Magnification Changes Research Articles

Magnification and accommodation with phakic intraocular lenses

The calculation of phakic lenses (PL) was described by van der Heijde et al. [Klin. Monatsbl. Augenheilkd (1988) Vol. 193, pp. 99-102], but a formalism for estimating relative magnification compared with spectacle correction and accommodation effects are not yet published. The purpose of this study was to describe a mathematical strategy for calculating PL and relative magnification as a function of object vergence (phakic accommodation). Parameters used for the calculations are the spectacle refraction before and after (target refraction) surgery, the vertex distance, corneal refraction, and the predicted position of the phakic intraocular lens. The lens power is determined as the difference in vergences between the spectacle-corrected eye and the uncorrected eye at the reference plane of the predicted lens position. If we simplify the crystalline lens to a single refracting surface located at the principal plane of the crystalline lens, the vergence of the eye with spectacle correction and with PL is determined as a function of object distance [object vergence 0 D (infinity) to 10 D (object at a distance of 10 cm)] to evaluate accommodation effects of the crystalline lens. The method was applied to two clinical examples. In example 1 we calculated the power of a PL for correction of a 10-D myopia and determined the relative magnification and the vergence at the principal plane of the crystalline lens as a function of object vergence. Magnification gain increases with objects at near from 17% to 26%, whereas the vergence at the principal plane of the crystalline lens changes by 3.04 D less than in the spectacle-corrected eye. In example 2, a 20-D myopia was corrected with a PL. The gain in magnification changed from 33% to 58% with nearer objects. The change in vergence at the principal plane of the crystalline lens with objects at near was much higher with the PL compared with the spectacle correction, which implies that the refractive change necessary for focusing objects at near distance is much higher in the PL correction. Even if the predictability of postoperative refraction with PL is comparable or better than in other methods of correcting high or excessive ametropia, the effects of lateral magnification change and accommodation have to be considered to avoid image-size disparities (aniseikonia) and to maintain binocular vision, especially with monocular PL implantation and anisometropia.

Magnification-corrected photodynamic therapy

To present a method for performing photodynamic therapy (PDT) with a constant predictable light fluence based on actual laser spot magnification. A calibrated Gullstrand-type model eye with a scale of half circles in the centre of the artificial fundus was used for this study. The axial length of the model eye was set to different values ranging from 20 to 31 mm, and the actual laser spot magnification of four indirect condensing laser lenses were determined using a PDT laser unit. Equations for determining the actual laser spot magnification were calculated for each laser lens. The total change in laser spot magnification from hyperopia (axial length 20 mm) to myopia (axial length 31 mm) was -20% to +24.8% for Mainster Standard lens (Ocular Instruments Inc, Bellevue, Washington, USA), -15.7% to +27.7% for Mainster Wide Field lens (Ocular Instruments Inc), -16.3% to +33.1% for Volk Transequator lens (Volk Optical Inc, Mentor, Ohio, USA), and -19.2% to +24.4% for Volk PDT Laser lens (Volk Optical Inc). Axial length of the eye has a considerable effect on PDT laser spot magnification when an indirect laser lens is used. By calculating the actual laser spot magnification in conjunction with knowledge of the true greatest linear dimension of the neovascular lesion, the clinician may be able to deliver a constant predictable amount of light fluence to the fundus independent of the axial length of the PDT treating eye.

Objective real-time measurement of instrument myopia in microscopists under different viewing conditions

While instrument myopia is known to occur when microscopes are used, little is known about the accommodation response during microscopy, or about the factors which may alter the magnitude of instrument myopia. In addition, there has been no real-time objective measurement of instrument myopia during the microscopy task. Twenty inexperienced subjects and 10 experienced microscopists (average work experience of 4.8 years (SD 3.2 yr)) with mean age of 24.1 years (SD 2.9 yr) and 31.2 years (SD 2.9 yr) respectively were recruited to the study. Instrument myopia was measured using an infrared photorefractor (PowerRefractor) under different viewing conditions and microscope settings (with different forms of refractive error correction, changes in target quality, changes in eyepiece power settings, changes in magnification and changes in illumination of the target). Instrument myopia was greater in inexperienced (1.98 D (SD 0.91 D)) than in experienced (1.38 D (SD 0.75 D)) microscope users. There was no statistically significant change in the level of instrument myopia under the different viewing conditions or different microscope settings, and there were large individual variations. Other factors may play more of a role in determining the degree of instrument myopia during microscopy than the task variables altered here.

