Many corneal refractive procedures, including automated lamellar keratoplasty, photorefractive keratectomy (PRK), laser in situ keratomileusis (LASIK), holmium:YAG (Ho:YAG) laser, and conductive keratoplasty, have been available to treat low-to-moderate hyperopia. The safety and the accuracy of PRK and LASIK for the treatment of hyperopia have improved over the years, but are still not as stellar as they are for the treatment of myopia. The quality of correction has advanced with the use of wavefront analysis and its seamless incorporation in refractive surgery.
Today, the quality of corneal refractive procedures is improving. Lens-related procedures are getting more popular. They include phakic intraocular lenses and a procedure like clear lens extraction with high-plus power lens implantation. Clear lens extraction causes a loss of accommodation but is preferred if the patient is older than 45 years or has any degree of cataract. However, presbyopia-correcting lenses, ie, multifocal (bifocal, trifocal, quadrifocal), accommodative, extended depth of focus, varifocal, and polyfocal intraocular lenses can overcome the problem of near vision.
Two types of intraocular lenses (IOLs) are mainly used in hyperopes: the precrystalline lens implant (implantable Collamer lens) and the iris-fixated lens (Artisan lens).
The Artisan lens is shown in the image below.
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The dimensions of the Artisan phakic lens. The lens is 8.5 mm at the widest point, far away from the angle of the anterior chamber. The optic is vault....
An angle-supported lens has been used very rarely in hyperopes and has fallen out of fashion owing to associated complications related to increased intraocular pressure and loss of endothelial cells.
Each lens has its advantages and disadvantages. The early problems are related to the design of the lens and the meticulous details of surgery. The late postoperative complications are related to the interaction of the IOL and the intimate ocular tissues during the lifetime of the patient. Lifelong, regular follow-up care is essential in all cases. Explantation of the phakic lens may ameliorate some of the complications.
Later in life, if the patient develops a cataract, performing an atraumatic explantation, followed by extracting the cataract and implanting another appropriate IOL, should be possible. A foldable Visian ICL hyperopia lens is easier to explant than a rigid Artisan hyperopia lens.
Refractive corneal surgery had the potential to rival the visual results of phakic lens implants, as it can correct both the spherical error and the cylindrical error. Wavefront analysis and its incorporation in the ablation process improve the image definition. The authors no longer advocate the use of laser refractive corneal surgery because of the possibility of regression in such a surgical (hyperopia) profile. Laser hyperopic corneal corrections results in loss of effect over time because of the natural or sometimes hyperplastic healing response of the cornea to fill in this ablated step between the treated and untreated zones.
In 1977, Worst designed and used a pure iris support lens. This iris claw lens was fixed to the anterior surface of the iris independent of the pupil. Over the next 9 years, it was well tolerated and used extensively in aphakes of Holland and India. An iris claw lens is shown in the image below.
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The iris claw lens for a phakic hyperopic eye, implanted in the eye of a blue-eyed patient. Minimal essential iris fold in the lens claw exists for th....
In 1986, Fechner used a negative-power iris claw lens for treating phakic myopes. Soon after, Singh used it in phakic hyperopes. In 1998, Fechner, Singh, and Wulff presented their 10-year experience with 69 cases.[1]
In 1996, Davidorf, Zaldivar, and Oscherow presented their results with the STAAR Collamer plate haptic posterior chamber phakic IOL in 24 phakic hyperopes.[2] In 1998, Rosen and Gore followed with 9 cases; in 1999, Pesando, Ghiringhello, and Tagliavacche followed with 15 eyes; and, in 1999, Sanders followed with 10 eyes.[3, 4]
Koivula and Zetterstrom evaluated the use of PRL phakic IOL for hyperopia and found that the main complication was early pupillary block.[5]
At present, there are many presentations of small series of cases with a short follow-up, with both iris claw lenses and posterior chamber refractive lenses.
Angle-supported lenses in phakic hyperopes have not made headway.
Hyperopia is a common refractive error that exists from a young age. A unilateral hyperopia, with or without amblyopia, might remain undiscovered for a long time. The treatment of unilateral hyperopia is not easy. The child is not impressed by the glass or the contact lens for the affected eye, since the other eye is so much better. Most parents give up all efforts out of sheer frustration, and the magnitude of wasted sight is immense.
Numerous innovative corneal procedures have been tried. All have been discontinued because of the difficult nature of these procedures, the serious flaws, and the complications.
Two promising modalities have appeared: the excimer laser for use as PRK or LASIK and the newly designed phakic IOLs. While experience with these modalities exists in adult patients, experience with them in young patients is also receiving increased attention. Phakic lenses are hazardous in pediatric patients with hyperopia.
