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Topographic detection of photorefractive keratectomy
Letters to the Editor Might not a clinicopathologic correlation provide a better understanding of the pathologic processes involved, including upstream conditions? This would involve making serial sections through the regions of pathology, of uninvolved crossings, and of normals, with modeling by computer and possibly in wood. These would be studied together with the angioarchitectural changes noted, and include coordinated consultation with someone expert in the mechanics of flow. This technique could also be applied to occlusion of the central retinal vein, where the potential energy of intraocular pressure must also be dissipated (a localized braking effect), and which probably results from similar mechanisms. Such studies, which might well be quite involved, could be expected to better reveal the normal and pathologic physiology, and to support Kumar et al’s speculation. It might provide some suggestion of value in preventing or treating the pathology of these untoward effects, which would be a very worthwhile result. CHARLES J. RIFE, MD Mechanicsburg, Pennsylvania Reference 1. Kumar B, Yu DY, Morgan WH, et al. The distribution of angioarchitectural changes within the vicinity of arteriovenous crossing in branch retinal vein occlusion. Ophthalmology 1998; 105:424 –7.
Author’s reply Dear Editor: We agree with Dr. Rife that increased turbulence and velocities, particularly shear stress gradients, are likely to be important hemodynamic factors involved in the causation of branch retinal vein occlusion. There are two major difficulties with histopathologic examination. The major one is the lack of suitable material to examine. We simply do not receive eyes from patients soon after branch retinal vein occlusion. The other problem is that fixed-tissue examination does not give dynamic flow information, or information concerning blood–retinal barrier breakdown. Fluorescein angiography does give some dynamic information, the leakage of which also indicates sites of an impaired blood–retinal barrier. This study’s design,1 retrospectively reviewing 110 patients with branch retinal vein occlusion, allowed the site of major hemodynamic impact to be determined. That it is downstream from the arteriovenous crossing is a new finding. Dr. Rife’s suggestion that simulated modeling be performed is excellent, however, very little is known about core retinal vein hemodynamic questions, such as the intralumenal and transmural pressures and shear stresses in normal retinal veins.2, 3 To date, the use of animal models is problematic because branch retinal vein occlusions have been induced by acute endothelial trauma, usually with laser. There are no models described that use chronic venous compression. W. H. MORGAN, MBBS, FRACO Nedlands, Australia
References 1. Kumar B, Yu DY, Morgan WH, et al. The distribution of angioarchitectural changes within the vicinity of arteriovenous crossing in branch retinal vein occlusion. Ophthalmology 1998; 105:424 –7. 2. Morgan WH, Yu DY, Cooper RL, et al. Retinal artery and vein pressures in the dog and their relationship to aortic, intraocular, and cerebrospinal fluid pressures. Microvasc Res 1997;53:211– 21. 3. Attariwala R, Jensen PS, Glucksberg MR. The effect of acute experimental retinal vein occlusion on cat retinal vein pressures. Invest Ophthalmol Vis Sci 1997;38:2742–9.
Topographic Detection of Photorefractive Keratectomy Dear Editor: In their article, ‘‘Topographic detection of photorefractive keratectomy’’ (Ophthalmology 1998;105:507–16), Schallhorn et al of the Naval Medical Center examine the use of corneal topography ‘‘. . . to detect patients who have undergone photorefractive keratectomy (PRK)’’ [italics mine]. The authors found relatively low sensitivity (65%) for the measures examined. This negative result, while unfortunate for the Navy Department sponsoring the study, may be fortunate for prospective recruits, current military personnel, and refractive surgeons alike. The authors state, ‘‘Current military standards prohibit service entrance or commissioning of anyone who has had refractive surgery, including PRK.’’ Absent is any discussion of the rationale for such restrictions. The case can be made for reasonable restrictions against specific types of refractive surgery among selected military personnel. For example, a patient who has had eight-incision, metal-blade radial keratotomy may be disqualified for duty where ocular trauma is anticipated, or from flying a jet fighter, where changes in atmospheric pressure may induce unpredictable refractive shifts. To my knowledge, however, there is no support in the literature for an outright ban against all refractive procedures in the military. Eyebank studies have found no evidence that PRK or LASIK, when properly performed and leaving an appropriate amount of residual stroma, weakens the eye to traumatic rupture. Rather than a blanket ‘‘one size fits all’’ ban on refractive surgery, the military should set reasonable guidelines for its personnel, based on their specific occupations. Glare, contrast sensitivity, and night vision testing might all be employed to make a scientific assessment of their visual dysfunction, if any. Of course, such a science-based policy would be more work than the current policy, but well worth it. As a cornea and refractive specialist, I have often been approached by military recruits who have either had PRK or desire it. Too often, these earnest young people are forced to lie about their refractive history in order to pursue a lifelong dream of serving this country in the armed forces. Instead of sponsoring studies to ferret out hidden PRK patients, our military should begin developing more reasonable, scientifically based guidelines. The military has an-
