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Anterior Chamber Depth after Trabeculectomy
Letters to the Editor Anterior Chamber Depth after Trabeculectomy
Dear Editor: In the article entitled "Temporary Keratoprosthesis for Combined Penetrating Keratoplasty, Pars Plana Vitrec tomy, and Repair of Retinal Detachment" by Gelender et al and the subsequent discussion by Jay Federman, MD (Ophthalmology 1988; 95:897-901), the authors and Dr. Federman state that the only alternative available to a surgeon confronting the need to perform posterior seg ment repair in the presence ofan opaque cornea are either: (I) the use ofa keratoprosthesis; (2) an open-sky approach; or (3) waiting for a penetrating keratoplasty to clear and allow a closed pars plana approach. I have previously reported 1 an entirely different method which does not require the use ofa keratoprosthesis. With this method, the host cornea is partially trephined and a lamellar keratectomy performed. Topical glycerine will then immediately clear the corneal stroma of any edema, and the vitrectomy can be performed in the usual manner. After the completion of the vitrectomy, the deeper stroma and corneal endothelium and Descemet's membrane are removed and a penetrating keratoplasty is performed. This technique is most suited for patients with corneal edema or anterior corneal opacities, and would not be helpful for patients with deep corneal opacities. The great majority of patients with corneal opacification and posterior seg ment disease do indeed have bullous keratopathy ( 11 of the 13 patients reported by Gelender et al had corneal edema) and thus they would be candidates for the tech nique. I would add that it is not necessary to do a perfectly smooth lamellar keratectomy because the lubricating ma terial beneath the corneal contact lens (I prefer Goniosol) will convert any residual surface irregularities to a smooth optical surface. I have had occasion to use this technique in several instances and have always obtained an optimal view for the vitrectomy procedure. J. MACKOOL, MD New York, New York
RICHARD
Reference 1. Mackool RJ. Closed vitrectomy in the presence of corneal opacity, a new technique. Ophthalmology Times 1983; 11 :20.
Author's reply Dear Editor: The authors appreciate Dr. Mackool's remarks regard ing our recently published article. The temporary kera toprosthesis provides exceptional visualization to permit delicate repair ofseverely disorganized eyes with combined anterior and posterior segment damage. Use of a kera
toprosthesis does not add significantly to either the com plexity or morbidity of the combined surgical approach. We were unaware of Dr. Mackool's innovative lamellar keratoplasty technique, as described in his letter. Previous experience with lamellar keratoplasty, however, would suggest that it has limited application for posterior segment repair. Deep stromal opacities frequently occur with ocu, Jar trauma, and are not amenable to the lamellar kera toplasty procedure. Moreover, the intricate maneuvers required by posterior segment vitreoretinal surgery ne cessitate unobstructed visualization such as provided by the keratoprosthesis. It is the opinion of the authors that the improved vi sualization afforded by the keratoprosthesis enhances previous surgical techniques which attempted to address management of anterior and posterior segment pathology. We believe that lamellar keratoplasty and open-sky tech niques have limited application in such a setting. When extensive ocular disorganization is present, we are con vinced that the keratoprosthesis technique is the surgical approach of choice. HENRY GELENDER, ALBERT VAISER, WILLIAM SNYDER, DWAIN FuLLER, WILLIAM HUTTON,
MD MD MD MD MD
Dallas, Texas
The Diabetic Retinopathy Vitrectomy Study
Dear Editor: I was interested to find that The Diabetic Retinopathy Vitrectomy Study Research Group, in the article entitled, "Early Vitrectomy for Severe Proliferative Diabetic Ret inopathy in Eyes with Useful Vision: Results of a Ran domized Trial-Diabetic Retinopathy Vitrectomy Study Report 3" (Ophthalmology 1988; 95:1307), comments favorably on the merits of early vitrectomy in the treat ment ofsevere proliferative retinopathy in eyes with useful vision. This conclusion was based on a "randomized" trial, in which the outcome in a multiclinic study of 181 eyes treated by early vitrectomy was compared with the outcome in a control group of 189 eyes given conventional treatment. I note also that a similar conclusion of mine 1 based on a series of 140 eyes, 41 of which had an initial visual acuity of 20/40 or better, and all of which were treated by early vitrectomy, was not cited in the report; I used as a virtually concurrent control a very similar series of253 eyes treated less aggressively. 2 This omission would appear to be an example of an increasingly common misconception of the role of ran domization and of controls in clinical studies. Feinstein 3 points out that randomization is, in effect, an operational device, intended to work against unintended bias in the choice ofcontrols: it does not necessarily succeed in elim 1121
