Masaaki Nakahara

Residual bed thickness and corneal forward shift after laser in situ keratomileusis.

Purpose: To prospectively assess the forward shift of the cornea after laser in situ keratomileusis (LASIK) in relation to the residual corneal bed thickness. Setting: Miyata Eye Hospital, Miyazaki, Japan. Methods: Laser in situ keratomileusis was performed in 164 eyes of 85 patients with a mean myopic refractive error of −5.6 diopters (D) ± 2.8 (SD) (range −1.25 to −14.5 D). Corneal topography of the posterior corneal surface was obtained using a scanning‐slit topography system before and 1 month after surgery. Similar measurements were performed in 20 eyes of 10 normal subjects at an interval of 1 month. The amount of anteroposterior movement of the posterior corneal surface was determined. Multiple regression analysis was used to assess the factors that affected the forward shift of the corneal back surface. Results: The mean residual corneal bed thickness after laser ablation was 388.0 ± 35.9 &mgr;m (range 308 to 489 &mgr;m). After surgery, the posterior corneal surface showed a mean forward shift of 46.4 ± 27.9 &mgr;m, which was significantly larger than the absolute difference of 2 measurements obtained in normal subjects, 2.6 ± 5.7 &mgr;m (P<.0001, Student t test). Variables relevant to the forward shift of the corneal posterior surface were, in order of magnitude of influence, the amount of laser ablation (partial regression coefficient B = 0.736, P<.0001) and the preoperative corneal thickness (B = −0.198, P<.0001). The residual corneal bed thickness was not relevant to the forward shift of the cornea. Conclusions: Even if a residual corneal bed of 300 &mgr;m or thicker is preserved, anterior bulging of the cornea after LASIK can occur. Eyes with thin corneas and high myopia requiring greater laser ablation are more predisposed to an anterior shift of the cornea.

Corneal epithelial barrier function in diabetic patients

Purpose To evaluate the corneal epithelial barrier function in diabetic patients. Methods In 29 eyes of 29 diabetic patients and 55 eyes of 55 nondiabetic controls, corneal epithelial permeability to fluorescein was measured using an anterior fluorophotometer. The average fluorescein concentration in the central cornea was compared between diabetic patients and controls. Multiple regression analysis was used to assess the factors that affect corneal epithelial barrier function in diabetic patients. Results The average fluorescein concentrations in diabetic patients and nondiabetic controls were 44.1 ± 25.3 ng/mL and 29.9 ± 19.8 ng/mL (mean ± SD), respectively (P = 0.0057, unpaired t test). An explanatory variable relevant to the impaired corneal epithelial barrier function was the serum hemoglobin A1c (HbA1c) concentration (standardized partial regression coefficient = 0.466, P = 0.0163). Conclusions The corneal epithelial barrier function is impaired in diabetic patients. Diabetic patients with higher serum HbA1c levels are more predisposed to impaired barrier function in the corneal epithelium.

Efficacy and safety of the soft-shell technique in cases with a hard lens nucleus

Purpose: To evaluate the efficacy and safety of the soft‐shell technique in reducing corneal endothelial cell damage during cataract surgery in patients with a hard lens nucleus. Setting: Miyata Eye Hospital, Miyakonojo, Miyazaki, Japan. Methods: Sixty eyes of 57 cataract patients with a hard lens nucleus (Emery‐Little classification grade 3 or higher) had phacoemulsification using the soft‐shell technique with Healon® (sodium hyaluronate 1%) and Viscoat® (sodium hyaluronate 3.0%–chondroitin sulfate 4.0%) (soft‐shell group) or with Healon alone (control group). The visual acuity, intraocular pressure (IOP), flare intensity in the anterior chamber, central corneal thickness, and corneal endothelial cell density were evaluated postoperatively. Results: There were no significant IOP elevations in either group. The mean central corneal thickness in the control group was 539 &mgr;m ± 26.0 (SD) preoperatively and 578 ± 52.0 &mgr;m 1 day after surgery; the increase was significant (P = .0154). There was no significant change in the central corneal thickness in the soft‐shell group. There were no statistically significant differences between the 2 groups in uncorrected visual acuity, best corrected visual acuity, IOP, flare intensity in the anterior chamber, and central corneal thickness throughout the follow‐up. The rate of endothelial cell loss 3 months after surgery was 6.4% ± 9.6% in the soft‐shell group and 16.3% ± 9.8% in the control group (P = .0003). Conclusion: The results suggest that the soft‐shell technique is safe and effective in protecting corneal endothelial cells during cataract surgery in patients with a hard lens nucleus.

Corneal endothelial cell protection during phacoemulsification: Low- versus high-molecular-weight sodium hyaluronate

Purpose: To compare the efficacy of low‐ and high‐molecular‐weight sodium hyaluronate in protecting corneal endothelial cells during phacoemulsification. Setting: Miyata Eye Hospital, Miyakonojo, Miyazaki, Japan. Methods: One hundred forty‐nine eyes of 136 cataract patients were randomly assigned to have cataract surgery using sodium hyaluronate 1% with a low molecular weight (0.6 to 1.2 million d, Opegan®) or sodium hyaluronate 1% with a high molecular weight (4 million d, Healon®) during phacoemulsification. Each group was divided into 2 subgroups depending on the amount of ultrasound (% min) used during phacoemulsification, which was defined as the mean phacoemulsification energy (%) multiplied by phacoemulsification time (minutes). Corneal endothelial cell density was examined preoperatively and 3 months after surgery. The rate of cell loss was compared between the subgroups in the Opegan group and the Healon group. Results: In the subgroups with ultrasound of 50% min or less, the mean rate of endothelial cell loss 3 months after surgery was 3.2% ± 4.1% (SD) in the Opegan group and 5.9% ± 5.3% in the Healon group (P = .0214). In the subgroups with ultrasound over 50% min, the mean rate of endothelial cell loss 3 months after surgery was 7.5% ± 10.6% in the Opegan group and 14.8 ± 9.0% in the Healon group (P = .0029). Conclusions: The results suggest that Opegan is more effective than Healon in protecting corneal endothelial cells during phacoemulsification regardless of the amount of ultrasound energy used.

