Tadatoshi Tokunaga

Higher order wavefront aberrations of cornea and magnitude of refractive correction in laser in situ keratomileusis

OBJECTIVE To assess the relation between magnitude of refractive correction and changes in higher order wavefront aberrations of the cornea after laser in situ keratomileusis. DESIGN Prospective, consecutive, nonrandomized comparative trial (self-controlled). PARTICIPANTS One hundred eyes of 53 patients with myopia (-2.0 to -13.0 diopters) were included. INTERVENTION Laser in situ keratomileusis was performed. Videokeratography measurements were conducted before and 1 month after surgery. MAIN OUTCOME MEASURES The videokeratography data were used to calculate the higher order wavefront aberrations of the cornea for both small (3 mm) and large (6 mm) pupils. RESULTS For a 3-mm pupil, the surgery significantly increased coma-like (2.4 +/- 1.3-fold, P < 0.001, paired t test) and spherical-like (1.8 +/- 0.9-fold, P < 0.001) aberrations. For a 6-mm pupil, both coma-like (4.4 +/- 3.3-fold, P < 0.001) and spherical-like (9.4 +/- 5.2-fold, P < 0.001) aberrations were significantly increased by surgery. The amount of achieved correction showed significant correlations with the changes in coma-like (Pearson correlation coefficient r = 0.446, P < 0.001) and spherical-like (r = 0.348, P < 0.001) aberrations for a 3-mm pupil, and coma-like (r = 0.566, P < 0.001) and spherical-like (r = 0.693, P < 0.001) aberrations for a 6-mm pupil. The eyes that lost 2 or more lines of baseline spectacle-corrected visual acuity showed significantly larger induced increases in coma-like (P = 0.003, Mann-Whitney U test) and spherical-like (P = 0.009) aberrations for a 3-mm pupil than those that either improved or remained within 1 line of spectacle-corrected visual acuity CONCLUSIONS Laser in situ keratomileusis, performed using the current algorithms, increases higher order wavefront aberrations of the cornea, dependent on the amount of refractive correction.

Comparison of corneal thickness measurements using Orbscan II, non-contact specular microscopy, and ultrasonic pachymetry in eyes after laser in situ keratomileusis

Aims: To compare central corneal thickness measurements of three pachymetry devices in eyes after laser in situ keratomileusis (LASIK). Methods: Central corneal thickness was measured in 203 eyes after myopic LASIK. Orbscan II scanning slit topography (Bausch & Lomb), SP-2000P non-contact specular microscopy (Topcon), and ultrasonic pachymetry (Tomey) were used in this sequence. Results: Three devices gave significantly different corneal thickness readings (p<0.0001, repeated measure analysis of variance). The measurements of Orbscan II (445.6 (SD 60.0) μm) were significantly smaller than those of noncontact specular microscopy (467.9 (SD 40.2) μm; p<0.0001, Tukey multiple comparison) and ultrasonic pachymetry (478.8 (SD 41.9) μm; p<0.0001). The value obtained with SP-2000P non-contact specular microscopy was significantly smaller than that taken with ultrasonic pachymetry (p<0.001). There were significant linear correlations between scanning slit topography and non-contact specular microscopy (Pearson’s correlation coefficient r = 0.912, p<0.0001), non-contact specular microscopy and ultrasonic pachymetry (r = 0.968, p<0.0001), and ultrasonic pachymetry and scanning slit topography (r = 0.933, p<0.0001). Conclusion: In post-LASIK eyes, Orbscan II scanning slit topography significantly underestimated corneal thickness. Non-contact specular microscopy gave smaller thickness readings than ultrasonic pachymetry, but these two units showed an excellent linear correlation.

Effects of pterygium on corneal spherical power and astigmatism

OBJECTIVE To evaluate prospectively the corneal refractive status before and after pterygium surgery and its relationship with preoperative pterygium size. DESIGN Prospective, nonrandomized, comparative (self-controlled) trial. PARTICIPANTS One hundred thirty-six eyes undergoing primary pterygium removal surgery. MAIN OUTCOME MEASURES Corneal spherical power, astigmatism, surface regularity index (SRI), and surface asymmetry index (SAI) before and after surgery, and the preoperative pterygium size. RESULTS Before surgery, pterygium size significantly correlated with spherical power (Pearsons correlation coefficient, r = -0.370, P < 0.001), astigmatism (r = 0.600, P < 0.001), SRI (r = 0.367, P < 0.001), and SAI (r = 0.387, P < 0.001). The surgery significantly increased spherical power of the cornea, whereas astigmatism, SRI, and SAI were significantly decreased by the surgery (P < 0.01, paired t test with Bonferronis correction of P value for multiple comparison). Surgically induced changes in spherical power (r = 0.598, P < 0.001) and astigmatism (r = 0.653, P < 0.001) significantly correlated with the preoperative pterygium size. Precise prediction of the magnitude of refractive changes based on the preoperative pterygium size was difficult. CONCLUSIONS The presence of pterygium and its removal significantly influence the corneal refraction including spherical power, astigmatism, asymmetry, and irregularity, with the larger pterygium exerting the greater influence.

