Phakic Intraocular Lens (PIOL) Implantation

Overview

Myopia is a major public health concern across the world. People nowadays spend an increasing amount of time on computers and mobile phones. As a result, the number of patients suffering from myopia has increased. Because wearing thick glasses is not always comfortable, corneal laser refractive surgery and phakic intraocular lens (pIOL) implantation are commonly used to treat myopia.

 

What is Phakic IOL?

Phakic intraocular lenses (PIOL) are surgically implantable intraocular lenses consisting of synthetic materials such as plastic or silicon. This lens allows light to focus precisely on the retina, correcting and improving eyesight in myopic individuals. During the procedure, a tiny incision on the front of the eye is made to insert and position the lens just in front of or behind the iris (the colored portion of the eye).

The Visian ICL is the most popular type of PIOL implanted in the UK and across the world (intraocular collamer lens). This is a soft, flexible implant that is placed in the eye directly below the pupil and in front of the native lens. ICLs cannot be seen or felt after implantation, and they do not need to be cleaned.

The Artisan/Verysise PIOL is the second major form of PIOL. This PIOL is attached to the iris directly in front of the pupil and can occasionally be seen as a sparkle in the eye. Artisan/Verysise PIOLs, like ICLs, cannot be felt after implantation and do not need to be cleaned. If you are a candidate for PIOL implantation, your surgeon will advise you on the best kind for you.

 

Background of Refractive Error

Ametropia, or clinically severe refractive error, affects half of the general population in the United States. Hyperopia of 3.0 diopters (D) or larger, myopia of 1.0 D or greater, and astigmatism with a cylinder of 1.0 D or greater are all examples of significant ametropia. The presence and severity of ametropia varies according to gender, ethnicity, age, and anatomy. Correcting ametropia at a young age is critical to avoiding problems such as accommodative esotropia or refractive amblyopia.

Glasses, contact lenses, and cornea-modifying surgery are examples of extraocular interventions. Myopia can be corrected by glasses or contact lenses that include a minus D spherical concave or diverging lens, which moves the focus of light rays from anterior to the retina to the retina. Hyperopia can be rectified using a positive D spherical convex or converging lens, which changes the focus from the posterior to the retina. Toric contact lenses or cylindrical glass lenses are used to correct astigmatism by refocusing light rays in two distinct planes to compensate for an ovoid cornea.

The purpose of most ametropia surgeries is to reshape the cornea with a high-energy excimer laser or a femtosecond laser. Photorefractive keratectomy (PRK), transepithelial PRK (TransPRK), laser in situ keratomileusis (LASIK) and its modifications, sub-Bowman keratomileusis and epi-LASIK, and the SMILE (SMall Incision Lenticule Extraction) treatment are among the different approaches. Intrastromal corneal rings (INTACS) are implants that remodel the cornea and are another procedure.

Intraocular surgery options include refractive lens exchange, which is similar to cataract surgery, and phakic intraocular lens (pIOL) implants, which will be the focus of this article. Bioptics is a technique that combines laser surgery with phakic intraocular lenses to address severe ametropia.

 

Indications and Contraindications

While prescriptions for pIOLs range from mild to severe ametropia, implantation of pIOLs is often suggested for more severe degrees of refractive error. The most suitable candidates are:

• >21 years old, 
• Have had stable refraction (change in vision <0.5 D) over at least one year,
• Are poor candidates for excimer laser surgery,
• Have poor tolerance of contact lenses or glasses, 
• Have irido-corneal angle >30 degrees,
• Have central endothelial cell count >2300 cells/mm2 or >2500 if >21 years old and >2000 if >40 years old, and 
• Have a mesopic pupil size <5-6 mm. 

Candidates requiring careful consideration or contraindication for implantation are those with

• Active anterior segment disease, 
• Recurrent or chronic uveitis, 
• Cataracts, 
• Previous ocular surgery,
• Glaucoma or IOP >21mmHg,
• Preexisting macular pathology, 
• Retinal disease, 
• Anomalous irises or pupils, or
• Systemic diseases classically associated with poor postoperative healing (eg diabetes mellitus, connective tissue disease, autoimmune disease).

 

Calculations

After providing patient measurements, lens suppliers often supply software that calculates the right lens. Lens manufacturers often give a nomogram that a practitioner can utilize to select the appropriate lens strength based on patient anatomical measurements. A Binkhorst nomogram is used to determine the power of phakic intraocular lenses (PIOLs), which needs a patient's spectacle plane refraction, corneal power, and ACD.

PCIOLs may additionally require an angle-to-angle distance (or white to white) measurement for proper lens diameter sizing. Finally, clinicians upload patient measurements into software that uses secret manufacturer algorithms to generate a phakic IOL power that is preferably within 0.5-1.0 D of emmetropia and as near to 20/20 vision as possible. Newer lenses may require additional patient measures and employ formulae and nomograms not listed above.

 

What is the Purpose of Using a PIOL?  

  

A PIOL is used to adjust the eye's focusing capability (as seen in refractive errors). Light is focused on the retina by the cornea and natural lens inside the eye, which is required for image creation. Any loss of focusing capacity in the eye eventually results in the creation of a fuzzy (out of focus) picture on the retina. A PIOL corrects this inaccuracy, allowing a clean picture to be created on the retina without the use of glasses or contact lenses.

PIOL is typically utilized as an alternative to other refractive error correction operations like as photorefractive keratectomy (PRK) and laser-assisted in-situ keratomileusis (LASIK). People who are very nearsighted or have astigmatism (an abnormal curvature of the cornea or natural lens) are good candidates for PIOL. Furthermore, PIOL is appropriate for patients who have specific eye conditions, such as keratoconus or dry eye syndrome.