The optic-mechanical solution to the problem of hyperopia is only one side of the story. The prevention and management of amblyopia are equally important, but efforts in these areas are lagging. When the latter are strongly addressed, hyperopia surgery will become a hot topic.
The incidence of +2 diopters (D) or higher hyperopia under cycloplegic refraction is as follows: 19% of patients aged 7-8 years, 3.6% of patients aged 14-15 years, and approximately 25% of adults have some degree of hyperopic refractive error.
Much remains unknown about the developing eye, especially in relation to hyperopia. Hyperopia is known to result when the refracting optics of the eye can focus the parallel rays from infinity to a point behind the retina (relative to the length of the eyeball).
Newborns are moderately hyperopic, but they have a broad distribution of refractive errors. As the eye grows, a shift toward emmetropia occurs. Hyperopia perhaps represents a failure of the emmetropization process. Slow eyeball growth can be a cause of hyperopia and is the reason why hyperopia does not disappear with age.
The phakic posterior chamber lenses and the iris claw lenses contact different ocular tissues, so different mechanical and biological responses are elicited by each lens.
The precrystalline lens implant is made of soft lens material. It occupies a narrow space between the natural crystalline lens and the posterior surface of the iris. Despite its design to avoid touching the crystalline lens and the posterior surface of the iris, it is often difficult to achieve this situation. Touching or rubbing against the posterior pigment epithelium of the iris is inevitable. Similarly, touching the ciliary epithelium is unavoidable.
During blinking, squeezing, and rubbing, the pressure and friction between the IOL and the surrounding tissues are inevitable. Even if the frictional force is very small, it is bound to continue for life. When shed from the iris and ciliary process, the pigment may lead to glaucoma. Developing diabetes also is a concern. The disease causes changes in the posterior pigment epithelium of the iris, possibly causing excessive shedding of pigment. An inflammatory process can bind the lens to the iris, the ciliary body, or even the crystalline lens. An intermittent or a continuous touch with the anterior lens capsule can produce lens opacification. Sometimes, the presence of the artificial lens in the posterior chamber can crowd the angle of the anterior chamber, leading to glaucoma.
The posterior chamber lens is sized empirically by subtracting 0.5 mm from the white-to-white corneal diameter. A short lens rubs against the anterior lens capsule, and a long lens impinges on the ciliary body and the posterior pigment epithelium of the iris.
An iris-fixated lens (iris claw lens) is fixed to the anterior surface of the iris via the in-built claws in the haptic of the lens. To achieve fixation, the claw holds a fold of the iris on either side of the pupil. The lens does not produce complications related to the angle of the anterior chamber, the crystalline lens, pigment epithelia of the iris, or the ciliary body. Consider the possibility that the iris tissue inside the claw will atrophy, leading to a late dislocation or possible breakdown of blood-aqueous barrier at the site of fixation. Blinking and squeezing do not produce friction between the iris and the IOL. Rubbing and pressing may produce an endothelial touch.
In both types of phakic IOLs, increased crystalline lens size with increasing age and cataract formation tends to increase the aforementioned risks. While the results of phakic IOLs are highly predictable, the long-term pathological changes and safety factors have been known only for about a dozen years.
The eyeball may be placed normally, or it may be set deeply. The cornea may have a normal diameter, or some degree of microcornea may exist. The following may vary within the specified ranges:
Axial length - 15-23 mm
Keratometry reading - 38-50 D
Depth of the anterior chamber - 2.5-4 mm
Hyperopia - A low of +2 D or +3 D to as high as +18 D
The intraocular pressure (IOP) should be normal, and the patient should not be under treatment for any kind of glaucoma. In addition, unilateral moderate or severe hyperopia cases usually have amblyopia in the affected eye. The patient may have strabismus, nystagmus, or both.
Patients may experience unilateral or bilateral hyperopia. The corrected visual acuity may be normal in both eyes, normal in one eye with amblyopia in the other eye, or subnormal in both eyes. Strabismus or nystagmus may be present.
Patients may be dissatisfied and desire surgery because of thick glasses, cosmetic reasons, or poor visual acuity and peripheral vision. Two popularly misguided reasons why patients may desire surgery exist, frustration with (lack of) visual quality or the assumption that surgery will be as helpful for hyperopia as it is for myopia.
Refractive surgery by phakic IOLs among the hyperopes is not as popular as in myopes, simply because it has not been available as long. If the patient who is hyperopic agrees to refractive correction, especially if it is likely to help work-related tasks, then the search for the right modality of treatment begins. People do try to collect all information about the possibility of their getting benefited by a safe and proven technology through a trustworthy ophthalmologist. When patients are in the office, they do ask for clear-cut information on the various options and what option may suit them best. The ophthalmologist must consider personal experience and equipment. If resources are insufficient for a given case, the patient should be referred to a suitable institution.
