Basic Lens Dispensing Part 5

Types of Coatings

Hard Coating

Hard coating is generally applied to both surfaces of the plastic spectacle lens to improve the scratch resistancy of the material. Generally all plastic lenses of every different refractive index will be supplied with hard coating.

Why Hardcoat?

• To Improve Abrasion Resistance of Plastics
• Introduced in 1970’s. Ongoing Development  

Please refer to Eyetalk Reference Guide Lens Materials for further clarification.

NB: CR39 is not a recommended material for rimless or nylon frames.

AR Coating

Anti Reflective (AR) coating will improve the aesthetics of the lens as it virtually eliminates reflections. AR coating also benefits the customer as it allows more light to pass into the eye system (99 per cent) which in turn improves their visual acuity.

AR coating is sometimes referred to as Multi Coating, which is simply multi layer coatings deposited on the lens, which in turn creates an anti reflective AR coating.

How AR Coating Works

• An uncoated lens transmits and reflects all wavelengths (colours) of light equally
• An AR coated lens reflects some wavelengths more than others achieved by destructive interference more layers of coating = more efficient AR properties

Benefits

• Better cosmetics
• Better vision
• Increased transmission
• Reduced side glare
• Reduced side glare
• Reduced eyeball reflections

Mirror Coating

Generally applied to prescription sunglasses.

Transmission is the amount of light that passes through the lens. The more light that passes through the lens to the eye, the better the patient can see.

• CR39: Glass transmission 92 per cent, reflection 8 per cent
• With AR Coating: Transmission 99 per cent, reflection 1 per cent

Lens Design 

• Lens design today is about creating a lens that will give the wearer the most benefit.
•  When designing, you must adhere to basic principles and standards:
               - Focal Type: Single Vision or Multi-focal vision
               - Surface Design (Progressive lens, Aspheric)
               - Durability
               - Cosmetics

Bifocals

A range of different types of bifocals available, refer to image on right.

Trifocals

A range of different types of trifocals available, refer to image on right.

Progressive Lenses

• Progressives allow vision in the distance, intermediate and near zones, without having visible lines in the lens.
• Achieved by blending the different curvatures into the lens surface.
• Result is like a tracing of a key-hole.

Progressive Key-Hole

• The eye must be lined up in the correct position, to maximise the viewing area.
• Modern designs have increased the size of these areas.
• When comparing progressive designs, contour plots can show design differences.

Part 5 of the Basic Lens Dispensing series has been reproduced with kind permission from ODMA. This article appeared in the ODMA Retail Guide, in the Education and Training section, under the heading of ‘Basic Lens Dispensing Part 5’.

Independent practitioners, who would like to receive a copy of the ODMA Optical Retail Guide, should contact ODMA on E: marketing@odma.com.au.

ODMA gratefully acknowledges Carl Zeiss Vision’s contribution to the ORG’s five introductory Basic Lens Dispensing articles.