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Surgery for Refractive Errors
435
Surgery for Refractive Errors uncertain start,’I intraocular lens implantation for cataract/aphakia seems to have achieved respectability.2 At all events, we can scarcely ignore a procedure performed over one million times in 1984, even if 650 000 were done in just one country, the USA. Greater awareness of the handicap imposed by refractive errors-notably, the extremes of myopia and hypermetropia (not forgetting astigmatism)-has led to a re-evaluation of older methods for the surgical correction of refractive errors and the introduction of AFTER
an
new ones.
For
high myopia the globe can be shortened by means of scleral or fascial strips placed around it from back to front. Almost 100 years ago Fukala3 advocated removal of the clear crystalline lens to neutralise high myopia, but this operation frequently led to retinal detachment. Verzella4 has revived the concept by removing the lens through a pars plana incision and inserting a posterior chamber artificial lens to correct further the myopia and to stabilise the posterior chamber itself. He operates on very young patients, even in their teens. Many decades of follow-up will therefore be needed before we can reach a mature judgment on this bold strategy. What of corneal surgery? The great attraction of this approach to refractive errors lies in its non-invasiveness (so far as the chambers of the eye are concerned): surgery confined to the cornea should be free from all the complications associated with opening the eye, such as cystoid macular oedema, the uveitis-glaucomahyphaema syndrome, and retinal detachment. The operations are designed to alter refraction either by changing the shape of the cornea or by altering its power. Radial keratotomy was devised by Sato and coworkerss just over 30 years ago. Many of their incisions were posterior, and 15-20 years later at least three-
quarters of the eyes showed bullous keratopathy from continued loss of endothelial cells, the end result being a painful eye with very poor sight. Fyodorov,6 in Moscow, by concentrating exclusively on anterior cuts has succeeded in making radial keratotomy much more respectable. Even so, the absolute limit is - 6D of myopia-of no real value to the really high myope Although the ophthalmic profession (>-10D). remains deeply suspicious of this interference with a normal healthy cornea, patients express themselves highly satisfied, even when there is substantial residual refractive error which may not be correctable by spectacles or contact lenses.’ Keratomileusis (for myopia) and keratophakia were devised by Jose Barraquer of Bogota in 1958. A layer of cornea is excised, lathed into a predetermined shape after quick freezing, and sutured back into place either as a surface application or as an intrastromal inlay. Great care and precision are needed, 0-011 mm being the unit of tolerance. Several costly new and adapted instruments are required. Even in the best hands9 the results are somewhat unpredictable and unreliable and rarely match the visual acuity achieved with a contact lens. However, there are notable successes. For example, a prominent British boxing prospect had unilateral high myopia. After keratomileusis the residual refractive error was well within the limits laid down by the British Boxing Board of Control-so he continues to flatten his opponents, although one eye is
still anatomically, if not optically, myopic. Hoffmann’° has devised a procedure by which the outer radius of the cornea can be altered without freezing of the central stroma (which leads to tissue changes within). A centrally thinned corneal disc is removed from the patient’s eye by means of a newly developed microkeratome. Subsequent suturing in of a donor corneal lamella leads to a protrusion of the corneal surface and thus to an alteration of the refractive power. All the above techniques are irreversible. Kaufman and co-workers" have devised to be which is claimed both epikeratophakia, simple and reversible. Processing and lathing techniques were developed that permitted shaping of the needed dioptric power and storage of the tissue lens prepared from donor material until the time of surgery. These modifications have made it possible for the epikeratophakia lenticules to be commercially manufactured and distributed to order. The lenses are attached to the de-epithelialised cornea; no invasion of the central optical zone is required. The safety of this Fyodorov SN, Durner VV Operation of dosaged dissection of corneal circular ligament in cases of myopia of mild degree. Ann Ophthalmol 1979, 11: 1885 7. Waring GO. Evolution of radial keratotomy for myopia Trans Ophthalmol Soc UK
6
1. Ridley H. Intraocular acrylic lenses. Trans Ophthalmol Soc UK 1951, 71: 617. 2 Stark WJ, Terry AC, Worthen D, Murray GC Update of intra-ocular lenses implanted
in the United States. Am JOphthalmol 1984, 98: 238-39. 3. Fukala Operative Behandlung des Hochstgradigen Myopie durch Aphakie. V Graefes Arch Ophthalmol 1890; 36: 230-44 4 Verzella FV. Microsurgery of the lens in high myopia for optical purposes. Cataract 1984; 1: 8-12 5. Sato AK, Shibata H A new surgical approach to myopia Am J Ophthalmol 1953; 36: 823-29
1984, 104: 28-42. 8.
