Toric lenses | Contact Lenses for Astigmatism | Benefits of TL

Toric Lenses & Astigmatism

 ( Will Contact Lenses  be a Solution or Not?)

Toric lenses are contact lenses are used to correct astigmatism; a refractive error in the eye caused by an imperfect curvature of the cornea. When light enters the eye, it is not focused properly on the retina, resulting in distortion. The most common symptoms of this condition are blurred vision, sensitivity to light, squinting, headaches and eye strain.

A common eye condition known as an astigmatism often goes undetected because of the minimal effect it has on a patient's vision. Some astigmatisms can lead to blurred or impaired vision if they become moderate or severe. The cause of the blurred and impaired vision is the result of the eye's cornea or lens having an irregular shape. In a normal eye the cornea has a circular shape, whereas corneas with an astigmatism have a longer oval shape.

There are many approaches to correcting astigmatism for the contact lens wearer. One of the most common approaches has been to ignore astigmatic error, applying spherical equivalent correction. This is a legitimate approach for low amounts of astigmatism or situations where simplicity and cost are of higher priority than acuity. Performance in sports such as soccer or hockey, for example, while requiring good vision, is not likely to suffer due to a visual acuity that is not a perfect 20/20.

The design of a toric lens ensures that the lens does not rotate in your eye if you blink or move your eyes. This is necessary as toric lenses contain two powers perpendicular to each other, one to correct the astigmatism (CYL/Cylinder) and the other to correct either short-sightedness or far-sightedness (SPH/Power).

The selection of toric lens parameters is steadily increasing year by year, most notably in the range of available cylinders for monthly replacement toric lenses and axis measurements for daily replacement, single use toric lenses and silicone hydrogel torics. The manufacturing process for toric lenses is more complex and this is reflected in higher prices compared to standard soft contact lenses.

Unlike spherical lenses, toric lenses are designed not to rotate on the eye. Continual exposure of the inferior front surface of the lens to drying during the inter-blink interval could lead to deposit formation but the surface technology applied to some silicone hydrogel lenses renders them highly deposit resistant, especially for protein. Despite this advantage, some silicone hydrogels have been prone to lipid deposition particularly when a surface treatment is not used.

Lipids can diffuse into the lens matrix and cannot be extracted by lens care solution surfactants, leading to regions of reduced lens wettability. This response can vary between individuals and while deposition of native tear film lipid is important for lens lubrication, a buildup of oxidized lipid deposits can be problematic, leading to contact lens discomfort and intolerance. The addition of a ‘rub and rinse’ step to the lens care regimen is important for these wearers, especially in non-surface treated lenses.

Toric Contact lenses Advantages & Disadvantages 

The advantages of a soft toric contact lens include easy adaptability, as comfort is usually quite good even initially. Other advantages of soft toric lenses include:

• Extended wear option –allowing up to thirty days of continuous (overnight) wear.
• Eye color –soft torics are available in various colors that can change even the darkest eyes to a variety of colors.
• Convenient replacement schedules –conventional lenses allow you keep the same lenses for a year, or the more common "disposable lenses' allow you to wear for one month, 2 weeks, or only once and throw away, with no need to ever clean them.
• One of the chief benefits of fitting a toric lens is the improvement in vision over a spherical lens. Even for low levels of cylinder, the improvement can be significant. A three to 5.5 letter improvement in vision compared to the spherical equivalent or ‘masking’ was observed for low astigmats (≤1.00 DC) and 8.5 up to 12 letters of acuity improvement was observed in high astigmats (1.25 to 2.00 DC) when they were fitted with toric lenses rather than sphere (P<0.05). A one or two line improvement in visual acuity shows the visual benefits the practitioner can offer are significant, even for a low astigmat.

Their biggest disadvantage is the potential for fluctuating vision. No matter how good the lens design and fit, all soft toric lenses rotate and move a bit in the eye. As explained earlier, this can be a source of frustration when you can see clearly one minute, and are blurry the next. The more astigmatism a person has, the more likely he/she will be sensitive to the lens movement.

Conclusion

When choosing a toric lens, consider your patient's history, needs and demands in addition to optical and physical requirements. Previous contact lens wear experiences will also provide valuable clues to help you develop a successful contact lens program. Demands of perfect vision or perfect comfort, as well as occupational or athletic needs will guide you in your first decision: whether to proceed with a soft lens or a rigid lens.