Effect of incomplete blinking on tear film stability.

PURPOSE: The purpose of this study is to assess changes in tear film stability caused by incomplete blinking. METHODS: Eleven subjects (mean age, 21.3 years) participated in this study. All subjects had a visual acuity of 20/20 or better and normal ocular health. The subjects were asked to play a game for 60 min on a personal computer as part of a visual display terminal (VDT) experiment. Each subject's blinking was observed by a Web camera that was attached to the top of the display. Every 15 min, the VDT experiment was interrupted for measurement. An RT-7000 (Tomey Co., Ltd., Nagoya, Japan) was used to measure ring breakup time as a parameter of tear film stability. An OPD-Scan II ARK-10000 (NIDEK Co., Ltd., Aichi, Japan) was used to measure corneal aberrations. RESULTS: Although the total blink rate changed very little, the complete and incomplete blink rates fluctuated during the VDT experiment. Both types were plotted along symmetrical cubic approximation curves. Noninvasive (ring) breakup time at 30 min (4.33 ± 2.57 s) was significantly shorter (p < 0.01) than that at baseline before the VDT experiment (8.62 ± 1.54 s). After 30 min, the incomplete blink rate began decreasing (fewer incomplete blinks), whereas the complete blink rate began increasing. Ring breakup time increased (improved) after 45 min; however, the incomplete blink rate began to increase again after approximately 50 min. CONCLUSIONS: Even if the total blink rate decreases, the tear film remains stable so long as almost all blinks are complete. The incomplete blinking contributes to tear film instability and is variable with prolonged VDT exposure. Our study indicated that the tear film stability was determined by blinking quality, and the predominance of blinking type relates to tear film stability.

Fluid dynamics simulation of aqueous humour in a posterior-chamber phakic intraocular lens with a central perforation.

BACKGROUND: A modified implantable collamer lens (ICL) with a central hole (diameter, 0.36 mm), a "Hole-ICL", was created to improve aqueous humour circulation. The aim of this study was to investigate the fluid dynamic characteristics of aqueous humour in a Hole-ICL using computational fluid dynamics. METHODS: Fluid dynamics simulation using an ICL was performed with thermal-hydraulic analysis software FloEFD V5 (Mentor Graphics Corp.). For the simulation, three-dimensional eye models based on a modified Liou-Brennan model eye with conventional ICL (Model ICM, STAAR SURGICAL) and a Hole-ICL were used. Both ICLs were -9.0 diopters (D) and 12.0 mm in length, with an optic of 5.5 mm. The vaulting was 0.50 mm. The quantity of aqueous humour produced by the ciliary body was set at 2.80 µl/min. Flow distribution between the anterior surface of the crystalline lens and the posterior surface of the ICL was also calculated, and trajectory analysis was performed. RESULTS: The flow velocity 0.25 mm in front of the centre of the crystalline lens was 1.52 × 10(-1) mm/sec for the Hole-ICL and 1.21 × 10(-5) mm/sec for the conventional ICL. Outward flow from the hole in the Hole-ICL was confirmed by trajectory analysis. CONCLUSION: These results suggest that Hole-ICLs improve the circulation of aqueous humour to the anterior surface of the crystalline lens.

Effect of astigmatism on apparent accommodation in pseudophakic eyes.

PURPOSE: To investigate the factors affecting apparent accommodation in pseudophakic eyes from a clinical viewpoint and the effects of corneal and refractive astigmatism on this accommodation from an optical viewpoint. METHODS: We retrospectively examined 62 eyes of 33 patients who had undergone phacoemulsification with monofocal intraocular lens implantation. We quantitatively assessed the amplitude of apparent accommodation using an accommodometer 3 months after surgery. Multiple regression analysis was used to assess the factors affecting apparent accommodation. We also estimated the accommodation in eyes with corneal astigmatism by optical simulation. RESULTS: The mean amplitude of apparent accommodation was 1.58 = 0.65 D. Explanatory variables relevant to this accommodation were in order of influence, pupil diameter (partial regression coefficient B = 0.293, p = 0.008), and corneal multifocality (B = 0.101, p = 0.03). Other explanatory variables such as age, gender, axial length, corneal astigmatism, and refractive astigmatism showed no significant relationship with this accommodation. The estimated apparent accommodations for a 3.0 mm pupil by optical simulation were 1.25, 1.25, 1.25, 0.75, and 0 D, in eyes with corneal astigmatism of 0, 0.5, 1.0, 1.5, and 2.0 D, respectively. Similar results were obtained for a 4.0 mm pupil. CONCLUSIONS: Eyes with smaller pupil diameter and eyes with greater corneal multifocality are more predisposed to have greater apparent accommodation. However, from clinical and optical viewpoints, corneal or refractive astigmatism does not significantly contribute to apparent accommodation after cataract surgery, suggesting that it may be of less significance that the astigmatism is consciously retained in consideration of this accommodation in astigmatic eyes.

