What is Phakic Intraocular Lens Myopia?
Myopia, commonly known as nearsightedness, is when the eye focuses rays of light just before they reach the back of the eye, instead of right on the retina. This often happens when the eye is relaxed or at rest. Various surgical treatments have been developed for this condition, including laser procedures like LASIK, PRK, LASEK, and Epi-LASEK. Other methods involve inserting materials into the eye, such as intracorneal ring segments (ICRS or INTACS), clear lens extraction (CLE) or phakic intraocular lens/IOL (PIOL) implantation.
Laser procedures are effective for treating low and moderate myopia. Intracorneal ring segments can be used for low myopia, though the outcomes can be unpredictable. If the eyes have a high degree of myopia, laser procedures or ICRS might not be suitable. In such cases, phakic IOL implantation might be an option. This method offers a better vision quality that is not available with other techniques and has the benefits of preserving the focusing ability of the eye and requiring minimal changes to the natural lens.
Regarding the history of Phakic IOLs, in 1953, Benedetto Strampelli first used an anterior chamber IOL (ACIOL) to correct severe myopia. However, this wasn’t widely used due to complications such as damage to the inner layer of cornea, inflammation of iris, blockage in the fluid flow in the eye, and increased eye pressure (glaucoma). Later, Joaquin Barraquer introduced an improved version of IOL, but this model also had similar complications and didn’t become popular.
Over time, the design and effectiveness of phakic AC-IOLs improved, thanks to contributions from experts like Fechner and Worst, who worked on iris fixed IOLs, Baikoff, who developed angle-supported AC-IOLs, and Fyodorov, who introduced posterior chamber IOLs and fixed them in the groove of the eye’s ciliary muscle.
What Causes Phakic Intraocular Lens Myopia?
When a baby is born, their eyesight usually starts off a bit far-sighted (hyperopia), which means they see things clearer at a distance than up close. This far-sightedness is around +2 D (a unit used to measure the degree of far-sightedness or near-sightedness) at infancy. Then, during the first two years of their life, this far-sightedness drops to around +1 D. In other words, their vision changes to become more balanced or ‘normal’ (a state called emmetropia). This shift towards balanced vision usually continues slower after three years until about six years of age.
The speed of this vision development is often related to how fast a child’s eyeballs grow. For instance, in people who are near-sighted (myopic), the length of their eyeball increases much more speedily. This kind of near-sightedness, called axial myopia, is when your eyeball lengthens and there is thinning of the white of the eye (sclera) due to changes in collagen, a protein that provides structure to your eye. Near-sightedness could be mild (0 D to -1.5 D), moderate (-1.5 D to -6.0 D), or high (-6.0 D or more). When a person has a very high degree of near-sightedness (usually -8 D or more), they may develop retinal and macular degeneration (conditions where the back part of the eye deteriorates), and this condition is known as pathological myopia.
Although it’s not entirely clear yet, some daily activities and environmental factors may partially contribute to near-sightedness. These include spending less time outdoors, doing a lot of close-up activities such as using electronic devices, having a genetic predisposition (inherited tendency), getting little daily light exposure, and certain dietary habits.
Risk Factors and Frequency for Phakic Intraocular Lens Myopia
Myopia, also known as short-sightedness, is more common in some regions and ethnic groups than others. For instance, it affects around 70-90% of people in Asia, about 30-40% in Europe and America, and only 10-20% in Africa. It’s also more frequent in young adults, accounting for 10-20% of their population. Factors such as intensive schooling and not spending enough time outdoors can increase the risk of myopia. Children in Asia often develop myopia at a quicker pace as compared to Western children, but it’s important to note that it occurs in both boys and girls equally.
Myopia can lead to difficulties in seeing clearly and can sometimes cause irreversible vision loss if not corrected. That’s why it’s essential to correctly estimate how many people globally are affected by it so that necessary measures can be planned. A significant amount of people with moderate and high myopia often choose to correct their vision through surgery, about ten and sixteen times more than low myopes respectively.
- 70-90% of people in Asia have myopia
- 30-40% prevalence in Europe and America
- 10-20% incidence in Africa
- 10-20% of young adults experience high myopia
- Intensive education and limited outdoor playtime are key risk factors
- Myopia progresses faster in Asian children than Western children
- Myopia affects both genders equally
- Uncorrected myopia can lead to vision impairment and irreversible vision loss
- Moderate and high myopia patients are 10 and 16 times more likely to opt for corrective surgery compared to those with low myopia
Signs and Symptoms of Phakic Intraocular Lens Myopia
When considering an implantation of a phakic IOL (an intraocular lens implanted while leaving the natural lens in place), it’s essential to manage the patient’s expectations for the outcome. Doctors need to have a comprehensive understanding of the patient’s eye information, including details about their eyesight stability, their comfort and satisfaction with glasses or contact lenses, and the age they first started using glasses. Importance should be given to frequent changes to their glasses prescription, so that the doctors can assess conditions like keratoconus or pellucid marginal degeneration.