Barraquer JI. New orientation for refractive surgery. Arch Soc Am Oftalmol Optometr
9.
Barraquer JI Long-term results of myopic keratomileusis. Arch Soc Am Oftalmol Optometr 1982; 83: 137-48 Hoffmann F Keratomileusis, keratophakia and keratokyphosis. Trans Ophthalmol Soc
1958, 1: 271
10 11
UK 1984; 104: 48-51 Kaufman HE, McDonald MB Refractive surgery for Ophthalmol Soc UK 1984, 104: 43-48
aphakia and myopia.
Trans
436
procedure makes it a potential solution in infants and children with congenital and traumatic cataracts. In the future, the combination of epikeratophakia and alloplastic lenses may provide very high plus powers (eg, as needed after removal of infantile congenital cataract) and exchangeable dioptric corrections, if a
plastic can be found that the cornea will tolerate in the long term. The final possibility is to change the power of the cornea by alloplastic means. Krawicz used polymethylmethacrylate (PMMA) inlays to alter the shape of the cornea; but, fearful of later changes to its metabolism, he removed them after a few months, hoping to have induced permanent changes in the corneal curvature. Very soon the corneas reverted to their customary shape. PMMA inlays were also used 20-30 years ago by Choyce12 and were found to be of value if equipped with tinted haptics in aniridia and albinism (with a central aperture) but not for the correction of refractive errors. What was required was a plastic with higher refractive index (for thinner optics) and increased permeability. At the moment the best prospect appears to be ’Udel’ (polysulfone), first synthesised by Union Carbide in 1965, heat resistant, ultraviolet and infrared absorbent, autoclavable, and with a refractive index of 1-633 (that of PMMA is 1’ 49, and the cornea 1’ 36). It is the material from which US astronauts’
face-masks are fashioned. using polysulfone corneal inlays on his Choyeelbegan in 1981. If there are no late destructive changes patients induced in the cornea, polysulfone corneal inlays could well improve the visual performance of high myopes and high hypermetropes not happy with spectacles or contact lenses. What of astigmatism? The incisions made in radial keratotomy can be modified to reduce regular astigmatism; and polysulfone corneal inlays (because of their mechanical properties) tend to neutralise it. All who work in refractive surgery are agreed that there is a great demand from patients, and that even if the end result does not achieve emmetropia, any reduction in their visual disability without recourse to restrictive visual aids is much appreciated. "Patient power" seems to be overcoming the natural reluctance of ophthalmic surgeons to exercise their skills on the
healthy cornea. Arthritis and Parvovirus Infection HUMAN parvovirus (HPV) belongs to a group of very small single-stranded DNA viruses of insects and vertebrates.’ These are about 21 nm, and have a buoyant density in caesium chloride of 1- 36 to 1- 42 DP The treatment of bullous keratopathy with acrylic inlays Experience with Choyce two-piece acrylic keratoprosthesis Proceedings of Second International Corneo-plastic Conference, London, 1967: 399-403. 13 Choyce DP Semi-rigid corneal inlays used in the management of albinism, aniridia, and ametropia Proceedings of International Congress of Ophthalmology, San
12
Choyce
gained
Francisco, 1982, 1230-34 MJ, Pattison JR The human parvovirus. Arch Virol 1984, 82: 137-48.
1. Anderson
Some are defective and require "helper viruses", such as the adeno-associated viruses, but others are apparently capable of autonomous replication. It seems that the DNA is packaged in equal numbers of complementary strands in separate virions. This phenomenon may be a general property of the autonomous parvoviruses. They also have an absolute requirement for cells in S-phase, possibly explaining the predilection for gut epithelium in canine parvovirus infection and perhaps the bone-marrow with the human parvovirus. HPV was originally identified by chance in 1975 during a screening programme for hepatitis B surface antigen by counterimmunoelectrophoresis, much as the HBs antigen itself was discovered.2 It was then observed in large numbers in serum from blood donors by electron microscopy. At this stage no clinical syndrome was associated with infection with the agent. In 1981 workers at King’s College Hospital Medical School were able to associate HPV infection with aplastic crises in patients with homozygous sickle-cell anaemia.3 These crises had long been thought to be infectious in origin. Apparently, replication of HPV in the bone-marrow causes a reduction in haemoglobin concentrations that is clinically important because of the pre-existing anaemia, and we now know that patients with other haemoglobinopathies are likewise
g/dl.