Influence of excimer laser photorefractive keratectomy on the posterior corneal surface.

Purpose: To investigate the influence of excimer laser photorefractive keratectomy on the refraction and geometry of the posterior corneal surface. Setting: Miyata Eye Hospital, Miyazaki, Japan. Methods: Thirty‐seven eyes of 21 patients with refractive errors of −2.00 to −9.75 diopters (D) were treated with the VISX Twenty‐Twenty excimer laser system. The refractive and anteroposterior changes in the posterior corneal surface were measured using scanning‐slit corneal topography (Orbscan, Orbtek, Inc.) preoperatively and 1 week and 1 and 3 months postoperatively. Results: Mean posterior corneal refraction was −6.51 D ± 0.29 (SD) preoperatively; it decreased to −7.00 ± 0.49 D, −7.00 ± 0.55 D, and −6.92 ± 0.42 D at 1 week, 1 month, and 3 months, respectively (P < .001, Tukey multiple comparison). Mean forward shift of the posterior corneal surface was 29.5 ± 1.9 &mgr;m, 34.4 ± 3.4 &mgr;m, and 54.3 ± 4.0 &mgr;m at 1 week, 1 month, and 3 months, respectively. The amount of posterior corneal refractive change correlated with the degree of forward shift (r= −0.691, P < .001). The residual corneal thickness correlated with the refractive change (r = 0.524, P < .001) and the forward shift (r = −0.851, P < .001) of the posterior corneal surface. Conclusion: Photorefractive keratectomy induced significant refractive changes in the posterior corneal surface and forward shift of the cornea, both of which correlated with the thinness of the residual cornea.

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.

A prospective, randomised comparison of single and three piece acrylic foldable intraocular lenses

Aims: To compare the postoperative performance of single and three piece acrylic foldable intraocular lenses (IOLs). Methods: 20 patients underwent bilateral cataract surgery with a single piece SA30AL IOL in one eye and a three piece MA30BA IOL in the other eye. The eyes were randomly assigned to either a single or three piece lens. The amount of IOL decentration and tilt, area of anterior capsule opening, and degree of posterior capsule opacification were measured using the Scheimpflug anterior segment analysis system (Nidek EAS-1000). Visual acuity and contrast sensitivity were examined. Measurements were performed by masked examiners before and 1 day, 1 week, 1, 3, 6, and 18 months after surgery. Results: There were no significant differences between the two groups (p>0.05, paired t test) in the amount of IOL decentration, IOL tilt, area of anterior capsule opening, degree of posterior capsule opacification, best corrected visual acuity, and contrast sensitivity throughout the 18 month follow up period. Conclusion: The single and three piece acrylic foldable IOLs are equally stable in the eye after surgery.

Central corneal thickness measurements using orbscan II scanning slit topography, noncontact specular microscopy, and ultrasonic pachymetry in eyes with keratoconus

Purpose: To compare corneal thickness measurements using Orbscan II scanning slit topography, Topcon SP-2000P noncontact specular microscopy, and ultrasonic pachymetry in eyes with keratoconus. Methods: Central corneal thickness was measured in 22 eyes with keratoconus. Eyes with apparent corneal opacity were excluded. Scanning slit topography, noncontact specular microscopy, and ultrasonic pachymetry were used in this sequence. The acoustic equivalent correlation factor (0.92) was used for Orbscan readings. Results: Three devices gave significantly different corneal thickness readings (P < 0.001, repeated-measure analysis of variance). Measurements with Orbscan scanning slit topography (449.5 ± 43.2 [SD] μm) were significantly smaller than those of ultrasonic pachymetry (485.0 ± 29.3 μm; P < 0.001, Tukey multiple comparison) and SP-2000P noncontact specular microscopy (476.7 ± 28.3 μm; P = 0.002). There were significant linear correlations between ultrasonic pachymetry and scanning slit topography (Pearson correlation coefficient r = 0.741, P < 0.001), between scanning slit topography and noncontact specular microscopy (r = 0.880, P < 0.001), and between noncontact specular microscopy and ultrasonic pachymetry (r = 0.811, P < 0.001). Conclusion: In eyes with keratoconus, Orbscan II scanning slit topography system gave significantly smaller corneal thickness readings than the other 2 devices. Measurements taken by noncontact specular microscopy and ultrasonic pachymetry were comparable. Three devices showed significant linear correlations with one another.