Tilt-series and electron microscope alignment for the correction of the non-perpendicularity of beam and tilt-axis

In electron tomography the sample is tilted in the electron microscope and projections are recorded at different viewing angles. In the correct geometric setting, the tilt-axis of the object under scrutiny is perpendicular to the beam direction. However, we will demonstrate that this does not necessarily apply to all electron microscopes equipped with the default column alignment. The resulting effect is that a conical tilt is performed, which has to be considered in the reconstruction to avoid artifacts and to improve the resolution. A novel solution, with significantly improved convergence properties, will be introduced for calculating the three-dimensional marker model, which is necessary for the alignment of the tilt-series. Thereby, the angle between the beam direction and the tilt-axis is calculated, together with other geometrical distortions, like magnification and rotation changes, and incorporated in the reconstruction. Hereby, artifacts can be eliminated at the image processing basis, and the resolution can be significantly improved at the medium to high range frequencies. Synthetical and real data are used to demonstrate the obstructions caused by this effect and the quality improvement of the reconstructions. Finally, we also present a way to align the hardware of the microscope to correct for the non-perpendicularity between the beam direction and the tilt-axis, which is specifically tailored for tomographic applications.

Mapping Dark Matter with Cosmic Magnification

We develop a new tool to generate statistically precise dark matter maps from the cosmic magnification of galaxies with distance estimates. We show how to overcome the intrinsic clustering problem using the slope of the luminosity function, because magnification changes strongly over the luminosity function, while intrinsic clustering only changes weakly. This may allow precision cosmology beyond most current systematic limitations. The Square Kilometre Array is able to reconstruct the projected matter density map at smoothing scale approximately 10' with S/N > or = 1, at the rate of 200-4000 deg2 per year, depending on the abundance and evolution of 21 cm emitting galaxies. This power of mapping dark matter is comparable to, or even better than, that of cosmic shear from deep optical surveys or 21 cm surveys.

줌 광학계를 이용한 원적외선 열상장비의 설계 및 제작

[ <TEX>$480{\times}6$</TEX> ] 배열 HgCdTe(MCT) 검출기를 사용하는 고성능의 원적외선(LWIR) 줌 열상센서를 개발하였다. 광학계는 대략 190 mm 직경을 갖는 대물 망원경과 광학적으로 잘 정렬된 주사장치로 구성된다 망원경의 줌 비율은 3:1이며 배율의 변환은 2개의 렌즈 그룹을 이동시킴으로써 수행된다. 이동하는 2개의 렌즈 그룹으로 열상장비의 비열화도 함께 수행한다. 비열화 수행을 통해 광범위한 운용온도 범위에서도 시스템의 성능 저하 없이 활용이 가능하다. 한편 개발된 열상장비는 16:9 양상비를 갖는 고화질 텔레비전(HDTV)에 시현도 가능하다. HDTV 형태의 경우 주사장치는 62만 화소까지 영상 시현이 가능하다. 이 기능은 일반적인 TV 시현의 경우보다 성능의 저하 없이 수평 시계각을 넓혀 주는 역할을 한다. 설계 및 제작된 원적외선 열상장비의 고배율에서 최소분해가능온도차(MRTD)를 측정한 결과, 2 cycles/mrad의 공간주파수에서 0.04 K 이하 및 8 cycles/mrad의 공간주파수에서 0.23 K의 우수한 결과를 보였다. A high performance LWIR(long wavelength infra red) zoom thermal imaging sensor using <TEX>$480{\times}6$</TEX> HgCdTe(MCT) linear detector has been developed by ADD Korea. The optical system consists of zoom telescope having large objective about 190 mm diameter and optically well corrected scanning system. The zoom ratio of the telescope is 3: 1 and its magnification change is performed by moving two lens groups. And also these moving groups are used for athermalization of the system. It is certain that the zoom sensor can be used in wide operating temperature range without any degradation of the system performance. Especially, the sensor image can be displayed with the HDTV(high definition television) format of which aspect ratio is 16:9. In case of HDTV format, the scanning system is able to display 620,000 pixels. This function can make wider horizontal field of view without any loss of performance than the normal TV format image. The MRTD(minimum resolvable temperature difference) of the LWIR thermal imaging sensor shows good results below 0.04 K at spatial frequency 2 cycles/mrad and 0.23 K at spatial frequency 8 cycles/mrad at the narrow field of view.