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Ophthalmology Volume 105, Number 9, September 1998 other ‘‘don’t ask, don’t tell’’ policy that is both confusing and hypocritical. Let’s try to do better on this one. EMIL W. CHYNN, MD New York, New York Author’s reply Dear Editor: In response to Dr. Chynn’s letter, it was not the intent of our study to justify the current ban on refractive surgery in the military. Likewise, we did not justify why other employers have restrictions, such as major airlines; or that eyebanks exclude donor corneas that have undergone refractive surgery. The study was designed simply to determine how well PRK could be detected using corneal topography. The ban on refractive surgery in the military was established in the early 1980s when RK was being popularized. There were those at the time who thought the military position was illogical and not scientifically based. We now know there can be problems with RK, such as significant refractive changes after exposure to high altitude.1 The cautious approach taken by the military in the 1980s makes sense. It took time to conduct studies to more fully evaluate RK. What about PRK or LASIK? Are there specific military concerns about these procedures that have not been addressed? Dr. Chynn mentions glare, contrast sensitivity, and night vision. How secure is a LASIK flap to mild trauma? Are there refractive changes after LASIK when exposed to high altitude? Potential performance ramifications from side effects of refractive surgery within the general population are considerably different than those affecting military personnel.2
The potential for refractive surgery to improve uncorrected vision and reduce the dependence on glasses and contact lenses has not been ignored by the military. Military institutions have been studying PRK since 1993 and took part in the Food and Drug Administration phase III clinical trials of two different excimer lasers. Glare, contrast sensitivity, and night vision evaluation have been at the forefront of these studies.3 Today there are over 12 active protocols that are analyzing various aspects of the procedure. Regulations should and will be scientifically based. Already military studies have helped to establish a set of uniform waiver criteria for service entry into the Navy. It is understandable that Dr. Chynn would like to treat potential military recruits. There are many young people who desire both the surgery and the opportunity to serve in the military. However, time is needed to develop reasonable entrance guidelines through ongoing and upcoming scientific studies. STEVE SCHALLHORN, MD San Diego, California References 1. Mader TH, Blanton CL, Gilbert BN, et al. Refractive changes during 72-hour exposure to high altitude after refractive surgery. Ophthalmology 1996; 103:1188 –95. 2. Ivan DJ, Tredici TJ, Perez-Becerra J, et al. Photorefractive keratectomy (PRK) in the military aviator: an aeromedical perspective. Aviat Space Environ Med 1996; 67:770 – 6. 3. Schallhorn SC, Blanton CL, Kaupp SE, et al. Preliminary results of photorefractive keratectomy in active-duty United States Navy personnel. Ophthalmology 1996; 103:5–22.
Robert C. Drews to Retire The Editor-in-Chief announces the well-deserved retirement from Ophthalmology’s Editorial Board of Robert C. Drews, MD, who has served with distinction since the 1980s. Our electronic records, which began in 1986, list 191 manuscripts reviewed by Dr. Drews through 1998. The Journal’s staff greatly appreciates his completion of reviews in a timely manner, his good humor, candor, and common sense appraisals of so many manuscripts. On behalf of the Academy, we thank him profusely.
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Author’s reply Dear Editor: We agree with Dr. Rife that increased turbulence and velocities, particularly shear stress gradients, are likely to be important hemodynamic factors involved in the causation of branch retinal vein occlusion. There are two major difficulties with histopathologic examination. The major one is the lack of suitable material to examine. We simply do not receive eyes from patients soon after branch retinal vein occlusion. The other problem is that fixed-tissue examination does not give dynamic flow information, or information concerning blood–retinal barrier breakdown. Fluorescein angiography does give some dynamic information, the leakage of which also indicates sites of an impaired blood–retinal barrier. This study’s design,1 retrospectively reviewing 110 patients with branch retinal vein occlusion, allowed the site of major hemodynamic impact to be determined. That it is downstream from the arteriovenous crossing is a new finding. Dr. Rife’s suggestion that simulated modeling be performed is excellent, however, very little is known about core retinal vein hemodynamic questions, such as the intralumenal and transmural pressures and shear stresses in normal retinal veins.2, 3 To date, the use of animal models is problematic because branch retinal vein occlusions have been induced by acute endothelial trauma, usually with laser. There are no models described that use chronic venous compression. W. H. MORGAN, MBBS, FRACO Nedlands, Australia
References 1. Kumar B, Yu DY, Morgan WH, et al. The distribution of angioarchitectural changes within the vicinity of arteriovenous crossing in branch retinal vein occlusion. Ophthalmology 1998; 105:424 –7. 2. Morgan WH, Yu DY, Cooper RL, et al. Retinal artery and vein pressures in the dog and their relationship to aortic, intraocular, and cerebrospinal fluid pressures. Microvasc Res 1997;53:211– 21. 3. Attariwala R, Jensen PS, Glucksberg MR. The effect of acute experimental retinal vein occlusion on cat retinal vein pressures. Invest Ophthalmol Vis Sci 1997;38:2742–9.