[Comparison of central visual field visualization while using a combination of spherical intraocular lenses with vitreous contact lenses].

OBJECTIVE: To investigate intraocular lens (IOL) and vitreous contact lens (VCL) combinations that provide good central visual field visualization in vitreous surgery. METHOD: ZEMAX optical design software was used to perform optical simulations using the ray tracing method on a Gullstrand eye model. The implanted IOL was assumed to consist of material with a refractive index of 1.550 (high refractive index acrylic IOL), 1.470 (low refractive index acrylic IOL) and 1.413 (silicon IOL), and was set as a biconvex spherical lens (optical diameter 6 mm, 23.5 D). The VCL was assumed to have a refractive index of 1.900 (HEMA VCL), 1.490 (PMMA VCL) and 1.413 (silicon VCL), and was set as a concave lens (optical diameter 10 mm) with a flat anterior surface and a posterior surface with a radius of curvature of 7.70 mm. The spherical aberration of the overall optical system, including the IOL-implanted eyeball and the VCL, was calculated. RESULTS: Spherical aberration was lowest with the silicon VCL for the high refractive index acrylic IOL and with the PMMA VCL for the low refractive index acrylic and silicon IOLs. CONCLUSION: The combinations providing the best central visual field visualization in vitreous surgery are a silicon VCL for implantation of a high refractive index acrylic IOL and a PMMA VCL for implantation of a low refractive index acrylic or silicon IOL.

Evaluation of ocular biometry in the Japanese population using a multicenter approach: Prospective observational study.

This prospective observational study aimed to evaluate the ocular biometry of Japanese people through a multicenter approach. The uncorrected and corrected distance visual acuity (UDVA and CDVA, respectively) in the log minimum angle of resolution (logMAR), subjective and objective spherical equivalent values (SE) of ocular refraction, anterior and posterior corneal curvature (ACC and PCC, respectively), anterior and posterior corneal asphericity (ACA and PCA, respectively), central corneal thickness (CCT), anterior chamber depth (ACD), and ocular axial length (AL) were measured in the eyes of 250 participants (mean age = 46.5 ± 18.0 years, range: 20-90 years) across five institutions in Japan. The mean UDVA, CDVA, subjective SE, objective SE, ACC, PCC, ACA, PCA, CCT, ACD, and AL were 0.68, -0.08, -2.42 D, -2.66 D, 7.77 mm, 6.33 mm, -0.31, -0.39, 0.55 mm, 2.92 mm, and 24.78 mm, respectively. Age-related changes and sex-based differences were noted in the visual acuity, refraction, corneal shape, ACD, and AL. Our results serve as basis for future studies aiming to develop refractive correction methods and various vision-related fields.

Modulation transfer function of intraocular collamer lens with a central artificial hole.

BACKGROUND: A modified implantable collamer lens (ICL) with a central hole (diameter 0.36 mm), "Hole-ICL", was created to improve aqueous humour circulation. The aim of this study is to investigate the effects of ICL power and the relationship between pupil size and modulation-transfer functions (MTFs) in a Hole-ICL in vitro. METHODS: The ICL and intraocular lens (IOL) studied were the Collamer ICL (Model ICM, STAAR Surginal) and the monofocal IOL AF-1 (VA-60BBR, HOYA). The ICLs' powers were -20.0 diopters (D), -10.0 D, -5.0 D, +3.0 D, and +10.0 D. A modified ICL with a central hole (diameter 0.36 mm), "Hole-ICL", was created. The monofocal IOL, which was used as an artificial crystalline lens, was +30.0 D in power, and it was 13.0 mm in length with an optic diameter of 6.0 mm. The line-spread function (LSF) was recorded with the OPAL Vector System (Image Science Ltd.), and a model eye (Menicon Co.) was used that consisted of a wet cell. A conventional ICL or Hole-ICL was placed in the posterior chamber of the model eye. The MTF was calculated from the LSF using fast Fourier transform techniques. Furthermore, we investigated the relationship between pupil size and the MTF of the ICL for -5.0 D. The sizes of the effective aperture were 2.0, 3.0, 4.0, and 5.0 mm. RESULTS: The in-focus contrasts of the conventional ICL at 100 cyc/mm for a 3.0-mm effective aperture were 37%, 40%, 39%, 38%, and 39% for -20.0 D, -10.0 D, -5.0 D, +3.0 D, and +10.0 D respectively. The in-focus contrasts of the Hole-ICL at 100 cyc/mm for a 3.0-mm effective aperture were 37%, 40%, 39%, 38%, and 38% for -20.0 D, -10.0 D, -5.0 D, +3.0 D, and +10.0 D respectively. The results for a 2.0-mm effective diameter showed that the in-focus MTF in the Hole-ICL was lower than in the conventional ICL, although the difference was small. CONCLUSION: These results suggest that differences in MTF between the Hole-ICL and the conventional ICL for various ICL powers and effective pupil diameters were small and clinically negligible.

