Scheimpflug photographic imaging following implantation of anterior and posterior chamber phakic intraocular lenses: preliminary results

BACKGROUND: For the correction of refractive errors lenticular procedures are increasingly used in addition to corneal refractive surgery. One of those techniques is the implantation of intraocular lenses into phakic eyes (pIOL). Due to the close neighborhood of the implant to delicate intraocular structures, exact positioning and high postoperative stability are required. Scheimpflug photography has been shown to be a suitable instrument for the biometry of the anterior eye segment and the examination of IOL position. PATIENTS AND METHODS: Four anterior chamber phakic IOLs (pIOLs) (Bausch & Lomb NuVita) and 7 posterior chamber pIOLs (Staar ICL) were examined 1 week, 1 month and 3-6 months following implantation. At each examination 1 Scheimpflug slit image and 1 infrared retroillumination image were taken using the anterior eye segment analysis system EAS-1000 (Nidek Co., Gamagori, Japan). Evaluation of the images was performed with a personal computer and the software provided by the manufacturer. The distance of the pIOL to cornea and human lens was calculated and incidence and amount of pIOL rotation around the optical axis and potential crystalline lens opacification were assessed. RESULTS: The distance between the anterior chamber pIOL and the cornea 1 week after implantation was 1.61 +/- 0.10 mm. The distances between the myopic posterior chamber pIOL and the human lens were 0.34 +/- 0.11 mm and between the hyperopic posterior chamber pIOL and the human lens 0.26 and 0.29 mm, respectively. The values were constant over a period of 3-6 months. The pIOL showed no movement or change of position around the optical axis. There was no detectable cataract formation in the human lens. CONCLUSIONS: All implanted phakic anterior and posterior chamber IOLs showed a stable position in the eye within the observation period. Scheimpflug photography is proved to be a useful technique for the postoperative evaluation of the positioning of phakic IOLs.     

Image analysis and Sheimpflug photography of anterior segment of the eye--a review

BACKGROUND: Light scattering properties of the cornea and lens change in relation to age. This process is influenced by noxious factors which may induce the formation of cataracts. Four different camera types based on the Scheimpflug principle have been developed for documentation and evaluation of light scattering in the eye. Topcon SL-45. Zeiss SLC, Oxford CASE 2000, Nidek EAS 1000. Only the SL-45 and EAS 1000, however, have found a wider application in clinical and experimental studies. MATERIAL AND METHODS: Documentation of the eye with a Scheimpflug system is performed in a dark room after mydriasis induction. The rotating axis of the camera is aligned to the optical axis of the eye with fixation devices. Four meridians have been found appropriate for routine documentation. Image analysis is based on peak height and distance evaluation of 2 layers in the cornea and 10 layers in the lens. Standardization devices allow correction of technical differences in the recording process. RESULTS: Evaluation of the ageing properties of the lens has evidenced typical density developments for each individual layer, the cortex increasing in density earlier than the nucleus. Cataract classification using a Scheimpflug camera provides an objective characterization of cataract type and progression. The outcome of surgical procedures changing the refractive power of the eye can be evaluated with a Scheimpflug camera as well. Its application in studies dealing with the ocular effects of Quinolones and HMG-CoA-reductase inhibitors, has demonstrated that Scheimpflug photography is the method of choice for establishment of a safety profile for a new drug. CONCLUSIONS: Scheimpflug photography has proven to be ideal for objective documentation of the anterior eye segment in human and animal eyes, although both documentation and image analysis demand technical expertise to be reproducible.     

