- Email: [email protected]
Reply: Assessing intraocular lens accommodation
LETTERS
imaging plane of the UBM relative to the eye changed between these images. Misalignment of the UBM probe of as little as 3 pixels between compared images of the eye can be responsible for significant artifactitious changes owing to perspective distortion.6,7 Ben-nun and Alio´ did not control for spurious eye movements relative to their imaging devices. The resultant induced distortions in perspective confound their attempts to assess the presence of IOL accommodation. Without such controls, it is premature for the authors to conclude that their IOL is capable of in vivo accommodation. RONALD A. SCHACHAR, MD, PHD Dallas, Texas, USA REFERENCES 1. Ben-nun J, Alio´ JL. Feasibility and development of a high-power real accommodating intraocular lens. J Cataract Refract Surg 2005; 31:1802– 1808 2. Schachar RA. Effect of accommodation on the cornea [letter]. J Cataract Refract Surg 2004; 30:531–533 3. Schachar RA. The cornea is stable during accommodation. J Cataract Refract Surg 2006; 32:376 4. Buehren T, Collins MJ, Loughridge J, et al. Corneal topography and accommodation. Cornea 2003; 22:311–316 5. Mandell RB. Contact Lens Practice; Hard and Flexible Lenses, 2nd ed. Springfield IL, 1974; 57–80 6. Schachar RA, Kamangar F. Computer image analysis of ultrasound biomicroscopy of primate accommodation. Eye 2006; 20:226–228 7. Schachar RA, Kamangar F. Proper evaluation of accommodating IOLs. J Cataract Refract Surg 2006; 32:4–6
Reply: We thank Schachar for his interest in our work, although he misleadingly makes some observations that we would like to clarify further. 1. Schachar has noted from Figure 7 in our article that the camera angle toward the implanted device was not aligned accurately between measurements. He therefore concluded that such misalignment would result in distortion of perspective and
questionable value of these measurements. The attached Figure 1 shows graphically the maximal extent of optical distortion that the camera angle might induce. The pin distance from the plate edge is very short (50 mm), as can be assessed from the device picture (Figure 3 in our original article). Even complete transition of the camera from parallel to the plate to near vertical induces around 80 mm of perspective-related error. From the same image that Schachar mentioned in his letter, it is easy to see that the angle of photography that we used was within angle B as appeared in Figure 1 of this reply. The maximal perspective error induced by deviation within angle B range is less then 40 mm. If the total movement of the pin was at the 50 mm range, Schachar’s criticism would have been accepted without hesitation. However, the pin movements were in the range of 300 mm to 500 mm; therefore, the effect of such perspective error is minimal for force calculations and insignificant at the conceptual level. The key issue is, therefore, a well-known fact that the significance of a measuring technique and consequential errors must always be related to the results magnitude. 2. Schachar further argues that the changes in corneal shape as appeared in Figure 8 of the article indicate that our ultrasound biomicroscopy (UBM) measurements were not taken from the same accurate position and are therefore responsible for significant artifactitious results. This is just more of the same. Figure 2 of this reply shows an eye 1 week postoperative and the same eye 3 weeks later. The UBM shows the significant change in the corneal architecture but only a minor effect on the flexible lens under similar ciliary muscles stimulation. Our UBM measurements were taken in radial sections to enable computer-assisted 3-dimensional construction of the findings. Because of the monkey’s face morphology, it was possible to manipulate the probe only over the central 1.0 mm of the lens. No sharp angulations were possible even when attempted in an effort to demonstrate the lens haptics. Figure 3 of this reply shows the computer-assisted 3-dimensional construction of the lenses from Figure 8 of our article. The magnitude of change in lens curvature is very large; therefore, any cross section through the lens center (vertical or oblique) still strongly supports the concept of operation of the lens, which is the main message of this report. The only parameter from the known accommodation mechanism that we use for our design is the unarguably accepted fact of ciliary muscle contraction during the accommodative process.
Figure 1. Spatial relation between the plate and the pin shows that maximal perspective error is limited to less than 40 mm.
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J CATARACT REFRACT SURG - VOL 32, MAY 2006
LETTERS
Figure 2. A: Corneal edema 1 week postoperative. B: Same eye 4 weeks postoperative. Although significant changes are documented on the cornea, no effect could be noticed on the lens.