The practical options for the cornea are PRK and LASIK; for intraocular implantation procedures, a posterior chamber lens and an iris claw lens. Both types of intraocular lenses are available worldwide.
When planning for an IOL implant in phakic hyperopes, consider the following:
What is the minimum age at which the lens is to be implanted?
What is the minimum or the maximum refractive error to be treated?
What should be the lowest limit for anterior chamber depth?
What is the lowest limit for the diameter of the cornea beyond which there will be a refusal to perform surgery?
How accurate is the white-to-white diameter on the basis of which the length of a length is to be derived?
What are the smallest available lenses of the 2 types (ie, posterior chamber lens, iris claw lens)?
How can the risk of complications be minimized? What will those complications be? What will be the chances of occurrence?
The final decision to do lens implantation comes after careful contemplation and detailed consultations and discussions with the patient or the parents.
The following anatomical features involved in phakic lens implantation are important:
The space availability for the implanted lens
The structures with which the lens will intimately contact
The effect of age on the dimensions of various involved structures and spaces
The pupillary margin normally rests on the crystalline lens. Maximum contact is in a mid-dilated condition. The posterior chamber, which has a volume of 65 µL, is a triangular space on section. The base is toward the periphery, and the apex is toward the pupillary margin (where the chamber depth is zero). In the case of a posterior chamber lens, the thickest part of the implant, the optic, occupies the shallowest or the zero space.
If a plate haptic lens has to stay clear of the crystalline lens, it should vault in the central area. This can happen only if the haptic rests strongly on the ciliary processes and bows forward. Staying clear of the crystalline lens can lead to rubbing against the posterior pigment. It also means impinging on the ciliary epithelium of the ciliary processes. If the ciliary epithelium sheds, then the implanted lens will further touch the ciliary vasculature. The ciliary capillary endothelium has fenestrations of 30-100 µm, which are permeable to plasma proteins and tracer elements. Lying between the crystalline lens and the iris, the phakic posterior chamber lens produces resistance to the flow of aqueous. The increasing volume of the crystalline lens with age encroaches on the posterior chamber volume. The crystalline lens volume increases by almost 50% from 150 µL to 240 µL in a matter of 60 years.
The average anterior chamber depth is 3.15 mm (2.6-4.4 mm). The volume of the anterior chamber is 250 µL, which decreases by 7.5% per decade.
The iris is 0.5 mm thick at the root and 0.6 mm at the collarette. An iris claw lens is attached to the peripheral anterior surface of the iris by pushing a fold of the iris into the 2 claws of the lens. Consider the following 3 points:
The space available around the lens and the distance from the corneal endothelium and the crystalline lens
The anatomy of the iris, especially the vasculature, as it is fixed in the claws of the lens
The pupil movements and the friction between the iris and the phakic iris claw lens
The posterior surface of the IOL is concave and cannot touch the crystalline lens. A respectable distance exists between the various parts of the lens and the corneal endothelium. The maximum height of the optic, which is in the center, is less than 1 mm. The haptic of the lens in the periphery is 0.18 mm. The growth of the crystalline lens with age tends to reduce the depth of the anterior chamber. The maximum width of the implant lens is 8.5 mm, which allows it to remain away from the structures of the angle of the anterior chamber.
The vasculature of the iris is peculiar. The vascular endothelium of the human iris is not fenestrated. The endothelial cells of the iris vessels are joined by 2 types of intercellular junctions, the zonular tight junctions and the gap junctions. The vessels are covered in layers in the following order:
Pericytes
0.5-3 µm wide basal lamina
7 µm zone of sparse, longitudinally directed collagen fibers
Granular ground substance
Another 10 µm wide connective tissue layer
Vessels that are located in the more cellular parts of the stroma (eg, anterior border layer) are invested in thicker and more cellular adventitia. These vascular peculiarities explain why the claw lens can grip the iris fold.
Friction between the iris claw lens and the anterior surface of the iris is possible at 2 points, in the immediate vicinity of the 2 claws. Nothing serious happens in aphakes, and it is unknown if, on a long-term basis, phakic eyes respond similarly.
These guidelines should prevent early or late postoperative problems, which permanently may threaten vision. Two basic factors are quintessential, as follows:
Patients should come for regular follow-up care throughout their lifetime. If a patient cannot comply, that patient is not a suitable candidate.
A fail-safe IOL design should be chosen. If the surgeon cannot confidently explant the lens after months and years without incurring any trauma to the eye, do not implant.
Eyes that already have vision-threatening problems (eg, uveitis, diabetic retinopathy glaucoma) are excluded to avoid precipitating more complications.
The patient and ocular parameters and the proposed lens design impose many restrictions. The patient should not rub the operated eye. Young children who cannot follow these instructions should not receive implanted phakic lenses. Hyperopic children older than 14 years have been more reliable and cooperative. Amblyopic patients deserve much-needed refractive crutches at an early age.
