Yoshiaki Nawa

Accommodation obtained per 1.0 mm forward movement of a posterior chamber intraocular lens.

Purpose: To clarify the amount of accommodation per 1.0 mm forward movement of a posterior chamber intraocular lens (IOL). Setting: Department of Ophthalmology, Nara Medical University, Nara, Japan. Methods: A ray‐focusing equation of pseudophakic eyes was obtained with the ray‐tracing method using Mathematica® computer software (Wolfram). At first, it was assumed that the anterior radius of curvature of the cornea was 7.7 mm, the thickness was 0.5 mm, and the refractive index was 1.3375, and an AcrySof® IOL (Alcon) was implanted in the capsular bag. Anterior and posterior radii of curvature and IOL thickness data were provided from the manufacturer and inserted in the equation. Next, the amount of accommodation per 1.0 mm of forward movement of a posterior chamber IOL was calculated under the assumption that the axial length (AL) varied from 21.0 to 27.0 mm and the implanted IOL from 30.0 to 11.0 diopters (D). The AL was fixed at 24.0 mm, and the anterior radius of curvature was varied from 6.5 to 9.5 mm and the IOL from 10.0 to 30.0 D. Similar calculations were then performed. Results: Under the assumption of a fixed corneal anterior radius of curvature of 7.7 mm, when the AL was 24.0 mm and the implanted IOL 20.0 D, 1.0 mm of forward IOL movement corresponded to 1.3 D of accommodation. When the AL was 21.0 mm and a the IOL 30.0 D, 1.0 mm of forward IOL movement corresponded to 2.3 D of accommodation. When the AL was 27.0 mm and the IOL 11.0 D, 1.0 mm of forward IOL movement corresponded to 0.8 D of accommodation. Similarly, when the anterior radius of corneal curvature was varied from 6.5 to 9.5 mm and the IOL from 10.0 to 30.0 D and the AL was fixed at 24.0 mm, 1.0 mm of forward IOL movement corresponded to 0.5 to 1.9 D of accommodation. Conclusions: Accommodation obtained per 1.0 mm of forward IOL movement varied with AL from 0.8 D in a long eye to 2.3 D in a short eye. It also varied with the corneal power. Thus, one should not state that 1.0 mm of forward IOL movement always corresponds to a certain amount of diopters of accommodation.

Evaluation of apparent ectasia of the posterior surface of the cornea after keratorefractive surgery

Purpose: To calculate the apparent posterior corneal changes after keratorefractive surgery and reevaluate corneal ectasia displayed by Orbscan (Orbtek). Setting: Department of Ophthalmology, Nara Medical University, Nara, Japan. Methods: Postoperative:preoperative magnification ratio of the posterior surface of the cornea was calculated in a theoretical eye model. Results: Assuming the preoperative corneal thickness is 600.00 μm, the preoperative refractive power of the anterior corneal surface is 48.0 diopters (D), the refractive power of the cornea is 1.376, the ablation diameter is 6.0 mm, the postoperative corneal thickness is 480.00 μm, the postoperative refractive power of the anterior corneal surface is 38.0 D, and the posterior surface of the cornea does not change postoperatively, the apparent image of the posterior surface of the cornea becomes 0.778% smaller postoperatively. If the posterior radius of curvature of the cornea is 6.2 mm, it becomes smaller by 48.24 μm. If this change directly affects the difference map, the posterior surface of the cornea moves forward by 48.24 μm. Conclusion: The results correspond to the amount of ectasia in previous reports. This artifact may explain the apparent ectasia detected by Orbscan.

Effect of total higher-order aberrations on accommodation in pseudophakic eyes.

PURPOSE: To analyze the effect of total higher‐order aberrations (HOAs) on the range of accommodation in pseudophakic eyes and the size of near‐vision optotypes. SETTING: Department of Ophthalmology, Nara Medical University, Nara, Japan. METHODS: The study comprised 30 patients (44 eyes) who were diagnosed with cataract at Nara University of Medical Science Hospital and Municipal Oyodo Hospital. Inclusion criteria included no other eye disorder and a best corrected distance acuity of 20/20 or better 1 month after cataract surgery. All patients had small‐incision phacoemulsification followed by in‐the‐bag implantation of a monofocal intraocular lens (SA60AT, Alcon). All incisions were self‐sealing. Accommodation in pseudophakic eyes was measured by the lens‐loading method in an examination room under constant illumination. Ocular HOAs were measured using the KR‐9000PW Hartmann‐Shack wavefront analyzer (Topcon). RESULTS: The mean patient age was 75.8 years ± 5.4 (SD) (range 64 to 83 years). The Pearson correlation coefficient (r) showed a significant positive correlation between the range of accommodation and Z7 (vertical coma) for a 4.0 mm pupil using the 1.0 near‐vision optotype. There was a significant negative correlation between the range of accommodation and Z12 (spherical aberration) for a 4.0 mm pupil using the 1.0 near‐vision optotype (r = .311, P = .040 for Z7; r = −.365, P = .015 for Z12). No other parameter was significantly correlated with the range of accommodation. CONCLUSIONS: Measurement of accommodation in pseudophakic eyes by the lens‐loading method using the 1.0 near‐vision optotype showed that eyes with larger vertical coma aberrations achieved a larger range of accommodation. In contrast, eyes with larger spherical aberrations had smaller amounts of accommodation. The size of the near‐vision optotype may affect accommodation analysis in pseudophakic eyes.

