Phakic intraocular lens

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Phakic intraocular lens
PIOL in oog.jpg
Photo of an eye after PIOL-implantation, 24 hours after surgery. The lens is visible in front of the iris; the pupil is still small due to presurgery eyedrops.

A phakic intraocular lens (PIOL) is an intraocular lens that is implanted surgically into the eye to correct refractive errors without removing the natural lens (also known as "phakos", hence the term). Intraocular lenses that are implanted into eyes after the eye's natural lens has been removed during cataract surgery are known as pseudophakic.

Contents

Phakic intraocular lenses are indicated for patients with high refractive errors when the usual laser options for surgical correction (LASIK and PRK) are contraindicated. [1] [2] Phakic IOLs are designed to correct high myopia ranging from −5 to −20 D if the patient has enough anterior chamber depth (ACD) of at least 3 mm. [3]

Three types of phakic IOLs are available:

Medical uses

An installed PIOL, with flash photography Intraocular lens under cornea, six years after installation (with flash).jpg
An installed PIOL, with flash photography
An installed PIOL, without flash photography Intraocular lens under cornea, six years after installation (no flash).jpg
An installed PIOL, without flash photography

LASIK can correct myopia up to -12 to -14 D. The higher the intended correction the thinner and flatter the cornea will be post-operatively. For LASIK surgery, one has to preserve a safe residual stromal bed of at least 250  µm, preferably 300 µm. Beyond these limits there is an increased risk of developing corneal ectasia (i.e. corneal forward bulging) due to thin residual stromal bed which results in loss of visual quality. Due to the risk of higher order aberrations there is a current trend toward reducing the upper limits of LASIK and PRK to around -8 to -10 D. [4] Phakic intraocular lenses are safer than excimer laser surgery for those with significant myopia. [5]

Phakic intraocular lenses are contraindicated in patients who do not have a stable refraction for at least 6 months or are 21 years of age or younger. Preexisting eye disorders such as uveitis are another contraindication.

Although PIOLs for hyperopia are being investigated, there is less enthusiasm for these lenses because the anterior chamber tends to be shallower than in myopic patients. A hyperopic model ICL (posterior chamber PIOL) is available.

A corneal endothelium cell count of less than 2000 to 2500 cells per mm2 is a relative contraindication for PIOL implantation. [2]

Advantages

PIOLs have the advantage of treating a much larger range of myopic and hyperopic refractive errors than can be safely and effectively treated with corneal refractive surgery. The skills required for insertion are, with a few exceptions, similar to those used in cataract surgery. The equipment is significantly less expensive than an excimer laser and is similar to that used for cataract surgery. In addition, the PIOL is removable; therefore, the refractive effect should theoretically be reversible. However, any intervening damage caused by the PIOL would most likely be permanent. When compared with clear lens extraction, or refractive lens exchange the PIOL has the advantage of preserving natural accommodation and may have a lower risk of postoperative retinal detachment because of the preservation of the crystalline lens and minimal vitreous destabilization. [1]

Disadvantages

PIOL insertion is an intraocular procedure. With all surgeries there are associated risks. In addition, each PIOL style has its own set of associated risks. In the case of PIOLs made of polymethylmethacrylate (PMMA), surgical insertion requires a larger incision, which may result in postoperative astigmatism. By comparison, PIOLS made of a foldable gel-like substance require a very small incision due to the flexibility of the material and thus significantly reduces astigmatism risk. In the cases where refractive outcomes are not optimal, LASIK can be used for fine-tuning. If a patient eventually develops a visually significant cataract, the PIOL will have to be explanted at the time of cataract surgery, possibly through a larger-than-usual incision.[ citation needed ]

Another concern is progressive shallowing of the anterior chamber which normally occurs with advancing age due to the growth of the eye's natural lens. Multiple studies have shown a 12–17 µm/year decrease in the anterior chamber depth with aging. [6] [7] If a phakic IOL patient is assumed to have a 50-year lifespan, the overall decline in ACD may add up to 0.6–0.85 mm, long-term data about this effect are not available. This concern is more important in implantable collamer lens because it is implanted in the narrowest part of the anterior segment.[ citation needed ][ clarification needed ]

Contraindications

Lower levels of acceptable risk may be appropriate for implantation of phakic lenses than for cataract surgery, as the risk-benefit trade-off is less for improving vision than for restoring vision.[ citation needed ]

Complications

Preoperative evaluation

Anterior chamber depth (ACD, i.e. the distance between the crystalline lens and cornea including the corneal thickness) is required before the surgery and measured with the use of ultrasound.