The smallest available posterior chamber phakic lens diameter is 11 mm. The length of the lens is calculated by subtracting 0.5 mm from the white-to-white limbal diameter. The minimum white-to-white diameter should be 11.5 mm. Any degree of microcornea from this size is a contraindication for posterior chamber lens implantation. In the case of an iris claw lens, customized, smaller lenses are possible. While the normal phakic lens is 8.5 mm wide, the iris claw lens may be made as small as 6 mm, thus greatly extending its application.
Anterior chamber depth is an important consideration for posterior chamber lenses and iris claw lenses. A depth of less than 2.75 mm is a contraindication. The posterior chamber lens may cause crowding of the angle, but the iris claw lens will encroach on the central depth of an already shallow anterior chamber.
The presence of amblyopia should not be a contraindication for the following purposes:
To reduce the power of the glasses and to improve the chances of spontaneous improvement of amblyopia
To provide a greater freedom of movement
Later, to attempt to improve the eyesight with pleoptic exercises
The lens, which is fixed to the anterior surface of the iris, can be examined from end-to-end under the slit lamp microscope throughout the patient's life. A posterior chamber lens cannot be examined in this manner. In the latter case, it can only be presumed that all is well at the haptic-ciliary junction or implant-iris touch areas. If inflammation develops and the pupil fails to dilate, only indirect inferences can be drawn. Therefore, the emphasis on contraindication can shift from patient to the implant and vice versa, depending upon the peculiarities of each patient.
If a substantial difference exists between the manifest refraction and the cycloplegic refraction, then calculate as follows: cycloplegic refraction minus 0.5 multiplied by (cycloplegic refraction minus manifest refraction).
IOL power calculation
The van der Heijde nomogram may be used to calculate the iris claw lens power.
The Feingold formula (proprietary) may be used for a precrystalline lens implant.
Fifteen days before the posterior chamber (Visian ICL hyperopia and Visian ICL toric hyperopia) phakic lens implant, consider performing 2 Nd:YAG iridotomies, 90° apart. The new EVO+ ICL aspheric EDOF has a CentraFLOW technology that allows aqueous fluid to flow through the center hole of the optic, precluding the need for preplacement Nd:YAG iridotomy.
An Nd:YAG laser iridotomy is easier to perform on a light colored iris than a brown or dark iris.
Preoperative eye preparation depends on the type of IOL to be implanted.
Precrystalline lens: Dilate the pupil with tropicamide with phenylephrine (5%), instilled 3 times at 15-minute intervals, starting 1 hour before surgery.
Iris claw lens: Contract the pupil with 1% pilocarpine drops, instilled at 15-minute intervals, starting 45 minutes before surgery.
Nonsteroidal anti-inflammatory drug (NSAID) drops are instilled 2 times before surgery to minimize inflammation.
Anesthesia
Some patients prefer general anesthesia, but most patients opt for local anesthesia.
Surface leading to intraocular anesthesia: Use preservative-free 2% intraocular lidocaine.
Preparation of the surgical field
Use 5% povidone. Paint the periorbital skin with iodine, then apply the same solution 2-3 times to the lid margin and the conjunctival fornices. Then, the eye is washed with saline.
Exposure of the surgical field
An eye speculum may be used.
Adhesive plastic, applied to the surface of the eyelids, is used to pull the eyelashes.
One 0.6 mm side port is needed to inject viscoelastic material in the anterior chamber. This injection is started at the opposite limbus. As the aqueous drains, it should be replaced with viscoelastic agent. The depth of the anterior chamber is not reduced at any time.
For iris claw lens implantation, 2 side ports are needed to introduce the instruments, which fix the iris to the claw.
Making the larger incision to insert the IOL
The size of this incision depends on the type of IOL to be implanted.
For a soft precrystalline lens, make a 3.0- to 3.2-mm 3-plane clear corneal incision at the temporal area (0° for the left eye or 180° for the right eye).
For an iris claw lens, the width of the incision depends on the diameter of the optic (5 mm). The incision may be made at the limbus or in the clear cornea. If a pocket section is made, it will allow a wound closure without sutures.
Insertion of foldable lens in the precrystalline space
The lens is introduced with angled-suture forceps, then it is positioned behind the iris on a horizontal axis with a cyclodialysis spatula.
The lens is manipulated to center the optic on the pupil.
The viscoelastic (hydroxypropyl methylcellulose) material is removed from the anterior and posterior chambers with an aspiration syringe (24-gauge cannula).
The anterior chamber is washed thoroughly with saline.
The pupil is contracted with intraocular acetylcholine 1%, carbachol 0.01%, or pilocarpine 0.5% solution.