3D roadmap in neuroangiography: technique and clinical interest

We present the first clinical results obtained with a novel technique: the three-dimensional [3D] roadmap. The major difference from the standard 2D digital roadmap technique is that the newly developed 3D roadmap is based on a rotational angiography acquisition technique with the two-dimensional [2D] fluoroscopic image as an overlay. Data required for an accurate superimposition of the previously acquired 3D reconstructed image on the interactively made 2D fluoroscopy image, in real time, are stored in the 3D workstation and constitute the calibration dataset. Both datasets are spatially aligned in real time; thus, the 3D image is accurately superimposed on the 2D fluoroscopic image regardless of any change in C-arm position or magnification. The principal advantage of the described roadmap method is that one contrast injection allows the C-arm to be positioned anywhere in the space and allows alterations in the distance between the x-ray tube and the image intensifier as well as changes in image magnification. In the clinical setting, the 3D roadmap facilitated intravascular neuronavigation with concurrent reduction of procedure time and use of contrast medium.

Digital image correlation for whole field out-of-plane displacement measurement using a single camera

Digital image correlation (DIC) using a single camera has been widely used for in-plane displacement and strain measurement. However, in order to obtain out-of-plane displacement, one should employ stereo vision systems which enable multiple directions detection. In this paper, we develop a simple method for whole field out-of-plane displacement measurement using only one camera. The proposed method employs digital image correlation to calculate an apparent in-plane displacement field which is introduced by magnification change due to an unknown out-of-plane displacement. The unknown out-of-plane displacement is subsequently determined from a pinhole camera model and the apparent in-plane displacement. Experiments conducted on a plate, a cantilever beam and a surface with height variation demonstrate that the method is simple, accurate and suitable for measurement of non-structured objects.

Quantification of the magnification and distortion effects of a pediatric flexible video-bronchoscope

BackgroundFlexible video bronchoscopes, in particular the Olympus BF Type 3C160, are commonly used in pediatric respiratory medicine. There is no data on the magnification and distortion effects of these bronchoscopes yet important clinical decisions are made from the images. The aim of this study was to systematically describe the magnification and distortion of flexible bronchoscope images taken at various distances from the object.MethodsUsing images of known objects and processing these by digital video and computer programs both magnification and distortion scales were derived.ResultsMagnification changes as a linear function between 100 mm (×1) and 10 mm (×9.55) and then as an exponential function between 10 mm and 3 mm (×40) from the object. Magnification depends on the axis of orientation of the object to the optic axis or geometrical axis of the bronchoscope. Magnification also varies across the field of view with the central magnification being 39% greater than at the periphery of the field of view at 15 mm from the object. However, in the paediatric situation the diameter of the orifices is usually less than 10 mm and thus this limits the exposure to these peripheral limits of magnification reduction. Intraclass correlations for measurements and repeatability studies between instruments are very high, r = 0.96. Distortion occurs as both barrel and geometric types but both types are heterogeneous across the field of view. Distortion of geometric type ranges up to 30% at 3 mm from the object but may be as low as 5% depending on the position of the object in relation to the optic axis.ConclusionWe conclude that the optimal working distance range is between 40 and 10 mm from the object. However the clinician should be cognisant of both variations in magnification and distortion in clinical judgements.

Improved depth of field in the scanning electron microscope derived from through‐focus image stacks

The depth of field limit in the scanning electron microscope (SEM) can be overcome by recording stacks of through-focus images (as in conventional and confocal optical microscopy) which are postprocessed to generate an all-in-focus image. Images are recorded under constant electron optical conditions by mechanical Z-axis movement of the sample. This gives rise to a change in magnification through the stack due to the perspective projection of the SEM image. Calculation of the necessary scaling as well as the derivation of best focus information at every patch in the image--and a contour map function derived from the selected patch depths--are incorporated in a new software package (Auto-Montage Pro). The utility of these procedures is demonstrated with examples from the study of human osteoporotic bone, where results show uncoupling of resorption and formation. The procedure can be combined with pseudo-colour coding for the direction of apparent illumination when using backscattered electron (BSE) detectors in contrasting positions.

Magnification-corrected indirect biomicroscopy of the optic nerve head.