susceptible.1 The syndrome associated with HPV infection in the normal population remained for a while elusive, though the development of serological techniques such as antibody capture provided the tools for the search. 1,4 It was known, however, that antibody was acquired during childhood, that about 80% of adults had evidence of past infection, and that a transient disease with rash and malaise had been reported on follow-up of some viraemic blood donors and their children. This led to the idea that one of the as yet unexplained epidemic diseases of childhood might be involved. Among these "fifth" disease, or erythema infectiosum, seemed a prime candidate. An epidemic of this disease involving 162 children in North London soon afterwards provided the opportunity to test the hypothesis. Serological and epidemiological studies of this outbreak established HPV as the likely agent of erythema infectiosum, 1,6 and its aetiological role Ihas since been confirmed by inoculation of volunteers. First described in 1889 by Tschameras a "localised form of rubella", erythema infectiosum is principallya mild exanthem of childhood, well recognised and well described after an extensive epidemic in Port Angeles, 2. Cossart YE, Field AM, Cant B, Widdows D. Parvovirus-like particles in human sera. Lancet 1975, i. 72-73. 3. Pattison JR, Jones SE, Hodgson J, et al. Parvovirus infection and hypoplastic crises in sickle-cell anaemia Lancet 1981; i: 664-65. 4. Cohen BJ, Mortimer PP, Periera MS. Diagnostic assays with monoclonal antibodies for the human serum parvovirus-like virus (SPLV) J Hyg 1983; 92: 113-30 5. Anderson MJ, Jones SE, Fisher-Hoch SP, et al. Human parvovirus, the cause of erythema infectiosum (fifth disease)? Lancet 1983; i: 1358. 6 Anderson MJ, Lewis E, Kidd IM, Hall SM, Cohen BJ. An outbreak of erythema infectiosum associated with human parvovirus infection. J Hyg 1984; 93: 85-93. 7 Tschamer A. Uber ortliche Rotheln. Jahrb Kinderh 1889, 29: 379
Surgery for Refractive Errors uncertain start,’I intraocular lens implantation for cataract/aphakia seems to have achieved respectability.2 At all events, we can scarcely ignore a procedure performed over one million times in 1984, even if 650 000 were done in just one country, the USA. Greater awareness of the handicap imposed by refractive errors-notably, the extremes of myopia and hypermetropia (not forgetting astigmatism)-has led to a re-evaluation of older methods for the surgical correction of refractive errors and the introduction of AFTER
an
new ones.
For
high myopia the globe can be shortened by means of scleral or fascial strips placed around it from back to front. Almost 100 years ago Fukala3 advocated removal of the clear crystalline lens to neutralise high myopia, but this operation frequently led to retinal detachment. Verzella4 has revived the concept by removing the lens through a pars plana incision and inserting a posterior chamber artificial lens to correct further the myopia and to stabilise the posterior chamber itself. He operates on very young patients, even in their teens. Many decades of follow-up will therefore be needed before we can reach a mature judgment on this bold strategy. What of corneal surgery? The great attraction of this approach to refractive errors lies in its non-invasiveness (so far as the chambers of the eye are concerned): surgery confined to the cornea should be free from all the complications associated with opening the eye, such as cystoid macular oedema, the uveitis-glaucomahyphaema syndrome, and retinal detachment. The operations are designed to alter refraction either by changing the shape of the cornea or by altering its power. Radial keratotomy was devised by Sato and coworkerss just over 30 years ago. Many of their incisions were posterior, and 15-20 years later at least three-
quarters of the eyes showed bullous keratopathy from continued loss of endothelial cells, the end result being a painful eye with very poor sight. Fyodorov,6 in Moscow, by concentrating exclusively on anterior cuts has succeeded in making radial keratotomy much more respectable. Even so, the absolute limit is - 6D of myopia-of no real value to the really high myope Although the ophthalmic profession (>-10D). remains deeply suspicious of this interference with a normal healthy cornea, patients express themselves highly satisfied, even when there is substantial residual refractive error which may not be correctable by spectacles or contact lenses.’ Keratomileusis (for myopia) and keratophakia were devised by Jose Barraquer of Bogota in 1958. A layer of cornea is excised, lathed into a predetermined shape after quick freezing, and sutured back into place either as a surface application or as an intrastromal inlay. Great care and precision are needed, 0-011 mm being the unit of tolerance. Several costly new and adapted instruments are required. Even in the best hands9 the results are somewhat unpredictable and unreliable and rarely match the visual acuity achieved with a contact lens. However, there are notable successes. For example, a prominent British boxing prospect had unilateral high myopia. After keratomileusis the residual refractive error was well within the limits laid down by the British Boxing Board of Control-so he continues to flatten his opponents, although one eye is
