|Year : 1989 | Volume
| Issue : 2 | Page : 54-57
"Present state of management of aphakia. Future of spectacles and contact lenses".
5311, W9TH, Amarillo, Texas, 79106 - 4161, USA
5311, W9TH, Amarillo, Texas, 79106 - 4161
|How to cite this article:|
Alpar J. "Present state of management of aphakia. Future of spectacles and contact lenses". Indian J Ophthalmol 1989;37:54-7
|How to cite this URL:|
Alpar J. "Present state of management of aphakia. Future of spectacles and contact lenses". Indian J Ophthalmol [serial online] 1989 [cited 2013 May 25];37:54-7. Available from: http://www.ijo.in/text.asp?1989/37/2/54/26094
"In order to have a discussion between two people it is necessary that one should know the subject. If neither one knows the subject the discussion will be more spirited and profound."
It is now recognized that aphakia is a crippling condition; severely restricting the activities and the lifestyle of those depicted. These are rather strong words deliberately chosen to make both the doctors and the public aware of the suffering of such patients.
Aphakia, with very rare and a few exceptions, is a traumatically or surgically induced entity (surgery is really a controlled trauma).
If the anterior hyaloid membrane is disrupted, there is a higher incidence of cystoid macular edema (CME) or retinal detachment (RD) or even endothelial corneal decompensation (ECD) than in phakic eyes but such complications are mostly the result of surgical mishaps.
Aphakia comes from two Greek words; "a" meaning "none" and "phacos" meaning "lens". It refers to both an anatomicall and an optical condition. In the strict sense, in aphakia there is no crystalline lens inside the eye. That, of course, is not true in the case of a subluxated or luxated lens; yet, we still speak of aphakia because of the optical situation. In this presentation the term aphakia will be used to mean the optical condition where one of the main refractive elements of the eye, namely the crystalline lens, is not in the visual axis.
Aphakia might be the result of congenital problems which leads to a subluxation or luxation of the lens. In subluxation, the lens' relation to the pupil (visual axis) determines whether the vision is or should be considered predominantely phakic or aphakic. In the subluxated or luxated phakic state the optical, if not the anatomical aphakia, is complete. After all the lens still is in the eye yet the optical condition is similar to the retropupillary situation following an intracapsular cataract extraction (ICCE).
Traumatic aphakia is often the result of absorption of the crystalline lens creating, in effect, a condition one finds after extracapsular cataract extraction (ECCE). Of course the lens also could have been subluxated, luxated or even expelled from the eye during the trauma.
Surgical aphakia is the consequence of either an ICCE or an ECCE by whatever means the surgeries were performed, including couching procedures when the lens remains in the eye but is pushed away from the visual axis. The correction of the aphakic condition depends on the economic conditions of the country or the patient; and, even in industralized and relatively prosperous countries, upon the condition of the eye and the intelligence of the patient.
Aphakic spectacle correction still has its place in the world. Indeed, in many countries and in many economic strata of such countries, a basic aphakic lens (spherical without any astigmatic corrective component) is the only feasible way of rehabilitating the aphakic cripple. This is not to say that we have to consider people in these groups less valuable as human beings, or even as workers, than others but, given their vast numbers, their life expectancy, and their visual needs, inexpensive corrective spectacles easily available in village or district dispensaries would suffice for the next fifteen or twenty years.
Certainly as far as the eyes themselves are concerned aphakic spectacles are the least traumatic modalities.
Of course the drawbacks of aphakic spectacles are well known to all and need not be elaborated upon.
Aphakic spectacle correction has undergone great changes in the past ten years or so. Sturdy frames and new manufacturing techniques make such glasses much more attractive than before, needing less adjustments. The weight has been reduced and the plastic lens made more resistant to scratches. Ultraviolet filtering dyes have been added to the lens to offer extra and important protection to the vulnerable, elderly - retina. Both the central and peripheral optical qualities have been greatly imporved, reducing the `pincushion effect' and the `jack-in-the-box' phenomenon so troublesome with the old lenses. Such sophisticated spectacles, however, are quite expensive and in the long-run even more expensive that an intraocular lens.
I am not advocating this type of correction; I am only trying to be realistic.
Successful contact lens correction includes fitting, wearing and, follow-ups, and depends upon the educational level of the patients. Personal hygiene, trustworthiness, ocular condition, corneal sensitivity, the availability of the proper contact lenses, sterilization of the lenses, and the availability of a competent contact lens specialist are some of the indispensible ingredients of success. Disposable contact lenses, however attractive they are, are not yet for the vast numbers of our aphakic patients living under so different economic, geographic and educational conditions.