Regardless of the primate crystalline lens accommodative mechanism in the adult eye, the product is few diopters only. Measuring error within such small range of performances might prove critical. However, the magnitude of optical power generated by our design in the eyes of primates is 10 times higher and more. Our concept was only preceded by millions of years of evolution that enables waterfowls’ eyes to generate 50 to 70
Figure 4. A: A waterfowl eye during diving creating a secondary highpower lens. B: Image processing of A imitating UBM imaging of the same eye. C: A UBM image of Nulens intraocular lens in the monkey’s eye shows similarity of the mechanism that creates the secondary lens of the bird.
diopters of accommodation by localized deformation of the center of the natural crystalline lens to a secondary small but powerful lens through the pupil (Figure 4). We therefore see no contradiction in concluding that on the principle level, our design provides wide range of accommodation. Meanwhile, ongoing research and development of this new concept is proceeding to enable better understanding and construction of an efficient accommodating intraocular lens that is safe for human use.dJoshua Ben-nun, MD, Jorge L. Alio´, MD, PhD
Perioperative antibiotics in phacoemulsification
Figure 3. Three-dimensional construction of the lenses created in 3 principal conditions (cycloplegic, normal, and cyclospasm). The change in curvature is so large that it supports the principle mechanism of a strong secondary lens formation regardless of the scanning angle.
We disagree with the recommendation of Moshirfar et al.1 In our hospital, postoperative endophthalmitis after cataract surgery occurred in 11 of 16 293 patients (0.06%) over the past only 8 years. We use a single preoperative application of ofloxacin because most of our patients are outpatients. Directly before the operation, the conjunctival sac is irrigated with povidone–iodine 1%. The intraoperative irrigation fluid contains gentamycin 0.02 mg/mL. At the end of the surgical procedure, each patient is given a bandage with gentamycin. Thereafter, no further antibiotic agents are prescribed. There is evidence for the hypothesis that the patient’s own flora is the most common cause of postoperative endophthalmitis
J CATARACT REFRACT SURG - VOL 32, MAY 2006
705
imaging plane of the UBM relative to the eye changed between these images. Misalignment of the UBM probe of as little as 3 pixels between compared images of the eye can be responsible for significant artifactitious changes owing to perspective distortion.6,7 Ben-nun and Alio´ did not control for spurious eye movements relative to their imaging devices. The resultant induced distortions in perspective confound their attempts to assess the presence of IOL accommodation. Without such controls, it is premature for the authors to conclude that their IOL is capable of in vivo accommodation. RONALD A. SCHACHAR, MD, PHD Dallas, Texas, USA REFERENCES 1. Ben-nun J, Alio´ JL. Feasibility and development of a high-power real accommodating intraocular lens. J Cataract Refract Surg 2005; 31:1802– 1808 2. Schachar RA. Effect of accommodation on the cornea [letter]. J Cataract Refract Surg 2004; 30:531–533 3. Schachar RA. The cornea is stable during accommodation. J Cataract Refract Surg 2006; 32:376 4. Buehren T, Collins MJ, Loughridge J, et al. Corneal topography and accommodation. Cornea 2003; 22:311–316 5. Mandell RB. Contact Lens Practice; Hard and Flexible Lenses, 2nd ed. Springfield IL, 1974; 57–80 6. Schachar RA, Kamangar F. Computer image analysis of ultrasound biomicroscopy of primate accommodation. Eye 2006; 20:226–228 7. Schachar RA, Kamangar F. Proper evaluation of accommodating IOLs. J Cataract Refract Surg 2006; 32:4–6
Reply: We thank Schachar for his interest in our work, although he misleadingly makes some observations that we would like to clarify further. 1. Schachar has noted from Figure 7 in our article that the camera angle toward the implanted device was not aligned accurately between measurements. He therefore concluded that such misalignment would result in distortion of perspective and