Proper use of the new Super VitreoFundus and SuperPupil XL non-contact slit-lamp lenses for clinical disc biometry requires knowledge of their comparative magnification. The optical performance of each fundus lens is described in terms of axial magnification, lens position, and the correction factor p (in degrees per millimeter) using a calibrated Gullstrand-type model eye adjusted for axial ametropia between -12.5 D and +12.6 D. The total change in axial magnification from myopia to hyperopia was -13.3% to +15.6% (Super VitreoFundus lens), and -13.9% to +14.1% (SuperPupil XL lens). When the fundus lens position was altered with respect to the model eye by +/-2 mm under myopic conditions the change in axial magnification was -5.1% to +7.7% (Super VitreoFundus lens), and -6.5% to +9.7% (SuperPupil XL lens). In the hyperopic condition the change was -3.8% to +5.8%, and -4.9% to +7.3%. Both fundus lenses exhibited a linear relationship between p and degree of ametropia of the model eye, while only the Super VitreoFundus lens displayed a constant relationship between p and ametropia of -5 D to +5 D. Using the fundus lens correction factor (p), the clinician may be able to estimate the dimensions of optic nerve head features with sufficient accuracy to allow clinical decisions to be made in the evaluation of patients with diagnosed or suspected glaucoma.

Magnification changes in scanning laser tomography.

It is important when evaluating glaucomatous optic disc progression in longitudinal images that image magnification remains unchanged. We studied the effect of changed lens power on magnification in scanning laser tomography. The relative contribution to magnification of axial length, eye-scanner distance, and image-to-image scaling was also assessed. A simulated optic disc in a model eye was imaged using the Heidelberg Retina Tomograph. Lens power was alterable by exchanging intraocular lenses (IOL) mounted at the lens plane of the eye to mimic changes in the crystalline lens. IOL power of +20.0D and axial length of 21.5 mm was compatible with emmetropia. The optic disc was imaged through IOLs differing in power (+16.0D to +25.0D) but with axial length kept constant. IOL power was then held constant and imaging was repeated for various axial lengths (17.5-23.5 mm). Model eye-scanner distance was varied with each test sequence. The distances between landmarks on the disc was measured before and after contour lines were exported. Image size varied with IOL power and axial length (r > 0.98; P < 0.0001), with the magnification effect of a +1D increase in lens power equivalent to a third the magnification effect of a 1-mm increase in axial length. Magnification tended to increase with myopia (IOL power > +20.0D) and was accentuated by longer eye-scanner distances. Image-to-image scaling corrected some magnification though this varied with ametropia. Changed lens power, axial length, and eye-scanner distance can affect the size of the optic disc in scanning laser tomography images. The exported contour line partly compensates for changed magnification.

Weak field limit of Reissner-Nordström black hole lensing

We study gravitational lensing by a Reissner-Nordstrom (RN) black hole in the weak field limit. We obtain the basic equations for the deflection angle and time delay and find analytical expressions for the positions and amplifications of the primary and secondary images. Due to a net positive charge, the separation between images increases, but no change in the total magnification occurs.

Improved digital SEM of cancellous bone: scanning direction of detection, through focus for in-focus and sample orientation.

Three-dimensional (3D) study of cancellous bone tissue organization is necessary to understand how modelling and remodelling processes regulate bone structure and connectivity. It requires imaging methods that have both sufficient resolution power and width and depth of field. Since clinical imaging methods fall far short of the first requirement, we can only study prepared tissue in isolation from the body. Scanning electron microscopy (SEM) of macerated plane parallel slices is the most productive method, but we meet special technical problems in imaging porous bone because samples need to be relatively thick to maintain both continuity and context. Problems due to charging under the electron beam can be controlled by imaging with only high-energy backscattered electrons (BSE). This gives an important additional benefit that the direction of apparent illumination can be manipulated by positioning the detector, and multiple detector positions can be employed strategically to generate images in which colour is used to help in coding surface morphology. However, we next confront the difficulty of the limited depth of field. This can be improved by taking series of images, moving the sample along the electron optic axis, and combining these to generate a single extended-focus image. SEM imaging geometry gives a change in magnification with change of working distance, and it is shown that this must be corrected for each image of the through-focus sequence. Colour coding the lighting direction and increasing the depth of field are approaches that can be combined, and are well matched to the possibilities offered by communication by digital data projection. Finally, the latter means also offer another powerful technique for 3D representation through the display of through tilt image sequences. The novel routines considered here are generally applicable to all classes of microanatomical SEM sample.