The incision is closed by hydrating the corneal incisions. A suture rarely is needed.
Intracameral antibiotics are contraindicated for Collamer lenses.
Protective eye goggles are worn.
Insertion of an iris claw lens
The main incision is made at the 12-o'clock position. The width is equal to the size of the optic, which may be 4.25-5 mm. The side incisions are 1.5 mm wide.
The hyperopic convexo-concave polymethyl methacrylate (PMMA) iris claw lens is inserted vertically. The lens is rotated inside the viscoelastic-filled anterior chamber; therefore, both claws of the lens are placed horizontally.
Fixating the iris claw lens
Fixating the iris claw lens is a bimanual procedure.
A vertically holding lens forceps, which enters the anterior chamber through the main incision, centers the optic on the pupil and holds it. The lens is rotated horizontally using a special manipulator. The optic is regrasped at the center and held steadily.
A thin enclavation needle is introduced from the side incision and grasps the iris close to the claw, passing a fold of the iris through the claw, and results in fixing one of the claws. A new VacuFix enclavation system is now available. The VacuFix is connected to a phaco unit; once it contacts the iris, the suction allows for an easier grasp of iris tissue and lifting the fold of iris through the slot of the claw.
Both instruments are withdrawn, and the surgeon changes hands for holding each tool.
The anterior chamber is again deepened with viscoelastic material, and the lens-fixation instruments are reintroduced.
Second claw-fixation maneuver
The second claw-fixation maneuver is performed through the incision on the opposite side.
A peripheral iridectomy is performed at 12-o'clock position.
The viscoelastic material is aspirated through the 3 incisions, then the anterior chamber is irrigated gently and inflated with air to remove all viscoelastic material.
Closure of the incision line
For a pocket incision, the apposition may be achieved by 1-2 very superficial sutures. Alternatively, a large air bubble may be left inside the anterior chamber to effect an apposition.
If the limbal incision was made without a pocket, a regular closure of the incision line should be performed. A placido disc is used to monitor the corneal curvature at the end of the operation.
End of surgery
Intracameral antibiotics may be given. Antibiotics are generally given topically. Some surgeons still apply subconjunctival injection of 20 mg of gentamicin and 2 mg of dexamethasone.
Monitor the patient as with any other IOL surgery. In particular, carefully look at the incision line and be watchful of the IOP and any inflammation.
The first examination is performed 2 hours after surgery. Intraocular pressure is monitored every 2 hours. A corneal incision ”burp” maneuver may be performed to decrease intraocular pressure if there is retained viscoelastic. The patient is not discharged until ocular pressures are within normal limits.
Protecting the eye from injury: The restrictions are less rigid for posterior chamber lens cases. Patients should use protective goggles during the day and a protective shield at night. Do not bump the eye when applying eye drops.
Cleaning the eye
The corners of the eye and the surrounding area may be cleaned with sterile cotton swabs.
The patient should be careful when bathing.
Using the eye
No restrictions exist (eg, watching television, reading).
Physical activity
No restriction on walking exists.
The patient should avoid heavy exercise for 2 weeks.
Contact sports should be avoided for 2 months.
Swimming is allowed after 2 months, but diving should be avoided.
Rubbing of the eye
This should be avoided throughout life regardless of the lens design.
On postoperative days 0, 1, and 7, perform slit lamp examination, and record any uncorrected or corrected visual acuity and IOP.
Long-term follow-up care
Patients should receive follow-up care after 1 month, 3 months, 6 months, 9 months, 12 months, and once annually thereafter.
The pupil is dilated at every visit.
Use slit lamp examination to find evidence of inflammation, pigment dispersion, adhesion formation with the uveal tissues, and touch to the anterior lens capsule. Look for any opacification of the crystalline lens.
Perform a careful refraction.
Regularly monitor the endothelial cell density with specular endothelial microscopy.
Use gonioscopy to look for peripheral anterior synechiae formation. Look for the presence of pigment that is derived from the iris and the ciliary body.
Observe any crowding of the angle that is due to the IOL behind the iris.
Early problems can develop within 24 hours of the operation. Pupillary block glaucoma may develop because of the blockage of previous laser iridotomies or viscoelastic material residue in the posterior chamber. The vasovagal response causes pain, blurred vision, and systemic symptoms. Red eye, corneal edema, shallow anterior chamber, dilated pupil, and a marked rise in IOP occur.
If the condition does not respond to systemic therapy with acetazolamide, hyperosmotic agents, local miotics, and beta-blockers, opening the eye under general anesthesia to explant the lens is recommended. In 2-3 weeks, the eye might regain the earlier corrected vision.
Specular endothelial microscopy may reveal a substantial loss of endothelial cells. The closure of the peripheral iridotomies and pupil block glaucoma can occur after 1 or more weeks. Such cases may be treated by a repeat laser iridotomy, surgical peripheral iridectomy, or a lens explantation.