Pattern-Reversal Visual Evoked Potentials in Patients with Human T-lymphotropic Virus Type 1 Uveitis

Purpose: The purpose of this study was to evaluate the possible injury in the optic pathway by measuring P100 peak latency of pattern-reversal visual evoked potentials (PVEPs) in patients with human T-lymphotropic virus type 1 uveitis (HU). Methods: The P100 peak latency of PVEP was measured during the period without macular abnormalities observed by fluorescein angiography in 23 patients (46 eyes) with HU and 24 patients (48 eyes) with Vogt-Koyanagi-Harada disease (VKH) with a corrected visual acuity of 20/25 or more. To determine the normal upper limit of P100 peak latency, PVEPs were measured in 31 normal subjects (31 eyes). In addition, in the HU patients, the serum anti-HTLV-1 antibody titer was measured by particle agglutination assay within 3 months of PVEP recording, and the period of HU was retrospectively surveyed. Results: Delayed latency was observed in 4 (7 eyes) of the 23 patients (46 eyes) with HU but none of the 24 patients (48 eyes) with VKH. All four patients with delayed latency showed a serum anti-HTLV-1 antibody titer of more than ×4000. The HU period in the HU patients was 0.2–14.0 years, and the HU periods in the four patients with delayed latency were 0.8, 2.7, 4.2, and 14.0 years, respectively. Conclusions: We measured pattern-reversal visual evoked potentials and observed delayed P100 peak latency in 7 of the 46 eyes in 4 (17.4%) of the 23 HU patients. This suggests injury in the optic pathway including the optic nerve by HTLV-1 in some patients with HU. In the future, consideration should also be given to the possible development of optic neuropathy due to HTLV-1.

Influence of cataract surgery on pupil size in patients with diabetes mellitus

Editor, A spiration of residual cortical matter, especially if located in the subincisional area, can pose a challenge to the cataract surgeon. Various methods have been described to aid the aspiration of residual cortical matter, including use of bimanual IA systems, J-shaped cannulas (Dewey 2002) and transparent irrigation cannulas (Shimada et al. 2002). We describe a hybrid bimanual technique of aspiration of residual cortical matter that uses a combination of the coaxial and bimanual IA hand pieces and averts the requirement of an additional side port. An informed consent was obtained from all the patients undergoing cataract surgery. The study followed the tenets of the Declaration of Helsinki. Two incisions are made at the start of cataract surgery. A 2.75-mm main port is made using a 2.75-mm blade (Alcon Labs, Fort Worth, TX, USA) for the coaxial phacoemulsification probe (Infiniti System, Alcon Labs, USA) and a side port made two clock hours away from the main port with a 20G MVR blade (Alcon Labs). Following the completion of nuclear and epinuclear phacoemulsification, aspiration of cortical matter is begun using the traditional coaxial hand piece. The hybrid bimanual technique may be used if the surgeon is unable to completely aspirate the cortical matter. The coaxial IA probe connected only to the irrigation tubing is introduced into the anterior chamber through the 2.75-mm main incision. The aspiration hand piece of the bimanual system (Appasamy, India) is inserted in the anterior chamber through the 20G side port. The bimanual aspirating hand piece is used to aspirate the remaining cortical matter (Fig. 1). The tip of the coaxial hand piece is kept just below the interior lip of the valve. This allows for better visualization of the aspiration port of the aspirating hand piece. We used this technique in 27 eyes of 27 patients with residual cortex. Cortex could be successfully aspirated in 26 of 27 eyes with the use of the modified technique. One eye that had extensive cortex under the area where the side port was made required conversion to the standard technique of bimanual irrigation and aspiration (IA). No posterior capsular rupture occurred in any of the cases. Residual cortex, especially located in the subincisional area, can pose challenges to the surgeon. Bimanual irrigation and aspiration can greatly ease the removal of residual cortical matter. However, if the surgeon uses a single side port for phacoemulsification, an additional side port needs to be created during the surgery to enable bimanual IA. Our technique obviates the requirement for an additional side port. When the traditional bimanual IA system is used through the two side ports, the larger, main port tends to leak during IA, as it is not occluded by the hand piece. This may lead to surge and instability of the anterior chamber. As the main port is effectively occluded by the coaxial hand piece during IA using our technique, the anterior chamber is more stable during irrigation and aspiration. The only drawback that we experienced with our technique is the occasional inadequate visualization of subincisional cortical matter in the area below the side port as compared to the use of a traditional bimanual IA technique. In such cases, one can make a second side port and shift to the standard bimanual IA technique. In conclusion, the hybrid bimanual technique is a useful modification that can be safely used for aspirating the residual cortical matter during cataract surgery. It combines the benefits of the traditional bimanual IA system with that of the coaxial IA system and at the same time circumvents the need for creation of the second side port.