EYE ANATOMY

The eyes are organs that provide coloured images of near, far, bright and dark objects.

The eye is externally covered by a membrane called sclera, that protects the most internal and delicate parts of the eye. In the front part of the eye the sclera is transparent and it is called cornea. Focused by the cornea, the light reaches the back of the eye called iris, which is a coloured part of the eye. It absorbs and controls the amount of light that enters into the eye, opening and closing the pupil, which is a dark circular opening at the centre of the iris. 
Then, the light reaches the eye’s crystalline lens, a flexible lens that can modify its thickness and its bending thanks to the eye muscles. This ability allows to focus objects at different distances. 
Retina is the last organ reached by light. It is the light-sensitive inner layer of the back of the eye. The retina, stimulated by the light reaching it, sends information as electrical signals to the brain through the optic nerve.
The human eye is so one of the most delicate and complex human organs that, being exposed to various risks in work environment, has to be protected. For this reason, safety glasses have to be considered as P.P.E.. To protect the worker’s health and safety and to choose the right type of protection, it is important to know and classify these risks, which can be divided as follows:

	MECHANICAL RISKS High-speed particles, chips, metal powders, droplets and liquid splashes.
	CHEMICAL RISKS Mist, vapour and gas, liquid aerosols, fine dusts, splashes of chemicals.
	OPTICAL RADIATIONS RISKS Ultraviolet and infrared radiations, glare caused by high intensity light.

 

RISKS

 

MECHANICAL RISKS

The protection against mechanical risks is recommended for all those manufacturing operations where there is a risk of accidental eye contact with high-speed objects or particles. Typical operations are: turning, milling, sandblast, riveting, grinding and other operations in which there are frequent projections of solid volatile particles (metal, stone, sand, wood) with a consequent impact at different speeds.

According to the impact extent, the hazards may be: lesion of the cornea, laceration of the iris, crystalline lens opacity, irritation, pain and conjunctivitis. It is necessary, then, to choose the appropriate eye protector in accordance with impact speed to which you can be subjected:

SYMBOL MARKING* lenses and frame	IMPACT		TYPE OF EYE PROTECTOR
	Impact level	Impact speed	Glasses	Goggles Masks	Face masks
F	Low energy impact	45 m/s  (162 km/h) Steel ball with a diameter of 6 mm and a mass of 0,86 g
B	Medium energy impact	120 m/s (432 km/h) Steel ball with a diameter of 6 mm and a mass of 0,86 g	Not applicable
A	High energy impact	190 m/s  (684 km/h) Steel ball with a diameter of 6 mm and a mass of 0,86 g	Not applicable	Not applicable

* If the symbol F, B or A is not found on both the lenses and the frame, then the lower value is assigned to the complete set of safety glasses.

 

CHEMICAL RISKS

Protection against chemical risks is recommended for some types of applications, such as handling of toxic dusts or corrosive liquids, which may represent a potential risk to the eyes of the operator. This risk may occur especially in the medical, agricultural and food fields or in waste management, where micro-organisms may contaminate the operator.
The risks to which the operator may be exposed to are: conjunctivitis, ulceration of the cornea, viral infection and partial or total blindness.

It’s important to choose properly the suitable eye protector in compliance with the required protection:

SYMBOL MARKING* frame	PROTECTION AGAINST	TYPE OF EYE PROTECTOR
		Glasses	Goggles Masks	Face masks
3	Droplets of liquid	Not applicable		Not applicable
	Splashes of liquid	Not applicable	Not applicable
4	Dust particles of big dimensions  (> 5 μm)	Not applicable		Not applicable
5	Gas and particles of fine dust (< 5 μm)	Not applicable		Not applicable

* If the frame of eye protector is not marked with none of the symbols 3, 4 and/or 5 the eye protector cannot be considered as suitable to protect against chemical risks.

 

OPTICAL RADIATIONS RISKS

Protection against this type of risk is provided by lenses or filters, that refer to appropriate European Standards such as: ultraviolet filters (EN 170), Solar Protection filters for industrial use (EN 172) and welding filters (EN 169). 

To understand the usefulness of these filters, it is appropriate to explain the basic principles: solar light is propagated through a beam of electromagnetic waves, of which only a part hits earth overcoming the ozone layer.

What we perceive is made up of:

• visible radiations (which compose the so-called “visible spectrum”): they are electromagnetic radiations with a wavelength between 380 and 750 nm; they are composed of the only rays visible to the human eye that materialize in the form of colours.

• ultraviolet radiations (UV): they are electromagnetic radiations with a wavelength between 100 and 380 nm. These rays are not visible to the human eye and they can be especially found in environments with the presence of solar light. Moreover, such radiations are harmful to humans because they are made up of magnetic waves which penetrate into the eye thus causing uncomfortable feelings and/or illnesses after a prolonged exposure (like it happens for the skin: little quantities of UV rays penetrate the skin causing tan, but prolonged exposure could be harmful to health). The risks connected to such radiations may be: lesion of the cornea, conjunctivitis, partial blindness, premature ageing of crystalline and cataract.

• infrared radiations (IR): they are electromagnetic radiations with a wavelength between 780 and 2.000 nm. These radiations are harmful to humans because they emit heat coming from all warm bodies (including the Sun, but even during welding or manufacturing of metals and glass). For this reason, the damages caused by such radiations are perceived in a nearly immediate way (unlike those caused by ultraviolet radiations which, on the other hand, appear later). Actually, we should consider that the ozone layer filters good part of IR rays of solar light which, therefore, come to us in a very restricted and not dangerous quantity; the rays we should defend from are those artificially created, resulting from incandescent materials. The risks connected to such radiations may be: crystalline lens opacity, cataract and partial blindness.

DANGERS FOR EYES AND FACE

We can consider the following table, If we wish to list all kinds of risks, associating them with relative sources of danger to which we may be subjected in an industrial context:

RISKS	DANGER	SOURCE
MECHANIC	Projection of metal particles	Metal working machinery, welding chips, riveting, cutting of metal wires, grinding
	Projection of stone particles or minerals	Sandblasting, stone working, sculpture, grinding, rock drilling
	Projection of wood/fibrous particles	Wood turning, felling tree, bush removal
	Coarse particles suspended in the air	Cement mixing, stone working, sawdust, sanding, grain storage, flour milling, coal mining and processing
	Sprays/splashes of molten metal	Metal castings, metal skimming, die-casting, oxy-cutting/cutting with torch, brazing
	High pressure water	Water jet cutting
	Electric short-circuit arch	Power transmission systems
CHEMICAL	Splashes of chemical products	Bleaching, battery filling, plating, degreasing, paint stripping, mixture
	Liquid aerosols	Spraying of crops, painting and spray varnishing, fumigation/disinfestation
	Steam jets	Leaking pipes, valves of containers under pressure
	Fine dusts	Cement mixing, wall sandblasting, cement sprinkling, varnishing
	Fumes, vapours and gases	Varnishing, adhesive application, exhaust gas analysis, welding, fumigation/disifenstation
	Biological agents/viruses	General surgery, dental surgery, first aid, medical research, waste management
OPTICAL RADIATIONS	Infrared	Furnace, metal castings and metal melting, gas welding/brazing, oxy-cutting/cutting with torch
	Glare	High-temperature furnaces, high-intensity artificial light, intense sunlight
	Ultraviolets	Electrical arc welding, high-energy electroluminescence lamps, dental care lamps, short-circuit electric arcs, intense sunlight, machinery for varnish polymerization
	Laser	Laser measuring equipments, laser cutting, diffused radiation by laser systems, production/repair of laser system