still anatomically, if not optically, myopic. Hoffmann’° has devised a procedure by which the outer radius of the cornea can be altered without freezing of the central stroma (which leads to tissue changes within). A centrally thinned corneal disc is removed from the patient’s eye by means of a newly developed microkeratome. Subsequent suturing in of a donor corneal lamella leads to a protrusion of the corneal surface and thus to an alteration of the refractive power. All the above techniques are irreversible. Kaufman and co-workers" have devised to be which is claimed both epikeratophakia, simple and reversible. Processing and lathing techniques were developed that permitted shaping of the needed dioptric power and storage of the tissue lens prepared from donor material until the time of surgery. These modifications have made it possible for the epikeratophakia lenticules to be commercially manufactured and distributed to order. The lenses are attached to the de-epithelialised cornea; no invasion of the central optical zone is required. The safety of this Fyodorov SN, Durner VV Operation of dosaged dissection of corneal circular ligament in cases of myopia of mild degree. Ann Ophthalmol 1979, 11: 1885 7. Waring GO. Evolution of radial keratotomy for myopia Trans Ophthalmol Soc UK
6
1. Ridley H. Intraocular acrylic lenses. Trans Ophthalmol Soc UK 1951, 71: 617. 2 Stark WJ, Terry AC, Worthen D, Murray GC Update of intra-ocular lenses implanted
in the United States. Am JOphthalmol 1984, 98: 238-39. 3. Fukala Operative Behandlung des Hochstgradigen Myopie durch Aphakie. V Graefes Arch Ophthalmol 1890; 36: 230-44 4 Verzella FV. Microsurgery of the lens in high myopia for optical purposes. Cataract 1984; 1: 8-12 5. Sato AK, Shibata H A new surgical approach to myopia Am J Ophthalmol 1953; 36: 823-29
1984, 104: 28-42. 8.
Barraquer JI. New orientation for refractive surgery. Arch Soc Am Oftalmol Optometr
9.
Barraquer JI Long-term results of myopic keratomileusis. Arch Soc Am Oftalmol Optometr 1982; 83: 137-48 Hoffmann F Keratomileusis, keratophakia and keratokyphosis. Trans Ophthalmol Soc
1958, 1: 271
10 11
UK 1984; 104: 48-51 Kaufman HE, McDonald MB Refractive surgery for Ophthalmol Soc UK 1984, 104: 43-48
aphakia and myopia.
Trans
436
procedure makes it a potential solution in infants and children with congenital and traumatic cataracts. In the future, the combination of epikeratophakia and alloplastic lenses may provide very high plus powers (eg, as needed after removal of infantile congenital cataract) and exchangeable dioptric corrections, if a
plastic can be found that the cornea will tolerate in the long term. The final possibility is to change the power of the cornea by alloplastic means. Krawicz used polymethylmethacrylate (PMMA) inlays to alter the shape of the cornea; but, fearful of later changes to its metabolism, he removed them after a few months, hoping to have induced permanent changes in the corneal curvature. Very soon the corneas reverted to their customary shape. PMMA inlays were also used 20-30 years ago by Choyce12 and were found to be of value if equipped with tinted haptics in aniridia and albinism (with a central aperture) but not for the correction of refractive errors. What was required was a plastic with higher refractive index (for thinner optics) and increased permeability. At the moment the best prospect appears to be ’Udel’ (polysulfone), first synthesised by Union Carbide in 1965, heat resistant, ultraviolet and infrared absorbent, autoclavable, and with a refractive index of 1-633 (that of PMMA is 1’ 49, and the cornea 1’ 36). It is the material from which US astronauts’
face-masks are fashioned. using polysulfone corneal inlays on his Choyeelbegan in 1981. If there are no late destructive changes patients induced in the cornea, polysulfone corneal inlays could well improve the visual performance of high myopes and high hypermetropes not happy with spectacles or contact lenses. What of astigmatism? The incisions made in radial keratotomy can be modified to reduce regular astigmatism; and polysulfone corneal inlays (because of their mechanical properties) tend to neutralise it. All who work in refractive surgery are agreed that there is a great demand from patients, and that even if the end result does not achieve emmetropia, any reduction in their visual disability without recourse to restrictive visual aids is much appreciated. "Patient power" seems to be overcoming the natural reluctance of ophthalmic surgeons to exercise their skills on the
healthy cornea. Arthritis and Parvovirus Infection HUMAN parvovirus (HPV) belongs to a group of very small single-stranded DNA viruses of insects and vertebrates.’ These are about 21 nm, and have a buoyant density in caesium chloride of 1- 36 to 1- 42 DP The treatment of bullous keratopathy with acrylic inlays Experience with Choyce two-piece acrylic keratoprosthesis Proceedings of Second International Corneo-plastic Conference, London, 1967: 399-403. 13 Choyce DP Semi-rigid corneal inlays used in the management of albinism, aniridia, and ametropia Proceedings of International Congress of Ophthalmology, San
12
Choyce
gained
Francisco, 1982, 1230-34 MJ, Pattison JR The human parvovirus. Arch Virol 1984, 82: 137-48.