Iris-fixated IOLs are fixated to iris therefore they have the advantage of being one size (8.5 mm).

Sulcus-supported IOLs need to be implanted in the ciliary sulcus which may have various diameters among individuals, therefore anterior chamber diameter needs to be measured with a calliper or with the use of eye imaging instruments such as Orbscan and high frequency ultrasound. A calliper and Orbscan measure the external limbus-to-limbus diameter of anterior chamber (white-to-white diameter) which provides an approximate estimation of AC diameter but UBM and OCT offer a more adequate measurement of the sulcus diameter (sulcus-to-sulcus diameter) and should be used when available. [4]

Power calculation

The power of phakic lens is independent of the axial length of the eye. Rather it depends on central corneal power, anterior chamber depth (ACD) and patient refraction (preoperative spherical equivalent). The most common formula for calculating the power of phakic IOL is the following: [2]

P : Power of phakic IOL

n : Refractive Index of Aqueous (1.336)

K : Central corneal power in diopters

R : Patient Refraction at the corneal vertex

d : Effective lens position in mm

The effective lens position is calculated as the difference between the anterior chamber depth and the distance between the PIOL and the crystalline lens. From ultrasonographic examinations of PIOLs, the lens-optic distance shows less variability compared with the cornea-optic distance. Therefore, it is preferable to use measured ACD and subtract it with an ‘optic-lens’ constant to obtain the value of ELP. For the Artisan/Verisyse lens the optic-lens constant is 0.84 mm. The ICL power is calculated using the Olsen-Feingold formula by using a four variable formula modified by a regression analysis of past results. [3]

Surgical technique

The Artisan (Verisyse) lens is implanted under pharmacological miosis. After creating proper incision the lens is grasped with curved holding forceps and inserted. Once in the anterior chamber and while firmly holding the lens with forceps, temporal and nasal iris tissue is enclavated with a special needle. The operation is completed with an iridectomy and the incision is sutured.

The EVO ICL (STAAR® Surgical's phakic IOL) is implanted under pharmacological mydriasis and implanted in the retropupillary position, between the eye's iris and the crystalline lens, using cartridge-injector or forceps. Both eyes can usually be done on the same day.

Steroid antibiotic eye drops are usually prescribed for 2–4 weeks after surgery. Regular follow-ups are recommended. [4]

Risk

Though ICL surgery has shown to be effective, it sometimes can result in complications such as:

Related Research Articles

<span class="mw-page-title-main">Farsightedness</span> Eye condition in which light is focused behind instead of on the retina

Far-sightedness, also known as long-sightedness, hypermetropia, and hyperopia, is a condition of the eye where distant objects are seen clearly but near objects appear blurred. This blur is due to incoming light being focused behind, instead of on, the retina due to insufficient accommodation by the lens. Minor hypermetropia in young patients is usually corrected by their accommodation, without any defects in vision. But, due to this accommodative effort for distant vision, people may complain of eye strain during prolonged reading. If the hypermetropia is high, there will be defective vision for both distance and near. People may also experience accommodative dysfunction, binocular dysfunction, amblyopia, and strabismus. Newborns are almost invariably hypermetropic, but it gradually decreases as the newborn gets older.