A suitable phakic IOL patient is typically young, with stable eyesight and less than 0.5 D of refractive change in one year. The notion of presbyopia (age-related loss of near vision) should be explained clearly to the patient while discussing refractive surgery. The size of the patient’s pupils under low light conditions (scotopic) needs to be considered as pupil sizes larger than the optical zone of the implant may lead to glare and halos, potentially causing strong discomfort post-surgery to the point of even requiring the removal of the IOL.
Before planning for phakic IOL implantation, a thorough corneal evaluation is required, including determining the endothelial cell count and corneal shape. It is crucial for the patient to have a sufficiently deep anterior chamber – most phakic IOLs require this to be at least 3 mm.
The phakic IOL procedure is not recommended (contraindicated) for patients with:
- Cataract
- Chronic uveitis
- Low endothelial cell count
- Visually significant retinopathies
- Iris abnormalities
- Angle abnormalities
- Glaucoma
The US Food and Drug Administration (FDA) approves the use of phakic IOLs such as Visian ICL and Artisan/Verisyse IOL, for patients fulfilling certain criteria. However, these IOLs are not suitable for patients having specific issues such as pregnant or nursing females and those with certain iris abnormalities or specific endothelial density ranges, determined by age.
Testing for Phakic Intraocular Lens Myopia
Before a particular kind of eye surgery involving an artificial lens implant, known as phakic IOL, there are several things your doctor needs to look at:
Refraction: This is a routine eye test that helps your doctor determine if you have any problems that need correction like nearsightedness or farsightedness. Your doctor will measure your visual acuity (how well you can see) both before and after dilating (widening) your pupils with certain eye drops containing drugs like homatropine or tropicamide.
Anterior chamber depth (ACD): This is the space in the front part of your eye, right behind your cornea and in front of your iris. For phakic IOL implants, it needs to be at least 3 mm deep.
Anterior chamber angle and gonioscopy: Gonioscopy is a test that allows your doctor to inspect this critical angle where the cornea and iris meet. It’s important to assess this region because an unusual or narrow angle could increase the risk of developing glaucoma, a dangerous condition that can damage your optic nerve, after getting a phakic IOL implant. Specialists recommend that this angle must be at least 30 degrees for safely implanting phakic IOLs.
Your doctor will also study a map of your cornea’s shape and curvature, known as corneal topography, similar to all refractive evaluations.
Specular microscopy: This is a non-invasive test that allows your doctor to take precise images of the cells lining the back surface of the cornea (endothelium) before the surgery. This check-up helps ensure that the number of these cells is sufficient because the implant might cause some of them to be lost, especially a specific type called ACIOLs. A count of at least 2300 cells per square millimeter is desirable before surgery.
Sulcus to sulcus (STS) measurements: This is a critical measure that helps improve the fit of phakic IOLs. It refers to the distance across the eye from one side of the indentation at the edge of the iris to the other. The size of the implant is linked to this measurement, so it’s important to get it right. Some different methods can be used, and it’s usually better to use an average of the obtained values for accuracy.
For a kind of phakic IOL implant called posterior chamber IOLs, the distance between the IOL and the anterior lens capsule, termed vault, should ideally be 1 plus or minus 0.5 times of the corneal thickness, lying in a range of 250 to 750 micrometers.
IOL power calculation: Your doctor will use specific tools and formulas to calculate the power required for your IOL implant. This will involve taking precise measurements of various eye elements like the front part of your eye (biometry), the curvature of your cornea (keratometry), anterior chamber depth (ACD), your lens thickness, and your current prescription (preoperative refraction).
Finally, your doctor will perform a peripheral retinal examination and, if necessary, treat any detected potential weak points in your retina with a laser. This step helps to lower the risk of complications like a detached retina after surgery, mainly because pupil dilation remains limited with anterior chamber IOLs.
Treatment Options for Phakic Intraocular Lens Myopia
High myopia, also known as severe nearsightedness, can be treated in several ways, including glasses, contact lenses, and certain surgical procedures.
Glasses are a simple solution, but they may distort images in cases of severe nearsightedness, making them uncomfortable for some patients to wear. Contact lenses are another option, but they require meticulous care, including regular cleaning and replacement, which can be inconvenient and unsuitable for some people.