Age-related light scattering in rat lenses observed in a 2-year inhalation toxicity study

Normal light scattering in the eye is determined primarily by the size of alpha-crystalline molecules. Ageing effects appear as an increase in normal lens light scattering in distinct layers. Subliminal effects of toxins on lens transparency can also cause an increase in light scattering due to protein molecule aggregation before visible opacities appear. Scheimpflug photography of the anterior eye segment with subsequent densitometric image analysis is the method of choice to evaluate such effects. To gain more insight into normal ageing and the potential effects of complex aerosols, a subset of Wistar rats (both sexes) belonging to a larger chronic inhalation toxicity study was documented at baseline and after 2 years with a Topcon SL-45 Scheimpflug camera on Kodak T(max) 400 ISO film. The recording procedure, film development, and microdensitometric image analysis were all performed according to standard protocol. A second group from the same study was documented at the start and after 5 months of a 6-month posttreatment period immediately following the inhalation period. Rats were nose-only exposed for 6 h/day, 7 days/week, for 2 years to low (3 microg/l) or high (10 microg/l) concentrations of room-aged cigarette sidestream smoke or diesel engine exhaust. Control animals were exposed to filtered fresh air. At the baseline examination, there were no relevant differences between groups with respect to corneal density or density of defined layers in the lens capsule (1), epithelium and superficial cortex (2), deep cortex (3), supranuclear layer (4) and nucleus (5). At the 2-year examination, mean corneal density was significantly lower in females than in males. This same trend, although not significant, was also found in most layers of the lens. The most prominent differences in density over time were measured in lens layers 3 and 4, but neither corneal density nor lenticular density showed any consistent treatment-related effects in any of the layers. The data from the posttreatment period confirmed the results of the 2-year study. The depth of the anterior chamber increased constantly over the 2.5-year period, but again, treatment did not affect this. This study provided completely new data on age-related light scattering in the cornea and in defined layers of the lens in long-term toxicity studies in Wistar rats.     

人和动物眼前段的Scheimpflug照相及计算机图像分析

目的 应用Ｓｃｈｅｉｍｐｆｌｕｇ照相技术在活体内对人眼和几种动物眼的眼前部图像进行测量分析。方法 应用眼前部图像分析系统（ＥＡＳ－１０００,日本Ｎｉｄｅｋ）,对正常成人以及豚鼠、大鼠、兔和 眼前部照相并作图像分析。结果 用ＥＡＳ－１０００系统能在人眼、豚鼠和大姒眼得到清晰的眼前部图像,而在兔和猫眼仅得到前半部晶状体以前的图像。测量并比较分析了各种眼球的角膜及晶状体的多个生理参数。结论 Ｓｃｈｅｉｍ     

Ten-year follow-up of a ciliary sulcus-fixated silicone phakic posterior chamber intraocular lens

In 1992, a ciliary sulcus-fixated, silicone, phakic posterior chamber intraocular lens (PPC IOL) (Adatomed, Fyodorov type) was implanted in both eyes of a 42-year-old white woman to correct high myopia (right eye, -17.0 diopters [D]; left eye, -11.5 D). In the right eye, localized cortical opacification was present in the anterior part of the natural lens preoperatively but did not progress during a 10-year follow-up period. With Scheimpflug photography, it was possible to detect a space between the natural lens and the IOL that was not evident on slitlamp examination. Maintenance of space between an IOL and the natural lens appears to be an important factor in preventing cataract formation after PPC IOL implantation.     

Effect of vitamin E eye drops on naphthalene-induced cataract in rats.

The effect of vitamin E acetate (VEA) eye drops on naphthalene-induced cataract in rats was investigated by Scheimpflug image analysis. The control group was administered only naphthalene (1 g/kg), while the other group was additionally given 1% VEA eye drops into both eyes 5 times a day every day for 9 weeks from the start of naphthalene treatment. During those 9 weeks, the changes of the crystalline lens were documented by an anterior eye segment analysis system (EAS-1000, NIDEK) once a week in mydriasis (Mydrin-P, Santen Pharmaceutical Co., Ltd.). The characteristic density values of the anterior deeper cortex regions were measured. The light scattering intensity of lenses from VEA eye drop-treated animals was significantly lower than that of animals without VEA treatment. This difference was found 1 week, 4 weeks, and from 7 to 9 weeks after the start of naphthalene application. VEA eye drops may have the potential to delay the progression of naphthalene-induced cataract in rats.     