Topographic Detection of Photorefractive Keratectomy Dear Editor: In their article, ‘‘Topographic detection of photorefractive keratectomy’’ (Ophthalmology 1998;105:507–16), Schallhorn et al of the Naval Medical Center examine the use of corneal topography ‘‘. . . to detect patients who have undergone photorefractive keratectomy (PRK)’’ [italics mine]. The authors found relatively low sensitivity (65%) for the measures examined. This negative result, while unfortunate for the Navy Department sponsoring the study, may be fortunate for prospective recruits, current military personnel, and refractive surgeons alike. The authors state, ‘‘Current military standards prohibit service entrance or commissioning of anyone who has had refractive surgery, including PRK.’’ Absent is any discussion of the rationale for such restrictions. The case can be made for reasonable restrictions against specific types of refractive surgery among selected military personnel. For example, a patient who has had eight-incision, metal-blade radial keratotomy may be disqualified for duty where ocular trauma is anticipated, or from flying a jet fighter, where changes in atmospheric pressure may induce unpredictable refractive shifts. To my knowledge, however, there is no support in the literature for an outright ban against all refractive procedures in the military. Eyebank studies have found no evidence that PRK or LASIK, when properly performed and leaving an appropriate amount of residual stroma, weakens the eye to traumatic rupture. Rather than a blanket ‘‘one size fits all’’ ban on refractive surgery, the military should set reasonable guidelines for its personnel, based on their specific occupations. Glare, contrast sensitivity, and night vision testing might all be employed to make a scientific assessment of their visual dysfunction, if any. Of course, such a science-based policy would be more work than the current policy, but well worth it. As a cornea and refractive specialist, I have often been approached by military recruits who have either had PRK or desire it. Too often, these earnest young people are forced to lie about their refractive history in order to pursue a lifelong dream of serving this country in the armed forces. Instead of sponsoring studies to ferret out hidden PRK patients, our military should begin developing more reasonable, scientifically based guidelines. The military has an-
1583
Ophthalmology Volume 105, Number 9, September 1998 other ‘‘don’t ask, don’t tell’’ policy that is both confusing and hypocritical. Let’s try to do better on this one. EMIL W. CHYNN, MD New York, New York Author’s reply Dear Editor: In response to Dr. Chynn’s letter, it was not the intent of our study to justify the current ban on refractive surgery in the military. Likewise, we did not justify why other employers have restrictions, such as major airlines; or that eyebanks exclude donor corneas that have undergone refractive surgery. The study was designed simply to determine how well PRK could be detected using corneal topography. The ban on refractive surgery in the military was established in the early 1980s when RK was being popularized. There were those at the time who thought the military position was illogical and not scientifically based. We now know there can be problems with RK, such as significant refractive changes after exposure to high altitude.1 The cautious approach taken by the military in the 1980s makes sense. It took time to conduct studies to more fully evaluate RK. What about PRK or LASIK? Are there specific military concerns about these procedures that have not been addressed? Dr. Chynn mentions glare, contrast sensitivity, and night vision. How secure is a LASIK flap to mild trauma? Are there refractive changes after LASIK when exposed to high altitude? Potential performance ramifications from side effects of refractive surgery within the general population are considerably different than those affecting military personnel.2
The potential for refractive surgery to improve uncorrected vision and reduce the dependence on glasses and contact lenses has not been ignored by the military. Military institutions have been studying PRK since 1993 and took part in the Food and Drug Administration phase III clinical trials of two different excimer lasers. Glare, contrast sensitivity, and night vision evaluation have been at the forefront of these studies.3 Today there are over 12 active protocols that are analyzing various aspects of the procedure. Regulations should and will be scientifically based. Already military studies have helped to establish a set of uniform waiver criteria for service entry into the Navy. It is understandable that Dr. Chynn would like to treat potential military recruits. There are many young people who desire both the surgery and the opportunity to serve in the military. However, time is needed to develop reasonable entrance guidelines through ongoing and upcoming scientific studies. STEVE SCHALLHORN, MD San Diego, California References 1. Mader TH, Blanton CL, Gilbert BN, et al. Refractive changes during 72-hour exposure to high altitude after refractive surgery. Ophthalmology 1996; 103:1188 –95. 2. Ivan DJ, Tredici TJ, Perez-Becerra J, et al. Photorefractive keratectomy (PRK) in the military aviator: an aeromedical perspective. Aviat Space Environ Med 1996; 67:770 – 6. 3. Schallhorn SC, Blanton CL, Kaupp SE, et al. Preliminary results of photorefractive keratectomy in active-duty United States Navy personnel. Ophthalmology 1996; 103:5–22.
Robert C. Drews to Retire The Editor-in-Chief announces the well-deserved retirement from Ophthalmology’s Editorial Board of Robert C. Drews, MD, who has served with distinction since the 1980s. Our electronic records, which began in 1986, list 191 manuscripts reviewed by Dr. Drews through 1998. The Journal’s staff greatly appreciates his completion of reviews in a timely manner, his good humor, candor, and common sense appraisals of so many manuscripts. On behalf of the Academy, we thank him profusely.
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