1. Anderson
Some are defective and require "helper viruses", such as the adeno-associated viruses, but others are apparently capable of autonomous replication. It seems that the DNA is packaged in equal numbers of complementary strands in separate virions. This phenomenon may be a general property of the autonomous parvoviruses. They also have an absolute requirement for cells in S-phase, possibly explaining the predilection for gut epithelium in canine parvovirus infection and perhaps the bone-marrow with the human parvovirus. HPV was originally identified by chance in 1975 during a screening programme for hepatitis B surface antigen by counterimmunoelectrophoresis, much as the HBs antigen itself was discovered.2 It was then observed in large numbers in serum from blood donors by electron microscopy. At this stage no clinical syndrome was associated with infection with the agent. In 1981 workers at King’s College Hospital Medical School were able to associate HPV infection with aplastic crises in patients with homozygous sickle-cell anaemia.3 These crises had long been thought to be infectious in origin. Apparently, replication of HPV in the bone-marrow causes a reduction in haemoglobin concentrations that is clinically important because of the pre-existing anaemia, and we now know that patients with other haemoglobinopathies are likewise
g/dl.
susceptible.1 The syndrome associated with HPV infection in the normal population remained for a while elusive, though the development of serological techniques such as antibody capture provided the tools for the search. 1,4 It was known, however, that antibody was acquired during childhood, that about 80% of adults had evidence of past infection, and that a transient disease with rash and malaise had been reported on follow-up of some viraemic blood donors and their children. This led to the idea that one of the as yet unexplained epidemic diseases of childhood might be involved. Among these "fifth" disease, or erythema infectiosum, seemed a prime candidate. An epidemic of this disease involving 162 children in North London soon afterwards provided the opportunity to test the hypothesis. Serological and epidemiological studies of this outbreak established HPV as the likely agent of erythema infectiosum, 1,6 and its aetiological role Ihas since been confirmed by inoculation of volunteers. First described in 1889 by Tschameras a "localised form of rubella", erythema infectiosum is principallya mild exanthem of childhood, well recognised and well described after an extensive epidemic in Port Angeles, 2. Cossart YE, Field AM, Cant B, Widdows D. Parvovirus-like particles in human sera. Lancet 1975, i. 72-73. 3. Pattison JR, Jones SE, Hodgson J, et al. Parvovirus infection and hypoplastic crises in sickle-cell anaemia Lancet 1981; i: 664-65. 4. Cohen BJ, Mortimer PP, Periera MS. Diagnostic assays with monoclonal antibodies for the human serum parvovirus-like virus (SPLV) J Hyg 1983; 92: 113-30 5. Anderson MJ, Jones SE, Fisher-Hoch SP, et al. Human parvovirus, the cause of erythema infectiosum (fifth disease)? Lancet 1983; i: 1358. 6 Anderson MJ, Lewis E, Kidd IM, Hall SM, Cohen BJ. An outbreak of erythema infectiosum associated with human parvovirus infection. J Hyg 1984; 93: 85-93. 7 Tschamer A. Uber ortliche Rotheln. Jahrb Kinderh 1889, 29: 379