Distortions in panoramic radiographs

Abstract This study was designed to investigate the factors affecting linear distortion in orthopantomography. A test model was constructed with metallic rods positioned to simulate maxillary teeth from the first permanent molar to the lateral incisor. In addition to examining the effects of varying the tilts of the test rods in a mesio-distal or bucco-palatal direction, spatial position changes (sagittal displacement, transverse displacement and horizontal rotation) of the test model were evaluated by determining the magnification changes in the width and length of the test rods. Results showed that significant errors occurred with all variations in magnification when test rods were inclined buccopalatally (p &lt; 0.001) at or exceeding 5 degrees relative to the true perpendicular, and for spatial positioning errors (p &lt; 0.05) at or exceeding ±5 degrees and ±5 mm. Bucco-palatally inclined objects in the lateral incisor-canine region were particularly susceptible to large changes in horizontal magnification. Linear measurements and clinical assessments from panoramic radiographs should therefore be undertaken cautiously. To minimise errors in orthopantomography, it is important to position the patient in the focal trough precisely according to the manufacturer’s specification.

Thresholds for human detection of patient setup errors in digitally reconstructed portal images of prostate fields

Purpose/Objective: Computer-assisted methods to analyze electronic portal images for the presence of treatment setup errors should be studied in controlled experiments prior to use in the clinical setting. Validation experiments using images that contain known errors usually report the smallest errors that can be detected by the image analysis algorithm. This paper offers human error-detection thresholds as one benchmark for evaluating the smallest errors detected by algorithms. Unfortunately reliable data describing human performance is lacking. The most rigorous benchmarks for human performance are obtained under conditions that favor error detection. To establish such benchmarks controlled observer studies were carried out to determine the thresholds of detectability for in-plane and out-of-plane translation and rotation setup errors introduced into digitally reconstructed portal radiographs (DRPRs) of prostate fields. Materials/Methods: Seventeen observers comprising radiation oncologists, radiation oncology residents, physicists, and therapy students participated in a two-alternative forced choice (2AFC) experiment involving 378 DRPRs computed using the National Library of Medicine Visible Human data sets. An observer viewed three images at a time displayed on adjacent computer monitors. Each image triplet included a reference digitally reconstructed radiograph (DRR) displayed on the central monitor, and two DRPRs displayed on the flanking monitors. One DRPR was error free. The other DRPR contained a known in-plane or out-of-plane error in the placement of the treatment field over a target region in the pelvis. The range for each type of error was determined from pilot observer studies based on a Probit model for error detection. The smallest errors approached the limit of human visual capability. The observer was told what kind of error was introduced, and asked to choose the DRPR that contained the error. Observer decisions were recorded and analyzed using Repeated Measures Analysis of Variance (REPM ANOVA). Results: The thresholds of detectability averaged over all observers were approximately 2.5 mm for in-plane translations, 1.6 degrees for in-plane rotations, 1 degree for out-of-plane rotations, and 8% change in magnification for out-of-plane translations along the central axis. When one inexperienced observer is excluded, the average threshold for change in magnification is 5%. Experienced observers tended to perform better but differences between groups were not statistically significant. Thresholds were computed as averages over all observers. Because of the broad range of observer capabilities some detection tasks were too difficult for some observers, leading to missing threshold values in our data analysis. The missing values were excluded from computation of the average thresholds reported above. The effect of the missing values is to bias the average values toward the best human performance. Conclusions: Under favorable conditions humans can detect small errors in setup geometry. The thresholds for error detection reported in this study are believed to represent rigorous but reasonable benchmarks that can be incorporated in studies to evaluate algorithms for computer-assisted detection of setup errors in electronic portal images. Research supported by NCI R01 CA67183.

Thresholds for human detection of patient setup errors in digitally reconstructed portal images of prostate fields

