For most people with astigmatism, eye doctors recommend contact lenses and specifically toric contact lenses. How do toric contact lenses work? Most contacts are shaped like a semicircle that conforms to the eye. That is where toric contact lenses come into play. These lenses work with your eye motion and gravity to help with your visual distortion and blurry vision. The majority of toric contacts feature soft lenses, but if you have severe astigmatism, the eye doctor may suggest gas-permeable toric contacts hard lenses that help oxygen reach your eyes.
Both options are great for correcting symptoms of refractive errors. You can order toric contacts in many forms, including daily wear and extended wear. If you prefer to dispose of your contacts at the end of each day, daily wear is the way to go. However, if you want contacts that can last longer and that are okay to sleep in if you forget to take them out one night , extended wear is the better choice.
Many people with astigmatism are farsighted or nearsighted, too, so the corrective eyewear will often cover an additional prescription.
People who treat one refractive error may wear soft contacts that do not treat their astigmatism. If you want to wear contact lenses and have astigmatism , toric lenses are a great option to correct corneal shape while also correcting other refractive errors.
Toric contact lenses use specific meridians to stay in place and improve your visual acuity. Meridians are measured from your pupil out, like a radius in a circle. These meridians are measured to specific powers to correct your astigmatism. There are also design elements like slightly weighted or thickened edges to help keep these soft lenses in place. There are also different brands of toric contact lenses, which offer different fits.
If you try one brand and it does not situate properly in your eye, another brand is likely to suit your needs. A study published in examined three groups of people subjects with astigmatism who had not worn contact lenses before. Over a one-month trial involving daily wear soft contact lenses, 88 percent of toric lenses fit on the first attempt. While there were reports of discomfort and visual problems leading to some participants quitting the use of the contacts, most reported that their overall vision was as good as with glasses.
When you have low to moderate astigmatism, simple soft or RGP lenses can neutralize it with relative ease. Doctors prefer toric lenses to correct severe amounts of astigmatism. Toric contacts are designed to align with the 6 to 12 o'clock axis. After inserting them into your eyes, blinking makes the lenses rotate and adjust while the weight makes it position itself to its proper alignment.
This can sometimes be irritating to users. Of course, traditional glasses do not have this problem. Generally, many people prefer hard lenses to soft options. But technological advancements and newer designs have greatly improved the comfort and vision that soft lenses can achieve. Large amounts of progressive astigmatism may also indicate other underlying conditions like keratoconus.
These astigmatisms can be treated by using specially designed GPC contacts. Although toric soft contact lenses work very well for many people with mild or moderate astigmatism, they are still not a perfect solution. For example, although toric lenses are weighted in certain places, they can still slip out of alignment fairly often. The refractive strength increases or decreases gradually as you move around the lens.
Toric contact lenses correct for astigmatism issues that arise from a different curvature of the cornea or lens in your eye referred to as regular astigmatism, corneal astigmatism or lenticular astigmatism. In these cases, the cornea or lens is curved so that the refraction of your eye differs between the vertical and horizontal planes.
This causes blurry vision and trouble seeing fine details. Sometimes, vertical lines will appear to tilt. The ability for toric contact lenses to provide different refractive powers on the vertical and horizontal orientations addresses this specific peculiarity that causes astigmatism.
Toric contacts, like all contact lenses, need to be prescribed by your doctor, who can choose the lenses that are right for your vision, and fit them for your eyes. Talk to your eye doctor if you think you need contact lenses for astigmatism or other vision problems. Since toric contact lenses have a particular orientation, they need to stay on your eye in the correct way. Manufacturers design toric contact lenses with features to help the lenses stay put, including:. This means that fitting the contact lenses to your eyes is even more important than usual.
Axis misalignment causes a cross-cylinder effect, resulting in residual astigmatism for the patient. Table 1 shows how the amount of residual astigmatism changes with different amounts of lens cylinder power. Even in low cylinder powers, it's important to adjust for axis misalignment if possible. Here are a few examples of using LARS to adjust for axis misalignment. By rotating the beam on the slit lamp and using the built-in protractor, I measured the lens rotation as 20 degrees left and stable at that rotation.
Patient 2 has a spectacle prescription of —1. The closest soft toric diagnostic lens I had available was —1. The axis is only five degrees off, which should be acceptable in this fairly low cylinder power. Without knowing how the lens might rotate on the eye, that's as close as I could come. The lens was rotating five degrees to the right CCW.
This didn't appear like much rotation, and the lens I was using is available only in degree steps anyway, so the temptation would be to leave everything alone.
However, this rotation means that the patient is looking through axis —10 degrees off-axis from what he needs. With this much cylinder power, you would not accept a pair of glasses being off by 10 degrees, and you shouldn't with soft torics either, if it can be fixed. Using LARS, I subtracted the five-degree rotation from the spectacle axis of to obtain a new lens axis of Assuming the new lens rotates the same five degrees to the right , the patient will end up looking through axis and have no axis misalignment.
Adjusting the axis to reduce misalignment only works if the lens rotation is stable. If it isn't consistent, then visual acuity will always fluctuate as the axis shifts around every time the patient blinks. A loosely fitting lens will tend to exhibit large amounts of rotation with each blink.
Normally, lenses will rotate about five degrees with each blink, but a loose lens will move more than that. It will still tend to drift back to its original position if the patient doesn't blink, however. In this case, you should change to a steeper base curve or larger diameter if these options are available. A tightly fitting lens will tend to not move much between blinks, but won't always stabilize to the same position each time it is worn.
If you manually rotate the lens using the lids, it will tend to stay at that new position. You would need to change to a flatter base curve or a smaller diameter if available. Many brands of toric lenses now come in only one base curve and diameter.
If the lens is inconsistently rotating, the only choice would be to switch brands. It might help to switch to a lens with a different type of mechanism for preventing rotation. Check the manufacturer's promotional materials if you are unsure of the lens design. Ideally, with the proper lens power and axis, the over-refraction would be plano.
If there is axis misalignment, then the SCOR provides clues as to how to fix the lens. It is most likely easiest to use a contact lens over-refraction calculator to adjust the prescription using the SCOR.
To use the calculators, you input the spectacle Rx, contact lens power, and the SCOR, and it outputs the correct lens power to order. It may help to understand the basic principles of SCORs. In general, the more the axis is misaligned, the farther the SCOR will be from plano. Axis misalignment results in crossed-cylinder effects, which can be challenging to decipher.
0コメント