Protecting the optical defense line of the "window to the soul": based on ISO15004-2

Executive Summary

Ophthalmic optical instruments (such as fundus cameras, scanning laser ophthalmoscope (SLO), slit lamps, etc.) play an indispensable role in clinical diagnosis. However, due to the fact that the light beams of these devices directly enter the eye and focus on the retina, or stay on the corneal surface for a long time, their optical radiation safety testing becomes the most complex and important aspect of medical device compliance.

ISO 15004-2, as a globally recognized standard, not only sets limit values for different levels of equipment, but also constructs a testing logic based on the biophysical model of the human eye. This white paper will provide an in-depth analysis of its testing parameters, retinal luminance conversion logic, light spot testing methods, and regulatory requirements.

1. Core test parameters of ISO 15004-2

The standard defines the following key physical quantities for the spectrum ranging from 250nm to 2500nm:

1. Cornea/Lens-related: Irradiance (E)

Test location: corneal plane.

Key limitations: UV band (to prevent photokeratitis) and IR band (to prevent cataracts).

2. Retina-related: Radiance (L) and Irradiance (Eret)

Test location: Simulate the retinal plane of the human eye.

o Physical significance: It describes the energy distribution within a unit area and unit solid angle of the retina. It is the core for evaluating photochemical damage and thermal damage to the retina caused by blue light.

3. Radiant Exposure (H)

For pulsed devices (such as flash lamps), it is used to assess the cumulative energy of single or multiple pulses.

II. Standard testing logic and hazard assessment logic

The assessment logic of ISO 15004-2 is based on the "worst-case principle" and "spectral biological weighting".

1. Spectral weighting function

Photons with different wavelengths have varying destructive powers on tissues. The standard introduces weighted functions for S(λ) (ultraviolet), B(λ) (blue light), and R(λ) (thermal hazard).

· Blue light hazards: Light rays near 440nm have a very high weighted coefficient. Even if the total power is not high, due to the high photon energy, they are highly prone to cause photochemical damage.

· Thermal hazard: The focus is on evaluating the temperature rise effect on tissues caused by visible light to near-infrared wavelengths.

2. Scale logic

The standard not only considers the magnitude of energy, but also the angle (aperture angle α) covered by the energy on the retina. For thermal hazards, the smaller the light spot (the more concentrated the energy), the stricter the limit.