The shape of the aging human lens: curvature, equivalent refractive index and the lens paradox

Scheimpflug slit images of the crystalline lens are distorted due to the refracting properties of the cornea and because they are obliquely viewed. We measured the aspheric curvature of the lens of 102 subjects ranging in age between 16 and 65 years and applied correction for these distortions. The procedure was validated by measuring an artificial eye and pseudophakic patients with intraocular lenses of known dimensions. Compared to previous studies using Scheimpflug photography, the decrease of the radius of the anterior lens surface with age was smaller, and the absolute value for the radius of the anterior and posterior lens surface was significantly smaller. A slight decrease of the posterior lens radius with age could be demonstrated. Generally, front and back surfaces were hyperbolic. Axial length was measured of 42 subjects enabling calculation of the equivalent refractive index of the lens, which showed a small, but highly significant decrease with age. These new findings explain the lens paradox and may serve as a basis for modelling the refractive properties of the lens.     

Cataract epidemiological study: Correlation of cataract morphology with health status

Data on 288 cataract patients were collected with respect to sex, age, disease status, drug intake, and blood chemistry. Eight different types of lens opacities could be discriminated using slit-lamp examination, Scheimpflug photography of the anterior eye segment, and microdensitometric image analysis of the film negatives. The statistical method of fitting log linear models was used to investigate the association between cataract morphology and other variables. The following variables were shown to be important and to contribute independently to the differentiation of cataract types: cholelithiasis, pneumonia, heart insufficiency, allergy, and age.     

Anterior capsule dyes and labeled viscoelastic solutions to enhance contrast in EAS-1000 Scheimpflug images

PURPOSE: To enhance contrast in images produced by the EAS-1000 to facilitate evaluation of the rheological properties of viscoelastic substances during simulated cataract surgery. SETTING: Department of Preclinical Ophthalmology, Scientific Affairs, Pharmacia AB, Uppsala, Sweden. METHODS: Cataract surgery was performed in 200 fresh porcine cadaver eyes and documented by EAS-1000 Scheimpflug photography. The light scattering caused by anterior capsule dyes, labeled irrigation solutions, and labeled viscoelastic solutions was statistically analyzed in the images. RESULTS: Visualization by light scattering was significantly enhanced by a fluorescein labeled viscoelastic solution and by an eosin-Y- or phloxine-B-dyed capsule (P < .05). A side effect of eosin Y and phloxine B was that the capsule became fragile, making it difficult to perform a continuous curvilinear capsulorhexis. CONCLUSIONS: Fluorescein-labeled viscoelastic solutions are recommended to enhance contrast in the images when retention capacity is evaluated. Light scattering from capsule dyeing facilitated anterior chamber depth measurements in the images.     

Estimation of anterior nucleus of lens by Scheimpflug image before and after pupil dilatation

PURPOSE: To compare the accuracy of lens transparency evaluations by Scheimpflug image in the anterior nucleus of the lens before and after pupil dilatation. METHODS: Scheimpflug lens images were recorded in 70 eyes of 38 subjects (age: 28-75 years) before and after pupil dilatation, and light scattering intensity measurements before and after dilatation were compared. RESULTS: There was a significant positive correlation between the light scattering intensity before and after dilatation at the anterior cortex, anterior nucleus, and central clear zone of the lens (r > 0.9, P <.0001). CONCLUSIONS: It is possible to estimate the transparency in the anterior nucleus of the lens from the Scheimpflug image without pupil dilatation. If nuclear type cataracts are regarded as a structural marker of aging in epidemiological studies, measuring the light scattering intensity in the anterior nucleus of the lens without dilatation seems to be a safe, useful, and quantitative method.     

