Overview of Toric Intraocular Lenses
Ocular astigmatism, a vision condition that makes images appear blurry, is responsible for 13% of all vision issues that patients experience. The first effort to treat this condition was made in 1825 by George Airy who used cylindrical lenses to fix his own vision.
The exact reason why people develop astigmatism is unclear. But scientists believe it could be due to things like genetics, the way the eyelids put pressure on the eyes, muscle tension around the eyes, and the way our brain processes what we see. Overall, ocular astigmatism is a combination of corneal astigmatism, due to changes on the surface of the eye, and internal or residual astigmatism that comes from irregularities in the lens of the eye.
In the past, doctors used keratometry and videokeratography to measure corneal astigmatism. These methods were useful for gauging the anterior cornea’s curvature (the front part of the eye). Today, thanks to advanced imaging technologies, we can now also measure the curvature of the back of the cornea. This has resulted in a better outcome for patients undergoing cataract surgery.
These days, cataract surgery is being used to eliminate both kinds of vision defects (spherical and cylindrical power), helping patients to get rid of their glasses or contact lenses. Around 40% of patients with more than a small amount of corneal astigmatism who are undergoing cataract surgery.
Different methods are used to correct corneal astigmatism during cataract surgery. They include the use of toric intraocular lenses (IOL), making a small cut on the cornea (clear corneal phacoemulsification incision) at the part that’s most curved, making cuts on opposite sides of the cornea (paired opposite clear corneal incisions), and relaxing the curvature of the cornea (limbal relaxing incisions).
Toric IOLs, which were introduced in 1992, are considered the most predictable way to correct corneal astigmatism. This type of lens has seen many improvements over the years to make it more stable and better aligned after surgery.
Why do People Need Toric Intraocular Lenses
Toric IOLs are special types of lens implants used in eye surgery. They are a great option for people who have more than 1 D (diopter, a unit used to measure the correction needed in an eyeglass prescription) of corneal astigmatism. Astigmatism is a condition where the front surface of your eye, the cornea, is not perfectly round but is more like a football shape. This can lead to blurry or distorted vision.
Here’s when toric IOLs might be used:
1. For older adults with astigmatism and advanced cataracts: If you have more than 1.00 D of astigmatism as well as severe age-related cataracts that require surgery, you might be a good candidate for toric IOLs. If you wish to see clearly up close without glasses, you might be advised to consider multifocal toric IOLs which provide both distance and near correction.
2. For people with mild to moderate keratoconus or other corneal deformities: Keratoconus is a condition where the cornea bulges out, creating a cone-like shape. If your astigmatism is regular and has not progressed over time, toric IOLs could be beneficial for you. In some cases, customized IOLs, which are not standardly used but can be designed specifically for a person’s eye, may also help those with irregular astigmatism. However, this option should be fully discussed with the doctor so that your expectations can be clearly understood.
People who have had a specific type of corneal transplant surgery (penetrating keratoplasty) and have a lot of irregular astigmatism, as well as those with stable astigmatism due to corneal scars, might also benefit from toric IOLs. Corneal scars could be the result of healed corneal ulcers, surgery to remove a growth (pterygium) on the eye, or surgical repairs done after a tear in the cornea. Regardless of the situation, it’s important for the condition to be stable before considering these lenses.
When a Person Should Avoid Toric Intraocular Lenses
If you have zonulopathy, a condition affecting the fibers (zonules) holding your lens in place, eye surgery can be more difficult. Zonulopathy occurs for various reasons and can be present from birth or develop later. These fibers need to be strong to ensure the stability of the eye’s lens implant (IOL).
Scarring on the cornea or irregular curvedness of the eye’s surface (astigmatism) can make it less suitable for placement of toric IOLs, a type of lens implant designed to correct astigmatism. The surgery might not completely eliminate the astigmatism, but it often reduces its effect. But before choosing this, your ophthalmologist will discuss this with you depending on your expectations.
If your pupils don’t widen (dilate) enough, it limits the doctor’s view, making the alignment of the lens implant more challenging.
If you have retina conditions, or if you had surgery related to the vitreous (clear gel filling in the back of the eye), it might affect the success of the surgery and the improvement in your vision. Likewise, if you have uveitis (a type of eye inflammation), glaucoma or had glaucoma surgery, the original eye issues may prevent you from getting the best possible vision after the surgery.
An accident during surgery where the back part of the lens capsule tears can also make the surgery more complicated as it may lead to the lens implant moving or tilting after the surgery.
Finally, this surgery might not be the best option for you if you have unrealistic expectations about how much your vision will improve.
Equipment used for Toric Intraocular Lenses
The process of inserting a special type of lens, known as a toric Intraocular Lens (IOL), into the eye requires specific equipment for different steps. Here’s an outline of what these steps are, and what equipment is used.
Firstly, we need to figure out the amount of astigmatism in the cornea, which is the curved, clear front surface of your eye. For this, we make use of devices like Schiempflug imaging devices, scanning slit devices, anterior segment optical coherence tomography, and ray tracing devices.