Late complications
An anterior subcapsular cataract may form due to contact with the natural lens. A small IOL has greater chances of having direct contact with the crystalline lens. Uveitis also can occur in an acute or a chronic form. Pigment dispersion may be seen on the artificial lens or the natural lens. Late glaucoma may occur because of crowding of the angle and pigment deposits in the angle. In some cases, the pupil may become partially dilated and not respond to the usual miotics. The implanted lens may dislocate due to the dissolution of the zonular fibers.
Iris claw lens
Early dislocation is due to inadequate fixation. Early or late anterior uveitis can occur. If a patient compulsively rubs the eyes and produces recurrent endothelial touch, late corneal decompensation can occur. Postoperative endophthalmitis has not been reported; however, since it is an intraocular procedure, the possibility cannot be excluded.
A successful IOL procedure does not cause a loss of best-corrected visual acuity. The vision improves from day 1. Many patients with amblyopia may recover partially or completely in several months.
A sutureless procedure exists for inserting a soft, biocompatible lens. The optical correction is good. Although empirically measured from a formula (white-to-white diameter minus 0.5 mm), this IOL size works in most cases.
An extremely small lens will rub against the lens epithelium, iris pigment epithelium, and ciliary epithelium. A lens that is larger than required lifts in the middle and develops more than desired intimate contact with the posterior surface epithelium of the iris. In some cases, especially eyes with dark irises, the iridotomies might fail to remain patent, and the IOP may rise. A surgical iridectomy is often necessary in these situations; sometimes, the IOL must be removed.
A regular follow-up visit is essential to detect cataract formation, in which event the lens must be explanted with appropriate treatment for the cataract. With increasing age, consider crowding of the angle and increasing IOP.
An ophthalmologist who has received training to implant such lenses should perform an iris claw lens.
Although it may not be cosmetically acceptable by some patients with light-colored irises, a surgical iridectomy always is performed. Early dislocation of the lens is rare but indicative of improper fixation. Late dislocation is not reported. The lens avoids the angle of the anterior chamber, never touching the crystalline lens, posterior pigment layer of the iris, or the ciliary processes. Therefore, the lens is devoid of the above complications in connection with the posterior chamber lens. The edge and the optic of the IOL are far removed from the corneal endothelium; under normal circumstances, touch does not occur. If a patient rubs the eye vigorously for any reason, an endothelial touch can occur. Many people rub their eyes during sleep.
The phakic iris claw lens has been used and well tolerated for 20 years. Even this long follow-up is not sufficient to address all the long-term safety concerns. If necessary, the lens is easy to explant (eg, natural cataract development). A regular follow-up examination is essential, with particular emphasis on counting endothelial cells on an annual basis. The lens is available in the United States under the name of Verisyse.
IOL implantation for phakic eyes is only one of many controversial modalities to alleviate hyperopia. Several attractions include the following:
Minimum surgical injury to the ocular tissues occurs, even though it means opening the eye and closing it after making a few manipulations.
Viscoelastic materials make lens implantation easy and safe, although the viscoelastic material should be removed thoroughly from the eye at the end of the surgery.
As long as surgical quality is not compromised, the optical results are highly predictable, immediate, and lasting.
No large investment is involved for beginning this kind of refractive surgery. It can be performed in the most remote corners of the world.
The ocular tissues tolerate and survive the presence of an IOL in a phakic eye. However, it will only survive if the lens implantation occurs as a one-time event and not as the beginning of a process, which may initially appear innocuous. Thus, every new modality, especially an IOL, must prove itself over a long period. In spite of the many modifications of posterior chamber lens designs, a stigma of cataract formation still exists.
It has been proven repeatedly that pressure or friction between the IOL and the ocular tissue damages this tissue. For this reason, a phakic lens in the posterior chamber suffers from certain serious flaws. The posterior chamber lens permanently positioned in narrowly confined space raises the following concerns:
What is the right size for the posterior chamber phakic lens? How is it realized that the selected lens is really the right size for a particular eye?
The IOL is thickest in the central area, and the pupillary margin of the iris naturally touches the crystalline lens. How can a posterior chamber phakic lens possibly avoid touching or rubbing both the posterior surface of the iris and the crystalline lens? It is inevitable that 1 of the 2 surfaces will be constantly touched or rubbed. What will be the consequences of such a friction over years? Decades? A lifetime? When raising this question, it is presumed that the surgery was flawless without immediate postoperative problems.
