Page 164 - The Indian Optician Digital Edition Jan-Feb 2020

Argon laser which has a high
optical density for a wavelength
from 200 to 523 nm. This high
optical density protects the wearer
in the wavelength zone for Argon
lasers. However, the optical density
drops back to almost zero above
600 nm, as the light above 600 nm
can be easily seen.
done in a combination of ophthalmic surfaced for the prescription and
grade layers). edged for the frame and afterwards, It is important to minimise one’s
the lens is fired by heating in a eyes’ exposure to the sun, dust,
POLARISED LENSES
hydrogen atmosphere. This reduces and other unforeseen materials like
Polarised lenses contain a special the silver halide crystal by eliminating pollen and gushes of wind. Eyes are
filter that blocks intense reflected the silver so the lens is not darkened. a strong organ but protecting them
light and reduces glare. Light reflected The front surface of the lens must can help avoid unnecessary optical
from surfaces such as a flat road or be reground to remove the altered issues. There are multiple methods
smooth water is generally horizontally layer. The altered back layer that to protect the eyes of the wearer and
polarised. This means that instead gives the lens its unique spectral finding the correct filters, keeping in
of light typically being scattered in absorbing properties remains in mind one’s customised requirements,
all directions, reflected light travels place. Some of the glare control dyes would be useful. Time to put these
in a more horizontally-oriented are also available to fulfil the desired requirements at the forefront and
direction. This creates an annoying transmission requirements. protect the eyesight.
and sometimes dangerous intensity SPECIALITY ABSORPTIVE REFERENCES:
of light that we experience as glare. LENSES 1. ALAN M. ROTH, MD: EPITOMES-
These lenses offer advantages in many OPHTHALMOLOGY, THE WESTERN
different situations, like reduce driving 1. Glass Blower’s Lenses: They JOURNAL OF MEDICINE, page-325.
in fatigue and focus on safe driving, filter out the yellow band of the 2. Pitts DG, Kleinstein RN: Environment
vision, Boston, 1993, Butterworth-
for fishing and for boating on the spectrum so that they may see Heinemann.
water, for more visual comfort at the more clearly on the heated glass. 3. Guidance document for prescription
beach, to block UV radiation, bright This function is fulfilled by the sunglass, US department of Health
and Human Services FDA, Center
and snowy days. didymium filter lens which is for devices and radiological health,
dichroic, meaning the lens will division of ophthalmic devices, office
GLARE CONTROL LENSES appear rose-coloured in natural of device illumination, Rockville, MD

and incandescent lighting, but October 9, 1998.
Some of the glare cannot be 4. Brooks & Borish, Systems for
eliminated by polarised lenses aqua under fluorescent lighting. Ophthalmic Dispensing, 2nd edition,
alone. There are two types of glare 2. X-Ray Lenses: For x-ray protection, Butterworth-Heinemann 1996, pages
329 - 364.
- discomfort glare (glare produces 1.80 index lenses are made with 5. Torgersen D: UV radiation and the
discomfort but does not necessarily heavy glass material, meaning eye, lab talk, 1998.
interfere with visual performance or this particular glass is prone to 6. Hunter lab: https://www.hunterlab.
ability) and disability glare (reduces scratching. Such lenses are not com/blog/color-plastics/uv-analysis-
ophthalmology-spectrophotometer-
visual performance and visibility too). capable of being chemically- applications-eyeglasses-contact-
hardened and cannot be heat lenses.
Corning developed a series of 7. ANSI Z80.3-2001: American national
photochromatic lenses, referred to as tempered. standard for ophthalmic non
the Glare Control CPF lenses (corning 3. Laser Protective Eyewear: Laser prescription sunglasses and fashion
eye wear requirements, Merrifield, Va,
protective filter). Such lenses are protective eyewear is used around 2002, Opt Lab Assoc.

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