There’s a lot of talk these days about contact lens discomfort and improving wearability. Alan Saks says this is not new. It’s been a topic since CLs were invented.
Insertion comfort and maintenance of all day comfort is a major focus of industry research and development, academic research and for patient and practitioner alike. Much has been said and done about the importance of lower modulus silicone-hydrogel materials and reducing surface friction. Terms such as lubricity and tribology have become part of our lexicon. Listening to Johnson and Johnson’s Acuvue research and development team during my recent trip to New Orleans, I wouldn’t be surprised if the term ‘disadhesion’ isn’t soon part of our jargon. Their new Acuvue Oasys 1 Day lens boasts a ‘tear infused design’ with ‘tear-like’ properties throughout the si-hy matrix and surface.
Read more about the lens, material, technology, testing and terminology, as well as clinical feedback, at this link via the online version of mizone.
Hard Edges
Although some people don’t think edge design is that important in contact lens comfort, I believe it is one of the most critical factors. I get the impression it’s been underplayed by some recent groups who looked at CL discomfort. I learnt the importance of CL comfort at a young age, when I used to help my Dad re-edge and fine tune PMMA and RGP lens edges. He, in turn, had learned the importance of edge design and shape from the legendary American, George Jessen, one of the truly great contact lens pioneers. We still use his edging techniques today, some 60 years on, and my Dad, now in his 66th year of optometric practice, still hand finishes every one of the RGP lenses he prescribes!
For those that complain about the added cost, I point out they spend more on hair products than they do on their eye products, never mind booze!
On many occasions I’ve seen how modifying the edge shape can be the difference between discomfort and comfortable lens wear, success or failure. With my very own hands, I’ve at times simply modified the edge profile of a struggling patient’s existing lenses and seen them turn into long-term successful and happy wearers. We use a combination of 60°, 90° and 105° degree cone tools to reduce the thick, stepped and bevelled edge one sees on higher minus lenses. We thus create a more tapered profile and then ‘spin’ and very slightly roll the edge on a velveteen or sponge pad. It can work wonders.
Today I rarely need to do this. My primary lab, Corneal Lens Corporation in Christchurch – who also make lenses for Australia via their subsidiary Contact Lens Centre Australia – have highly sophisticated multi-axis DAC lathes that can create the edge shape I desire. They also lightly roll or polish the edge. I’ve sat down with them and shown them what I want. By placing a lens on a DMV holder, concave side up and viewing the backlit lens, side-on through a 20X magnifier, one can clearly view the edge profile. Of course it takes time, skill, mentoring – a touch of obsessive compulsive behaviour – and many patients, to get to the point that one can judge a good edge from a bad one and know how to fix it. Essentially I describe the edge I want as a well-tapered ‘sharpish’ edge. Some people think my edges are too ‘sharp’ and not ‘rounded’ enough. My uncle, who preferred a blunter, more rounded, rolled edge once took a look at one of my edges and pronounced, “You could shave with that edge!”
I felt a lot better about it after I re-edged one of his unhappy patients’ lenses, while he was away on leave and they were ‘happy as’ afterwards.
My feeling and experience tells me that a thin, sharp, tapered edge offers lower resistance, less of a hurdle and less work for the lids to negotiate. Hence the lens edge will likely be less insulting to the lid wiper and tarsal conjunctiva.
Surface quality, finish, polish and condition are of course also important. Hence why my patients are prescribed separate cleaners and conditioners and where necessary, deproteinising enzyme cleaners too. None of this multipurpose all-in-one nonsense. If a patient whinges about this extra care, I ask if they use an all-in-one conditioner/shampoo. None have ever admitted to that sin. For those that complain about the added cost, I point out they spend more on hair products than they do on their eye products, never mind booze!
The Soft Option
We see a wide variation in edge design of soft lenses too. Many of you will have seen the shadowgraph images of commonly used disposable lens edges. Some edges look like a ski-tip, while others look like a chisel with a pronounced angular bevel and most things in between. Some of this is due to the manufacturing and moulding techniques. The edge on lenses made with Alcon’s Lightstream UV-cured lenses, are determined by the shape of the glass moulds and the mask. The mask delineates the junction between the liquid polymer exposed to UV that cures, versus that which is occluded by the mask, remains liquid and is then rinsed away. This creates a different edge shape to wet, cast-moulded lenses that are not UV cured, or to those that are spun-cast, which are again different to lathe-cut conventional soft lenses.
Keep An Open Mind
Interestingly, we see different patients respond to different lenses. One can fit a given brand on a given eye and get a poor comfort response and then try another brand and get a rave review. Even though a lens like Dailies Total 1 provides superb comfort for most patients, there are a few who say it feels thick or ‘moves too much’.
For another patient – with a smaller or larger HVID than average – a smaller or larger diameter is sometimes called for in order to obtain the best comfort. Sometimes we even need to make a custom lens.
Keep an open mind: Prescribe and have access to a variety of lens designs and brands.
There’s no panacea or a single brand ‘one stop shop’ in contact lenses. I doubt there ever will be. Humans are simply too diverse to fit in one box.
2016 is gearing up for the release of some exciting new lenses. I suspect we may also see some new materials, range extensions, myopia control and even drug-eluting contact lenses for allergy management, but maybe not quite yet in Australia?
It’s all good.
Have a great year.
Alan P Saks MCOptom(UK) Dip.Optom(ZA) FCLS(NZ) FAAO(USA) is a third generation optometrist based in Auckland, New Zealand and columnist for mivsion. He is actively involved in the profession, having served multiple terms as president of Contact Lens Societies and arranged numerous conferences. He has also served on education committees, as examiner in contact lenses and clinical optometry examinations, lectured contact lenses to ophthalmology registrars and written several columns about eye health and the practice of optometry.