When discussing phakic posterior chamber lenses, only 2 structures (the iris and crystalline lens) usually are mentioned. A safety concern should exist for the delicate ciliary processes, its epithelia, and its vasculature. The plate haptic lens owes its survival to the support and leverage that it gets from there, so as to stay clear of the crystalline lens. Lifelong contact, pressure, and micropressure or macropressure/movements (pressing or rubbing the eye) adversely affect the integrity of the ciliary epithelia and the ciliary vasculature. For this reason, closely monitoring blood-aqueous barrier breakdown in this group of patients for months and years is important. Presently, this measure is not observed.
Reports have emphasized the accuracy of correction and the improvement of uncorrected visual acuity. However, the much larger issue, long-term tissue tolerance, is more significant than any short-term benefits (which some cite as justification for proliferating use).
In aphakic eyes, posterior chamber lens implantation in the sulcus was abandoned in favor of a more difficult, in-the-bag implantation. The reason is that sulcus-fixation leads to many unacceptable complications, which are produced in the roomy aphakic compartments by the sulcus-supported lenses. It is difficult to believe that sulcus-supported phakic lenses fare any better in a more restricted space (ie, the normal posterior chamber). Another responsibility is saving the crystalline lens from inadvertent damage, which leads to cataract formation.
In a group of patients who are prone to angle-closure glaucoma, nothing prevents the plate haptics of the phakic posterior chamber lens from pushing forward the iris periphery and crowding the angle.
The phakic posterior chamber lens is pushed intentionally into the space, so the ocular structures that bound the space catch the lens. This phenomenon is possible only if the lens is larger than the fixation space. A slightly smaller lens moves freely in the space and rubs against the crystalline lens. It logically follows that no lens design can perfectly fit an individual eye.
The iris claw lens is a pure iris support lens. The lens is smaller than the area where it is fixed. The ocular tissues cannot catch this lens (unlike the posterior chamber lens), so the lens is designed to catch the tissues (the anterior surface of the iris).
The surgeon who centers it controls the fixation site. The lens remains permanently placed unless it dislocates because of poor fixation or injury. The principle of iris fixation inside the claws was tested clinically on thousands of aphakic eyes over 9 years before the lens was redesigned for phakic eyes. These changes help the implant lens to stay clear of the natural crystalline lens and the corneal endothelium, but the principle of time-tested claw fixation remains the same.
The lens design permits it to stay far from the angle tissues and allows freedom to the pupillary movements. The lens floats in the aqueous humor, while fixated at 2 points. It totally avoids the narrow posterior chamber, which is surrounded by potentially reactive tissues. The iris claw lens has proven itself for a long time, both in aphakic eyes (>34 y) and phakic eyes (>25 y). Other lenses must surmount many difficult problems before they can become a serious alternative.
Hypermetropia is a childhood disease and is present at birth. Unequal refractive error or high refractive error can and does produce severe amblyopia. The youngest age for a phakic lens implantation in a patient with hyperopia has not yet been determined, considering that many patients with hyperopia have a shallow anterior chamber. Also, children are more prone to eye trauma than adults. Thus, phakic lenses for this important group of patients with hyperopia are contraindicated.
Refractive corneal procedures have come of age. Wave analyzed supported customized ablation (WASCA) has brought greater confidence in application and results.
Using MEL 70 excimer laser, during the course of 5 years, the author treated 69 patients with hyperopia (age range 5-68 y, average 24.6 y) with WASCA. The spherical error varied between 2 D and 11 D, with an average of 5.86 D. The cylindrical error varied between 0 D and 5 D, with an average of 0.84 D. The average follow-up period is 11 months. The final spherical error varied between -2.5 D and 6 D, with an average of -0.003 D. The cylindrical error varied between -1 D and 0 D, with an average of 0.08 D.
Preoperatively, the best visual acuity varied between 6/6 and 6/60, with an average of 6/26.56. Postoperatively, the best visual acuity varied between 6/6 and 6/60, with an average of 6/22.66. One patient lost 2 lines, and 12 patients lost 1 line. Among the rest, 32 patients had no change, 10 patients gained 1 line, 8 patients gained 2 lines, and 6 patients gained 3 lines.
One patient required the removal of the epithelium because of haze formation. Two patients had transient superficial punctate keratitis (SPK). Six patients had minor haze that disappeared over time. No cases of steroid glaucoma occurred.
In refractive laser surgery, the author finds many advantages. It is independent of the internal anatomy of the eye and is applicable to very young patients. One year of follow-up care is usually sufficient to determine that no more active follow-up care is needed for the rest of that patient's life. Some patients with very high hyperopia and with a favorable depth of the anterior chamber are best served with a phakic intraocular lens plus laser refractive surgery.
Amblyopia is common among hyperopes, especially in unilateral cases. Orthoptic and pleoptic exercises, which have proven useful, are not used widely to improve these patients. The goal of refractive hyperopia surgery should not only be freedom from glasses but also freedom from the clutches of amblyopia. Unfortunately, today's only effort to overcome amblyopia is patching. All other measures are avoided because they are costly. The fight against hyperopia should go hand-in-hand with the fight against amblyopia; only then will a universal interest in recognizing hyperopia exist.