Influence of tilt and decentration of scleral-sutured intraocular lens on ocular higher-order wavefront aberration

Aim: To investigate the influence of tilt and decentration of scleral-sutured intraocular lenses (IOLs) on ocular higher-order wavefront aberrations. Methods: In 45 eyes of 36 patients who had undergone scleral suture fixation of posterior chamber IOL, tilt and decentration of IOLs were determined by Scheimpflug videophotography, and higher-order aberration for a 4-mm pupil was measured using the Hartmann–Shack aberrometer. In another 100 eyes of 100 patients after standard cataract surgery with posterior chamber IOL implantation, ocular higher-order aberration was measured. Results: In eyes with scleral-sutured IOL, the mean (SD) tilt angle and decentration were 4.43° (3.02°) and 0.279 (0.162) mm, respectively. Ocular coma-like aberration in the sutured IOL group was 0.324 (0.170) µm, which was significantly greater than that of the standard cataract surgery group (0.169 (0.061) µm, p<0.001, Student’s t test). No significant difference was found in ocular spherical-like aberration between the sutured IOL group (0.142 (0.065) µm) and standard surgery group (0.126 (0.033) µm; p = 0.254). In the sutured IOL group, IOL tilt significantly correlated with ocular coma-like aberration (Pearson’s correlation coefficient r = 0.628, p<0.001), but no significant correlation was found between IOL tilt and ocular spherical-like aberration (r = 0.222, p = 0.175). The IOL tilt did not correlate with corneal coma-like (r = 0.289, p = 0.171) and spherical-like (r = 0.150, p = 0.356) aberrations. The IOL decentration did not correlate with any higher-order aberrations. Conclusion: In eyes with scleral-sutured posterior chamber IOL, tilting of the lens induces considerable amount of ocular coma-like aberrations.

Structural analysis of the cornea using scanning-slit corneal topography in eyes undergoing excimer laser refractive surgery.

Purpose To review the time course of corneal anteroposterior shift and refractive stability after myopic excimer laser keratorefractive surgery. Methods We examined 65 eyes undergoing photorefractive keratectomy (PRK) and 45 eyes undergoing laser in situ keratomileusis (LASIK). Corneal elevation maps and pachymetry were obtained by scanning-slit corneal topography before; 1 week; and 1, 3, 6, and 12 months after surgery. Results Both PRK and LASIK induced significant forward shifts of the cornea. Corneal forward shift was progressive up to 6 months after PRK, but no progression was seen after LASIK. Progressive thinning and expansion of the cornea were not observed after either procedure. The amount of corneal forward shift showed a significant negative correlation with preoperative corneal thickness (r = −0.586; P < 0.01) and a significant positive correlation with the amount of myopic correction (r = 0.504; P < 0.01). A significant correlation was found between the amount of forward shift and the degree of myopic regression after surgery (r = −0.347; P < 0.05). Conclusion Myopic PRK and LASIK induce significant forward shifts of the cornea, which are not true corneal ectasia. Eyes with thinner corneas and higher myopia requiring greater ablation are more predisposed to anterior protrusion of the cornea. Corneal forward shift was progressive up to 6 months after PRK but not progressive after LASIK. Forward shift of the cornea can be one of the factors responsible for myopic regression after surgery.

Standardized color-coded scales for anterior and posterior elevation maps of scanning slit corneal topography

PURPOSE To find the most appropriate color-coded scales for the anterior and posterior elevation maps of scanning slit topography in the screening of abnormal corneas such as keratoconus. DESIGN Retrospective case-control study. PARTICIPANTS Eighty eyes of 40 normal subjects and 175 eyes of 95 patients with keratoconus. INTERVENTION Anterior and posterior corneal elevations were assessed using Orbscan 2. Best-fit sphere maps were drawn with several color-coded scales: 2-, 5-, 10-, and 20-microm height per each color interval. MAIN OUTCOME MEASURES The maps were judged to be abnormal when more than three colors (discriminant number) were found within the central 3-mm area. For each color-coded scale, sensitivity, specificity, positive predictive value, negative predictive value, and sensitivity + specificity were calculated. After determining the most appropriate color-coded scales for the anterior and posterior elevation maps, validity of the discriminant number was assessed. By varying the discriminant number from two to eight, receiver operator characteristic (ROC) curves were created using the sensitivity and specificity for each threshold number. RESULTS The highest sensitivity + specificity values and highly balanced predictive values were obtained with the 10- and 20-microm scales for the anterior and posterior elevation maps, respectively. The ROC curve analyses showed that the best discriminant color number is three, indicating that maps with four or more colors within the central 3-mm area are judged abnormal in screening. CONCLUSIONS The 10- and 20-microm interval color scales are most appropriate for the anterior and posterior elevation maps of the scanning slit topography, respectively.