How to care for and clean optical surfaces
Many ophthalmic devices have optical components such as windows, lenses, mirrors, filters, and prisms. These components, usually made out of glass and sometimes plastic, are used to magnify and control the path and quality of images and illumination sources. The surfaces of these components are extremely smooth since even very small irregularities can cause scattering of light. The surfaces of lenses, prisms and windows are often coated with an antireflective layer to prevent loss of light due to reflection. Mirrors have a highly reflecting coating to get maximum reflection of light. Filters have coatings to cut out undesired wavelengths. The coatings are very thin and delicate and can be easily ruined by improper handling and cleaning.
By following these suggestions, you will help ensure that all of the exposed optical surfaces in your eye care equipment perform optimally:
- Place a dust cover over eye care equipment when not in use.
- Always replace the lens caps, if available, when not in use.
- Keep eye care equipment in an environment that is not humid to prevent the growth of fungus on optical components.
- If the optical component is not dirty, do not clean it. Handling optics increases their chance of dirty or damaged, so you should clean optics only when necessary.
- Read the manufacturer's instructions before cleaning any optical surface
- Always place optical components on a soft surface. Resting them on a hard surface can cause scratches in their surface.
- Do not touch optical surfaces with your bare fingers since they leave behind grease and moisture marks that are hard to remove. Try holding loose optical components by their edge. It is also a good idea to wear cotton lint free gloves when handling optical components.
- Be careful when using sharp instruments, including your fingernails, near optical surfaces.
- You can reduce the chance of damage by using wooden, bamboo or plastic implements to handle optics.
- Dust particles can produce scratches if you do not remove them properly. These scratches produce unwanted scattering of light, thereby reducing the quality of the optical element.
- Because of this, you should never wipe dust off optical surfaces, especially when they are dry. You should first blow off the dust by using a dust blower (fig 1). You can also used canned air but it is expensive and the freon gas in the can may fog up the optics. Use a camel hair brush, sometimes included as part of the blower (fig 2) to remove any dust that sticks to the surface.
- To remove stains, you can use a lint free cotton swab or a lens cleaning tissue dipped in lens cleaning solution (see optical cleaning solutions box). For round surfaces move the swab in a circular fashion starting from the center and going in a spiral towards the edge (fig 2). For rectangular optical elements, always move in the same direction. Repeat this step using a fresh swab every time until the stain is no longer visible at any angle under a bright light. If cotton lint is left on the component remove it by blowing or using a clean camel hair brush
- To remove stains on plastic components use a mild solution of mild detergent and distilled water. Do not use other cleaning solutions on plastic, unless indicated by the manufacturer, because it can permanently cloud the surface.
- When removing stains, avoid excess pressure since it can wear off the surface coating causing the optical component to lose its specific properties.
- To remove fungus, use an optical fungicide, such as that sold by Zeiss. If is not available in your markets, you can use surgical scrub soap.
- Do not spray lens cleaning solutions directly on the optical components of a device, since the solution can leak into the machine and cause spots on other lenses and rust or damage the internal components of the device. Instead, spray the cleaning solution on the lens paper or swab first.
- For mounted lenses, glue is usually used to hold the lens in place. Hot water, heat, alcohol, acetone or general drying out over time will cause the lens to dislodge.
- Laser optics should only be cleaned by trained qualified specialists
- Repeated cleaning will wear out the surface coating described earlier and the property of the surface may change. Keeping optical components protected from dust, stain and fungus is preferable to frequently removing them.
Materials for optical surface cleaning
- dust blower (fig 1 & 2 )
- lens brush (fig 2 )
- cotton swab (fig 4 )- use non-sterile medical grade cotton swabs, with degreased fibers that won’t release lint. Alternatively, if non-sterile, medical-grade cotton swabs are not commercially available, fresh cotton swabs can be prepared with wooden sticks and medical-grade cotton
- lint free lens tissue (fig 5)
- lens cleaning solution (fig 6)
- lint free cotton gloves to use when handling loose optics
- bamboo tweezers for holding small loose optics while cleaning
Fig 1. Always blow dust off of an optical surface. Never wipe it off.
Fig 2. A dust blower can be found at most photography shows. Some blowers, such as the one pictured, has a built in dust brush.
Fig 3. Always handle loose optical components by the edges. Clean round components from the center to the edge in a spiral fashion
Fig 4. Always use medical grade, greaseless and lint free cotton swabs
Fig 5. Lint free lens tissue available in photography shops
Fig 6. You can find lens cleaning solutions at photography shops
Optical cleaning solutions
- Always consult the manufacturer about which solutions to use for optical cleaning
- Camera shops sell lens cleaning solutions which you can use for most optical cleaning
- If lens leaning solutions are not available, or if no information from the manufacturer is available, then try the following, going from weakest to strongest until the desired results are obtained:
- Distilled water
- Water-based solution: 1 part of a mild neutral detergent, 19 parts of distilled water
- 60% acetone and 40% methanol (acetone alone dries too quickly to dissolve all of the debris. The methanol slows the evaporation time, and also cleans debris that acetone alone will not remove). This solution should not be used on plastic lenses since acetone damages plastic.
- Isopropyl alcohol (90% purity) can be also be used but its slow evaporation can leave drying marks on the surface.
Written by: Ismael Cordero