Centration analysis of ablation over the coaxial corneal light reflex for hyperopic LASIK

PURPOSE: To analyze postoperative topographic centration when the coaxially sighted corneal light reflex was used for laser centration in hyperopic LASIK. METHODS: Centration photographs of 21 eyes (12 patients) that underwent hyperopic LASIK with centration over the coaxially sighted corneal light reflex were reviewed to determine the distance from the entrance pupil center to the coaxially sighted corneal light reflex. Postoperative ablation centration was determined topographically at day 1 and 3 months by four different methods. The difference between the actual decentration and the decentration that would have occurred had the ablation been centered over the entrance pupil center was calculated. RESULTS: The mean deviation of the coaxially sighted corneal light reflex from the entrance pupil center preoperatively was 0.34 +/- 0.24 mm nasal or 4.5 +/- 3.0 degrees. At 1 day, the average decentration was 0.10 mm or 1.3 degrees temporal. The mean decentration that would have occurred if the ablation had been centered over the entrance pupil center was 0.44 mm or 5.5 degrees temporal. At 3 months, the average decentration was 0.07 mm or 0.25 degrees temporal. The mean decentration that would have occurred if the ablation had been centered over the entrance pupil center was 0.45 mm or 5.6 degrees temporal. Mean uncorrected visual acuity (logMAR) improved 3 lines from 0.54 +/- 0.14 (20/70) to 0.22 +/- 0.17 (20/32). No eye lost >2 lines of best spectacle-corrected visual acuity (BSCVA); 2 (10%) eyes lost 1 line of BSCVA at 3-month follow-up. CONCLUSIONS: Excellent centration in hyperopic ablation is possible even in eyes with positive angle kappa when the ablation is centered over the corneal light reflex.     

Ablation auf der Unterseite eines LASIK-Flaps

BACKGROUND: The risk of iatrogenic keratectasia after laser in situ keratomileusis (LASIK) increases with thinner posterior stromal beds. Ablations on the undersurface of a LASIK flap could only be performed without the guidance of an eye tracker, which may lead to decentration. A new method for laser ablation with flying spot lasers on the undersurface of a LASIK flap was developed that enables the use of an active eye tracker by utilizing a novel instrument. The first clinical results are reported. PATIENTS AND METHODS: Patients wishing an enhancement procedure were eligible for a modified repeat LASIK procedure if the flaps cut in the initial procedure were thick enough to perform the intended additional ablation on the undersurface leaving at least 90 microm of flap thickness behind. (1) The horizontal axis and the center of the entrance pupil were marked on the epithelial side of the flap using gentian violet dye. (2) The flap was reflected on a newly designed flap holder which had a donut-shaped black marking. (3) The eye tracker was centered on the mark visible in transparency on the flap. (4) Ablation with a flying spot Bausch & Lomb Technolas 217z laser was performed on the undersurface of the flap with a superior hinge taking into account that in astigmatic ablations the cylinder axis had to be mirrored according to the formula: axis on the undersurface=180 degrees -axis on the stromal bed. (5) The flap was repositioned. RESULTS: Detection of the marking on the modified flap holder and continuous tracking instead of the real pupil was possible in all of the 12 eyes treated with this technique. It may be necessary to cover the real pupil during ablation in order not to confuse the eye tracker. Ablation could be performed without decentration or loss of best spectacle-corrected visual acuity. Refractive results in minor corrections were good without nomogram adjustment. CONCLUSIONS: Using this novel flap holder with a marking that is tracked instead of the real pupil, centered ablations with a flying spot laser on the undersurface of a LASIK flap are feasible. Thus, the additional risk of iatrogenic keratectasia associated with stromal enhancement ablations is avoided.     

Dynamic measurement of accommodation and pupil size using the portable Grand Seiko FR-5000 autorefractor.