Effect of pupil size on visual acuity in a laboratory model of pseudophakic monovision.

PURPOSE: To investigate the effect of pupil size on visual acuity in pseudophakic monovision. METHODS: For the simulation, a modified Liou-Brennan model eye was used. The model eye was designed to include a centered optical system, corneal asphericity, an iris pupil, a Stiles-Crawford effect, an intraocular lens, and chromatic aberration. Calculation of the modulation transfer function (MTF) was performed with ZEMAX software. Visual acuity was estimated from the MTF and the retinal threshold curve. The sizes of the entrance pupil were 2.0, 2.5, 3.0, and 4.0 mm. RESULTS: Decreasing pupil diameter and increasing myopia progressively improved near visual acuity. For an entrance pupil size of 2.5 mm and a refractive error of -1.50 diopters, the logMAR value (Snellen; metric) in the non-dominant eye at 40 cm was 0.06 (20/23; 6/6.9). CONCLUSIONS: Knowledge of the patient's pupil diameter at near fixation can assist surgeons in determining the optimum degree of myopia for successful monovision.

Repeatability and reproducibility of corneal curvature measurements using the Pentacam and Keratron topography systems.

PURPOSE: To compare the repeatability and reproducibility of corneal curvature measurements using the Pentacam eye scanner (Oculus Optikgeräte GmbH) and Keratron corneal topographer (Optikon 2000 SpA). METHODS: Axial topography maps were used to acquire measurements. Twenty-six eyes of 26 healthy patients were measured to determine repeatability and reproducibility. Another 10 eyes of 10 healthy patients were included in a parallel study. Three measurements per eye were performed. Repeatability was assessed via the coefficient of variation. Reproducibility was assessed using Bland-Altman plots. Linear correlations were used to determine the agreement between devices. A P value < .05 was considered statistically significant. RESULTS: The majority of coefficient of variations for both devices were within 1%. The coefficient of variation of the Pentacam was higher in the superior cornea (P < .01). The mean difference (95% limits of agreement) in the flattest meridian between examiners was -0.03 +/- 0.27 diopters (D) (range: -0.56 to +0.49 D) for the Pentacam and -0.08 +/- 0.21 D (range: -0.50 to +0.33 D) for the Keratron. The mean difference (95% limits of agreement) in the steepest meridian was -0.10 +/- 0.26 D (range: -0.60 to +0.41 D) for the Pentacam and -0.11 +/-0.22 D (range: -0.53 to +0.31 D) for the Keratron. The mean axial power for the central 3.0 mm of the Pentacam was statistically significantly lower than that of the Keratron (P < .01). CONCLUSIONS: Although statistically significant differences were noted, both devices provided repeatable and reproducible corneal measurements centrally. Pentacam repeatability outcomes indicate that superior corneal measurements should be interpreted with caution.

Optical performance in rezoom and array multifocal intraocular lenses in vitro.

PURPOSE: To investigate the modulation transfer function (MTF) of two refractive multifocal intraocular lenses (IOLs). METHODS: The ReZoom and Array (AMO) multifocal IOLs were evaluated using the OPAL Vector system (Image Science Ltd) and a model eye with a variable aperture (2.1 to 5.5 mm). Modulation transfer functions were evaluated at distant, near, and intermediate (-1.50 diopter defocus) focus lengths. RESULTS: The ReZoom IOL distant focus MTF for a 5.1-mm effective diameter was higher than that of the Array IOL. At intermediate distance, the ReZoom lens showed a slight increase compared with the Array. The near focus MTF for the ReZoom IOL began to increase at an effective diameter of 2.1 mm and remained constant for diameters > 3.45 mm. CONCLUSIONS: The ReZoom IOL gave better image quality than the Array, particularly at distant focus. To enhance near vision with the ReZoom lens, the desirable real pupil diameter should be at least 3.45 mm.

