechanical interferences, minimizing packaging volume, ensuring manufacturability, developing test protocols, and ensuring that desired features do not overshadow the critical function of the device.

Any misstep in these functions can add time and cost, significantly impacting the device's utility.

To achieve optimal device performance, the optical design engineer must define tolerances in concert with the optomechanical design engineer while balancing labor and material costs with performance requirements. Critical parameters, including surface figure, thickness, tilt, and centering, must be considered.

Medical devices often include flat, spherical, and aspherical optics as part of the design and must operate over a wide temperature range. Some medical device original equipment manufacturers (OEMs) face challenges immediately.

Insufficient tolerance analysis can affect the entire project, causing issues in sourcing materials, inspecting incoming components, selecting a manufacturing partner, determining how each component will be tested, and even determining the best shipping method to avoid misaligning or damaging delicate optics.

Tolerance analysis must be complete and accurate to eliminate errors that could occur further down the line.

Avoiding Pitfalls

Postponing testing until the end of the development process is ineffective. Likewise, developing specifications without the required expertise in application knowledge can lead to issues. Testing and validating the components before assembly is crucial to achieving optimal system performance.

One of the critical factors to consider is the required level of precision, measured in microns and nanometers. Laser interferometers or 3D profilers are suitable instruments for this task.

Methods such as modulation transfer function (MTF) or encircled energy can be used for final system testing. Wavefront error remains a more straightforward and robust option, although it requires proper interpretation. At this level of precision, in-house equipment and knowledge may not be sufficient.

This is where an experienced optics supplier can be valuable. Such a supplier will have a solid understanding of optical materials and their properties, as well as the necessary equipment and expertise in grinding, polishing and finishing techniques, assembly methods, and component and system testing.

Looking Ahead

Effective planning is essential in the development of medical device optics. The process should begin with a clear understanding of the functional requirements necessary to ensure positive clinical outcomes. The design should then incorporate a comprehensive tolerance analysis to ensure precision and accuracy.

Adherence to government compliance requirements can help avoid costly delays. Partnering with an experienced and knowledgeable business partner can help ensure the cost-effective and successful development of robust medical devices.

This information has been sourced, reviewed and adapted from materials provided by Zygo Corporation.

For more information on this source, please visit Zygo Corporation.

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