<span class="mw-page-title-main">LASIK</span> Corrective ophthalmological surgery

Laser-Assisted in Situ Keratomileusis (LASIK), commonly referred to as laser eye surgery or laser vision correction, is a type of refractive surgery for the correction of myopia, hyperopia, and an actual cure for astigmatism, since it is in the cornea. LASIK surgery is performed by an ophthalmologist who uses a laser or microkeratome to reshape the eye's cornea in order to improve visual acuity.

<span class="mw-page-title-main">Eye surgery</span> Surgery performed on the eye or its adnexa

Eye surgery, also known as ophthalmic surgery or ocular surgery, is surgery performed on the eye or its adnexa. Eye surgery is part of ophthalmology and is performed by an ophthalmologist or eye surgeon. The eye is a fragile organ, and requires due care before, during, and after a surgical procedure to minimize or prevent further damage. An eye surgeon is responsible for selecting the appropriate surgical procedure for the patient, and for taking the necessary safety precautions. Mentions of eye surgery can be found in several ancient texts dating back as early as 1800 BC, with cataract treatment starting in the fifth century BC. It continues to be a widely practiced class of surgery, with various techniques having been developed for treating eye problems.

<span class="mw-page-title-main">Radial keratotomy</span> Refractive surgical procedure to correct myopia (nearsightedness

Radial keratotomy (RK) is a refractive surgical procedure to correct myopia (nearsightedness). It was developed in 1974 by Svyatoslav Fyodorov, a Russian ophthalmologist. It has been largely supplanted by newer, more accurate operations, such as photorefractive keratectomy, LASIK, Epi-LASIK and the phakic intraocular lens.

<span class="mw-page-title-main">Refractive surgery</span> Surgery to treat common vision disorders

Refractive surgery is optional eye surgery used to improve the refractive state of the eye and decrease or eliminate dependency on glasses or contact lenses. This can include various methods of surgical remodeling of the cornea (keratomileusis), lens implantation or lens replacement. The most common methods today use excimer lasers to reshape the curvature of the cornea. Refractive eye surgeries are used to treat common vision disorders such as myopia, hyperopia, presbyopia and astigmatism.

<span class="mw-page-title-main">Phacoemulsification</span> Method of cataract surgery

Phacoemulsification is a cataract surgery method in which the internal lens of the eye which has developed a cataract is emulsified with the tip of an ultrasonic handpiece and aspirated from the eye. Aspirated fluids are replaced with irrigation of balanced salt solution to maintain the volume of the anterior chamber during the procedure. This procedure minimises the incision size and reduces the recovery time and risk of surgery induced astigmatism.

<span class="mw-page-title-main">Intraocular lens</span> Lens implanted in the eye to treat cataracts or myopia

An Intraocular lens (IOL) is a lens implanted in the eye usually as part of a treatment for cataracts or for correcting other vision problems such as short sightedness and long sightedness; a form of refractive surgery. If the natural lens is left in the eye, the IOL is known as phakic, otherwise it is a pseudophakic lens. Both kinds of IOLs are designed to provide the same light-focusing function as the natural crystalline lens. This can be an alternative to LASIK, but LASIK is not an alternative to an IOL for treatment of cataracts.

<span class="mw-page-title-main">Cataract surgery</span> Removal of opacified lens from the eye

Cataract surgery, also called lens replacement surgery, is the removal of the natural lens of the eye that has developed a cataract, an opaque or cloudy area. The eye's natural lens is usually replaced with an artificial intraocular lens (IOL) implant.

Howard V. Gimbel FRCSC, AOE, FACS, CABES, is a Canadian ophthalmologist, university professor, senior editor, and amateur musician. He is better known for his invention, along with Thomas Neuhann, of the continuous curvilinear capsulorhexis (CCC), a technique employed in modern cataract surgery.

The eye, like any other optical system, suffers from a number of specific optical aberrations. The optical quality of the eye is limited by optical aberrations, diffraction and scatter. Correction of spherocylindrical refractive errors has been possible for nearly two centuries following Airy's development of methods to measure and correct ocular astigmatism. It has only recently become possible to measure the aberrations of the eye and with the advent of refractive surgery it might be possible to correct certain types of irregular astigmatism.