PURPOSE: The purpose of this study was to evaluate the potential of the portable Grand Seiko FR-5000 autorefractor to allow objective, continuous, open-field measurement of accommodation and pupil size for the investigation of the visual response to real-world environments and changes in the optical components of the eye. METHODS: The FR-5000 projects a pair of infrared horizontal and vertical lines on either side of fixation, analyzing the separation of the bars in the reflected image. The measurement bars were turned on permanently and the video output of the FR-5000 fed into a PC for real-time analysis. The calibration between infrared bar separation and the refractive error was assessed over a range of 10.0 D with a model eye. Tolerance to longitudinal instrument head shift was investigated over a +/-15 mm range and to eye alignment away from the visual axis over eccentricities up to 25.0 degrees . The minimum pupil size for measurement was determined with a model eye. RESULTS: The separation of the measurement bars changed linearly (r2 = 0.99), allowing continuous online analysis of the refractive state at 60 Hz temporal and approximately 0.01 D system resolution with pupils >2 mm. The pupil edge could be analyzed on the diagonal axes at the same rate with a system resolution of approximately 0.05 mm. The measurement of accommodation and pupil size were affected by eccentricity of viewing and instrument focusing inaccuracies. CONCLUSIONS: The small size of the instrument together with its resolution and temporal properties and ability to measure through a 2 mm pupil make it useful for the measurement of dynamic accommodation and pupil responses in confined environments, although good eye alignment is important.     

Errors in determining the direction of the visual axis in the presence of defocus

The visual axis is the ray path from the fixation point to the fovea by way of the nodal points. Such a ray path does not exist in unaccommodated vision when the fixation point does not coincide with the far point of the eye because of induced or natural defocus. Nevertheless an approximation to the visual axis can be obtained by the position of a small pupil close to the cornea for which a bichromatic vernier target appears correctly aligned. When the visual axis is determined, an eye rotation from the visual fixation position must occur, which is reversed upon removing the small pupil. Upon engaging in any experiments for which the visual axis is then used as a reference, there is an error in this reference position. We develop simple paraxial equations to estimate this error. We show that these equations have good accuracy. The error associated with locating the visual axis at the cornea is 0.002 mm per dioptre of defocus, which is small enough to be ignored.     

Calculating the localization and dimension of the real pupil in keratoconus with ray tracing of corneal topography data]

BACKGROUND: It is crucial to center surgical procedures for optical indications on the pupil or the optical axis of the eye. In keratoconus the pupil appears to be dislocated due to optical aberrations of corneal topography. The purpose of this study was to evaluate the real pupil structure from the virtual image using exact raytracing techniques. PATIENTS AND METHODS: Eighty-eight patients with keratoconus (46 with mild and 42 with severe clinical signs) and a control group of 40 normal subjects were included in this study. Topographic height data were calculated from refraction data of a commercially available topographer (TMS-1) using a local approximation algorithm and a convex surface was modelled using a subdivision scheme. For the posterior corneal surface we postulated an aspherical surface with a central radius of curvature of 6.5 mm using Navarro's model eye. At the virtual pupil outline a bundle of parallel rays were intersected with the anterior and posterior corneal surface and refracted into the anterior chamber. The intersections of these rays with the pupil plane was defined as the real pupil outline. We assessed the amount and direction of pupil dislocation, the ratio between the virtual and real pupil size for each group and correlated these parameters with the central corneal power. RESULTS: The size of the virtual pupil exceeded the reference value of the real pupil in the normal group by 11%, in the group with mild keratoconus by 19% and in the group with severe keratoconus by 35%. The center of the virtual pupil was decentered 0.06 mm in the normal group, 0.49 in the group with mild keratoconus and 1.24 mm in the group with severe keratoconus. Whereas the direction of decentration was randomly in the normal group, we measured a preferred decentration to the inferior quadrants in mild keratoconus and a systematic decentration to the temporal inferior quadrant in severe keratoconus. Correlation of the optical dislocation did not correlate with central corneal power in any group. CONCLUSIONS: In keratoconic eyes the pupil outline is distorted and dislocated due to optical aberrations of the cornea. Exact raytracing technique allows the calculation of the real pupil outline from the virtual image and the topographic height of both corneal surfaces. Knowledge about the real pupil position may have an impact on adequate centration of keratorefractive surgery and penetrating keratoplasty.     