Posterior capsule rupture following closed globe injury: Scheimpflug imaging, pathogenesis, and management

PURPOSE. To report the Scheimpflug and clinical findings in a case of pediatric posterior capsule rupture due to blunt ocular trauma. METHODS. Interventional case report. Analysis of Scheimpflug findings and review of literature. RESULTS. An 11-year-old boy presented 2 days after blunt trauma to the left eye with a slingshot. On examination his best-corrected visual acuity (BCVA) was 20/20 in the right eye and 20/400 in the left. Slitlamp examination (left eye) revealed a Vossius ring, traumatic cataract, and traumatic posterior capsular rupture (TPCR).The contour of the posterior bulge corresponded to the edges of the TPCR. Scheimpflug imaging (Pentacam 70700: Oculus, Wetzlar, Germany) confirmed traumatic cataract in region of TPCR evidenced by increased lens density at cortex-vitreous interface, absence of vitreous prolapse into the anterior chamber, and the amount of residual nucleus. The extent of the TPCR in the greatest and least dimensions was documented before and after intraocular lens (IOL) implantation. Intraoperatively, TPCR was evident and phacoemulsification with IOL implant was performed. Postoperatively, his BCVA improved to 20/20 in the left eye with a well-centered in-thebag IOL as found on slit lamp and Scheimpflug images. CONCLUSIONS. This report highlights the use of Scheimpflug imaging in isolated posterior capsule rupture following closed globe injury, to visualize and quantify the size of posterior capsule rupture and its role in management.     

Unilateral electric cataract: Scheimpflug imaging and review of the literature

A 22-year-old man presented with diminution of vision in the left eye 1 month after sustaining an injury from a high-voltage electric current to the left side of his head. Slitlamp examination and Scheimpflug imaging confirmed the typical anterior subcapsular lenticular opacities in the left eye and also documented early anterior subcapsular vacuoles in the right eye. Based on history, the electric shock wound, and the typical appearance of the opacities, an electric cataract was diagnosed. The difference in lens density between the 2 eyes was also documented. The best corrected visual acuity (BCVA) was 20/20 in the right eye and counting fingers at 1 foot in the left eye. Phacoaspiration and posterior chamber intraocular lens implantation were performed in the left eye. Postoperatively, the BCVA improved to 20/20. The developmental mechanisms of these opacities after exposure to an electric current and the role of Scheimpflug imaging in assessing the earliest subclinical manifestations of electric cataract injuries are discussed.     

Photography of the anterior eye segment according to Scheimpflug's principle: options and limitations – a review

Scheimpflug photography and densitometric image analysis are very precise techniques for light scattering measurement and biometry in the anterior segment of the eye. They provide reproducible data on the characteristics of the anterior eye segment in clinical and experimental studies and the set of data obtained allows discrimination of light scattering changes because of ageing, disease or toxic effects. The techniques can also be used to determine no-effect levels or maximally tolerable dosages of physical and chemical noxious factors. Several Scheimpflug cameras have been marketed, but the only cameras commercially available today are the Nidek EAS 1000 and the Oculus Pentacam. This review outlines the development of the technique and its introduction into ophthalmology. Furthermore, the application of the technique in clinical and experimental ophthalmology as well as in ocular toxicology are presented and discussed.     

Light scattering observed on the surface of acrylic intraocular lenses ten years after implantation

PURPOSE: To report the long-term status of acrylic intra-ocular lenses. CASES: We describe two cases of increased light scattering on the surface of acrylic intraocular lenses ten years after implantation. The scattering was non-symptomatic and visual acuity was normal. Biomicroscopy and a Scheimpflug photography system showed that the scattering apparently derived from the anterior surface of the lens, but no deposit or membranous structure was observed on the lens surface. CONCLUSION: Surface scattering from acrylic intra-ocular lenses is a new finding in long-term observations. A possible etiology may be structural changes of the internal polymer.     

Einsatzmöglichkeiten der Scheimpflug-Technologie in der Kataraktchirurgie

Background

Since its first use in geography 100 years ago Scheimpflug photography has undergone much refinement making it a standard technique in anterior segment diagnostics and even surgical therapy. This review presents the perioperative applications of Scheimpflug photography in cataract and refractive lens surgery.

