Considerations on Clear Lens Extraction in High Myopia LUCIO BURATTO

Centro Ambrosiano di Microchirurgia Oculare, Piazza Repubb/ica 21, 20124 Milan, Italy

Statistical data on the complications associated with cataract surgery in axial myopia are reported and the advantages and disadvantages of clear lens extraction (CLE) are evaluated.

Keywords: Axial myopia; Clear lens extraction; Capsule opacification; Cystoid macular oedema

INTRODUCTION

Although surgical techniques have always been used to resolve problems existing in pathological structures or organs, the last few years have seen surgery becoming widely used for aesthetic and functional reasons. Ophthalmologists who have received a traditional medical and surgical edu­cation are usually reluctant to perform surgery on 'healthy' eyes for purposes that are not strictly ther­apeutic. In particular, this applies to refractive sur­gery. The degree of reluctance, already present in cases of surface surgery such as RK, epikeratop­lasty, etc., increases if intraocular surgery is required or if the structure involved is frail, weak or predisposed to serious complications that could jeo­pardise visual function and the globe itself.

In the 1980s, Verzella's proposal [1, 2] for a tech­nique to remove the clear lens to correct high myo­pia was harshly criticised. Verzella omitted to report precise statistical data on the results of his oper­ations, giving the impression that the results were satisfactory, not only for the surgeon, but also for the patient. As a result, some ophthalmologists from different parts of the world began implementing the technique while other, more cautious surgeons, employed Verzella's technique only for selected patients, using the definition 'extraction of early cataract'. The result is that, independently of the quality of the technique itself, many surgeons now either explicitly or tacitly use it.

In the early 1980s, I was invited by Verzella to carry out a parallel study on this type of surgery. For ethical reasons, and also because of the clear impression that I had of the problems involved, I turned this proposal down.

During the last five years, I have submitted over 600 highly myopic eyes with an axial length equal to, or greater than 26.5 mm, to cataract surgery. The

0955-3681/91/030221 +06 $03.00/0 © 1991 Bailliere Tindall

experience acquired has confirmed my initial impression of the problems involved in this type of surgery [3]. The concept of clear lens removal for the correction of high myopia was first introduced by Fukala in 1890. As ocular surgery evolved, the con­cept was reviewed numerous times by various sur­geons. However, results have always been poor due to the high incidence of complications. Verzella [1, 2] has exploited Fukala's idea in a surgical approach that makes use of a perfected method for extracapsu­lar cataract extraction under a surgical microscope. This is done by means of sophisticated surgical instruments, with the residual defect being cor­rected by implantation of an artificial lens, and post­operative prophylactic treatment of retinal detach­ment (RD) being made by either Argon laser or cryocoagulation. All of these innovations have con­tributed to the improvement of surgical results and have reduced intraoperative risks to a minimum. The clear lens extraction technique has therefore become quite widespread both in Italy and abroad [4,5].

Clear lens extraction (CLE) can lead to consider­able optical improvement in myopia. However, from an ethical viewpoint, the technique must guarantee a high degree of safety for the patient, in fact more so than in the case of lens extraction due to strictly medical reasons [6]. Unfortunately, this is not the case, since, compared with the emmetropic globe, the myopic eyeball is more likely to suffer from intra- and postoperative complications following lens extraction, independently of its cataractous or clear nature [7-10].

In surgical terms, the question of whether a lens is clear or cataractous makes no difference to surgical exitus, complications or postoperative problems. Although clear lens extraction can sometimes be easier than extraction of a cataractous lens, surgery on young patients (CLE is performed on younger

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individuals than the usual cataractous population) can infer a greater risk of retinal detachment in aphakic or pseudo aphakic eyes as will be discussed later.

In order to better understand and describe the problems related to CLE, literature data concerning cataract extraction from the myopic eye is discussed.

THE MYOPIC GLOBE

The highly myopic globe shows degrees of anatom­ical variation involving the sclera, choroid, retina and vitreous [9, 10]. As axial length increases, ana­tomical and clinical alterations occur in the ocular structures and so turn a simple ametropia into myo­pic 'disease'. The anterior chamber is deeper, the zonular fibres of the lens are weaker, the sclera is thinner, the choroid becomes stretched, tapered and atrophic, the vitreous is liquefied and frequently posteriorly detached, and the retina undergoes both peripheral and central degenerative processes [9, 10] that predispose to vitreoretinal complications. An elongation and widening of the globe follows. This process is asymmetric in most cases, due to the presence of staphylomas that can develop at the level of both the posterior sclera and the superior temporal sectors. In practical terms, the highly myo­pic patient is characterized by an increase in all diameters of the eyeball, as well as increase in ocu­lar volume of up to 50% [11].