Pupil diameter and the principal ray.

Placement of the surgical zone is critical in refractive procedures that alter a portion of the corneal curve. An improperly centered optical zone may produce glare, decrease best corrected visual acuity, and decrease contrast sensitivity. For proper placement, the new surface should be centered around the line of sight, which is the principal ray from the object of regard that passes through the image of the patient's pupil as projected on the cornea. This point is not necessarily at the geometric center of the cornea and is found by locating the center of the pupil while the patient is maintaining fixation coaxially with the surgeon. However, the pupil does not dilate concentrically and its geometric center moves as the pupil diameter changes. We have found a shift up to 0.7 mm in the geometric center of the pupil as it dilates. Therefore, centration of an ablated or a radial keratotomy zone is most efficiently done when the diameter of the modified corneal optical zone is centered around the line of sight and is superimposed upon the entrance pupil. This will minimize extension of the edge of the large pupil beyond the ablated zone and reduce unwanted secondary optical effects from degrading vision.     

Intraoperative corneal topography for image registration

PURPOSE: To present a method to measure the three-dimensional shape of the cornea and to use the data for registration purposes in order to optimize ablation pattern alignment during corneal laser surgery. METHODS: The three dimensional shape of the cornea can be measured with a modified fringe projection technique using UV laser pulses. A method to register these shape images is presented. The registration is done via established algorithms that use peripheral elevation data, which is not affected during the laser treatment. The method also provides a means to control the absolute amount of tissue removal. The three-dimensional registration method is compared with conventional two-dimensional eye tracking. RESULTS: Due to the parallax of the cornea with respect to the pupil center, considerable decentration of laser ablation patterns can occur when tracking just the pupil center. Registration using three-dimensional shape measurements provides a more accurate means to control ablation pattern application. CONCLUSIONS: A new method to register corneal shapes is discussed. It should allow monitoring the real ablation rate online during the treatment and might eventually serve as an online feedback system to control the laser ablation-induced corneal shape changes.     

Assessment of the optical image quality of the eye using raytracing technique of corneal topography data

BACKGROUND: Optical aberrations in the optical system may downgrade image quality and cannot be fully compensated by spherocylindrical glasses. The subjectively evaluated visual acuity may be significantly reduced. The purpose of this study was to calculate the image forming properties of the eye using a spotlight source or alternatively extended objects. METHODS: A convex and first derivative continuous (C1) surface from the rough height data of the anterior corneal surface (TMS-1, Tomey, Erlangen) or the anterior and posterior corneal surface (Orbscan, Orbtec, USA) was calculated by means of an interpolating subdivision scheme (modified Butterfly algorithm). The characteristics of the residual refractive surfaces were used according to Navarro's eye model. The focal distance was calculated from the exact raytracing calculation (Snellius' law) of the point-spread function by minimising the variance of the point-spread function. The diffraction property of the aperture stop was implemented with a transmission characteristic according to a radially symmetrical Bessel function within the entrance pupil. The algorithm was realised with a C code on the LINUX platform and applied to a normal eye (example 1, TMS-1), an eye with severe keratoconus (example 2, TMS-1) and an eye with corneal scars (example 3, Orbscan). RESULTS: The focal distance in example 1 (22.5 mm, 22.6 mm, and 22.8 mm) increased with the pupil diameter (2 mm, 3 mm, and 5 mm). The variance of the approximately radially symmetrical point-spread function in the focal plane attained a minimum value with a pupil size of 3 mm (0.164, 0.104, and 0.230). In example 2, the focal distance changed inconclusively (21.1 mm, 21.0 mm, and 21.3 mm) with the pupil size (2 mm, 3 mm, and 5 mm). The variance of the markedly asymmetrical point-spread function in the focal plane was systematically higher compared to the values of example 1 and reached a minimum value with a pupil size of 3 mm (0.255, 0.224, and 0.371). The imaging of the sinus-modulated pattern is anisotropic due to the asymmetry of the point-spread function. In example 3, the focal distance (22.3 mm, 22.3 mm, and 22.5 mm) did not change systematically with the pupil size (2 mm, 3 mm, and 5 mm). The variance of the nearly radially symmetrical point-spread function changed only marginally between pupil sizes of 2 mm and 3 mm (0.231, 0.239, and 0.338). CONCLUSIONS: Raytracing of corneal topography height data based on refined eye models with the option of auto-focussing has the potential to trace the optical resolution of the eye for arbitrary objects. Further studies on contrast sensitivity and the conversion of the real image to a perceived image by the retina and brain are required for complete modeling of subjective visual acuity.     