Even under the most ideal conditions, the "permanent wear" contact lenses prove to be only "extended wear" lenses at best, the maximum time being a week for a few and forty-eight hours for most. Severe complications occur more often, and one cannot be confident in describing them as "safe". Yet under certain circumstances and for some patients contact lens correction, at least in monocular cataract, will remain a viable alternative.
Stark, et al, reported corrected visions comparable to that after intraocular lens implantation. Several of the patients could wear the extended lenses for months at a time.
I would like to point out, however, a few aspects of the IOLs and IOL implantation.
The first and most important law to remember is what Ridley postulated at the dawn of implantation: an eye will tolerate an intraocular lens, which really is a foreign body, if (a) the intraocular lens (IOL) does not move inside the eye, (b) if the eye does not not move over the IOL. Virtually every complication of IOLs, almost always predictable, is the result of violating this axiom.
Certainly microscopes with their superior lights, the ability to provide coaxial illumination, the variable, often zooming magnification, greatly improved the accuracy of cataract surgery and made extracapsular extraction the operation of choice for all but a handfull of patients.
Yet cataract surgery, even ECCE, and lens implantation is possible to perform with relative inexpensive instrumentation. Indeed a bad microscope is worse than no microscope at all as I learned through my own problems in operating in different countries. Intermediate technology has much to be recommended in vast parts of the world. Remember that such technology does not necessarily reflect the current status of inducing and correcting aphakia. What I would like to do is to tell you what is available now and what will be available shortly, even if not in the eye camps of India or the mountains of Nepal or the Alti-Plano of South America, or even Average Town, USA. I am not selling high tech ophthalmology, or even judging its merits.
Primary intraocular lens implantation today is usually safer and almost always more effective than secondary implants. In the early age of IOL implantation preoperative intraocular power calculation was difficult and unrealiable, hence secondary implantation was advocated for accurate lens power determination. Today very accurate power prediction is the rule rather than the exception. This, of course, requires a keratometer and an ultrasonic axial lens measuring device, the price of which is dropping very rapidly. It would be relatively inexpensive to equip strategically located district centers with the tools necessary for biometry and putting them in a car, travel around the countryside, checking preoperative patients. Several ophthalmologists may pool their resources together to invite such traveling biometric diagnostic teams.
Today management of aphakia also involves intra and postoperative astigmatic control. This problem will also be discussed at length. I only want to emphasize this very important point: aphakic rehabilitation today means a rapid restoration of good, uncorrected visual function. A beautifully looking eye with poor vision because of optical problems is not acceptable anymore.
The Worst Iris Claw Lens, its Singh modification and its Amar modification allowing the placement of the lens behind the iris, has proven to be a very good lens in many thousands of patients observed for over ten years for primary and for secondary implantation, following extra or inracapsular extraction, with or without sector iridectomy, with or without vitreous loss, and even in phakic eyes in high myopia.
In addition to the Worst Iris Claw lens which can be inserted with relative ease, posterior chamber lenses can be placed with some combined manouvers in all eyes. Drews, Malbrsan, Stark and myself have presented techniques of placing posterior chamber lenses of different designs (modified J-Loop lenses, C-Loop lenses) into eyes following ICCE or vitreous loss and securing the lens with sutures to the iris or sclera.
Many of today's procedures, especially secondary lens implantations were made possible by viscoelastic materials. Chamber maintenance with air, with fluids or with the patient's own serum are acceptable in many if not in most cases but they do not even approach the safety that good viscoelastic materials provide. Economics play a great roll in visco surgery but it is only a question of time until we have high quality, reliable viscoelastic material available for a very reasonable prices. Until such times comes, 1 % sodium Hyaluronate in the form of Healon (R) is still the material of choice.
Eyes that are considered for secondary implantation must be carefully examined pre-operatively. Intraocular pressure (IOP), anterior chamber angle assessment with a goniolens, the evaluation of the cornea and its endothelial cell lining is imperative. In case there is a pathology present, alternative steps should be considered.
One also has to remember that loss of a couple of lines of vision after secondary implantation is more the rule than the exception.
I will not enter the field of cataract removal techniques but I must tell you that endocapsular excimer laser removal of cataract is a fascinating evolution. I was overwhelmed as I watched a nucleus disappear as I applied the Excimer probe in experimental animals. The best scientific term to describe the experience is, "WOW".