RETINAL DETACHMENT

Retinal detachment in phakic myopic patients

The overall incidence of retinal detachment is rela­tively low, and ranges from 0.005% to 0.01 % [12, 13]. Axial myopia is a significant risk factor in terms of retinal detachment. In phakic patients affected by myopia the risk amounts to c. 1% [10] and is directly related to the anatomical and vitreoretinal charac­teristics of the myopic eye, as well as to the greater predisposition to retinal complications. Retinal rup­ture due to traction, for instance, is five times more common in myopic eyes and asymptomatic retinal holes are observed twice as often as in non-myopic eyes.

In high myopia, the risk of retinal detachment is c. 34 times greater than in light myopia and c. 45 times greater than in emmetropic eyes [13].

Retinal detachment in aphakic myopic patients

Regardless of the method used, cataract extraction

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implies a significant increase in the risk of retinal detachment [6-8, 15, 16].

Wetzig et al. [17] reported an incidence of retinal detachment of 0.45% following non-complicated ECCE in eyes that were not at risk. Scheie [18] claimed an incidence of retinal detachment follow­ing both intra- and extracapsular cataract extrac­tion of 2.2% (in 5541 eyes) [18]. The risk of retinal detachment increases if complications occur, and during surgery on eyes at risk.

Cannon et al. [19] reported an incidence of retinal detachment of 3.5% in eyes with myopia greater than 8 dioptres while Praeger observed 6.4% retinal detachment following ECCE in eyes with an axial length greater than 27 mm [20]. Lindstrom et al. [21] reported an incidence of retinal detachment of 7 .04% of 71 myopic eyes with an axial length greater than 25 mm, an intact capsule and no intraoperative complications.

ECCE implies fewer vitreoretinal complications [18, 22, 23]. According to Jaffe et al. [24] the inci­dence of ARD in myopic eyes amounted to 5.74% after ICCE, and 0.66% after ECCE, only taking into account eyes with an intact hyaloid and posterior capsule respectively, as well as without an IOL.

Retinal detachment in the aphakic eye with complications in both the myopic and the non­

myopic aphakic patient

In the case of intraoperative complications, such as vitreous loss, the risk of retinal detachment increases considerably. Armstrong and Lichtenstan reported a 25% incidence of retinal detachment in four eyes that required intraoperative vitrectomy [25]. Cannon et al. reported a frequency of, 8.6% following ECCE complicated by vitrectomy (3/35 eyes) [19]. Chambless observed retinal detachment in 9.4% of 85 patients that suffered from vitreous problems during surgery [26].

Retinal detachment and capsular opening

Although intraoperative complications rarely occur with skilled surgeons, since most cataract and clear lens extractions are performed via either ECCE or PKE, the secondary opening of the opacified capsule increases the risk of retinal detachment as com­pared with those patients with intact capsules [15, 27].

Capsular opacification in eyes without IOLs occurs with a mean incidence ranging from 45% to 60% [15, 16,22, 23]. This value decreases consider­ably in those eyes that have received posterior

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chamber IOLs, due to the inhibiting and blocking effect exerted by the optic disk against capsular opa­cification [15, 16, 22]. However, long-term follow-up has shown that the lower opacification rate increases in time and approaches the rate observed in ECCE-aphakic eyes [25]. From this it can be inferred that young, cataract-operated and CLE­operated patients will have a 50% chance of needing YAG-laser capsulotomy, notwithstanding the presence of an IOL.

Cannon et al. [19] observed a 2.75% incidence of retinal detachment when primary and secondary capsulotomies were performed. The percentage value in the population at large is 1.4%, and this rate drops to 0.8% in patients with intact capsules. Chambless reported a 2% incidence in 184 eyes sub­mitted to posterior capsule opening and 0% in 2863 eyes wth intact capsules [26]. Lindstrom et al. [21] observed two retinal detachments in eight patients with axial myopia submitted to the Nd:YAG laser treatment (25%) and 4.76% retinal detachments in axial myopic eyes with intact capsules.