Posterior corneal surface changes after hyperopic laser in situ keratomileusis

PURPOSE: To evaluate posterior corneal surface topographic changes after hyperopic laser in situ keratomileusis (H‐LASIK) using Orbscan I (Orbtek, Inc.). SETTING: Department of Ophthalmology, Nara Medical University, Nara, Japan. METHODS: In 25 eyes of 15 patients who had H‐LASIK, the posterior corneal surface was measured with slit‐scanning corneal topography (Orbscan I) preoperatively and 1 year postoperatively. The center as a fit zone and calculated posterior corneal surface changes were taken at 4 points: nasal, temporal, superior, and inferior sides in the 5.0 mm diameter. The posterior corneal topographic changes were analyzed using an analysis of variance. The postoperative:preoperative magnification ratio of the posterior corneal surface was calculated in a theoretical eye model. RESULTS: When a “+” reading was defined as the forward displacement and “−” was defined as the backward displacement, the mean posterior corneal topographic changes were −2.8 μm ± 27.9 (SD) at the nasal side, −4.5 ± 27.8 μm at the temporal side, −3.9 ± 20.1 μm at the superior side, and −2.3 ± 20.1 μm at the inferior side. The posterior corneal surface between any 2 examined points showed no significant difference after H‐LASIK. In addition, the hypothetical change in the posterior cornea was −8.3 μm after +3.0 diopter H‐LASIK, which was approximately closer to the study results. In each side, the amount of the attempted correction was significantly correlated with the posterior corneal topographic change. CONCLUSIONS: Clinical measurement of the posterior corneal displacement after H‐LASIK with Orbscan revealed a backward shift. This change corresponded to the hypothetical artifactual changes with Orbscan; that is, changes in the magnification ratio.

Evaluation of the corneal endothelium after hyperopic laser in situ keratomileusis

Purpose: To evaluate corneal endothelial changes after hyperopic laser in situ keratomileusis (LASIK) considering overestimation and underestimation of the cell count measurement. Setting: Department of Ophthalmology, Nara Medical University, Nara, Japan. Methods: The data were from the clinical trial of the Nidek EC‐5000 excimer laser for hyperopic LASIK. The mean correction was 3.59 diopters (D) ± 1.54 (SD) (range 2.0 to 6.0 D). Using noncontact specular microscopy, the corneal endothelial changes in 25 eyes of 15 patients who had hyperopic LASIK were measured. Follow‐up ranged from 6 months (n = 25) to 1 year (n = 21). The overestimation and underestimation of the corneal endothelial cell count that would occur after +5.0 D hyperopic LASIK was hypothetically calculated. Results: The measured endothelial cell count per 1.0 mm2 did not significantly decrease up to 1 year after hyperopic LASIK (preoperatively, 2508 ± 395; at 1 year, 2814 ± 349). The hypothetical calculation revealed that a +5.0 D hyperopic correction corresponded to a 0.1% underestimation of the corneal endothelial cell count. Conclusions: Underestimation of the corneal endothelial cell count after hyperopic LASIK was negligible. Hyperopic LASIK with the Nidek EC‐5000 excimer laser did not significantly decrease corneal endothelial cells up to 1 year after surgery.

Relationship between the retinal thickness of the macula and the difference in axial length

PurposeThe purpose of this study was to evaluate the relationship between the retinal thickness of the macula and the difference in axial length with A-scan ultrasonography (UD-6000) and partial coherence interferometry (IOLMaster).MethodsIn 38 eyes of 26 patients with macular edema (ME), we measured axial length using both instruments and the retinal thickness of the macula using optical coherence tomography (OCT). To compare the difference in axial length between both methods, the Wilcoxon signed-ranks test was used. In addition, the relationship between macula thickness and axial length difference was analyzed by Spearman’s correlation coefficient.ResultsThere was a significant difference between axial-length measurements (p<0.001). In addition, the retinal thickness of the macula and the difference in axial-length measurements were positively correlated (correlation coefficient = 0.55, p=0.003).ConclusionsThe difference in axial length obtained by both methods was considered to be the difference in optical and acoustic reflection site. This study may suggest that IOLMaster is sufficient for measuring axial length in eyes with macular edema and reducing postoperative refractive errors.

Evaluation of LASIK treatment with the Femto LDV in patients with corneal opacity.