Horizontal versus vertical dark-adapted pupil diameters in normal individuals

PURPOSE: To determine the distribution of the difference between the horizontal and vertical dark-adapted entrance pupil diameters (PDs) in normal individuals. SETTING: Texas Tech University Health Sciences Center, Lubbock, Texas, USA. METHODS: In this observational cohort study, high-magnification infrared pupil photography was performed of the right eye of 26 normal volunteers from 20 to 47 years of age. The horizontal and vertical PDs were measured using commercially available digital-image software, taking into account the effect of photographic parallax. RESULTS: In 24 subjects (85%), the vertical PD was larger than the horizontal PD; in 8 subjects (31%), it was 0.30 mm to 0.50 mm larger. In 2 subjects, the horizontal diameter was slightly larger but the difference was <0.10 mm. The mean horizontal to vertical PD ratio was 0.97. CONCLUSIONS: In this study population, the vertical PD was larger than the horizontal PD in most subjects. Although the difference was a fraction of the total PD, it may be important for laser refractive surgery planning and preoperative risk counseling of some patients.     

两种白内障手术联合Toric IOL植入术在长眼轴患者中的应用

目的：观察飞秒激光辅助白内障手术(FLACS)与传统白内障手术(Phaco)联合Toric IOL植入术在眼轴大于24mm的患者中的应用疗效。

方法：前瞻性研究。选取2017-01/2018-03在我院行手术治疗的白内障患者49例49眼,飞秒组行FLACS术联合Toric IOL植入术,传统组行Phaco术联合Toric IOL植入术。观察两组患者视力、散光度、斯特列尔比(strchl)、高阶像差情况。

结果：术后3mo,飞秒组和传统组患者视力(0.092±0.089和0.131±0.096)均较术前(0.855±0.213和0.948±0.135)显著改善(P<0.05),但两组之间视力、总残余散光、strchl值、角膜和全眼高阶像差均无差异(P>0.05)。飞秒组全眼4mm瞳孔直径下4s3、4s4、4Total和6mm瞳孔直径下6s5与strchl值均呈负相关,传统组全眼4mm瞳孔直径下4s3、4Total和6mm瞳孔直径下6s3、6s3+s5、6Total与strchl值均呈负相关。

