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Ultraviolet light and stem cells
Ophthalmology Volume 111, Number 1, January 2004 Ultraviolet Light and Stem Cells Dear Editor: We read with interest the study on so-called idiopathic limbal stem cell deficiency by Espana et al.1 However, it remains unclear to what lengths (if any) ultraviolet light was excluded as a cause of depletion in limbal stem cell populations in study patients. Ultraviolet light exposure is a well-recognized cause of limbal stem cell deficiency, and ultraviolet exposure may be rising in frequency.2,3 A history of exposure may be challenging to obtain, but is certainly possible. Neither this study nor its inclusion criteria (set out in another study) mention whether any such attempt was made, unless the authors include it under “radiation,” though they also use this term for radiation therapy.1,4 In sunny Miami, from where the study hails, ultraviolet light exposure is more frequent than in most places. In the study, impression cytology showed conjunctivalization: goblet cells in the superior cornea with vascularization. Though apparently shielded by the upper lid from sunlight, goblet cells are in any case concentrated in the superior limbus, and neither depletion nor vascularization here is an unexpected effect of ultraviolet light. Is it thus correct to say that these patients all suffered from an “idiopathic” deficiency of limbal stem cells? Without evidence that ultraviolet light exposure was excluded, many may feel that the limbal stem cell depletion was of uncertain etiology and not truly idiopathic, or even whether “idiopathic” limbal stem cell deficiency exists as a separate entity independent of ultraviolet light exposure. H. ZAIDI, FRCS, MRCOPHTH ROBERT WEIR, MRCOPHTH RICHARD CHEONG-LEEN, MRC MELANIE C. CORBETT, FRCS London, United Kingdom EAMON SHARKAWI, MRCOPHTH Oxford, United Kingdom EMERSON R. KING, PHD New York, New York References 1. Espana EM, Grueterich M, Romano AC, et al. Idiopathic limbal stem cell deficiency. Ophthalmology 2002;109:2004 –10. 2. Zaidi FH, Bloom PA, Corbett MC. Limbal stem cell deficiency: a clinical chameleon. Eye 2003;17:837–9. 3. Marshall J. Ultraviolet radiation and the eye. In: Passchier WF, Bosnjakovic BFM, eds. Human Exposure to Ultraviolet Radiation: Risks and Regulations: Proceedings of a Seminar Held in Amsterdam, 23–25 March 1987. Amsterdam: Elsevier; 1987; 125– 42. 4. Puangsricharern V, Tseng SC. Cytologic evidence of corneal diseases with limbal stem cell deficiency. Ophthalmology 1995; 102:1476 – 85.
Author reply Dear Editor: We are indebted to Dr Zaidi for raising an interesting question, whether ultraviolet radiation could be a possible cause of idiopathic limbal stem cell (SC) deficiency. Ultra-
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violet radiation has been implicated as a cause of pterygium, a disease known to manifest focal limbal SC deficiency.1,2 This may be explained by an in vivo demonstration of albedo focus of incident light on the nasal limbal sclera.3 This is also supported by a theoretical calculation showing that ultraviolet radiation might be concentrated at the nasal limbal area.4 For the following reasons, we do not believe our reported cases of idiopathic limbal SC deficiency are caused by ultraviolet radiation. First, unlike pterygium, we noted that conjunctivalization of the cornea occurred predominantly from the superior limbal area, followed by the inferior limbal area,5 which are highly protected and unlikely to be exposed to ultraviolet radiation. Only 2 of 7 patients had nasal corneal conjunctivalization. Second, the majority of our patients were not from areas with high ultraviolet exposure such as Miami or the Caribbean. Therefore, we believe that the etiology of our reported patients with limbal SC deficiency remains poorly known—that is, idiopathic. EDGAR M. ESPANA, MD SCHEFFER C. G. TSENG, MD, PHD Miami, Florida References 1. Tseng SC. Concept and application of limbal stem cells. Eye 1989;3:141–57. 2. Tseng SC, Lee SB, Li DQ. Limbal stem cell deficiency in the pathogenesis of pterygium. In: Taylor HR, ed. Pterygium. The Hague: Kugler Publications; 2000;41–55. 3. Coroneo MT. Albedo concentration in the anterior eye: a phenomenon that locates some solar diseases. Ophthalmic Surg 1990;21:60 – 6. 4. Kwok LS, Coroneo MT. A model for pterygium formation. Cornea 1994;13:219 –24. 5. Espana EM, Grueterich M, Romano AC, et al. Idiopathic limbal stem cell deficiency. Ophthalmology 2002;109:2004 –10.