Dear Editor: In the article entitled "Temporary Keratoprosthesis for Combined Penetrating Keratoplasty, Pars Plana Vitrec tomy, and Repair of Retinal Detachment" by Gelender et al and the subsequent discussion by Jay Federman, MD (Ophthalmology 1988; 95:897-901), the authors and Dr. Federman state that the only alternative available to a surgeon confronting the need to perform posterior seg ment repair in the presence ofan opaque cornea are either: (I) the use ofa keratoprosthesis; (2) an open-sky approach; or (3) waiting for a penetrating keratoplasty to clear and allow a closed pars plana approach. I have previously reported 1 an entirely different method which does not require the use ofa keratoprosthesis. With this method, the host cornea is partially trephined and a lamellar keratectomy performed. Topical glycerine will then immediately clear the corneal stroma of any edema, and the vitrectomy can be performed in the usual manner. After the completion of the vitrectomy, the deeper stroma and corneal endothelium and Descemet's membrane are removed and a penetrating keratoplasty is performed. This technique is most suited for patients with corneal edema or anterior corneal opacities, and would not be helpful for patients with deep corneal opacities. The great majority of patients with corneal opacification and posterior seg ment disease do indeed have bullous keratopathy ( 11 of the 13 patients reported by Gelender et al had corneal edema) and thus they would be candidates for the tech nique. I would add that it is not necessary to do a perfectly smooth lamellar keratectomy because the lubricating ma terial beneath the corneal contact lens (I prefer Goniosol) will convert any residual surface irregularities to a smooth optical surface. I have had occasion to use this technique in several instances and have always obtained an optimal view for the vitrectomy procedure. J. MACKOOL, MD New York, New York
RICHARD
Reference 1. Mackool RJ. Closed vitrectomy in the presence of corneal opacity, a new technique. Ophthalmology Times 1983; 11 :20.
Author's reply Dear Editor: The authors appreciate Dr. Mackool's remarks regard ing our recently published article. The temporary kera toprosthesis provides exceptional visualization to permit delicate repair ofseverely disorganized eyes with combined anterior and posterior segment damage. Use of a kera
toprosthesis does not add significantly to either the com plexity or morbidity of the combined surgical approach. We were unaware of Dr. Mackool's innovative lamellar keratoplasty technique, as described in his letter. Previous experience with lamellar keratoplasty, however, would suggest that it has limited application for posterior segment repair. Deep stromal opacities frequently occur with ocu, Jar trauma, and are not amenable to the lamellar kera toplasty procedure. Moreover, the intricate maneuvers required by posterior segment vitreoretinal surgery ne cessitate unobstructed visualization such as provided by the keratoprosthesis. It is the opinion of the authors that the improved vi sualization afforded by the keratoprosthesis enhances previous surgical techniques which attempted to address management of anterior and posterior segment pathology. We believe that lamellar keratoplasty and open-sky tech niques have limited application in such a setting. When extensive ocular disorganization is present, we are con vinced that the keratoprosthesis technique is the surgical approach of choice. HENRY GELENDER, ALBERT VAISER, WILLIAM SNYDER, DWAIN FuLLER, WILLIAM HUTTON,
MD MD MD MD MD
Dallas, Texas
The Diabetic Retinopathy Vitrectomy Study
Dear Editor: I was interested to find that The Diabetic Retinopathy Vitrectomy Study Research Group, in the article entitled, "Early Vitrectomy for Severe Proliferative Diabetic Ret inopathy in Eyes with Useful Vision: Results of a Ran domized Trial-Diabetic Retinopathy Vitrectomy Study Report 3" (Ophthalmology 1988; 95:1307), comments favorably on the merits of early vitrectomy in the treat ment ofsevere proliferative retinopathy in eyes with useful vision. This conclusion was based on a "randomized" trial, in which the outcome in a multiclinic study of 181 eyes treated by early vitrectomy was compared with the outcome in a control group of 189 eyes given conventional treatment. I note also that a similar conclusion of mine 1 based on a series of 140 eyes, 41 of which had an initial visual acuity of 20/40 or better, and all of which were treated by early vitrectomy, was not cited in the report; I used as a virtually concurrent control a very similar series of253 eyes treated less aggressively. 2 This omission would appear to be an example of an increasingly common misconception of the role of ran domization and of controls in clinical studies. Feinstein 3 points out that randomization is, in effect, an operational device, intended to work against unintended bias in the choice ofcontrols: it does not necessarily succeed in elim 1121