Considerations on retinal detachment and aphakic myopia

On the basis of the data reported, it is suggested that myopic phakic eyes are exposed to the risk of retinal detachment in 1% of cases, a risk that is c. 45 times greater than in emmetropic eyes.

Removal of the lens leads to an increased risk ranging from 3.5% to 6.4% [14, 24] over a 2-3-year follow-up period. Statistical data show that the risk of detachment is always present although its inci­dence decreases in time. Long-term effects are unknown. Toyofuky's speculation [28], which defines a mean time interval of c. 22 years between surgery of congenital cataracts and subsequent detachment of the retina, may be correct [15, 19].

The above remarks hold true for as long as the capsule is intact, but as soon as the capsule is opened, another mechanism is activated and the risk increases. Lindstrom's study shows an alarm­ingly high incidence of retinal detachment in axial myopia following uncomplicated cataract surgery and this stresses the need for careful consideration before cataract extraction is performed for refractive reasons alone.

It should be borne in mind that the patients requesting such an operation are usually young in­dividuals with a vision expectancy of at least 40-50 years after the operation. This is a very long period of time, in particular if it is considered that most reports of cataract surgery have follow-up periods of only 5 years or less and therefore further compli-

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cations may occur as the follow-up period becomes longer.

The above observations should be considered whenever clear lens extraction is planned as a refractive surgery technique to correct strong myo­pia. The risk of a strongly myopic patient submitted to clear lens extraction being affected by retinal detachment in the five years following the operation is considerable and a risk only to be taken when clinical reasons are present.

LITERATURE ON CLE

Verzella is the only author who has published statis­tical data on CLE in scientific journals: in 1981 [1], 1983 [3], 1984 [29] and 1985 [2]. He operated on the following cases with myopia greater than 10 dioptres: between January 1977 and December 1985, 763 eyes were submitted to CLE; 354 eyes were implanted with a primary posterior chamber IOL and 182 eyes were submitted to cataract extrac­tion; a further 1020 highly myopia eyes were sub­mitted to cataract extraction; 427 received a pri­mary IOL and 199 received a secondary implant. Argon laser treatment was performed in 47% of the CLE cases and in 20% of the cataract-operated eyes.

Verzella's studies provided no data on: (1) the period of time that elapsed between the first oper­ation and the secondary implantation; (2) the number of cases included in the follow-up study; (3) the number of intraoperative complications (although Verzella himself observed that the zonu­lar-capsular diaphragm was very weak); and (4) the incidence of retinal detachment and other compli­cations. The data published are too incomplete to recommend the technique of CLE for use in eyes with high myopia without cataract for refractive reasons only. If the complications that are common to all other endocular techniques (such as endoph­thalmitis, choroidal haemorrhages, corneal decom­pensation, etc.), which are typical of the implant (such as IOL dislocation), as well as on the possible long-term complications ofthe lens (i.e. Chafing syn­drome) are considered, it is clear that CLE should be restricted.

PROSPECTIVE BENEFITS

Highly myopic individuals with spectacles have poor near vision capability since spectacles make retinal images smaller [19]. When spectacles are removed and reading is from a considerably reduced distance, the retinal image is enlarged. However, in this way, highly myopic patients lack binocular vision [30].

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In highly myopic individuals far VISIOn is impaired by the frequent subcorrection of spectacle lenses, aberrations and distortions caused by the strong dioptric power, the erroneous distance be­tween corneal vertex and lens, poor centring of the lenses on the visual axis, and the .use of either too large or too light frames to hold the heavy lenses [9].

Surgery can eliminate the problems related to the strong negative correction, increasing far visual acuity [31] and displacing the nodal point away from the retina, with the consequent enlargement of the retinal image (occurring in all aphakic patients). With regard to near vision, some problems can occur, in particular if the operation has led to emme­tropia. In this case, positive lenses of adequate power are necessary.

INDICATIONS

In Italy, as well as throughout the world, there is a high percentage of strongly myopic individuals. In many cases these patients are truly visually handi­capped, even if they wear spectacles or contact lenses. When such patients develop cataract and are submitted to cataract surgery, refraction is calcu­lated by careful biometry and a posterior chamber IOL is implanted. This relieves the patient from the necessity of wearing thick and heavy lenses and from the visual and aesthetic problems associated with the strongly concave surface of these lenses. After surgery, these patients enjoy not only the enhanced vision resulting from the removal of the cataract, but they also achieve the correction of myo­pia. The high degree of satisfaction from this oper­ation must certainly be considered by the surgeon when evaluating the usefulness of early cataract surgery, and it is, most probably, this factor that has strongly influenced those surgeons who implement CLE. Notwithstanding the preliminary statements made in the first part of this article, unconditional refusal to consider clear lens extraction is unadvis­able, since this operation can be indicated for certain specific cases. However, it must be preceded by a careful preoperative selection of the patients, who will require great care and attention in both the postoperative short and long terms.