The use of a small incision proved to make sense, even without small incision lens. Although suture induced astigmatism as high as 13 diopters has been reported after closure of a 3mm. phaco incision, in the majority of patients the smaller the incision the less the astigmatism there will be, leading to faster recovery and faster full rehabilitation. Although wounds do not heal from end to end but from side to side, the length of the wound has much to do with strong healing and the globe is much stronger in the area where it has not been cut. The size of the wound and the time of its healing is becoming less important with the epithelial growth factors, and the topical application of Insulin and other biological materials at the time of the surgery resulting in very rapid and strong wound healing.
To many people, however, small incision makes little sense if it has to be enlarged to place an intraocular lens. Hence the evolution of small incision and foldable lenses. A number of relatively "new" materials, that is, materials which are relative new for intraocular lens implantation, are being tried. Silicone, Hema and hydrophylic materials can be implanted through a 3 mm. incision, some of which then swells to fill the space available once in the eye. There are many difficulties which must be overcome before such lenses reach the quality of the lathe cut, well cured PMMA.
Once small incision cataract removal is perfected, the endocapsular silicone lens (phaco-Erzatz), which is even capable of accommodating, will have an important role to play in correcting aphakia.
Nishi places a silicone balloon through a small limbal and capsular incision into the capsular bag, the contents of which he had removed with phacoemulsification. Ultrasonic cleaning of the capsule is essential. He injects the balloon with optically proper material (organosilicone gel). He then sutures the capsule. This manuever in humans is extremely difficult because the capsule tears. Heat sealing of the capsular hole as well as other method have been tried.
Indeed there are many new materials tried experimentally. Some are described in the literature; some have come to my attention in strictest confidence in my capacity as a friend or as Chairman of the National Standards Institute (ANSI) Committee that is charged to rewrite the intraocular standards for the industry.
I would like to mention, however, a few points. Although not too long ago the haptics of the one piece PMMA lenses were more brittle, this problem has been greatly reduced, indeed, almost eliminated. One piece PMMA lenses are going to be marketed in growing numbers.
Polypropylene haptics in the posterior chamber are working out well and are quite acceptable.
Polymid haptics, however soft, can and do erode into and through the ocular tissues and can be incapsulated in uveal tissue in the anterior chamber leading to the same complications as other lenses with, flexible and semi-flexible loops gave us.
Because of its high refractive index and because of its autoclaveability, glass is an attractive intraocular lens material. However glass is a compound chemical and therefore biologically less pure than PMMA in "Clinical Quality" (Perspex "CO"). Glass may also cracks under YAG laser. Because of these and other reasons presently glass lenses are not approved by the FDA.
There are still several rigid anterior chamber angle fixated lenses around: the Choyce Mark VIII and Mark IX variety and the Tennant lens, which was really a copyrighted copy of the now copyrighted Choyce Mark VIII lens. Many of the results are still excellent except for the tenderness. Indeed, many of my own rigid anterior chamber angle fixed lens patients do better than the ones with flexible haptics.
Likewise I have patients with iris supported lenses in situ now for fifteen years or more with excellent results although a slight decay of the vision is sometimes observed, even without loss of corneal endothelial cells or alteration of the cell structures and even without measurable retinal macular changes. Even so the overall complication rate from both the anterior chamber angle fixed lenses and the iris fixed lenses is much higher than acceptable today.
There are also hundreds of thousands of iridociliary sulcus supported lenses in patients' eyes, the majority of whom are still in good condition yet late problems are occuring in increasing numbers. The progressive iris pigment loss I reported in 1978 are now being observed with the sulcus fixated J-loop lenses and their modifications. Late peripheral anterior synechiae (PAS) formation and erosion of loops through the iris does occur. There is an increased incidence of PAS formation in eyes which had no iridectomy. In my own practice since I reinstated iridotomy using a Grieshaber # 681.05 discission knife, the number of peripheral anterior synechiae decreased indicating that at least some of them were the result of pupillary block.
There were several of us who were never comfortable with sulcus fixation and advocated in-the-bag placement of the IOLs. Indeed, eyes with IOLs within the capsular bag do much better, especially in cases with pre-existing glaucoma, uveitis, and diabetic retinopathy. Of course such in-the-bag placement requires the abandonment of the till now popular lens designs. The capsular bag diameter is only about 10.5 mm. and does not accept a 13.5 or 14 mm. tip-to-tip diameter lens without complications such as pea-podding of the lens, severe bending of the haptics, dislocation of one haptic and decentration of the lens, etc. More logical and physiological designs are emerging; the disc lenses of Galand and others and the closed circular loop lenses of Anis and others. Such IOLs, if placed with their convexity towards the posterior chamber, greatly decrease the opacifications of the posterior capsule even without a laser ridge, reducing the need for posterior capsulotomy.
