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Conventional versus anterior stromal pocket hydration
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Conventional versus anterior stromal pocket hydration The article by Mifflin et al.1 comparing 2 techniques of stromal hydration during routine cataract surgery requires further discussion. According to the authors’ conclusions, anterior stromal hydration is better because it exerts direct pressure on the posterior lip of the incision. I would like to highlight and elaborate on this technique. A common clinical observation is that corneal stromal edema manifests as folds in Descemet membrane because the cornea can swell only posteriorly (corneal curvature and diameter remain normal).2 Therefore, balanced salt solution injected during the conventional technique might reach the posterior corneal layers, causing them to expand; this expansion could limit the effect on wound stabilization. In contrast, during anterior stromal hydration as described by Mifflin et al.,1 the balanced salt solution would tend to remain in the anterior corneal layers, which would resist further expansion. The pressure on the wound would be greater, creating a better watertight closure. We know from anatomy that the density of corneal fibrils is lower in the anterior cornea than in the posterior cornea.3 Hence, there is a possibility of greater and more complete hydration from a higher amount of extracellular matrix in the anterior cornea. The persistent anterior hydration effect in the stromal pocket hydration technique shown in the anterior segment optical coherence tomography at 24 hours could be explained by the fact that the clear corneal incision lies between the endothelium and the anterior pocket. As endothelial transport maintains the cornea in a dehydrated state, clearing of the balanced salt solution injected in the anterior layers would be delayed by the presence of an incision. Mifflin et al. noted a few possible risks of anterior stromal pocket hydration, including epithelial defects, scarring, and recurrent epithelial erosions. I have been using a similar supraincisional pocket in my routine phacoemulsification surgeries and have found that few patients experience pain in the early postoperative period. A probable reason for this is that the corneal nerves enter the middle stroma from the limbus and run forward as well as anteriorly, forming subepithelial and subbasal plexuses.3 Injection of balanced salt solution in the anterior stroma might lead to stimulation of nerves and pain similar to that reported in cases of bullous keratopathy. It would be interesting to know whether the authors noted similar complaints in their group of patients. Saurabh Kamal, MS, DNB New Delhi, India 2060
Q 2012 ASCRS and ESCRS Published by Elsevier Inc.
REFERENCES 1. Mifflin MD, Kinard K, Neuffer MC. Comparison of stromal hydration techniques for clear corneal cataract incisions: Conventional hydration versus anterior stromal pocket hydration. J Cataract Refract Surg 2012; 38:933–937 2. Klyce SD. Corneal physiology. In: Foster CS, Azar DT, Dohlman CH, eds, Smolin and Thoft’s The Cornea: Scientific Foundations and Clinical Practice 4th ed. Philadelphia, PA, Lippincott Williams & Wilkins, 2004; 37–58 3. Edelhauser HF, Ubels JL. Cornea and sclera. In: Kaufman PL, Alm A, eds, Adler’s Physiology of the Eye; Clinical Application 10th ed. St. Louis, MO, Mosby, 2003; 47–114
Reply : The mechanisms suggested for efficacy and persistence of anterior stromal hydration are reasonable, if not proven. With regard to risks or side effects, we are happy to comment on our experience using this technique over the past 7 years. Our opinion is that the anterior stromal hydration pocket should be used cautiously in patients with loose or potentially loose epithelium, such as occurs in anterior basement membrane dystrophy. Disruption of epithelial integrity has been observed, although rarely, in these patients, sometimes creating a relatively large defect or loose area. Our practice has been to place a bandage contact lens at the time of surgery in these rare instances, and this has been effective in preventing pain. In the absence of epithelial disruption, few of our patients complain of postoperative pain. To date, we have not seen recurrent erosions associated with the anterior stromal hydration technique, but acknowledge it as a potential complication.dMark Mifflin, MD, Krista Kinard, MD, Marcus Neuffer, MD
Small-aperture contact lenses for presbyopia In their recent article, García-Lazaro et al.1 provide metrics of visual function at different object vergences in patients wearing 4 contact lens–based artificial pupil designs in the nondominant eye. They state that a basic objective of their study was to provide a surrogate model for the Acufocus Kamra intracorneal inlay. Soft contact lenses are designed to center on the cornea, and the embedded pinhole aperture is centered on the contact lens. Because the eye is an inherently asymmetric optical system, the geometric center of the cornea is significantly displaced from both the visual axis and the center of the entrance pupil in most patients. Therefore, a well-fitted small-aperture soft contact lens would not be optimally centered relative to the average pupil location and its spatial position within the contact lens might have to be customized for optimal performance in individual patients. Unlike the Kamra small-aperture corneal inlay, which is stationary once implanted in a corneal pocket or 0886-3350/$ - see front matter http://dx.doi.org/10.1016/j.jcrs.2012.08.034