结论：眼轴大于24mm的白内障患者植入Toric IOL能有效矫正角膜规则散光,FLACS术和传统超声乳化手术均能使其保持眼内旋转稳定性,显著改善术后视觉质量。     

轴性高度近视眼高阶像差与眼轴长度及屈光度的相关性研究

目的　研究轴性高度近视眼4 mm及6 mm瞳孔直径下眼球高阶像差的特点及其与眼轴长度和眼球屈光度的相关性。方法　选取北京大学国际医院眼科轴性高度近视患者共30例（30眼）,眼轴长度均≥26 mm,等效球镜度数≤-6.00 D。OPD-Scan Ⅲ光学视觉质量分析仪测量4 mm及6 mm瞳孔直径下患者角膜、眼内及全眼高阶像差,应用IOL-Master测量患者眼轴长度。使用SPSS 20.0软件进行统计学分析,采用配对样本t检验比较4 mm与6 mm瞳孔直径下角膜、眼内及全眼高阶像差的差异,Pearson相关性分析用于分析4 mm与6 mm瞳孔直径下各高阶像差与眼轴长度及等效球镜度数的相关性。结果　4 mm瞳孔直径下角膜高阶像差、眼内高阶像差及全眼高阶像差分别为（0.125±0.040）μm、（0.140±0.042）μm和（0.136±0.052）μm,均较6 mm瞳孔直径下的（0.422±0.110）μm、（0.348±0.101）μm、（0.341±0.109）μm显著降低,差异均有统计学意义（均为P＜0.001）;4 mm瞳孔直径下角膜高阶像差与全眼高阶像差相比差异无统计学意义（P=0.193）;6 mm瞳孔直径下角膜高阶像差比全眼高阶像差显著升高（P=0.002）。4 mm瞳孔直径、6 mm瞳孔直径下各高阶像差与等效球镜度数和眼轴长度均无显著相关性（均为P>0.05）。结论　轴性高度近视患者6 mm瞳孔直径比4 mm瞳孔直径下角膜高阶像差、眼内高阶像差及全眼高阶像差均显著增加。4 mm瞳孔直径及6 mm瞳孔直径下各高阶像差与等效球镜度数和眼轴长度均无显著相关性。眼内高阶像差对角膜高阶像差可能有补偿作用,眼内球差在角膜高阶像差的补偿中可能起重要作用。     

配戴RGPCL后水平彗差的变化及其与瞳孔中心位移的关系

目的分析RGPCL配戴前后,全眼球和角膜像差的变化情况以及与瞳孔中心位移之间的关系。方法前瞻性病例自身对照研究。21例志愿者（42眼）,平均年龄（26.7±4.1）岁,平均屈光度（-3.59±1.36）D,散光度（-0.67±0.24）D;用鹰视角膜地形图测量瞳孔中心相对于角膜中心的偏移量、瞳孔直径以及角膜像差,鹰视波前像差仪测量裸眼的全眼球像差。然后由同一名视光师给予验配美尼康RGPCL,在配戴RGPCL 1个月后回访,用相同仪器分别测量戴镜时的瞳孔中心偏移、瞳孔直径、角膜像差和全眼球像差。统计分析6 mm直径下的前4阶14项波前像差。采用配对t检验和相关分析对数据进行分析。结果配戴RGPCL 1个月后,双眼瞳孔中心向颞侧水平偏移,瞳孔直径轻微增大,其变化量如下：?譹?訛水平位移：右眼戴前为（-0.067±0.141）mm,戴后（-0.103±0.129）mm（t=2.240,P＜0.05）;左眼戴前为（0.059±0.159）mm,戴后（0.114±0.132）mm（t=-3.371,P＜0.01）。?譺?訛瞳孔直径：戴前为（3.69±0.61）mm,戴后为（3.91±0.49）mm（t=-2.865,P＜0.01）。角膜和全眼球的水平彗差变化均有统计学意义：?譹?訛角膜水平彗差减少,右眼戴前为（-0.104±0.075）μm,戴后（0.019±0.050）μm（t=-5.697,P<0.01）,左眼戴前为（0.127±0.074）μm,戴后（-0.001±0.079）μm（t=5.113,P<0.01）;?譺?訛全眼球水平彗差增加,右眼戴前为（0.012±0.072）μm,戴后（0.097±0.054）μm（t=-5.291,P<0.01）;左眼戴前为（-0.038±0.071）μm,戴后（-0.099±0.051）μm（t=4.378,P<0.01）。在这些有变化的参数中瞳孔中心水平位移分别与角膜和全眼球水平彗差差值呈负相关（r=-0.583、-0.534,P<0.01）;并且瞳孔中心水平位移与瞳孔直径的改变有较大相关性（r=0.501,P<0.01）。结论配戴RGPCL后,瞳孔中心发生颞侧向的水平位移,从而角膜和全眼球水平彗差也相应改变,原来的角膜和眼内彗差的互补平衡被打破。瞳孔直径的轻微增加可能是造成此种改变的原因之一。     