Repeatability, reproducibility, and agreement characteristics of rotating Scheimpflug photography and scanning-slit corneal topography for corneal power measurement.

PURPOSE: To evaluate the repeatability, reproducibility, and agreement in anterior, posterior, and in particular the total corneal power of 2 topography devices, rotating Scheimpflug photography and scanning-slit topography. SETTING: Department of Ophthalmology and Visual Science, Kitasato University Graduate School of Medical Sciences, Sagamihara, Japan. METHODS: Seventeen eyes of 17 subjects (mean age 24.7 years +/- 4.1 [SD]) were included in the study. The corneal shapes within the central 3.0 mm were measured with rotating Scheimpflug photography (Pentacam) and scanning-slit corneal topography (Orbscan II). The within-rater repeatability and reproducibility of 2 raters and the overall between-instrument agreement of the measurements were evaluated using intraclass correlation coefficients (ICCs) and the Bland-Altman method. RESULTS: The repeatability of Scheimpflug photography and scanning-slit corneal topography was high (ICC, 0.70 to 0.99). Scheimpflug photography outperformed scanning-slit corneal topography for anterior power, posterior power, and total corneal power. The reproducibility results were similar, with limits of agreement (LoA) consistently narrower for Scheimpflug photography. The between-instrument agreement was moderate, with LoA around the mean value of total corneal power of 0.46 diopter ranging from 0.032 to 0.889. CONCLUSIONS: The results suggest that repeatability and reproducibility are higher in Scheimpflug photography than in scanning-slit topography. The agreement between rotating Scheimpflug photography and scanning-slit topography for total corneal power was moderate.

[Effects of myopic correction by replacement of spectacles, laser in situ keratomileusis, and phakic intraocular lens implantation on modulation transfer function and retinal magnification].

PURPOSE: To compare the modulation transfer function and the retinal magnification after myopic correction by replacement of spectacles, laser in situ keratomileusis (LASIK), or phakic intraocular lens (phakic IOL) implantation. MATERIALS AND METHODS: Using the ray tracing method, we measured the modulation transfer function and the retinal magnification after these myopic corrections in a Gullstrand eye model. RESULTS: The modulation transfer function (3-mm pupil, 100 cycles/mm) after phakic IOL implantation for the correction of low, moderate, and high myopia was 45%, 44%, and 44%, respectively. These same measurements after LASIK were 50%, 47%, and 46%, respectively, and the same measurements after spectacle correction were 41%, 32%, and 21%, respectively. The retinal magnification was least changed by the amount of myopic correction after phakic IOL implantation, more changed by LASIK, and most changed by spectacle correction. Specifically, the improvement in the retinal magnification after phakic IOL implantation, LASIK, and spectacle correction for the correction of high myopia was 1.00, 0.97, and 0.88 times, respectively. CONCLUSIONS: There were no significant differences in the modulation transfer function after phakic IOL implantation and LASIK. On the other hand, the modulation transfer function was significantly decreased after spectacle correction, especially when the amount of myopic correction was large. The retinal magnification was least affected by phakic IOL implantation, more affected by LASIK, and most affected by spectacle correction. Phakic IOL implantation and LASIK are considered to be optically excellent correction methods.

New approach for treating vertical strabismus: decentered intraocular lenses.

PURPOSE: To evaluate a new surgical procedure that uses a decentered intraocular lens (IOL) to correct vertical strabismus in cataract patients. SETTING: Department of Ophthalmology, Kitasato University School of Medicine, Sagamihara, Japan. METHODS: Six patients (11 eyes) with vertical strabismus had small-incision cataract surgery. The continuous curvilinear capsulorhexis was decentered, and the asymmetrical span of the IOL haptics located on the side to be bent was inserted after phacoemulsification and aspiration. Some relaxing incisions were made in the anterior capsule. Postoperatively, the alternate prism cover test was used to assess changes in ocular position. In addition, the EAS-1000 (Nidek) and KR-9000PW (Topcon) were used to evaluate IOL decentration, tilt, and aberrations. RESULTS: The mean age of the patients was 66 years (range 58 to 77 years). The mean preoperative vertical strabismus was 7.3 prism diopters (PD) (range 4 to 12 PD). Two years after surgery, the mean angle of vertical deviation was 1.3 PD (range 0 to 5 PD) without affectivity coma-like aberrations (S3). The mean amount of decentration was 0.52 mm +/- 0.29 (SD) and the mean tilt, 4.30 +/- 2.85 degrees (n = 10 eyes). CONCLUSION: Decentered IOL implantation was effective in cataract patients with vertical strabismus and can be performed during cataract surgery.