Familiar and personal anamneses must be nega­tive for retinal detachments and macular haemor­rhages. Age must exceed 20-22 years; refraction must have been stable for at least 2-3 years; the refractive defect must not be less than 12-13 dioptres (otherwise RK is easier, safer and accompa­nied by fewer retinal complications). Moreover, post­operative near and far visual capability must be carefully evaluated since several patients (in par-

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ticular those with macular lesions and restricted visual capability) can encounter greater difficulties in near vision compared with the preoperative situation.

Accurate examination of the anterior and pos­terior segments is also mandatory. If vitreoretinal lesions are present, the operation should be rejected. If, however, the patient insists on the operation or if the operation is truly necessary, adequate prophy­laxis must be implemented (by Argon laser, cryoap­plications, etc.) and retinal stabilization must be accomplished prior to proceeding with surgery. The patient must also be informed of the risks related to surgery as well as any possible postoperative problems that might occur.

Given the above, the operation can be considered in the following instances.

(1) In the presence of initial cataracts that, in highly myopic patients, often evolve very slowly and cause the refractive defect to deteriorate further [19]. If the patient cannot tolerate the pathology any longer due to personal, professional or other reasons, it is possible to shorten the waiting time.

(2) In the presence of a cataract in one eye and either a transparent lens or initial cataract in the contralateral eye. In this situation the surgeon and patient are confronted with three possibilities: (a) surgery of the first eye and contact lens application in the second; (b) surgery of the first eye and CLE from the second eye; (c) if the cataract of the first eye is not mature, it is possible to wait until the cataract of the second eye develops and operate on both eyes with a short time interval between the two oper­ations. I prefer the first and third of the above hypotheses.

(3) Highly myopic patients who demand to be sub­mitted to refractive surgery, in particular RK (in a response to media pressure) but who cannot be sub­mitted to RK due to the degree of myopia being too high. In particular, if the lens is either sclerotic or shows initial opacifications that may lead to devel­opment of a cataract in the short term, CLE can be indicated. However, if the intraocular structures are clear I prefer to perform either epikeratophakia or keratomileusis.

(4) Intolerance of contact lenses due to recurrent ulcerations, vascularization of the cornea, etc., cou­pled with inability to wear spectacles.

(5) When the patient's professional activity is limited or inhibited by the use of spectacles and con­tact lenses (in the presence of dust, heat, steam, etc.).

(6) When personal reasons are important enough to offset the negative implications related to possible complications.

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Clear lens Extraction

Possible risks

The short and long-term surgical and postoperative risks described in the first part of this article include the following problems: (1) Loss of accommodation. Although highly myopic patients make only a re­stricted use of this ocular function, its importance should not be neglected. (2) Loss of the advan­tageous optical compromise that allows the correc­tion-free eye to enjoy very large images that are perfectly focused by simply putting the object closer. To achieve acceptable images and suitable focus, the patient should be left with a postoperative myopia of at least 4 dioptres (this is the postoperative refrac­tive defect to be considered in these cases, when an IOL of adequate power is inserted).

CLE: CONCLUSIONS

The complications associated with clear lens extrac­tion relate to preventative problems (macular pucker, RD, etc.) and intraoperative problems (cap­sular rupture, zonular disinsertion, vitreous loss). The latter considerably increase postoperative risks [32, 33] (involving RD, CME, etc.). Choroidal haem­orrhage and endophthalmitis can occur, although they are rare. Uveitis, IOL displacement, post­operative astigmatism, and dehiscence of the wound are of minor importance. Other possible effects, such as CME and vitreous detachment can decrease both visual acuity and macular function, already jeo­pardi sed by the myopic disease. The young age of the patients as well as the changes that have occurred in the weak anterior segment, in particular in the young vitreous, will undoubtedly have repercus­sions on the visual future of these patients. Serious complications, such as retinal detachment, can take place during the first postoperative year, as well as in subsequent years [24, 34-36], particularly after capsulotomy. Moreover, there are still a few doubts on the long-term effect of posterior chamber IOLs. Although their tolerance has been proven in many studies [37-39], cases ofloss of iris pigment accom­panied by the onset of microhyphaema and intra­ocular hypertension have been described in the literature.

