For all spectacle wearers, mist on the lenses is a major cause of visual disturbance. Many situations in everyday life can cause temporary "blindness" due to quick transition from cold to hot. This occurs in temperate regions, during the winter time when entering a warm room, when playing sport or simply cooking. In hot regions, transition from an air-conditioned environment to the outdoors has the same effect. The technical challenge to respond to this issue consists of combining a real anti-mist property with the other properties expected from an anti-reflective lens: anti-reflective efficiency, scratch-resistant, easy maintenance. This is the challenge that Optifog lenses intend to take up, making everyday life easier for spectacle wearers.

Anti-reflective and anti-fog lenses: the technical challenge

When an ophthalmic lens is taken from a cold environment into a warm environment, the humidity present in the warm environment condenses on the cold surface of the lens. This phenomenon depends on:

• the temperature difference between the two environments
• hygrometry in the warm environment
• exposure time to the temperature / humidity in the warmest environment.

This condensation phenomenon represents the change in the physical state of water (liquid/gas).

Depending on the surface properties of the ophthalmic lens, two types of condensation can happen and affect the wearer's vision:

• the formation of fine droplets: appearance of a white veil and loss of contrast
• the formation of big drops or a continuous film of water of nonuniform thickness: visual deformation.

To retain perfect vision a film of water of uniform thickness must be formed.

Solving the problem: the optifog system

To reduce the angle of contact with water, whilst retaining its high level dirt-resistance properties, a new type of molecule has been grafted by vacuum deposition onto the surface of anti-reflective lenses.

To obtain a contact angle of 0° and form a perfectly uniform film of water on the lens surface in case of exposure to mist, this layer has to be activated with a liquid solution (Optifog Activator). Just apply a drop of concentrate to each side of the lens, using an even, circular movement.

Only the synergy between this liquid and the surface of the lens treated by the molecule discovered in our work results in absolute antimist properties (no loss of contrast, no visual deformation). Also, dirtresistance properties have been maintained at a satisfactory level for wearers. The concentrate has cleaning properties which optimise lens cleaning on application.

An international patent has been registered for this system comprising an anti-mist layer + Optifog Activator (WO2011/080472 A2).

To assess properly the anti-mist efficiency of Optifog lenses, a new system of automated optical measurement has been developed.

This is used to evaluate the anti-mist performance (contrast/clarity) of the lens. IT processing is then used to trace graphs of percentage contrast and clarity according to time.

Compared to standard anti-reflective lenses with activation by an antimist solution, the Optifog system offers optimal anti-mist efficiency. Performance is effective for one week before reactivation is required, whereas the anti-mist solution is totally inefficient after standard AR lenses have been wiped once.

Fig. 1

Performance tested in a real life situation

For each benefit measured, Essilor has systematically cross-referenced the scientific data from Research and Development with the experience of wearers and opticians.

Wearer experience was collected in 3 different ways, to ensure that the benefits observed during instrumental tests are indeed perceived in real life situations.

Fig. 2

•  Sensorial analysis: this is a scientific method for evaluating products based on the various senses. The specialised independent laboratory Eurosyn tested Optifog lenses using this method, following a protocol validated by the staff of Professor José Sahel* at the Vision Institute. Eurosyn implemented a lens evaluation process amongst a panel of 100 wearers. In this specific case, only vision was tested.

*Professor José Sahel receives no compensation in a private capacity for the validation of these protocols.

•  Test on wearing. The product was evaluated with wearers in real life situations, over a period of several months. This test follows a well defined protocol which combines both subjective evaluation and objective tests of the product's efficiency.
   
•  Market tests performed in various countries, where wearers were asked questions after wearing Optifog for one month. The experiences of opticians was also collected through market tests performed in various countries (India, HK, Finland), after a minimum of 3 months testing.

Wearers who tested Optifog lenses in everyday life situations in which mist can occur on their lenses, were generally very well satisfied:

• 79%(1) of wearers were satisfied by the anti-mist effectiveness (2)
• 81%(1) of wearers were satisfied with their lenses after 1 week of activation (2)
• 77%(1) of wearers were satisfied by the ease of cleaning of their lenses.
• 87%(1) of wearers were satisfied by the transparency of their lenses after cleaning.

(1) Source: Comparative wearer tests carried out by an independent institute. France 2011, n=100 wearers

(2) Average assessment of anti-mist effectiveness after 0, 8 and 20 seconds.

Results of the market tests performed with opticians also show a high degree of satisfaction with the anti-mist performance of Optifog [1] lenses:

• 79% of opticians who had sold Optifog lenses confirm that their patients were satisfied with the anti-mist effectiveness [2] 
• Opticians confirm wearer satisfaction in terms of resistance to dirt (79%) and ease of cleaning (74%) [3].

The result of research undertaken by Essilor, Optifog lenses benefit from an exclusive anti-mist layer. Activated by a specific liquid, this layer guarantees lasting hydrophilic properties which avoid the loss of contrast and visual deformation generated by mist. Performance levels have been validated by the laboratory and confirmed by various tests carried out on spectacle wearers worldwide. We have been able to measure both efficiency against mist and ease of usage amongst both wearers and professionals. Further to these highly satisfactory results, Optifog lenses are now available in all the various geographic areas.

Fig. 3