This paper introduces in detail the application of optical lens processing in medical field.

Optical lens is widely used in the medical field, from diagnostic equipment to therapeutic instruments, its processing accuracy and performance directly affect the medical effect. The following details the processing process and application characteristics of optical lenses in the medical field from the aspects of processing flow, material selection, key technologies and typical application scenarios:

First, the material selection of medical optical lens

There are strict requirements for lens materials in the medical field, which need to meet:

Biocompatibility: avoid causing allergies or tissue reactions (such as medical-grade glass and special polymers).

Optical properties: high transmittance and low dispersion (such as fused Shi Ying, sapphire, PMMA, silicon crystal, etc.).

Physical stability: resistance to disinfection (high temperature, chemical reagents) and abrasion.

Typical materials:

Application scenario of material type characteristics

Fused Shi Ying high temperature resistant and low expansion coefficient laser surgical lens and endoscope lens.

Sapphire has high hardness and scratch resistance. Ophthalmic scalpel head lens and implantable lens.

Medical grade PMMA has good biocompatibility and is easy to process intraocular lens and contact lens.

Infrared image lens and thermal image equipment with high infrared light transmittance of silicon crystal

Second, the core process of medical optical lens processing

1. Pretreatment of raw materials

Cutting and rough machining:

Using diamond saw or laser cutting equipment, the block material is processed into lens blank, and the dimensional accuracy is controlled within 0.1 mm.

Example: molten Shi Ying needs to be cut in a dust-free environment to avoid impurity pollution.

Surface cleaning:

Ultrasonic cleaning (deionized water+neutral detergent) is adopted to remove the debris and oil pollution in the cutting process and ensure the subsequent processing accuracy.

2. High-precision molding

Grinding and polishing:

Rough grinding: grinding the surface of the blank with silicon carbide abrasive (particle size 80-200 mesh) to form a preliminary curved surface and remove cutting marks.

Fine grinding: use finer abrasive (such as cerium oxide, particle size of 1-5μm), and control the surface roughness Ra<1μm and the curvature radius error of 0.01 mm..

Polishing: asphalt polishing mold and polishing solution (including nano-alumina) are used to achieve mirror effect, and the surface roughness Ra is less than 0.1μ m, which is suitable for precision parts such as endoscope lens.

Typical technology:

Computer numerical control (CNC) grinding: the grinding head trajectory is controlled by programming to ensure that the lens surface meets the design parameters (such as spherical surface, aspheric surface and free-form surface).

Magnetorheological Polishing (MRF): Magnetic field is used to control the rheological properties of polishing solution to achieve nano-scale surface accuracy, which is often used in ophthalmic surgical lenses.

3. Surface treatment and functionalization

Coating process:

Plating different functional films according to application requirements:

Anti-reflection film: Improve the light transmittance in visible or infrared band (such as ophthalmic microscope lens, the light transmittance is more than 99%).

Anti-reflection film: reduce the interference of light path (such as endoscopic imaging system).

Anti-scratch film: improve the surface hardness of sapphire lens (hardness reaches HV2000+ after coating).

Coating method: electron beam evaporation and ion sputtering (to ensure the uniformity of film 1%).

Surface modification:

Medical polymer lens can improve biocompatibility and reduce protein adsorption by plasma treatment.

4. Precision detection and quality control

Optical performance testing:

Surface shape detection: Interferometer (such as Zygo interferometer) measures the surface shape error, and the PV value (peak-valley difference) is less than λ/10(λ=633nm).

Light transmittance test: ultraviolet-visible-near infrared spectrophotometer to ensure that the light transmittance in the band reaches the standard.

Focal length and aberration detection: optical bench cooperates with CCD camera to detect the focusing accuracy and distortion of lens (for example, the lens distortion of surgical microscope is less than 1%).

Biocompatibility test:

Cytotoxicity test (ISO 10993 standard), hemolysis test, to ensure non-toxic release of materials.