PURPOSE To evaluate the relative effectiveness and safety of LASIK using the Femto LDV (Ziemer Ophthalmic Systems AG) and IntraLase FS 60 (Abbott Medical Optics Inc) femtosecond lasers in patients with corneal opacity. METHODS Patients with corneal opacity were retrospectively selected between March and July 2009. For this study, 205 eyes with 90-μm corneal flaps created using the Femto LDV (LDV group) and 200 eyes with corneal flaps created using the IntraLase FS 60 (Intra-Lase group) were selected. The flap thickness of the IntraLase group was determined by observation with slit-lamp microscopy. Uncorrected distance visual acuity (UDVA), corrected distance visual acuity (CDVA), and manifest refraction spherical equivalent (MRSE) were measured pre- and postoperatively and were statistically evaluated using the Student t test and Mann-Whitney U-test. RESULTS Regardless of the levels of opacity, eyes in the LDV group experienced uneventful procedures with no complications. Eyes in the IntraLase group had corneal flaps of 100- to 130-μm thickness and uneventful procedures; however, gas breakthrough was observed in 27 eyes. Of all eyes, 117 eyes from the LDV group and 109 eyes from the IntraLase group were available for 3-month follow-up. Mean 3-month postoperative UDVA, CDVA, and MRSE for the LDV group were 20/12.5, 20/12.5, and 0.17±0.32 diopters (D), respectively, and for the IntraLase group were 20/12.5, 20/12.5, and 0.11±0.34 D, respectively. No statistically significant differenes were noted in UDVA, CDVA, or MRSE between groups (P>.05 for all). CONCLUSIONS Laser in situ keratomileusis with the Femto LDV created thin flaps regardless of level of opacity and induced no complications as compared to the IntraLase FS 60, where gas breakthrough was significantly more common.

Effect of pupil size on dynamic visual acuity.

This study was conducted to assess the effect of pupil size on dynamic visual acuity (DVA). 60 young healthy men (M = 28.1 yr., SD = 3.9) with normal vision were divided into three age-matched groups by pupil size: dilated (n = 20), unchanged (n = 20), and constricted (n = 20). DVA was measured binocularly with free-head viewing before and at 30 min. after each drop was instilled. Each of the three groups got a different amount. The sizes of the constricted, unchanged, and dilated pupils were 2.8 mm (SD = 0.5), 4.1 mm (SD = 0.3), and 7.8 mm (SD = 0.5), respectively. The pupil size x DVA interaction was significant (F2,114 = 6.07). DVA in the constricted pupil decreased, but that in the dilated pupil increased (paired t test). DVA in the unchanged pupil did not change significantly (paired t test). Pupil size is possibly one of the factors which may affect DVA measurement.

Effect of static visual acuity on dynamic visual acuity : A pilot study

The aim of this pilot study was to evaluate whether dynamic visual acuity changes with or without refractive correction. 42 healthy enrolled subjects with normal vision were divided into two age-matched groups. In Group A, dynamic visual acuity was measured first with the refractive error fully corrected and then without. In Group B, dynamic visual acuity measurements were taken in the reverse order of that performed by Group A. The measurements were binocularly performed five times using free-head viewing after dynamic visual acuity values were stable. Significant changes in dynamic visual acuity (static visual acuity 20/20 vs 12/20) were observed in both Group A (171.6 ± 36.0 deg./sec. vs 151.8 ± 39.6 deg./sec., Wilcoxon test, p< .001) and Group B (169.8 ± 30.0 deg./sec. vs 151.2 ± 36.0 deg./sec., Wilcoxon test, p<.001). The interaction was significant (F1,20 = 8.12, p = .009). These results indicated that refractive correction affected dynamic visual acuity.

Change in Dynamic Visual Acuity (DVA) by Pupil Dilation

Objective: This study was conducted to assess dynamic visual acuity (DVA) under pupil dilation. Background: Pupil dilation may negatively affect driving performance. Methods: Thirty healthy young adults (mean age 29.4 years) with pupil dilation participated in this study as the Mydrin P group. In addition to them, 15 healthy young adults (mean age 28.5 years) without pupil dilation were enrolled as the control group. DVA was measured binocularly with free-head viewing at 0, 30, 60, 120, and 360 min after mydriatic drop instillation in both eyes. Pupil size was measured at each time. Results: In the Mydrin P group, DVA significantly improved at 30, 60, and 120 min (ANOVA; p < .01) but returned to the predilation level at 360 min (ANOVA; p = .61). Pupil size changed from 4.1 to 7.8 mm (ANOVA; p < .01) at 30 min after the instillation, and this level was maintained up to 120 min but returned to normal within 360 min. In the control group, DVA did not significantly change at all measured times (ANOVA; p > .9). DVA was significantly (p < .05) correlated with the pupil size at all measured times. Conclusion: The improvement in DVA was related to the enlargement of the pupil. This study suggests that the pupil size is one factor that may affect DVA. Application: Potential applications of this study include useful information to assess the effect of pupil dilation on driving performance.