L11- Absorptve lenses & Safety eyewear

Optical radiation

Diferent ocular tissue absorb/filter different wavelength

• big impact on the ocular system

Type of optical radiation

• Infrared

• visible light (400-680nm)

• UV (UVA, UVB, UVC)

• IONIZING RADIATION

• NON - Ionizing radiation

Draper's law

radiation must be absorbed to have any biological effect

Non ionizing vs Ionzing radiation

non ionizing (long 入)

• uv, visible, IR - cause , photothermal, photochemical

Ionizing (short 入)

• xray, gamma - break chemical bond cause DNA Damage, Cataract

Photothermal effect

• can cause heating of tissues

• radiation increase kinetic energy - raise tissue temperature

• lead to protein denaturation & structural damage

Example of photothermal effect

• IR-A/IR-B cause thermal cataract - heating of crystalline lens (glassblower)

• Excessive exposure IR - burns retina

Photochemical effect

UV & high-energy visible light (blue light)

• cause chemical reaction and generate to Reactive Oxygen Species (ROS)

Photochemical effect mechanism

Photon energy absorbed by molecules(chromophores) and lead to:

• oxidative stress

• DNA damage

• lipid peroxidation

blue light induce photochemical damage to

Retinal pigment epithelium (RPE)

UVB induce photochemical in damaging

Cornea epithelium , cause photokeratitis

Chronic UV exposure induce photochemical in damaging

conjuctiva & lens, cause pinguecula, pterygium, cataract

Photoluminescene

re-emission of light after excitation

photoluminescence mechanism

• when certain material (fluorophores) absorb light and excited to higher energy

• then return to a lower energy state by emitting photons (glow)

photoluminescene

use for diagnostic, not damage

fluorescein dye glow under

blue light

lipofuscin in RPE used in

fundus autofluorescene (FAF)

UVA (320-400nm)

• longest in UV

• cause skin tan & aging, cataract (longterm)

UVB (280-320nm)

• shorter than UVA but more energy

• damage skin cell directly

• cause pinguecula, pterygium, photokeratitis, cataract

UVC (100-280nm)

• shortest in UV

• highest energy (most dangerous)

• absorbed in ozone layer, never reach earth surface

visible radiation : blue light

• high energy visible light : 400-450nm

blue light advantages

regulates circadian rythm (supress melatonin)

disadvantage of blue light

cause oxidative stress

why using phone in night wont feel sleepy?

devices produce blue light, which supress melatonin

WHEN melatonin increase?

in night time, make us feel sleepy

source of infrared

sun, man-made

prolonged exposure to infrared

denaturation of protein due to photothermal effect

• cornea - scar→opacity

• crystalline lens - capsule exfoliation, cataract

• retina - necrosis

absorptive lens

block/absorb selected wavelengths

UV Blocking lenses

BLock UVA/UVB

• CR39, Polycabonate, Trivex

Blue light filtering lenses

filter blue light

• use yellow-orange dyes → lens become more yellowish

• no conclusive benefit for eye strain, sleep improvement

photochromic lens

uv light triggers photochemical reaction and cause lens turn to darken.

factor influencing photochromic performance

• more UV = FASTER & DARKER

• Cooler temp = darker than in warm temp

• generation technology

POLARIZED Lens

block (absorb) horizontal light

function of polarized lenses

• reduce glare

• reduce transmission

• increase colour perception

Lens coating (6)

• colour

• anti reflective

• anti fog

• anti bacterial

• mirror

• edge

colour coating

add a tint for :

• fashion

• contrast

• enhancement

• reduce glare

Type of tint

• cosmetic - fashion

• occupational - job specific

• recreational - outdoor, sports

• therapeutic - glaucoma

Yellow contrast filter

reduce blue light

• pilot, skiers

Yellow absorb filter

Pale purple filter absorbs yellow light, transmit to red & blue

Anti reflective coating

reduce reflection on surface

Advantages of anti-reflective coating

• Better light transmission

• REDUCE GLARE

• COSMETIC

• Improve night vision

• reduce scattered light

Disadvantages of anti reflective coating

• Difficult to clean

• Dirt is more noticeable

• coating might peel off

scratch resistant coating

• increase surface hardness = protect lens from scratches

• coated before AR coating to maintain performance

Lens care for SR coating

Avoid extreme heat exposure

• lens will crazing & frosted

Anti fog coating

Avoid fogging due to change in temp or moist

How anti fog coating works?

Hydrophilic coating

Mirror coating

• reflect overall light transmission

• increase UV & IR reflection

• coated infront of lens via vacuum proses

Edge

cosmetic enhancement for semi/rimless

Anti bacterial coating

consist silver ion (Ag+) which control bacteria growth

Safety eyewear

protect eye from impact, radiation, chemicals, dust and give antifog performance

safety glasses

impact resistance - industry, sports

safety goggles

seal and chemical/dust protection - lab, healthcare

face shields

full face protection - welding, grinding

laser safety glasses

filter specific laser wavelengths - laser surgery

Materials for safety eyewear

• polycarbonate - high impact, UV block

• Trivex - lighter, clearer

Frames for safety eyewear

• high-strength nylon

• polyamide

Safety eyewear coating

• anti scratch - silicone oxide hard coat

• anti reflective - reduce surface glare

• anti fog

Standard for safety eyewear

1. ANSI Z87.1 - Industry; anti fog, wide optic

2. EN ISO 16321 - healthcare; stricter clarity, thermal resistance

Malaysia standard safety eyewear

• ANSI Z87.1

• EN ISO 16321

• DOSH SIRIM