The fact that CLE is most suited to young patients means that the implanted IOLs will remain in the eyes for long periods.

When CLE is performed and an IOL is implanted, it is necessary to position the lens in the capsular bag, even if this may cause greater difficulty to the posterior segment surgeon in the case of vitreoreti­nal complications [34]. However, the treatment of RD in pseudophakic patients often requires ab

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interno destructive surgery (i.e. vitrectomy either with or without silicone oil). This does not only impair the globe and retina but it also has signifi­cant repercussions on retinal and macular function. The confusion that surrounds the implementation of CLE thus becomes greater. Moreover, the best candidates for CLE have myopia equal to or greater than 15 dioptres. These patients can draw a con­siderable benefit from lens extraction. However, they also have a greater predisposition to compli­cations, e.g. a study by Perkins showed that the higher the refractive error the greater the risk ofRD [13]. Drews' [40] and Verzella's case studies [1-4] reported a low incidence of complications, including RD, whereas Lindstrom [21], Praeger [20], Cannon [19], Jaffe [24] and Kraff[32] report a high incidence of complications. In the case of very high myopia, the complication rate is probably even higher.

Such an incidence of complications cannot seem to be low or of little significance even to the most opti­mistic of surgeons since they could imply permanent reduction of vision, despite therapeutical, medical and surgical efforts made by the ophthalmologist. The principle 'primum non nocere' is now being dropped. At present, the risk-benefit ratio is too high and CLE cannot be implemented for mere optical purposes with professional certainty.

REFERENCES

1 F Verzella. P.E. and transparent lenses. In: F Ve~ella, Ed. Atlas of Extracapsular Technique. Phaco Emulsification and Intraocular Lenses. Bologna, Italy, Lens Editions, 1981; 98-108.

2 F Verzella. High myopia: in-the-bag refractive implantation. Ophthalmic Forum, 1985; 3(3): 174-175.

3 LU Buratto, LE Buratto. Cararact surgery in the strongly myopic eye. In: AE Maumenee, WJ Stark, I Esente. Cataract and Refractive Microsurgery. Procedings of the V Inter­national Congress, Florence, Italy, Giugno 1989: 139-142.

4 F Verzella. High myopia: microsurgical extracapsular extraction of the lens for optical purposes. Presented at the Keratorefractive Society Meeting, Chicago, October 29-30, 1983.

5 F Verzella. Lensectomy. Ophthalmic Forum, 1985; 3(3): 191-192.

6 MF Goldberg. Clear lens extraction for axial myopia. Oph­thalmology, 1987; 5: 571-582.

7 WE Benson, MG Grand, E Okun. Aphakic retinal detach­ment. Management of the fellow eye. Arch. Ophthalmol., 1975; 93: 245-249.

8 M Ruben, P Rajapurohit. Distribution of myopia in aphakic retinal detachments. Br. J. Ophthalmol., 1976; 60: 517-52l.

9 BJ Curtin. The Myopias: Basic Science and Clinical Manage­ment. Philadelphia, Harper & Row, 1985; 277-385,403-435.

10 BJ Curtin. Pathologic myopia. Ophthalmic Forum, 1985; 3: 192-195.

11 G Meyer-Schwickerath, E Gerke. Biometric studies of the eyeball and retinal detachment. Br. J. Ophthalmol., 1984; 68: 29-3l.

12 HR Bochringer. Statistisches and Haufigkeit und Risiko der Netzhautablosurug. Ophthalmologica, 1956; 131: 331-334.

13 ES Perkins. Morbidity from myopia. Sightsav Rev, 1979; 49: 11-19.

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14 SW Hyams, M Bialik, E Neumann. Myopia-aphakia: 1. Prevalence of retinal detachment. Br. J. Ophthalmol., 1975; 59: 480-482.

15 LU Buratto, LE Buratto, M Ferrari. Capsulotomia Yag laser e distacco di retina nell'afachico miope. Atti Soc. Oftalm. Italiana, 1988; 43: 481-487.

16 LU Buratto, LE Buratto. Cataratta, miopia assile e compli­cazioni vitreoretiniche. Atti LXVIII Soc. Oftalm. Italiana, 1988; 43: 109-112.