Third, special processing technology in the medical field

1. Micro-nano structure processing

Application scenario:

The microlens array is used in optical coherence tomography (OCT) equipment to improve the imaging resolution (up to 1μm).

Processing method:

Laser direct writing: using femtosecond laser to etch microstructure on the lens surface, the accuracy reaches submicron level.

Nano-imprint: periodic nanostructures (such as anti-reflective nano-pillar arrays) are formed by template imprint.

2. 3D free-form surface machining

Demand background:

Minimally invasive surgical instruments need lenses to adapt to complex light paths (such as curved endoscope lenses).

Technical scheme:

Five-axis CNC machining: the posture of grinding head is controlled by five-axis linkage, and the asymmetric free-form surface is machined with an error of < 5 μ m.

Example: Free-form lens of laparoscopic lens should satisfy both large field of view (120) and low distortion.

3. Miniaturization processing

Typical products:

Ophthalmic implantable intraocular lens (diameter < 6mm), intravascular imaging lens (diameter < 1mm).

Processing challenges:

Micro-grinding technology (tool diameter < 0.1mm) and microscope vision system are used to realize sub-micron control.

4. Typical application scenarios of medical optical lenses

1. Diagnostic equipment

Optical microscope lens:

High numerical aperture (NA>1.4) objective lens, combined with oil immersion technology, can achieve cell-level resolution (0.2μm).

Medical imaging equipment:

The optical coding lens of CT/MRI equipment is used for signal conversion and image reconstruction.

OCT lens group: through low coherence interference imaging, micron-scale tomographic scanning of biological tissue (such as fundus OCT lens) is realized.

2. Treatment and surgical equipment

Laser surgical lens:

Focusing lens for excimer laser myopia correction (LASIK) has an energy density control accuracy of 5% and a spot diameter of < 100μm m..

Holmium laser lithotripsy lens: resistant to high-energy laser (wavelength 2100nm), transmission efficiency > 80%.

Endoscopic lens system:

The front lens of optical fiber endoscope needs to meet the requirements of large depth of field (1-100mm) and high resolution, and gradient refractive index (GRIN) lens is often used.

3. Implantation and rehabilitation devices

Intraocular lens:

The foldable PMMA intraocular lens is coated with heparin to reduce postoperative inflammatory reaction.

Visual rehabilitation equipment:

Visual aid lens: high magnification (10-20 times) and wide field of view design, with anti-fatigue coating.

Five, the key difficulties and solutions of medical lens processing

Difficulties affect solutions

Biocompatibility requires limited material selection, medical-grade glass/polymer, and plasma passivation treatment on the surface.

High-precision shape control imaging clarity and error are introduced into deterministic processing technologies such as magnetorheological polishing and ion beam figuring(IBE).

Life and reliability of lens with disinfection resistance The coating layer is made of high-temperature resistant materials (such as silicon dioxide/titanium dioxide), which can withstand high-pressure steam disinfection at 134℃.

Miniaturization and integration of machining accuracy and assembly difficulty Micro-nano machining technology (such as electron beam lithography)+automatic micro-assembly system (accuracy < 1μm)

VI. Industry Standards and Quality Control

International standards:

ISO 13485 (Medical Device Quality Management System) and ISO 11979 (Ophthalmic Implant Standard).

Key control points:

Each lens should be accompanied by an optical inspection report (surface shape, transmittance, coating parameters).

Dust-free workshop grade: the processing environment should reach ISO 5 (Class 100) to avoid particle pollution.

summary

The processing of medical optical lenses combines precision optics, material science and biomedical engineering. From material screening to nano-scale surface treatment, optical performance and medical safety should be taken into account in every step. With the development of minimally invasive surgery and precision medical treatment, free-form surface machining, micro-nano structural design and other technologies will be more relied on in the future, which will promote the lens to be miniaturized and functionally integrated, and provide core optical support for early diagnosis and precision treatment.