Objectives

Possible perioperative applications of Scheimpflug photography in cataract surgery and refractive lens surgery.

Methods

Selective review of the literature and personal experiences.

Results

In recent years there have been numerous new applications for Scheimpflug photography, with its main use in preoperative diagnostics and surgical planning. There are also useful applications for intraoperative visualization and postoperative counseling.

Conclusion

Multifunctional devices which enable a variety of further examinations besides Scheimpflug technology alone make the use of this technology possible and reasonable even in hospitals and practices without a focus on refractive surgery.     

Cataract classification

Opacifications of the eye lens — generally defined as cataracts — develop in various different parts of the lens. Therefore, one has to differentiate the types of opacities. For epidemiological studies it is prerequisite to classify the cataracts according to their localization within the lens as well as to the size and intensity of the opacified area. Two approaches have been used in the past: 1) subjective methods of lens observation (based on slit lamp microscopy) and 2) objective methods with measurements of lens transparency or lens opacity respectively based on slit image documentation according to the Scheimpflug principle combined with the retroillumination technique. With ageing, the light transparency of the lens is subjected to considerable changes. Even without the formation of an opacity the transmission of the wavelengths in the UV-B/UV-A and the visible range is diminished. The single lens layers are affected by this phenomenon to different degrees. These changes which might also indicate an early stage of ‘cataract formation’ cannot be discerned by subjective methods. The densitometric image analysis of Scheimpflug slit images, however, allows the exact measurement of the light scatter in the single lens layers and enables the early recognition of disturbances in transparency which is of crucial importance particularly in cataract epidemiology. In view of our present knowledge the evaluation of risk factors which might be of importance in multifactorial cataract processes will hardly be possible by carrying out prevalence and/or incidence studies involving a single examination of the population. In this case follow-up studies (cohort studies) with repeated examinations are prerequisite. The ‘objective methods’ for classification alone are able to ensure the necessary reproducibility and the possibility to measure transparency changes in the lensbefore visible (and therefore subjectively recognizable) opacifications occured. The methodical procedure with respect to an epidemiological study on the involvement of UV-B radiation in the processes of cataract formation in man requires the application of objective methods for cataract classification.     

Automated biometry and densitography of anterior segment of the eye

Twenty-eight fresh donor eyes (Georgia Lions Eye Bank), ranging in age from 4 months to 87 years, were utilized for an in vitro study to determine the feasibility of obtaining accurate AC diameter measurements with our Scheimpflug UV-visible slit lamp densitography apparatus. The in vivo study was performed on 16 hybrid monkeys (of varying age). These data were within 0.1 mm of measurements obtained with a modified paracentesis needle specially designed to obtain such measurements (sensitivity within 0.01 mm). The results of the foregoing study demonstrate that Scheimpflug slit lamp photographic analysis can measure the AC diameter accurately without entering the globe surgically. This will enable the surgeon to determine the AC diameter and order an anterior chamber IOL of a specified size prior to surgery. We have devised an automated program to analyze the negatives and provide direct AC diameter measurements. In addition, this program can provide other data including: (1) radius of curvature of anterior and posterior cornea and corneal thickness; (2) depth of anterior chamber; (3) radius of curvature of anterior and posterior lens surfaces and lens thickness; and (4) densitographic analysis of cornea and lens with UV as well as visible light, thus providing fluorescence data for these two tissues as well.     

Lens changes following pneumatic retinopexy: preliminary results of linear densitometry image analysis of Scheimpflug photographs two months after operation

The small degree of morbidity and a better postoperative visual acuity are the advantages of pneumatic retinopexy in comparison to encircling procedures in the treatment of retinal detachment. The injection of air or gas into the vitreous cavity can theoretically induce a cataract postoperatively. Two months after pneumatic retinopexy (SF6-gas) Scheimpflug photography and microdensitometric evaluation of the negative were performed on 22 pairs of phacic eyes showing changes in the transparency of the lens. The deterioration of transparency in the operated eye was small but higher than that of the non-operated eye. Due to the short follow up period no prognosis is possible as to the future lens transparency changes.     