17 PC Wetzing, DB Thatcher, JM Christiansen. The intracapsu­lar versus the extracapsular cataract technique in relation­ship to retinal problems. Trans Am. OphthaZmoZ. Soc., 1979; 77: 339-347.

18 JG Scheie, PH Morse, A 'Aminlari. Incidence of retinal detachment following cataract extraction. Arch. Ophthal­mol., 1973; 89: 293-295.

19P Cannon, WE Fung, RG Webster Jr et aZ. The incidence of retinal detachment following extracapsular cataract extrac­tion: a ten-year study. Ophthalmology, 1985; 92: 1096-110l.

20 DL Praeger. Five years's follow-up in the surgical manage­ment of cataracts in high myopia treated with the Kelman phacoemulsification technique. Ophthalmology, 1979; 86: 2024-2033.

21 R Lindstrom, TD Lundquist, J Huldin, JB Rubenstein. Reti­nal detachment in axial myopia following. extracapsular cataract surgery. Ill: Cataracts: Transactions of the New Orleans Academy of Ophthalmology. New York, Raven Press, 1988; 253-268.

22 SPB Percival. High myopia: new definitions and significance of IOL implantation. Implant and Refractive Surgery, 1986; 3: 137-140.

23 SPB Percival. Long term complications from extracapsular cataract surgery. Trans. Ophthalmol. Soc. U.K .. , 1985; 104: 915-918.

24 NS Jaffe, HM Clayman, MS Jaffe. Retinal detachment in myopic eyes after intracapsular and extracapsular cataract extraction. Am. J. Ophthalmol., 1984; 97: 48-52.

25 TA Armstrong, SB Lichtenstain. Intraocular lenses in myopes. Ophthalmic Surg., 1984; 15: 653-657.

26 S Chambless. Incidence of anterior and posterior segment complications in over 3000 cases of extracapsular cataract extraction. Intact and open capsules. Am. Intra-Ocular Implant Soc. J., 1985; 11: 146-149.

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27 SPB Percival, V Anand, SK Das. Prevalence of aphakic reti­nal detachment. Br. J. Ophthalmol., 1983; 67: 43-45.

28 H Toyofuku, T Hirose, CL Schepens. Retinal detachment following congenital cataract surgery. Arch. Ophthalmol., 1982; 98: 669-675.

29 F Verzella. Microsurgery of the lens in high myopia for optical purposes. Cataract, 1984; 1(2): 8-12.

30 F Pintucci. La chirurgia della lente nella miopia. In: La Mio­pia. Rome, Verducci Editore, 1985; 243-249.

31 M Merlin. 11 razionale della chirurgia del cristallino nella miopia elevata. Unpublished data, 1987.

32 MC Kraff, DR Sanders, LM Jampol, HL Lieberman. Effect of primary capsulotomy with extracapsular surgery on the inci­dence of pseudophakic cystoid macular edema. Am. J. Oph­thalmol., 1984; 98: 166-170.

33 M Lusky, D Windberger, B Sirat. The prevalence of retinal detachment in aphakic high myopic patients. Ophthalmic Surg., 1987; 18: 444-445.

34 JC Falk, TC Burton. Bilateral aphakic retinal detachment. Retina, 1983; 2: 1-6.

35 MT Ashrafzadeh, CL Schepens, II Elzeneiny et al. Aphakic and phakic retinal detachment: 1. Preoperative findings. Arch. Ophthalmol., 1973; 89: 476-483.

36 PC Ho, FI Tolentino. Pseudophakic retinal detachment: sur­gical success rate with various types of IOLs. Ophthalmo­logy, 1984; 91: 847-852.

37 D Vitali, L Buratto. Long-term results of posterior chamber intraocular lens implantation. In: AE Maumenee, WJ Stark, I Esente. Cataract and Refractive Microsurgery. Proceedings of the V International Congress, Florence, Italy, Giugno 1989; 193-196.

38 PL Southwick, RJ Olson. Shearing posterior chamber intra­ocular lenses: five-years postoperative results. Am. Intra­Ocular Implant Soc. J., 1984; 10: 318-323.

39 S Shearing. Long term results with J-Ioop posterior chamber lenses. In: L Buratto, Extracapsular Cataract Microsurgery and Posterior Chamber Intraocular Lenses. Milano, Camoed. 1989; 516-519.

40 RC Drews. Results in patients with high and low power in­traocular lenses. J. Cataract Refract. Surg., 1986; 12: 154-157.

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