Although bifocal IOLs are now in clinical use (one with a precision diffractive optic is already being produced), even with such IOLs the need for glasses is not yet eliminated. Often near, sometimes distance, and even both distance and near corrective lenses may be needed post operatively. I, for one, rarely pleased my patients when I made one eye corrected for distance and the other for near. Most of the patients prefer to wear glasses at times, if not all the time. Although high astigmatism can and should be surgically corrected, many post operative and/or residual astigmatisms can and should be corrected with spectacles.
Other current techniques gaining popularity in correcting aphakia involve modification of the curvature and even the refractive index of the cornea.
The more viable methods are the Werblin-Kaufman-McDonald Epikeratophakia and the non-freezing hypermetropic keratomileusis of Krumeich and Ruiz.
None of these procedures are fully developed yet, but both are performed on an ever-increasing scale.
Since epikeratophakia does not require fresh and viable cornea tissue (although viable tissue may be preferable) and a centrally prepared corneal disc can be transported and stored easier, safer and for longer periods of time than the presently used corneal tissue for corneal grafts, once a national manufacturing center is set up which can process the eyes harvested throughout the country the procedure should be more easily done in even remote areas than the ordinary keratoplasty. The surgical technique is simpler, and the instrumentation is relatively inexpensive.
The original Barraquer hypermetropic keratomileusis required, among other things, an expensive and sensitive cryolathe few centers can afford.
The non-freeze techniques of Krumeich and Ruiz eliminate this hardware but introduce others which are also fairly highly priced. The Krumeich instrument proved to be rather unreliable in outcome although it provides an excellent way of doing lamellar keratoplasty. The Ruiz instrument seems to be simpler, less expensive and gives more uniform results. However at the present time neither of these procedures are uniformly good enough to brand these procedures as safe and effective.
Epikertophakia has the great advantage that it can be done in patients where, either because of age or because of ocular conditions a secondary implant or even a primary implant is not feasible. It does not require entry into the eye, eliminating many of the complications from such operations, and it can be repeated.
The Choyce Polysulfone Corneal Inlay, although tried by some very courageous pioneers in humans, is still experimental. The Choyce Corneal Inlay seems to be effective but it was safe only in less than two-thirds of the patients: in more than one-third of the operated eyes severe corneal problems occured from this procedure. The fenestrated corneal inlay, using laser drilled microholes which allow the easy transportation of oxygen and other nutrients through this inlay proved to be safer in animals but its efficacy has not yet been established. One has to find a material which is both optically and biochemically correct and which, because of its high refractive index, can be made very thin and very light so that together with the microholes drilled in such materials they can provide an effective and safe way of modifying the corneal surface and the corneal refractive index. (Several intraocular lens companies are now working experimentally with such fenestrated corneal inlays and soon we will have some results published.)
Employing a corneal lenticle slipped into the pocket of the patient's own cornea has been and still is employed with variable success.
Placing an epikeratophakic lenticle between corneal epithelium and Bowman's membrane had been reported. The advantage of this procedure is a faster epithelialization of the cornea.
Hypermetropic keratotomy or placing circle sutures in the cornea, such as the Singh wire suture, are used by some but either discontinued or the procedure not developed properly yet.
Heat induced corneal stromal shrinkage as advocated by Fyodorov is a possible method of correcting aphakia. It is now tested by Newman and others.
Excimer laser corneal surgery for hypermetropic correction is very experimental but it is also very promising. I am quite sure that it will become the surgery of choice in a few years, especially when a computer will perform the actual manipulations of the cutting beam.
In summary there are several ways to rehabilitate the cataract cripple. Presently and for a few years to come the most practical way to correct the condition is with intraocular lenses. The quality and the appearance of spectacles are improving rapidly and even patients who do not wish to wear glasses do wear them for cosmetic reasons because they are attractive and give them a "movie star" appearance. Furthermore, whereas at the present time, the ultraviolet chromophores placed into the intraocular lenses under the present manufacturing conditions are not without danger, ultraviolet filtering chromophores placed through spectacles are highly effective and totally without danger to the human eye.