Eye movement during laser in situ keratomileusis

PURPOSE: To measure eye motion in patients having laser in situ keratomileusis (LASIK) using a video technique and determine centration and variance of the eye position during surgery. SETTING: Laser refractive surgery center. METHODS: The procedure was videotaped in 5 consecutive eyes having LASIK performed by a single surgeon with the VISX Star S2 excimer laser. Following surgery, video images of the eyes were digitized and stored in a computer for processing. Digitized images were obtained at a rate of 25 images per second during the laser procedure. The pupil margin and a visual landmark, such as a scleral blood vessel, were identified in the initial image of each eye. Custom software was used to track the location of the landmark and the pupil center in subsequent images. RESULTS: Three of the 5 eyes were well centered on average. The remaining 2 eyes were decentered inferiorly by approximately 0.25 mm. The standard deviation in all eyes was approximately 0.10 mm. CONCLUSIONS: With these techniques, the position of the entrance pupil center relative to the excimer laser axis could be determined. Although the system is not fast enough to be used during surgery, it does allow quantification of centration and intraoperative motion after surgery.     

LASIK术后眼高阶像差和角膜非球面系数Q值的变化

目的:观察2mm小光斑飞点扫描伴主动眼球跟踪系统的激光机行常规LASIK术后,眼高阶像差和角膜非球面系数Q值的改变,同时观察术后不同瞳孔直径下眼高阶像差的变化。方法:近视患者33例60眼均接受常规LASIK手术,术前和术后3mo分别检查记录5mm和6mm瞳孔直径下总高阶像差、三阶彗差、四阶球差和角膜前表面非球面系数Q值,并进行统计学分析。结果:LASIK术后,5mm和6mm瞳孔直径下各高阶像差均较术前显著增加,其中四阶球差增加最为显著;术后水平彗差比垂直彗差增加显著;术前术后6mm直径下高阶像差均较5mm直径下显著增大;LASIK术后角膜非球面系数Q值向正值方向明显变化,差异具有显著性。结论:近视眼常规LASIK术后,各项高阶像差明显增大,其中球差增大最为显著。手术前后6mm瞳孔直径下高阶像差均比5mm瞳孔直径下高阶像差明显增大。术后角膜表面非球面系数Q值由负值变为正值,且增大显著。     

Theoretical effect of changes in entrance pupil magnification on wavefront-guided laser refractive corneal surgery

PURPOSE: To explore theoretically the effect on the correction of higher order aberrations of changes in the magnification between the aperture stop (iris) and entrance pupil of the eye, following myopic excimer laser ablation. METHODS: Using a simple schematic eye model, paraxial calculations were made of the position and magnification of the entrance pupil of the eye as a function of the power of a myopic photorefractive keratectomy correction. RESULTS: Corneal flattening following myopic corneal ablation results in a reduction in the magnification between the aperture stop (iris) and entrance pupil. This implies that an ablation designed to correct higher order errors on the basis of the preoperative wavefront aberration across the entrance pupil will result in an incomplete correction. Taking into account the fact that the total ocular aberration depends on the combined effects of all optical components of the eye, which are distributed in depth, rather than being associated simply with the anterior surface of the cornea, the exact effects depend on the methods used to measure the aberration and the distribution of the total aberration between the different components of the eye. The errors in correction increase with the magnitude of the myopic correction. CONCLUSIONS: To minimize the postoperative higher order aberrations in higher amounts of myopia, it may be desirable to remeasure them after a first ablation to correct the second-order refractive errors and then to carry out a second ablation to correct the higher order aberrations.     