The aim of an accurate intraocular lens power calculation is to provide an intraocular lens (IOL) that fits the specific needs and desires of the individual patient. The development of better instrumentation for measuring the eye's axial length (AL) and the use of more precise mathematical formulas to perform the appropriate calculations have significantly improved the accuracy with which the surgeon determines the IOL power.

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<span class="mw-page-title-main">Glued intraocular lens</span> Surgical treatment for eyes lacking functional lens capsules

In ophthalmology, glued intraocular lens or glued IOL is a surgical technique for implantation, with the use of biological glue, of a posterior chamber IOL in eyes with deficient or absent posterior capsules. A quick-acting surgical fibrin sealant derived from human blood plasma, with both hemostatic and adhesive properties, is used.

Intraocular lens scaffold, or IOL scaffold technique, is a surgical procedure in ophthalmology. In cases where the posterior lens capsule is ruptured and the cataract is present, an intraocular lens (IOL) can be inserted under the cataract. The IOL acts as a scaffold, and prevents the cataract pieces from falling to the back of the eye. The cataract can then be safely removed by emulsifying it with ultrasound and aspiration. This technique is called IOL scaffold, and was initiated by Amar Agarwal at Dr. Agarwal's Eye Hospital in Chennai, India.

An artificial iris is an intraocular implant that is used as both a cosmetic and to treat those with aniridia or other eye trauma. People with this condition experience photophobia, or increased sensitivity to light. The artificial iris, made from silicone, acts as a replacement iris. The artificial iris is implanted in the eye using different surgery techniques depending on the patient's eye trauma. Most of the major artificial iris manufacturers are European and the treatment is used sparingly in the United States because of limited FDA approval, in part due to possibility of vision loss and other risks.

<span class="mw-page-title-main">Phacolytic glaucoma</span> Medical condition

Phacolytic glaucoma (PG) is a form of glaucoma which is caused due to a leaking mature or immature cataract. Inflammatory glaucoma which occurs in phacolysis is a condition which is a result of the leakage of protein within the lens into the capsule of a mature or hyper mature cataract and involves a simple procedure to be cured that is referred to as cataract extraction.

Uveitis–glaucoma–hyphaema (UGH) syndrome, also known as Ellingson syndrome, is a complication of cataract surgery, caused by intraocular lens subluxation or dislocation. The chafing of mispositioned intraocular lens over iris, ciliary body or iridocorneal angle cause elevated intraocular pressure (IOP) anterior uveitis and hyphema. It is most commonly caused by anterior chamber IOLs and sulcus IOLs but, the condition can be seen with any type of IOL, including posterior chamber lenses and cosmetic iris implants.

Manual small incision cataract surgery (MSICS) is an evolution of extracapsular cataract extraction (ECCE); the lens is removed from the eye through a self-sealing scleral tunnel wound. A well-constructed scleral tunnel is held closed by internal pressure, is watertight, and does not require suturing. The wound is relatively smaller than that in ECCE but is still markedly larger than a phacoemulsification wound. Comparative trials of MSICS against phaco in dense cataracts have found no statistically significant difference in outcomes but MSICS had shorter operating times and significantly lower costs. MSICS has become the method of choice in the developing world because it provides high-quality outcomes with less surgically induced astigmatism than ECCE, no suture-related problems, quick rehabilitation, and fewer post-operative visits. MSICS is easy and fast to learn for the surgeon, cost effective, simple, and applicable to almost all types of cataract.

Clear lens extraction (CLE), also known as refractive lensectomy, custom lens replacement (CLR) or refractive lens exchange (RLE) is a surgical procedure in which clear lens of the human eye is removed. Unlike cataract surgery, where cloudy lens is removed to treat cataract, clear lens extraction is done to surgically correct refractive errors such as high myopia. It can also be done in hyperopic or presbyopic patients who wish to have a multifocal IOL implanted to avoid wearing glasses. It is also used as a treatment for diseases such as angle closure glaucoma.

References

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