Purpose : Computer-assisted methods to analyze electronic portal images for the presence of treatment setup errors should be studied in controlled experiments before use in the clinical setting. Validation experiments using images that contain known errors usually report the smallest errors that can be detected by the image analysis algorithm. This paper offers human error-detection thresholds as one benchmark for evaluating the smallest errors detected by algorithms. Unfortunately, reliable data are lacking describing human performance. The most rigorous benchmarks for human performance are obtained under conditions that favor error detection. To establish such benchmarks, controlled observer studies were carried out to determine the thresholds of detectability for in-plane and out-of-plane translation and rotation setup errors introduced into digitally reconstructed portal radiographs (DRPRs) of prostate fields. Methods and Materials : Seventeen observers comprising radiation oncologists, radiation oncology residents, physicists, and therapy students participated in a two-alternative forced choice experiment involving 378 DRPRs computed using the National Library of Medicine Visible Human data sets. An observer viewed three images at a time displayed on adjacent computer monitors. Each image triplet included a reference digitally reconstructed radiograph displayed on the central monitor and two DRPRs displayed on the flanking monitors. One DRPR was error free. The other DRPR contained a known in-plane or out-of-plane error in the placement of the treatment field over a target region in the pelvis. The range for each type of error was determined from pilot observer studies based on a Probit model for error detection. The smallest errors approached the limit of human visual capability. The observer was told what kind of error was introduced, and was asked to choose the DRPR that contained the error. Observer decisions were recorded and analyzed using repeated-measures analysis of variance. Results : The thresholds of detectability averaged over all observers were approximately 2.5 mm for in-plane translations, 1.6° for in-plane rotations, 1° for out-of-plane rotations, and 8% change in magnification for out-of-plane translations along the central axis. When one inexperienced observer is excluded, the average threshold for change in magnification is 5%. Experienced observers tended to perform better, but differences between groups were not statistically significant. Thresholds were computed as averages over all observers. Because of the broad range of observer capabilities, some detection tasks were too difficult for some observers, leading to missing threshold values in our data analysis. The missing values were excluded from computation of the average thresholds reported above. The effect of the missing values is to bias the average values toward the best human performance. Conclusions : Under favorable conditions, humans can detect small errors in setup geometry. The thresholds for error detection reported in this study are believed to represent rigorous but reasonable benchmarks that can be incorporated into studies evaluating algorithms for computer-assisted detection of setup errors in electronic portal images.

Practical Considerations in Restoring Images from Phase‐Diverse Speckle Data

ABSTRACTWe discuss practical problems and solutions associated with the “phase‐diverse” speckle (PDS) imaging technique for reconstruction of high‐resolution images from ground‐based telescope data. The PDS method uses an ensemble of short‐exposure images obtained simultaneously from multiple cameras to jointly estimate the object and the sequence of instantaneous phase distortions observed by each camera. Different known static phase aberrations are imposed on each optical channel; the known aberrations then function as constraints in the estimation problem. In this paper, we extend a previously derived model and present new data calibration techniques to compensate for various undesirable effects present in real‐world PDS data. These effects include relative tip‐tilt and image magnification changes between the diversity channels. The extended model and its associated (modified) objective functions lead to a new nonlinear optimization problem. Solution methods, software, and results using real telescope data are discussed.

Evaluation of new x-ray stepper, the XRA

The exposure performance has been evaluated for the new x-ray stepper, the XRA, which is equipped with global alignment and magnification correction systems. Dose uniformity in the exposure field of 3.9%, stage accuracy of less than 20 nm, and good linearity and stability between the magnification change and applied force were obtained. For the 100 nm node, both critical dimension (CD) control of 10 nm and overlay accuracy of less than 30 nm were obtained using two 4 Gbit masks of the gate and contact hole by the double exposure method. Possible improvements of the dose uniformity and mask pattern CD will result in more accurate CD control. By compensating for the alignment offset, overlay accuracy of 23 nm for the 70 nm node is also expected.

The effect of axial length on laser spot size and laser irradiance.

To determine the effect of the axial length of the eye on laser spot size and irradiance. Experimental study using a calibrated Gullstrand-type model eye. The model eye, which was fitted with a scale of half circles in the center of the artificial fundus, was first examined using 2 different fundus imaging systems, then with a setup of a slitlamp, 2 indirect condensing laser lenses, and a laser unit with a spot size of up to 7 mm. The axial length of the model eye was set to different values ranging from 20 to 31 mm, and the magnifications of the fundus imaging systems and the laser lenses were calculated and compared for a treatment spot with a diameter of 4 mm. The laser irradiance for treating the spot at different axial lengths was also recorded. Whereas the magnification of a fundus imaging system is inversely related to the axial length, the laser spot size is directly related to axial length when using indirect condensing laser lenses. Therefore, the changes of magnification produced by axial ametropia are mostly compensated, so that the intended size of the treatment spot is obtained even in eyes with a high axial ametropia. The laser irradiance, on the other hand, has a significant variation for the observed range of the axial length. Axial length has a significant effect on laser spot size and laser irradiance. The effect of axial length on laser spot size and laser irradiance may be ignored when administering photodynamic therapy with verteporfin but has to be considered for transpupillary thermal treatment of choroidal neovascular lesions.