Conventional versus anterior stromal pocket hydration The article by Mifflin et al.1 comparing 2 techniques of stromal hydration during routine cataract surgery requires further discussion. According to the authors’ conclusions, anterior stromal hydration is better because it exerts direct pressure on the posterior lip of the incision. I would like to highlight and elaborate on this technique. A common clinical observation is that corneal stromal edema manifests as folds in Descemet membrane because the cornea can swell only posteriorly (corneal curvature and diameter remain normal).2 Therefore, balanced salt solution injected during the conventional technique might reach the posterior corneal layers, causing them to expand; this expansion could limit the effect on wound stabilization. In contrast, during anterior stromal hydration as described by Mifflin et al.,1 the balanced salt solution would tend to remain in the anterior corneal layers, which would resist further expansion. The pressure on the wound would be greater, creating a better watertight closure. We know from anatomy that the density of corneal fibrils is lower in the anterior cornea than in the posterior cornea.3 Hence, there is a possibility of greater and more complete hydration from a higher amount of extracellular matrix in the anterior cornea. The persistent anterior hydration effect in the stromal pocket hydration technique shown in the anterior segment optical coherence tomography at 24 hours could be explained by the fact that the clear corneal incision lies between the endothelium and the anterior pocket. As endothelial transport maintains the cornea in a dehydrated state, clearing of the balanced salt solution injected in the anterior layers would be delayed by the presence of an incision. Mifflin et al. noted a few possible risks of anterior stromal pocket hydration, including epithelial defects, scarring, and recurrent epithelial erosions. I have been using a similar supraincisional pocket in my routine phacoemulsification surgeries and have found that few patients experience pain in the early postoperative period. A probable reason for this is that the corneal nerves enter the middle stroma from the limbus and run forward as well as anteriorly, forming subepithelial and subbasal plexuses.3 Injection of balanced salt solution in the anterior stroma might lead to stimulation of nerves and pain similar to that reported in cases of bullous keratopathy. It would be interesting to know whether the authors noted similar complaints in their group of patients. Saurabh Kamal, MS, DNB New Delhi, India 2060
Q 2012 ASCRS and ESCRS Published by Elsevier Inc.
REFERENCES 1. Mifflin MD, Kinard K, Neuffer MC. Comparison of stromal hydration techniques for clear corneal cataract incisions: Conventional hydration versus anterior stromal pocket hydration. J Cataract Refract Surg 2012; 38:933–937 2. Klyce SD. Corneal physiology. In: Foster CS, Azar DT, Dohlman CH, eds, Smolin and Thoft’s The Cornea: Scientific Foundations and Clinical Practice 4th ed. Philadelphia, PA, Lippincott Williams & Wilkins, 2004; 37–58 3. Edelhauser HF, Ubels JL. Cornea and sclera. In: Kaufman PL, Alm A, eds, Adler’s Physiology of the Eye; Clinical Application 10th ed. St. Louis, MO, Mosby, 2003; 47–114
Reply : The mechanisms suggested for efficacy and persistence of anterior stromal hydration are reasonable, if not proven. With regard to risks or side effects, we are happy to comment on our experience using this technique over the past 7 years. Our opinion is that the anterior stromal hydration pocket should be used cautiously in patients with loose or potentially loose epithelium, such as occurs in anterior basement membrane dystrophy. Disruption of epithelial integrity has been observed, although rarely, in these patients, sometimes creating a relatively large defect or loose area. Our practice has been to place a bandage contact lens at the time of surgery in these rare instances, and this has been effective in preventing pain. In the absence of epithelial disruption, few of our patients complain of postoperative pain. To date, we have not seen recurrent erosions associated with the anterior stromal hydration technique, but acknowledge it as a potential complication.dMark Mifflin, MD, Krista Kinard, MD, Marcus Neuffer, MD
Small-aperture contact lenses for presbyopia In their recent article, García-Lazaro et al.1 provide metrics of visual function at different object vergences in patients wearing 4 contact lens–based artificial pupil designs in the nondominant eye. They state that a basic objective of their study was to provide a surrogate model for the Acufocus Kamra intracorneal inlay. Soft contact lenses are designed to center on the cornea, and the embedded pinhole aperture is centered on the contact lens. Because the eye is an inherently asymmetric optical system, the geometric center of the cornea is significantly displaced from both the visual axis and the center of the entrance pupil in most patients. Therefore, a well-fitted small-aperture soft contact lens would not be optimally centered relative to the average pupil location and its spatial position within the contact lens might have to be customized for optimal performance in individual patients. Unlike the Kamra small-aperture corneal inlay, which is stationary once implanted in a corneal pocket or 0886-3350/$ - see front matter http://dx.doi.org/10.1016/j.jcrs.2012.08.034