Psychophysical measurement of the blur on the retina due to optical aberrations of the eye

The blur on the retina in the horizontal meridian due to monochromatic and chromatic aberrations has been measured using a novel psychophysical technique. Longitudinal chromatic aberration gives the dominant blur for pupil sizes of 4-5 mm, followed by monochromatic aberrations, and blur due to optical transverse chromatic aberration. In some eyes, coma was present as a result of a displacement of the axis of symmetry from the centre of the pupil, but in three eyes, coma was present without spherical aberration. The technique also allows a measurement of the effective pupil centre relative to the geometric centre and a partial analysis of the relative positions of the reference axes of the eye.     

Pupil center shift relative to the coaxially sighted corneal light reflex under natural and pharmacologically dilated conditions

PURPOSE: To evaluate the location and shift of the pupil center relative to the coaxially sighted corneal reflex on horizontal and vertical planes under natural and pharmacologically dilated conditions. METHODS: Ninety-four (64 myopic and 30 hyperopic) eyes of 47 patients underwent pupillometry with the NIDEK OPD-Scan under photopic and mesopic conditions before and after instillation of cyclopentolate 1%. Horizontal, vertical, and vectorial shift of the pupil center were calculated between each condition. RESULTS: The pupil center was located temporally to the coaxially sighted corneal reflex a mean distance of 0.336 +/- 0.181, 0.345 +/- 0.195, and 0.339 +/- 0.170 mm under photopic, mesopic, and pharmacologically dilated conditions, respectively. The pupil center shifted primarily inferotemporally (44%), followed by inferonasally (22%), superotemporally (19%), and superonasally (15%) from photopic to pharmacologic dilation. Mean magnitude of pupil shift was 0.084 +/- 0.069 mm (range: 0.010 to 0.385 mm) from mesopic to photopic, 0.149 +/- 0.080 mm (range: 0.013 to 0.384 mm) from photopic to pharmacologic dilation, and 0.102 +/- 0.104 mm (range: 0 to 0.530 mm) from mesopic to pharmacologic dilation. Mean distance between the pupil center and the coaxially sighted corneal reflex was greater in hyperopes than in myopes (P < .05), but no significant difference was observed in pupil center shifts between myopes and hyperopes under all three conditions (P > .05). CONCLUSIONS: The pupil center is located temporally and shifts in every direction, primarily inferotemporally, relative to the coaxially sighted corneal reflex with natural and pharmacologic dilation. The horizontal distance between the pupil center and the coaxially sighted corneal reflex was significantly higher in hyperopes than in myopes.     

The Julius F. Neumueller Award in Optics, 1989: change of pupil centration with change of illumination and pupil size.

Pupil centration is important to the optical blur on the retina. Using a dual Maxwellian view system we measured the centration of the pupil with respect to the achromatic axis of the eye as a function of pupil size. Significant shifts of the pupil center (up to 0.6 mm) with pupil dilation were measured in both nasal and temporal directions. The effect was usually symmetrical between the two eyes and the shift was linear with pupil size in one-half of the subjects. From their initial positions the linear pupil center shifts with dilation were in the direction of the achromatic axis.     

Simulated optical performance of custom wavefront soft contact lenses for keratoconus.