Manolette R Roque, MD, MBA, FPAO, Section Chief, Ocular Immunology and Uveitis, Department of Ophthalmology, Asian Hospital and Medical Center; Section Chief, Ocular Immunology and Uveitis, International Eye Institute, St Luke's Medical Center Global City; Senior Eye Surgeon, The LASIK Surgery Clinic; Director, AMC Eye Center, Alabang Medical Center
Disclosure: Nothing to disclose.
Specialty Editors
Francisco Talavera, PharmD, PhD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference
Disclosure: Received salary from Medscape for employment. for: Medscape.
Louis E Probst, MD, MD, Medical Director, TLC Laser Eye Centers
Disclosure: Nothing to disclose.
Chief Editor
Michael Taravella, MD, Director of Cornea and Refractive Surgery, Rocky Mountain Lions Eye Institute; Professor, Department of Ophthalmology, University of Colorado School of Medicine
Disclosure: Received income in an amount equal to or greater than $250 from: J&J Vision (Consultant)/Proctor<br/> for: Coronet Surgical (Consultant), no income received.
Additional Contributors
Daljit Singh, MBBS, MS, DSc, † Professor Emeritus, Department of Ophthalmology, Guru Nanak Dev University; Director, Daljit Singh Eye Hospital, India
Disclosure: Nothing to disclose.
Daniel S Durrie, MD, Director, Department of Ophthalmology, Division of Refractive Surgery, University of Kansas Medical Center
Disclosure: Received grant/research funds from Alcon Labs for independent contractor; Received grant/research funds from Abbott Medical Optics for independent contractor; Received ownership interest from Acufocus for consulting; Received ownership interest from WaveTec for consulting; Received grant/research funds from Topcon for independent contractor; Received grant/research funds from Avedro for independent contractor; Received grant/research funds from ReVitalVision for independent contractor.
Ravi S J Singh, MD, Vitreo-Retina Fellow, The Eye Institute at Medical College of Wisconsin
The dimensions of the Artisan phakic lens. The lens is 8.5 mm at the widest point, far away from the angle of the anterior chamber. The optic is vaulted suitably to stay clear of the iris cone.
The iris claw lens for a phakic hyperopic eye, implanted in the eye of a blue-eyed patient. Minimal essential iris fold in the lens claw exists for the purpose of fixation. Jan Worst, the designer of the lens, considers the peripheral part of the iris as a silent area. It is least affected by the pupillary movements.
A stereo pair demonstrates that the iris diaphragm is designed like a cone. The apex has been cut to make a pupil. An artificial lens behind the iris lifts this cone. An artificial lens to be kept in front of the iris has to be designed to stay clear of the cone. Otherwise, it impinges on the iris, the pupil, and the crystalline lens.
The dimensions of the Artisan phakic lens. The lens is 8.5 mm at the widest point, far away from the angle of the anterior chamber. The optic is vaulted suitably to stay clear of the iris cone.
The iris claw lens for a phakic hyperopic eye, implanted in the eye of a blue-eyed patient. Minimal essential iris fold in the lens claw exists for the purpose of fixation. Jan Worst, the designer of the lens, considers the peripheral part of the iris as a silent area. It is least affected by the pupillary movements.
An early version of the iris claw lens that was used to treat high hyperopia. The optic is 4.25 mm, and the overall length is much smaller. The optical section shows how far away the corneal endothelium is located. The lens is well tolerated, even by the pigmented iris.
An optical section, taken 7 years postoperatively, shows that this hyperopia lens is well tolerated by the eye. Iridectomy is an essential part of the procedure. The angle of the anterior chamber, the crystalline lens, and the corneal endothelium are not at risk because they are far away.
A phakic iris claw lens for hyperopia, fixed close to the collarette (an early version), the optic of which barely covers the pupil. It provides extreme safety, being wholly located in the deepest part of the anterior chamber. This lens size suffices for most people with black eyes, although some complain of glare from the edge of the optic. A small optic, small lens might be good in black eyes and in nonautomobile societies.
The phakic iris claw lens has no tendency to shift, either by itself or even by pupil dilatation with mydriatics. Because it does not touch the crystalline lens, there is no danger to its transparency. This red reflex picture after dilatation, taken 10 years postoperatively, shows that the lens is well tolerated.
This iris claw lens in an aphake shows how it is well tolerated by the iris. This 65-year-old patient had a primary implant 32 years ago. The claws are shifted upward (Singh variation of worst iris claw lens). No viscoelastic was available then. The endothelial cell count is 1980/sq mm. Best corrected vision is 6/6. The pictures are in 3D.
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