Removal of a Capsular Tension Ring Dear Editor: Ma et al1 reported on techniques for removal of a capsular tension ring (CTR) from the vitreous in 2 eyes. In both cases, prior cataract surgery had been performed, which was complicated by capsular rupture and loss of lens material. In addition, a CTR had been inserted in some phase of surgery and also dislocated posteriorly. Vitreoretinal revision surgery was indicated for both dropped lens material and the dislocated CTR. In one eye, the ring was removed by cutting it into 2 pieces and extracting the segments via a 6.5-mm corneal wound. In the other eye, the CTR was retracted into a CTR injector, which was introduced through a slightly enlarged sclerotomy site. The authors suggested the latter technique to be safer and less traumatic. Removal of posteriorly dislocated CTRs was previously reported by Lang et al2 and Bopp and Lucke.3 Lang et al2 had extracted an entire ECR3 ring (Hanita Lenses, Kibbutz Hanita, Israel) successfully through one sclerotomy. We cut the ring into 2 pieces because of its rigidity and large diameter (12-mm polymethyl methacrylate CTR, Morcher, Stuttgart, Germany). However, we were concerned that even the half rings may cause damage to the retina and
Author reply Dear Editor: We are indebted to Dr Zaidi for raising an interesting question, whether ultraviolet radiation could be a possible cause of idiopathic limbal stem cell (SC) deficiency. Ultra-
196
violet radiation has been implicated as a cause of pterygium, a disease known to manifest focal limbal SC deficiency.1,2 This may be explained by an in vivo demonstration of albedo focus of incident light on the nasal limbal sclera.3 This is also supported by a theoretical calculation showing that ultraviolet radiation might be concentrated at the nasal limbal area.4 For the following reasons, we do not believe our reported cases of idiopathic limbal SC deficiency are caused by ultraviolet radiation. First, unlike pterygium, we noted that conjunctivalization of the cornea occurred predominantly from the superior limbal area, followed by the inferior limbal area,5 which are highly protected and unlikely to be exposed to ultraviolet radiation. Only 2 of 7 patients had nasal corneal conjunctivalization. Second, the majority of our patients were not from areas with high ultraviolet exposure such as Miami or the Caribbean. Therefore, we believe that the etiology of our reported patients with limbal SC deficiency remains poorly known—that is, idiopathic. EDGAR M. ESPANA, MD SCHEFFER C. G. TSENG, MD, PHD Miami, Florida References 1. Tseng SC. Concept and application of limbal stem cells. Eye 1989;3:141–57. 2. Tseng SC, Lee SB, Li DQ. Limbal stem cell deficiency in the pathogenesis of pterygium. In: Taylor HR, ed. Pterygium. The Hague: Kugler Publications; 2000;41–55. 3. Coroneo MT. Albedo concentration in the anterior eye: a phenomenon that locates some solar diseases. Ophthalmic Surg 1990;21:60 – 6. 4. Kwok LS, Coroneo MT. A model for pterygium formation. Cornea 1994;13:219 –24. 5. Espana EM, Grueterich M, Romano AC, et al. Idiopathic limbal stem cell deficiency. Ophthalmology 2002;109:2004 –10.
Removal of a Capsular Tension Ring Dear Editor: Ma et al1 reported on techniques for removal of a capsular tension ring (CTR) from the vitreous in 2 eyes. In both cases, prior cataract surgery had been performed, which was complicated by capsular rupture and loss of lens material. In addition, a CTR had been inserted in some phase of surgery and also dislocated posteriorly. Vitreoretinal revision surgery was indicated for both dropped lens material and the dislocated CTR. In one eye, the ring was removed by cutting it into 2 pieces and extracting the segments via a 6.5-mm corneal wound. In the other eye, the CTR was retracted into a CTR injector, which was introduced through a slightly enlarged sclerotomy site. The authors suggested the latter technique to be safer and less traumatic. Removal of posteriorly dislocated CTRs was previously reported by Lang et al2 and Bopp and Lucke.3 Lang et al2 had extracted an entire ECR3 ring (Hanita Lenses, Kibbutz Hanita, Israel) successfully through one sclerotomy. We cut the ring into 2 pieces because of its rigidity and large diameter (12-mm polymethyl methacrylate CTR, Morcher, Stuttgart, Germany). However, we were concerned that even the half rings may cause damage to the retina and