Intraocular light scatter,reflections, fluorescence and absorption: what we see in the slit lamp

Purpose

Much knowledge has been collected over the past 20 years about light scattering in the eye‐ in particular in the eye lens‐ and its visual effect, called straylight. It is the purpose of this review to discuss how these insights can be applied to understanding the slit lamp image.

Results

The slit lamp image mainly results from back scattering, whereas the effects on vision result mainly from forward scatter. Forward scatter originates from particles of about wavelength size distributed throughout the lens. Most of the slit lamp image originates from small particle scatter (Rayleigh scatter). For a population of middle aged lenses it will be shown that both these scatter components remove around 10% of the light from the direct beam. For slit lamp observation close to the reflection angles, zones of discontinuity (Wasserspalten) at anterior and posterior parts of the lens show up as rough surface reflections. All these light scatter effects increase with age, but the correlations with age, and also between the different components, are weak. For retro‐illumination imaging it will be argued that the density or opacity seen in areas of cortical or posterior subcapsular cataract show up because of light scattering, not because of light loss.

Notes

(1) Light scatter must not be confused with aberrations. Light penetrating the eye is divided into two parts: a relatively small part is scattered, and removed from the direct beam. Most of the light is not scattered, but continues as the direct beam. This non‐scattered part is the basis for functional imaging, but its quality is under the control of aberrations. Aberrations deflect light mainly over small angles (<1°), whereas light scatter is important because of the straylight effects over large angles (>1°), causing problems like glare and hazy vision. (2) The slit lamp image in older lenses and nuclear cataract is strongly influenced by absorption. However, this effect is greatly exaggerated by the light path lengths concerned. This obviates proper judgement of the functional importance of absorption, and hinders the appreciation of the Rayleigh nature of what is seen in the slit lamp image.     

Image analysis and glare sensitivity in human age‐related cataracts

Background: A new glare disability test and a diagnostic instrument, the Halometer, were proposed for measuring intraocular light scattering in the presence of human cataracts. The objectives of this work were to introduce new methods of computer‐generated analysis of lens images and a glare disability test to validate the use of two new tests to measure the severity of cataract and to document and quantify changes in lens clarity at diagnosis in a group of patients with age‐related cataract with minimal to advanced opacities. Methods: The authors followed 28 patients (46 eyes) with an average age of 66.9 ± 6 years. Tests included ophthalmoscopy, visual acuity, the halometer glare disability test, stereocinematographic slit‐image and retro‐illumination photography with subsequent interactive digital image analysis and three‐dimensional (3‐D) computer graphics of the areas of lens light scattering/absorbing. Results: The intra‐reader reproducibility of measuring techniques for cataractous changes was good. The Halometer instrument measures the angular distance from the glare source from which a specific target can be recognised. The source and the target are in the same vertical and tangential planes and to measure the angular distribution of the glare light, it is necessary to measure the incident light angle between the source and the target, by measuring the distance between the source and the target. The clinical Halometry readings assessed the index of the forward scattered light that reaches the retina and produces a veiling luminance (glare). The glare sensitivity score was determined from the angle of the glare source using both red and green optotypes, so that the effects of light absorption were separated from those of light scatter. Discussion: The interactive and automated computerised system discriminated the photographic image features of the back light‐scattering/absorb centres within different grey thresholds and documented objective lens findings such as optical density, areas of equidensities, geometric surfaces, opacity grading. Digital image analysis gave a topographic and 3‐D assembling and visualisation for nuclear, cortical and posterior subcapsular opacities in human lenses revealed from the optical scanning tomographic study of the anterior eye segment. The results indicate on agreement between clinical findings and applied quantitative techniques of analysis. This system has the potential to be a useful objective clinical assessment of cataract.