Next, we calculate the areal power of the eye (the eye’s ability to focus light). We do this using optical biometry devices such as IOL master or Lenstar. These compute the curvature of the cornea and the length of the eye using manual keratometers and either A-scan or B-scan.
Planning where to make the incision and how to place the IOL is done with help from online calculators. They take into account different factors, including surgically induced astigmatism, which varies from surgeon to surgeon.
For pre-operative axis marking, different types of markers are used, such as the weighted thread, Geuder-Gerten pendulum marker. Nuijts-Solomon bubble marker, or tonometer marker.
During the surgery, alignment of IOLs is guided by marking tools and systems like the Mendez gauge and beveled degree gauge. In certain cases, a femtosecond laser might be used to mark the axis in the surgery. Image-guided marking systems like Verion, iTrace, true guide, Callisto, and Z aligns can also be of help.
The process of removing the natural lens to replace it with the IOL is done using a peristaltic or venturi-based machine. When using a femtosecond laser for the surgery (known as FLACS), the machine creates the incisions and breaks up the lens.
Toric IOL are single-piece lenses made of a material called hydrophobic acrylic, with markings on their rear surface that indicate the flatter axis and need to align with the pre-operative markings. They are more likely to stay in place compared to silicone IOLs and can correct astigmatism from 1.00 D to 6.00 D. Special versions of Toric IOLs are also available to correct higher astigmatism and can be either monofocal, multifocal, extended depth of focus, or phakic.
Who is needed to perform Toric Intraocular Lenses?
An eye specialist called an optometrist will check your eyes before surgery. They will measure your eyesight, both with and without glasses, and will also study the structure of your eye. This includes checking the length of your eye and the shape of your cornea (the clear, front part of your eye). They will assess if you are fit for the planned surgery by doing an anesthetic evaluation, which checks how your body will react to the medicine used during surgery.
Usually, the surgery is done under local anesthesia, meaning you’ll be awake but won’t feel any pain. But, if you are nervous, you may be given medicine to help you relax. Patients with other health conditions like heart or brain-related problems may need constant check-ups during the surgery.
An ophthalmologist (eye surgeon) typically carries out standard surgery techniques like phacoemulsification or Femtosecond Laser-Assisted Cataract Surgery (FLACS) to put in a new lens inside your eye. A skilled attendant will assist the surgeon during the procedure. After the surgery, either the nurses in the hospital ward, or the eye surgeon will take care of you and let you know what you need to do for recovery.
Preparing for Toric Intraocular Lenses
Before cataract surgery, the doctor will thoroughly examine the patient’s eyes to assess the condition of the cataract, pupil dilation, tear film (the protective layer of tears on the eye surface), and rule out any other eye health issues. If dry eyes or other surface disturbances are found, these will be treated first. The doctor will explain the surgery procedure and what to expect on the day and ask for written consent from the patient.
The steps in preparing for a specific type of cataract surgery called Toric Intraocular Lens (IOL) Implantation include:
1. Working out your total corneal astigmatism (the level of curving of your cornea, the clear front surface of your eye).
2. Calculating spherical power (the lens power needed to focus light onto your retina).
3. Making a plan for the incision (cut into the eye) and lens alignment.
4. Doing Phacoemulsification (a surgical method used to break up and remove cataracts) or FLACS (Femtosecond Laser-Assisted Cataract Surgery) for implanting the Lens.
5. Taking care of your eyes after the surgery.
To measure your total corneal astigmatism before the surgery, different tools and methods can be used, including specialised equipment or a chart called the Baylor toric nomogram.
Calculating spherical power involves considering various factors like the curvature of the back of your cornea, the position of the implanted lens and changes caused by the surgery. This can be done using ultrasonic or optical measurement systems and various specialised tools.
It’s essential to mark the central line of the eye to properly implant the toric IOL and achieve the best vision after the surgery. This marking can be done by hand or by using advanced technologies. Various online calculators and formulae are available to assist with this.
Several brands of toric IOLs are available. The specific lens chosen will depend on factors like availability, cost, and surgeon preference. The lens that leaves the least amount of distortion in the eye’s shape after surgery will be chosen. It’s important not to overcorrect the curving of the cornea as this could lead to a change in the direction of eye correction needed (also known as flipping the axis).
Before surgery, important points on the eye are marked to guide the surgeon. This is done before the patient is positioned at the operating table using manual marking methods, a slit lamp, a bubble, or a pendulum marker.
How is Toric Intraocular Lenses performed
An intraocular lens (IOL) implantation is a procedure done to replace the natural lens in your eye, usually because it has become cloudy due to a cataract. Here’s what you can expect during the surgery:
1. Anesthesia: Depending on what you and your surgeon are comfortable with, you may receive anesthesia. This could be applied directly to your eye (topical), injected around your eye (peri- or sub-tenon anesthesia), or to numb the inner parts of the eye (peribulbar anesthesia).
