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Home > Choosing Prescription Glasses Lenses at Posh Eyes

Choosing Prescription Glasses Lenses

Our standard thickness lenses are made of a plastic known as CR39, which has been the standard lens material for glasses for many years. CR39 lenses are half the weight of glass lenses. Also, high quality coatings, such as Crizal Sapphire UV, applied to plastic lenses offer scratch-resistance equivalent to glass.

Thinner lenses, known as high index lenses, are thinner and lighter than regular CR39 plastic. For a given prescription and frame design, the factor which determines lens thickness is the refractive index of the lens material. Material with a high refractive index bends light more than material with a lower refractive index. CR39 material has a refractive index of 1.5. Material with a refractive index above 1.5 is considered a high index material. Our high index plastic lenses are available as 1.6, 1.67 and 1.74 index. We also offer polycarbonate lenses (1.59 index) which are 10 times more impact resistant than regular plastic lenses.

In addition to the refractive index of a lens, final lens thickness is determined by a number of factors including:

-      Your prescription

-      You pupillary distance (PD)

-      The shape of the lenses

-      The size of the lenses (both vertically and horizontally)

-      The bridge size of the frame

-      The lens design

Please contact us with your prescription, PD and preferred frame if you would like us to calculate the maximum thickness of your lenses.

The majority of single vision lenses we fit are pre-moulded to a specific prescription. These are known as “stock” lenses, and our glasses prices reflect the value that these lenses offer. However, stock lenses are not suitable for certain prescriptions in rimless and semi-rimless frames as the resulting edges are too thin (a minimum edge thickness of 2mm is required for these types of frame). In such circumstances, specially made lenses, known as “surfaced” lenses are required. Surfaced lenses are priced differently to stock lenses due to the additional work involved in their manufacture. Surfaced and stock lenses are of equal visual quality.

We only recommend surfaced lenses where stock lenses are not suitable, as we always discuss the options with our customers prior to processing orders. Our surfaced lens supplements are as follows:

Lens Type

Surfaced Lens Supplement*

1.5 index


1.59 index


1.67 index


1.74 index


*Surfaced lenses include Crizal Easy UV, anti-reflection, scratch-resistant coating as standard. The 1.74 index lenses include the Crizal Sapphire UV coating as standard.

Photochromic Lenses (Transitions)

Photochromic lenses (Transitions) go dark when exposed to Ultra Violet (UV) light. Transitions are available in colours grey, brown, and now new graphite green.

The latest Transitions® lenses (Transitions® VII) achieve over 85% light absorption in direct sunlight and are more responsive to direct and indirect sunlight than standard photochromic lenses. This means the lenses go darker and fade back to clear quickly when you go inside. Transitions® lenses also provide 100% UVA and UVB blocking.

Transitions®  XTRActive lenses are the darkest outdoor photochromic lenses, and even go darker inside a car. Transitions®  XTRActive lenses are available in grey colour only. Please click HERE to watch the video on Transitions® and Transitions®  XTRActive lenses.

Lens Coatings

Selecting a high quality coating will extend the life of your lenses. All our top name designer glasses come with free single vision prescription lenses with scratch-resistant coating.

Our anti-reflection coating reduces distracting reflections for the wearer from both the back and front of the lenses.

Crizal Easy UV coating is an anti-reflection coating which offers excellent smudge and scratch-resistance , as well as 100% UV protection. The Crizal Alize+ UV provides the highest level of dust repellence. The top-of-the range Crizal Sapphire UV coating offers the best performance and attracts a 2 year no-scratch guarantee. The latest Crizal Prevencia coating absorbs harmful blue and violet light commonly emitted from computer screens and artificial indoor lighting. To find out more about Crizal Prevencia please see our video HERE

Crizal Coatings are applied only to the best lenses providing the clearest, crispest vision. By selecting a Crizal coating for your single vision lenses, you will be automatically upgraded to the highest quality lens of the same refractive index (thinness)

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