PURPOSE: Outstanding improvements in vision can theoretically be expected using contact lenses that correct monochromatic aberrations of the eye. Imperfections in such correction inherent to contact lenses are lens flexure, translation, rotation, and tear layer effects. The effects of pupil size and accommodation on ocular aberration may cause further difficulties. The purpose of this study was to evaluate whether nonaxisymmetric soft contact lenses could efficiently compensate for higher-order aberrations induced by keratoconus and to what extent rotation and translation of the lens would degrade this perfect correction. METHODS: Height topography data of nine moderate to severe keratoconus corneas were obtained using the Maastricht Shape Topographer. Three-dimensional ray tracing was applied to each elevation topography to calculate aberrations in the form of a phase error mapping. The effect of a nonaxisymmetric soft contact lens tailored to the corneal aberrations was simulated by adding an opposite phase error mapping that would theoretically compensate all corneal-induced optical aberrations of the keratoconus eyes. Translation (0.25, 0.5, 0.75, and 1.0 mm) and rotation (2.5 degrees, 5.0 degrees, 7.5 degrees, and 10 degrees ) mismatches were introduced. The modulation transfer function (MTF) of each eye with each displaced correction and with various pupil sizes (3, 5, and 7 mm) was deduced from the residual phase error mapping. A single performance criterion (mtfA) was calculated as the area under the MTF over a limited spatial frequency range (5 to 15 periods per degree). Finally, the ratio (RmtfA) of corrected mtfA over uncorrected mtfA provided an estimate of the global enhancement in contrast sensitivity with the customized lens. RESULTS: The contrast improvement ratios RmtfA with perfectly located lenses were for an average pupil size of 4.5 mm between 6.5 and 200. For small translation errors (0.25 mm), RmtfA ranged between 2 and 7. The largest lens translation tested (1 mm) often resulted in poorer performance than without correction (RmtfA <1). More than threefold improvements were achieved with any of the angular errors experimented. RmtfA values showed significant variations for pupil diameters between 3 and 7 mm. CONCLUSIONS: Three-dimensional aberration-customized soft contact lenses may drastically improve visual performance in patients with keratoconus. However, such lenses should be well positioned on the cornea. In particular, translation errors should not exceed 0.5 mm. Angular errors appeared to be less critical. It is further questioned whether the visual system is able to adapt to variations in optical performance of the correction in situ due to lens positioning and pupil size.     

Measurement of the spatial shift of the pupil center

PURPOSE: To evaluate the effectiveness of the pupil center as an anatomic landmark for excimer laser treatments. SETTING: Sekal-Microchirurgia-Rovigo Centre, Rovigo, Italy. METHODS: Pupillometry with the Costruzione Strumenti Oftalmici S.R.L. (CSO) pupil-measuring module (incorporated in Eye Top videokeratoscope) was performed in 52 patients with a diagnosis of myopia and in 25 patients with a diagnosis of hyperopia. Measurements both in mesopic and photopic conditions consisted of pupil diameters, spatial shift of the pupil center, and the distance between the pupil center and keratoscopic axis. RESULTS: The mean pupil diameter in photopic conditions of illumination in myopic eyes was 3.52 mm +/- 0.56 (SD), while in mesopic conditions it was 5.37 +/- 0.78 mm; in hyperopic eyes the mean photopic pupil diameter was 3.01 +/- 0.46 mm, while the mean mesopic diameter was 5.12 +/- 0.48 mm. The mean spatial shift of the pupil center in myopic eyes was 0.086 mm (maximum 0.269 mm), while in the hyperopic eyes it was 0.095 mm (maximum 0.283 mm). The mean distance between the pupil center and keratoscopic axis in myopic eyes was 0.226 +/- 0.13 mm (maximum 0.75 mm), while in hyperopic eyes it was 0.45 +/- 0.19 mm (maximum 0.8 mm). CONCLUSIONS: The mean of the measured pupil sizes was greater in myopic eyes than in hyperopic eyes. The spatial shift of the pupil center, as the pupil dilates, was relatively small in all groups; therefore, the pupil center is a good anatomic landmark for both traditional refractive surgery and wavefront-guided treatments. The mean distance between the keratoscopic axis and pupil center was greater in the hyperopic group than in the myopic group. Therefore, centration of any laser treatment on the basis of the keratoscopic analysis should be done carefully, especially in hyperopic eyes and in cases in which the pupil center is meaningfully shifted from keratoscopic axis, even in photopic conditions of illumination.