A person should preferably be over 21 years old and have had stable refraction for at least one year to be eligible for PIOL implantation. In ideal applicants, the iridocorneal angle (the angle between the cornea and the iris) should be more than 30° and the mesopic pupil size should be smaller than 5-6 mm.

Patients suffering from anterior segment illness, chronic uveitis, retinal issues, or macular degeneration are not candidates for PIOL implantation. A past history of ocular surgery, cataract, or glaucoma also predisposes a person to PIOL surgery. 

 

How is the PIOL Implanted?

In general, peripheral iridotomies are strongly advised for both anterior and posterior pIOLs to prevent pupillary obstruction. A newer version of the Visian ICL contains a central port and does not require peripheral iridotomies. Miotic drops are required for anterior chamber pIOLs to minimize pupil size. To decrease medically induced astigmatism, main incisions are often made on the steep corneal axis. The surgical procedures employed change slightly based on the kind of pIOLs used.

Toric lenses must be implanted with care to prevent cyclotorsion of the lens over the pupil. A corneal or scleral incision is created, and two paracenteses are performed to manipulate the lens. The Ophthalmic Viscosurgical Devices (OVD)is injected into the AC, followed by the pIOL, which is then fixed into the iris with an enclavation needle holding the iris and an implantation forceps depressing the claw into the iris. Centration of the lens above the pupil is critical, and slight ovalization following surgery is not unusual due to the miotic agent's action.

 

Clinical outcome

Phakic IOL surgery has been found to improve eyesight, increase patient happiness, and eliminate the danger of corneal ectasia. Phakic IOLs outperform LASIK and PRK in terms of best spectacle-corrected visual acuity (BSCVA), refractive predictability and stability, and patient satisfaction. The use of pIOLs eliminates the hazards of corneal ectasia associated with excimer laser surgery and refractive lens exchange.

The two current phakic IOLs used to treat hyperopia (anterior chamber iris-fixated pIOLs and posterior chamber implanted collamer lenses) are both safe and effective, with no significant complications. It was found that pIOL implantation might be the best refractive surgery for correcting high hyperopia. The use of phakic ICL implants is successful and safe, allowing for stable refractive outcomes in the treatment of moderate to severe myopia with good refractive stability after nearly 8 years of follow-up. In cases of severe ametropia (myopia more than 8 diopters), the quality of vision acquired following intraocular implant placement is superior to that obtained after corneal laser surgery.

In a research comparing ICL implantation to SMILE in extreme myopia (-6 to -10 D), ICL implantation produced superior refractive accuracy, uncorrected distance visual acuity, fewer higher order aberrations, and better subjective quality of vision than SMILE. A low myopia comparative study found comparable safety, effectiveness, long-term visual stability, and great patient satisfaction. Halo after ICL and starburst after SMILE were the most prevalent visual complaints.

 

Risks and Complications

There is concern of inflammation, infection, and bleeding as a result of surgical damage, particularly to the iris. Because some of these treatments need greater corneal and scleral incisions, endophthalmitis and retinal detachment are significant concerns. Elevated intraocular pressures caused by pupillary obstruction and angle scarring are both problematic following pIOL installation in or near the angle.

Chronic intraocular pressure increase might result in irreversible visual loss. If the pIOL is in close proximity to the cornea, the surgical technique can also cause endothelial cell injury, and persistent endothelial cell loss can lead to corneal decompensation. Finally, prolonged inflammation or contact with a prosthetic lens can cause cataract development.

Because of developments in imaging modalities used to appropriately design the lenses, the complication rate of pIOLs used today is significantly lower than in previous versions. Complications are most typically caused by incorrect lens size and vary depending on the kind of lens used. Following implantation, explantation or reoperation were required due to the development of anterior subcapsular cataracts, unacceptable endothelial cell loss, pupil ovalization, lens subluxation or dislocation, refractive error, and pigment dispersion glaucoma.

While individuals using pIOLs have experienced macular hemorrhage and retinal detachment, there has been no confirmation of causality because the morbidities occurred in the setting of trauma. Endothelial cell loss might be worsened by the patient touching their eyes often following surgery.

The positioning of PCIOLs predisposes the crystalline lens and iris to collide with the pIOL, resulting in the particular problems of pigment dispersion with secondary glaucoma and anterior subcapsular cataracts. A PCIOL that is too long may result in angle closure or pigmentary dispersion glaucoma, whereas a PCIOL that is too short may result in anterior subcapsular cataracts.

The newer Visian ICL (EVO) with central port appears to cause far less difficulties. To yet, no visually significant cataracts have been recorded in a research with up to 5 years of follow-up, and the frequency of nonvisually significant ASC opacities has remained low. Preclinical research suggests that the central port contributes to the health of the crystalline lens by permitting physiologic aqueous humor passage over the anterior lens capsule.

Angle-supported ACIOLs are known to promote chronic endothelial cell loss from the cornea, pupil ovalization, and the production of nuclear cataracts. They are now used mostly in the treatment of aphakia and are not indicated for the treatment of ametropia in young patients. Chronic endothelial cell loss and cataracts are common with iris-claw ACIOLs. The increasing corneal endothelial cell loss in Iris-claw ACIOLs remains a source of concern, limiting its use for ametropia therapy in young phakic patients.

 

Conclusion 

A Phakic Intraocular Lens (IOL) is a synthetic plastic lens that is put into the eye. Some IOLs are implanted to replace the natural crystalline lens, such as after cataract surgery, while a phakic IOL is a lens that is placed alongside the natural lens of the eye, leaving the natural lens in situ. They are placed directly in front of or behind the pupil.