Effects of ocular dominance and visual input on body sway.

PURPOSE: To clarify the role of ocular dominance and to investigate the importance of visual acuity and restriction of the visual field for the visual stabilization of posture. METHODS: The subjects were 31 healthy volunteers ranging in age from 18 to 27 years. The sway of the center of gravity in the upright position was measured by a stabilometer. The tracings of the center of gravity obtained with the stabilometer while the subjects were standing erect for 1 min under several conditions were analyzed. The root mean square (RMS) area of body sway in each case was determined by analysis of the data. The main visual conditions were as follows: with the eyes open; with fixation of the dominant eye or of the nondominant eye; with a binocular or a monocular visual field of 10 degrees; with a binocular or a monocular visual field of 10 degrees and a visual acuity of 0.01; and with the eyes closed. RESULTS: The main results were as follows: (1) The RMS area while fixation of the dominant eye was maintained was significantly greater than that with fixation of the nondominant eye, and (2) the RMS area showed marked differences between binocular and monocular visual fields restricted to 10 degrees. In monocular fixation of the same visual field, the RMS area increased significantly compared with in binocular fixation. CONCLUSIONS: Binocular vision with the field restricted to 10 degrees offered the greatest contribution to postural stability, but the nondominant eye was more concerned with postural control than the dominant eye.

Changes of corneal aberrations in sitting and supine positions.

PURPOSE: To examine the effect of posture change on corneal aberrations and corneal curvature. DESIGN: Observational case series. METHODS: The Keratron topographer, improved to measure patients in the supine position, was used to measure the corneal aberrations and the curvature in nine healthy volunteers. The first measurement took place with the subject in the sitting position and the others in the supine position, immediately after assuming the supine position and then 30 minutes later. RESULTS: The total higher-order and spherical-like aberrations were significantly increased from the sitting position to the supine position (P=.011, and P=.044, Scheffé test). CONCLUSIONS: These results suggest that the increase in the higher-order aberration from the sitting to the supine position acts to limit the improvements in visual performance after customized refractive surgery based on wavefront measurement.

Quantitative measurement of ocular dominance using binocular rivalry induced by retinometers.

PURPOSE: To develop a new method using binocular rivalry and retinometers to quantitatively examine ocular dominance and to investigate the magnitude of ocular dominance in cataract patients preoperatively and postoperatively. SETTING: Eye Clinic, Kitasato University School of Medicine Hospital, Sagamihara, Kanagawa, Japan. METHODS: The duration of exclusive visibility of the dominant and nondominant eye target in binocular rivalry were measured in 60 healthy volunteers (study 1) and preoperatively and postoperatively in 10 cataract patients (study 2). Rivalry targets were presented directly to the retina of each eye using 2 retinometers. Subjects reported the exclusive visibility of 1 eye target, and the total duration of exclusive visibility for each eye in dominant and nondominant eye trials was evaluated. RESULTS: In study 1, the magnitude of ocular dominance was quantitatively assessed with 4 grades based on differences in total duration of exclusive visibility between dominant and nondominant eyes. In study 2, magnitude of ocular dominance could be evaluated in all cataract patients regardless of refractive and cataract conditions. Magnitude of ocular dominance displayed significant correlations between preoperative and postoperative conditions (simple regression, P<.001). CONCLUSIONS: Ocular dominance can be quantitatively evaluated using this new method based on binocular rivalry and retinometers, particularly in cataract patients. Magnitude of ocular dominance may indicate preoperatively whether a patient with cataracts will have sufficient ocular dominance to adjust to monovision correction.

Relationship between corneal aberrations and contrast sensitivity after hyperopic laser in situ keratomileusis.