Certain eye surgeries can also be used to treat severe nearsightedness. Keratorefractive procedures, for example, reshape the cornea (the clear front surface of the eye). However, these procedures can have potential complications after surgery, such as clouding in the cornea or flap-related complications, including changes in the shape of the eye.
Another surgical procedure known as clear lens extraction (CLE) entails the removal of the eye’s natural lens and replaces it with an artificial one. Despite its potential benefits, this operation can result in the loss of the eye’s ability to focus, making it less suitable for younger people. It also bears an increased risk of retinal detachment, a serious condition where the light-sensing tissue at the back of the eye pulls away from its normal position.
In some surgical procedures, it’s necessary to create small holes in the iris, the colored part of the eye, to prevent a potential problem called pupillary block in the postoperative period. Pupillary block happens when the fluid inside the eye can’t circulate normally and may cause complications after surgery. This precaution applies to surgeries using specific types of intraocular lenses (IOLs), which are implanted inside the eye to improve vision.
What to expect with Phakic Intraocular Lens Myopia
The success of a lens implant largely depends on an accurate evaluation before the surgery. This evaluation determines the curve of the lens in a case of a Posterior Chamber Intraocular Lens (PCIOL) and sizes in the case of an Anterior Chamber Intraocular Lens (ACIOL). Modern lenses now designed to reduce contact with the iris and better fit the shape of the eye.
The result of lens implant surgery is usually good, with precise calculations, the implants can effectively correct nearsightedness up to -20 prescription strength with satisfactory results.
Studies have shown that Phakic Intraocular Lenses (PIOLs) can provide a good improvement in vision after surgery, with most patients experiencing a postoperative unaided visual acuity – meaning the clarity or sharpness of vision – better than 20/40. This essentially means that most patients see well without the need for glasses or contacts after surgery.
Possible Complications When Diagnosed with Phakic Intraocular Lens Myopia
Loss of endothelial cells is more common with ACIOLs (anterior chamber intraocular lenses). This could lead to corneal problems and in severe situations, if the endothelial cell count drops below 2000 per square millimeter, there may be a need to remove the intraocular lens (IOL). It has been seen that with angle fixed IOLs, there is a reduction of 1% in endothelial cell count every year if the lens edges are closer (1.43mm) to the endothelium. This reduction increases to 1.7% if the distance lessens to 1.2mm and is least when the distance is 1.66mm.
In a study about the implantation of AC-phakic IOLs (anterior chamber phakic intraocular lens), the NuVita IOL showed an annual endothelial cell loss of 2.35% and so, was removed from use. From other studies, the average endothelial cell loss in a year for other models was seen to be 3.86% in ZSAL-4, 1.83% in iris fixated IOL’s, 2% in IPCL, and 0.9% in ICL.
A retrospective study over 12 years that examined 144 eyes with ICL (implantable collamer lens), showed a surgically induced endothelial cell loss of 6.46% in the first year. The overall average yearly decrease rate was 1.20%.
Potential complications:
- Wrong lens size could result in IOL rotation and lead to induced astigmatism in cases of toric IOLs.
- Pigment dispersion might result in lens deposits but would generally need no intervention.
- Chronic inflammation and uveitis are more common with ACIOLs.
- ACIOLs can cause pupil distortion which might lead to intolerable glare and be cosmetically unacceptable.
- Glaucoma and pupillary block might occur due to inappropriate vaulting in the case of PCIOLs. Although it can resolve after pupil dilation and use of certain medications, the definitive treatment would be creating or enhancing a peripheral iridotomy.
- Glare and halos might occur if your pupil size when your eyes are adjusting to low light (scotopic pupil size) is larger than the lens’s optical part. Medications that make the pupil smaller (miotic agents) might be used for resolving this.
- In the case of low PIOL vault or undersized PCIOL, a cataract can form. The primary factor is the lens putting pressure on the natural lens of your eye and causing the formation of anterior subcapsular opacities. The material of the lens also plays a role.
- For the lens receivers with high myopia, there might be a risk of retinal detachment between 0.7% to 3.2%. However, more studies are needed to evaluate this risk as high myopia eyes are predisposed to retinal detachment.
Remember that these potential issues are generally low probability events but can be serious, so it’s important to make an informed decision with the help of your ophthalmologist when considering IOLs.
Preventing Phakic Intraocular Lens Myopia
Before going into surgery, it’s important for doctors to talk with patients and set clear expectations. They should explain all the treatment options available, what to hope for after the surgery, and what sort of results to expect. Patients should also be aware of potential complications that could arise during or after surgery.