questionable value of these measurements. The attached Figure 1 shows graphically the maximal extent of optical distortion that the camera angle might induce. The pin distance from the plate edge is very short (50 mm), as can be assessed from the device picture (Figure 3 in our original article). Even complete transition of the camera from parallel to the plate to near vertical induces around 80 mm of perspective-related error. From the same image that Schachar mentioned in his letter, it is easy to see that the angle of photography that we used was within angle B as appeared in Figure 1 of this reply. The maximal perspective error induced by deviation within angle B range is less then 40 mm. If the total movement of the pin was at the 50 mm range, Schachar’s criticism would have been accepted without hesitation. However, the pin movements were in the range of 300 mm to 500 mm; therefore, the effect of such perspective error is minimal for force calculations and insignificant at the conceptual level. The key issue is, therefore, a well-known fact that the significance of a measuring technique and consequential errors must always be related to the results magnitude. 2. Schachar further argues that the changes in corneal shape as appeared in Figure 8 of the article indicate that our ultrasound biomicroscopy (UBM) measurements were not taken from the same accurate position and are therefore responsible for significant artifactitious results. This is just more of the same. Figure 2 of this reply shows an eye 1 week postoperative and the same eye 3 weeks later. The UBM shows the significant change in the corneal architecture but only a minor effect on the flexible lens under similar ciliary muscles stimulation. Our UBM measurements were taken in radial sections to enable computer-assisted 3-dimensional construction of the findings. Because of the monkey’s face morphology, it was possible to manipulate the probe only over the central 1.0 mm of the lens. No sharp angulations were possible even when attempted in an effort to demonstrate the lens haptics. Figure 3 of this reply shows the computer-assisted 3-dimensional construction of the lenses from Figure 8 of our article. The magnitude of change in lens curvature is very large; therefore, any cross section through the lens center (vertical or oblique) still strongly supports the concept of operation of the lens, which is the main message of this report. The only parameter from the known accommodation mechanism that we use for our design is the unarguably accepted fact of ciliary muscle contraction during the accommodative process.
Figure 1. Spatial relation between the plate and the pin shows that maximal perspective error is limited to less than 40 mm.
704
J CATARACT REFRACT SURG - VOL 32, MAY 2006
LETTERS
Figure 2. A: Corneal edema 1 week postoperative. B: Same eye 4 weeks postoperative. Although significant changes are documented on the cornea, no effect could be noticed on the lens.
Regardless of the primate crystalline lens accommodative mechanism in the adult eye, the product is few diopters only. Measuring error within such small range of performances might prove critical. However, the magnitude of optical power generated by our design in the eyes of primates is 10 times higher and more. Our concept was only preceded by millions of years of evolution that enables waterfowls’ eyes to generate 50 to 70
Figure 4. A: A waterfowl eye during diving creating a secondary highpower lens. B: Image processing of A imitating UBM imaging of the same eye. C: A UBM image of Nulens intraocular lens in the monkey’s eye shows similarity of the mechanism that creates the secondary lens of the bird.
diopters of accommodation by localized deformation of the center of the natural crystalline lens to a secondary small but powerful lens through the pupil (Figure 4). We therefore see no contradiction in concluding that on the principle level, our design provides wide range of accommodation. Meanwhile, ongoing research and development of this new concept is proceeding to enable better understanding and construction of an efficient accommodating intraocular lens that is safe for human use.dJoshua Ben-nun, MD, Jorge L. Alio´, MD, PhD
Perioperative antibiotics in phacoemulsification
Figure 3. Three-dimensional construction of the lenses created in 3 principal conditions (cycloplegic, normal, and cyclospasm). The change in curvature is so large that it supports the principle mechanism of a strong secondary lens formation regardless of the scanning angle.
We disagree with the recommendation of Moshirfar et al.1 In our hospital, postoperative endophthalmitis after cataract surgery occurred in 11 of 16 293 patients (0.06%) over the past only 8 years. We use a single preoperative application of ofloxacin because most of our patients are outpatients. Directly before the operation, the conjunctival sac is irrigated with povidone–iodine 1%. The intraoperative irrigation fluid contains gentamycin 0.02 mg/mL. At the end of the surgical procedure, each patient is given a bandage with gentamycin. Thereafter, no further antibiotic agents are prescribed. There is evidence for the hypothesis that the patient’s own flora is the most common cause of postoperative endophthalmitis
J CATARACT REFRACT SURG - VOL 32, MAY 2006
705