PURPOSE: To evaluate the relationship between corneal aberrations and contrast sensitivity (CS) after hyperopic laser in situ keratomileusis (H-LASIK). METHODS: In 13 patients (13 eyes) who underwent H-LASIK, we measured CS and corneal topography preoperatively and at 1 year postoperatively. Photopic and scotopic CS values were measured at 3, 6, and 12 cycles/degree (cpd) using an MCT-8000 contrast tester. Corneal aberrations were determined from the data on corneal topography using CTView. The corneal high-order aberrations were defined as the sum of the third- and fourth-order aberrations in the 4-mm zone and the sum of the third- to sixth-order aberrations in the 6-mm-zone. RESULTS: Under scotopic conditions at 12 cpd, the changes in CS significantly correlated with changes in the corneal aberrations. Scotopic CS was significantly deteriorated by glare, but photopic CS was not significantly changed. H-LASIK induced a significant increase in corneal aberrations that positively correlated with the amount of correction, regardless of the improvement in logMAR corrected visual acuity. LogMAR corrected visual acuity did not significantly correlate with corneal aberrations. Furthermore, decentration significantly correlated with the changes in the 6-mm zone corneal aberrations. CONCLUSIONS: In eyes after H-LASIK, the changes in scotopic CS significantly correlated with those in the corneal aberrations, which might have resulted from decentration or ablation profiles in H-LASIK and a relatively small optical zone. Further studies will be needed to validate this relationship.

Modulation transfer function and pupil size in multifocal and monofocal intraocular lenses in vitro.

PURPOSE: To investigate the relationship between pupil size and the modulation transfer function (MTF) of a multifocal intraocular lens (IOL) in vitro and to predict the visual effects in vivo. SETTING: Department of Ophthalmology and Visual Science, Kitasato University Graduate School of Medical Sciences, Kitasato, Japan. METHODS: A refractive multifocal IOL (Array SA-40N, Allergan) and a monofocal IOL (PhacoFlex SI-40NB, AMO) were evaluated using the OPAL Vector system and a model eye with a variable effective aperture. With effective pupil diameters of 2.1, 3.0, 3.4, 3.9, 4.6, 5.1, and 5.5 mm, the in-focus and defocus MTFs were measured in the multifocal and monofocal IOLs. RESULTS: With increases in effective pupil diameter, the far MTF progressively decreased at all spatial frequencies. In contrast, the near MTF began to increase at effective pupil diameter 2.1 mm, showed a peak at 3.4 mm, and decreased at diameters greater than 3.4 mm. The ratio of near MTF to far MTF showed an increase with larger effective pupil diameters and at lower spatial frequencies. CONCLUSIONS: With a zonal progressive multifocal IOL, the pupil size effected a trade-off between the far and near MTFs: The near MTF increased at the expense of the far MTF at large pupil sizes (effective pupil diameter >3.4 mm). To enhance near vision with a multifocal IOL, the desirable effective pupil diameter should be 3.4 mm or larger.

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 microm, 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 microm, 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 microm. If this change directly affects the difference map, the posterior surface of the cornea moves forward by 48.24 microm. CONCLUSION: The results correspond to the amount of ectasia in previous reports. This artifact may explain the apparent ectasia detected by Orbscan.

Effects of ocular dominance on binocular summation after monocular reading adds.

PURPOSE: To investigate the relationship between ocular dominance and binocular summation with monocular reading adds. SETTING: Department of Orthoptics and Visual Science, School of Allied Health Sciences, Kitasato University, Sagamihara, Kanagawa, Japan. METHODS: Contrast sensitivities were measured by having subjects view contrast charts at spatial frequencies of 1.5, 3.0, 6.0, 12.0, and 18.0 cycles per degree after the addition of positive spherical lenses that ranged from +1.0 to +3.0 diopters (D). Through the use of a balance technique, the test group was quantitatively divided into 12 weak and 8 strong ocular dominance subjects on the basis of binocular rivalry. In study 1, binocular contrast sensitivity was measured in the weak and strong ocular dominances by adding a positive spherical lens in front of 1 eye, whereas the other eye was fixed at a corrected distance. RESULTS: In study 1, the binocular summation was observed only after adding positive spherical lenses in the nondominant eye. The differences in binocular contrast sensitivity that occurred after adding a positive spherical lens in the dominant eye versus that seen in the nondominant eye were statistically significant in the strong ocular dominance subjects who had +1.5 D and +2.0 D defocuses (P<.05; analysis of variance). CONCLUSIONS: Binocular summation was effectively maintained with reading adds in the nondominant eye and was significantly influenced by the magnitude of ocular dominance. Evaluating binocular summation after monocular reading adds seems to be a good method to evaluate adaptability to monovision.

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 microm +/- 27.9 (SD) at the nasal side, -4.5 +/- 27.8 microm at the temporal side, -3.9 +/- 20.1 microm at the superior side, and -2.3 +/- 20.1 microm 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 microm 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.