2. Marks for the IOL: The surgeon will mark the place where the IOL will go, keeping in mind the curvature and measurements of your eye. This can be done manually or using computer-assisted devices and images.
3. Making the incisions: Your surgeon will make a cut in your cornea (the clear front part of your eye). The cut won’t need to be stitched up at the end of the surgery because it will heal on its own.
4. Preparing the lens capsule: The surgeon will then open up a part of the thin membrane surrounding your lens (the lens capsule) using a technique known as “capsulorhexis.” This process should be done carefully and precisely to ensure that the IOL can be placed properly and doesn’t move around after the procedure.
5. Removing the lens: Your lens will be broken up and removed using ultrasound technology (phacoemulsification), and any remaining particles will be washed out. The surgeon will also polish the lens capsule to reduce the chances of cloudiness after surgery.
6. IOL placement: Once your lens has been removed, the surgeon will insert the IOL into the now-empty lens capsule. The IOL will be rotated into position, making sure it’s perfectly centered in your eye.
7. After surgery: You’ll be asked to lie on your back for about an hour after surgery to prevent any changes in the IOL position as your eye starts to heal. You’ll also be given eye drops to reduce inflammation, and a prescription for steroids that you’ll take at home. Your doctor will check your IOL placement several times during your follow-up visits.
Remember, everyone’s eyes are different, and so every IOL implantation surgery could be a little different. Your surgeon will explain your specific procedure and recovery process to you during your pre-operative consultation.
Possible Complications of Toric Intraocular Lenses
Installing toric intraocular lenses, or IOLs (artificial lenses that replace your eye’s natural lens), has a unique complication called IOL misalignment. This is when the artificial lens isn’t aligned correctly in your eye. Many factors can influence this, such as the technique of placing marks on the eye, the size of an opening made in the lens (capsulorhexis), whether the IOL is covered by the edge of this opening, how the cut on the cornea is sealed after surgery, how stable the IOL is in terms of rotation, and the experience of the surgeon.
This misalignment could be because the required alignment of the IOL was wrongly determined, or because it was misplaced during surgery or rotated after surgery. If the lens is misaligned by 30 degrees or more, it could negatively affect the vision. Even a slight misalignment of one degree can reduce the effectiveness of the lens, and by 30 degrees, the lens might lose all its effectiveness and seriously degrade vision quality.
The IOL can start rotating from one hour to ten days after surgery. This could be due to incomplete removal of a jelly-like substance (viscoelastic), used to maintain eye shape during surgery that remains in the eye bag. Late rotations might be due to aspects like how the IOL is designed, whether the opening made in the lens is extended, the size of the eye bag and the eye, and whether the IOL is adequately covered by the edge of the opening. Eyes with a specific misalignment of the cornea (astigmatism) can have a higher rate of post-surgery rotations.
If the lens has misaligned by more than 10 degrees, it may need to be realigned. To do this, a mark would indicate the new target position for the lens, and a long thin tube (cannula) would be used to gently rotate the lens to this position.
Surgery for implanting toric IOLs, as in any surgery, comes with potential complications either during or after surgery.
During surgery, you might encounter problems like corneal wounds, issues related to opening made in the lens (rhexis), infection related issues related to the lens.
Soon after surgery, complications may include corneal swelling, an increase or decrease in eye pressure, inflammation within the front part of the eye, presence of blood in the anterior chamber of the eye, leftover lens material after cataract surgery, or unexpected corrective results from the surgery.
Later issues may include opacification (clouding) of the lens’s posterior (back) capsule, swelling of the retina (the layer at the back of your eye that senses light), inflammation within your eye, retinal detachment (where the retina peels off the back of the eye), loosening or dislocation of the lens, complications with the cornea, or recurrent inflammation of the uvea (the middle layer of the eye).
What Else Should I Know About Toric Intraocular Lenses?
Toric IOLs, which are special lenses implanted in the eye, often lead to happy patients and improved vision, with many able to achieve 20/40 vision or better.
Before having these lenses implanted, doctors will carry out a detailed examination to select suitable patients and decide on the lens placement during the surgery. The doctor will also consider the risk of complications during and after the procedure.
New technologies now make it possible to measure both the front and back curvature of the cornea, helping doctors to estimate how well the toric IOLs will work.
In some cases, a type of surgery called femtosecond laser-assisted cataract surgery is used in combination with toric IOL implantation. This can further improve visual outcomes by reducing distortions, otherwise known as “higher-order aberrations.”
Newer toric IOLs are even better because they are less likely to rotate after surgery and, therefore, provide more predictable visual results. This technology can be used for a wider range of eye conditions, such as irregular astigmatism (which is an unusual curve of the cornea), very high corneal astigmatisms (a more severe curve of the cornea), post-keratoplasty (after corneal transplant surgery), and corneal ectatic disorders (where the cornea becomes weaker and changes shape).
