During the past 20 years there have been numerous studies that show the contact lens
dropout rate is about 20%. The main reason in almost all studies is comfort which when studied further is mostly related to dryness. The incidence of dry eye increases with age in men and particularly in women. To help keep patients comfortable in lenses doctors first address the underlying dry eye. Regarding contact lenses there are newer options to help address the comfort/drying as well as improve visual outcomes. These can be broken down into subgroups as follows:
Silicone hydrogels: These lenses now account for more than 80% of new toric soft lenses prescribed. They are a popular option because silicone materials have been shown to decrease complications, such as hyperemia, dryness and discomfort. Silicone is naturally more oxygen permeable so these can prevent corneal neovascularization due to low oxygen at the cornea.
Non-Hema Materials: These lens materials although they are not standard soft nor silicone have improved wetting and less drying properties. A typical soft lens will dehydrate 6-8% during a normal 10 hour day. Newer materials loose only 2-3% of their typical hydration.
Changing from more prolonged wear to daily disposables creates less problem with accumulation of surface deposits. This enhances tear spreading over the corneal surface and improves wetability. It also reduces the risk of infection. Controlled studies have shown a high bacterial colonization rate in cases when ulcers and infectious keratitis is present. A daily replacement lens is not stored so it reduces the infection risk as well as reduces drying.
Newer designs of lenses have a wider variety of both Multifocal (presbyopic) and astigmatism corrections. This shows maturity of the current market and an expansion of newer materials to better address both more difficult prescriptions or more specific tasks
Multifocal lenses which correct for astigmatism. In the past patient with astigmatism had little option but to wear reading glasses over their contact lenses. Today doctors have more freedom to incorporate both into a prescriptions.
With the advent of computerized lathing, newer rigid gas permeable materials and the knowledge gained through scanning laser topographers there has been a resurgence in the use of scleral lens designs. Scleral lenses have the advantage of vaulting the cornea. The lenses are much larger than standard soft or gas permeable lenses. This provides a tear film which in effect bathes the cornea in tears. That principal allows the lenses to be used for both diseased corneas such as dry eye, keratoconus and other specialty designs but also for regular astigmatism. Scleral lenses used to be quite uncomfortable but research on new designs have shown them to be comparable to soft lenses in comfort. The highly polished surfaces give more stable vision correction for patients with astigmatism.
Reverse Geometry lenses: These new lenses have oblate (thinking dipping down like a bowl) versus prolate (think curved like a cone) surfaces. They fit remarkably well for patients that have had corneal surgery such as lasik, Radial Keratotomy, and Photo-refractive keratotomy. In these cases the vision improvement can be quite remarkable as the lenses really replace small optic zones with larger improved optic zones.
Semi-scleral lenses: These lenses are bigger than normal gas permeable lenses but smaller than Scleral lenses. They correct really well for irregular corneal surfaces as well as edge to edge astigmatism. Like Scleral lenses they are also very comfortable.
With newer approaches and solutions contact lens wearers can successfully continue on much later in life and for more varied vision environments.