Comparison of Partial Coherence Interferometers: ACMaster Versus Laboratory Prototype

PURPOSE

To evaluate anterior segment biometry using the ACMaster (Carl Zeiss Meditec AG, Jena, Germany) in regard to precision of measurement and clinical performance compared to the original laboratory prototype of the partial coherence interferometry technique.

METHODS

Ten phakic (20 eyes) and 27 pseudophakic (44 eyes) patients were included in this study. Anterior segment biometry of phakic and pseudophakic study eyes was performed using the ACMaster and the laboratory prototype of the partial coherence interferometry technique. The ACMaster is a commercially available device based on the partial coherence interferometry technique, which provides high precision anterior segment measurements in a quick and user-friendly fashion. Examination included measurement of central corneal thickness, anterior chamber depth, and lens thickness, the latter only in the phakic eyes.

RESULTS

The consistency of anterior segment measurements performed with both units was excellent in phakic as well as in pseudophakic eyes. In pseudophakic eyes, the measurement of anterior chamber thickness and lens thickness with the ACMaster produced several (typical) measurement artifacts in some cases, which partially aggravated the identification of the A-scan peak representing the anterior intraocular lens surface.

CONCLUSIONS

The ACMaster is a user-friendly device that enables axial anterior segment biometry using the partial coherence interferometry technique with a reproducibility similar to that of the original laboratory prototype.

Wavefront Analyzers Induce Instrument Myopia

PURPOSE

To assess the accuracy of three wavefront analyzers versus a validated binocular open-view autorefractor in determining refractive error in non-cycloplegic eyes.

METHODS

Eighty eyes were examined using the SRW-5000 open-view infrared autorefractor and, in randomized sequence, three wavefront analyzers: 1) OPD-Scan (NIDEK, Gamagori, Japan), 2) WASCA (Zeiss/Meditec, Jena, Germany), and 3) Allegretto (WaveLight Laser Technologies AG, Erlangen, Germany). Subjects were healthy adults (19 men and 21 women; mean age: 20.8 +/- 2.5 years). Refractive errors ranged from +1.5 to -9.75 diopters (D) (mean: +1.83 +/- 2.74 D) with up to 1.75 D cylinder (mean: 0.58 +/- 0.53 D). Three readings were collected per instrument by one examiner without anticholinergic agents. Refraction values were decomposed into vector components for analysis, resulting in mean spherical equivalent refraction (M) and J0 and J45 being vectors of cylindrical power at 0 degrees and 45 degrees, respectively.

RESULTS

Positive correlation was observed between wavefront analyzers and the SRW-5000 for spherical equivalent refraction (OPD-Scan, r=0.959, P<.001; WASCA, r=0.981, P<.001; Allegretto, r=0.942, P<.001). Mean differences and limits of agreement showed more negative spherical equivalent refraction with wavefront analyzers (OPD-Scan, 0.406 +/- 0.768 D [range: 0.235 to 0.580 D] [P<.001]; WASCA, 0.511 +/- 0.550 D [range: 0.390 to 0.634 D] [P<.001]; and Allegretto, 0.434 +/- 0.904 D [range: 0.233 to 0.635 D] [P<.001]). A second analysis eliminating outliers showed the same trend but lower differences: OPD-Scan (n=75), 0.24 +/- 0.41 D (range: 0.15 to 0.34 D) (P<.001); WASCA (n=78), 0.46 +/- 0.47 D (range: 0.36 to 0.57 D) (P<.001); and Allegretto (n=77), 0.30 +/- 0.62 D (range: 0.16 to 0.44 D) (P<.001). No statistically significant differences were noted for J0 and J45.

CONCLUSIONS

Wavefront analyzer refraction resulted in 0.30 D more myopia compared to SRW-5000 refraction in eyes without cycloplegia. This is the result of the accommodation excess attributable to instrument myopia. For the relatively low degrees of astigmatism in this study (<2.0 D), good agreement was noted between wavefront analyzers and the SRW-5000.

Comparison Between Newly Developed Scanning Peripheral Anterior Chamber Depth Analyzer and Conventional Methods of Evaluating Anterior Chamber Configuration

PURPOSE

To compare the newly developed scanning peripheral anterior chamber depth analyzer (SPAC) with the Van Herick technique, the Shaffer grading system, and ultrasound biomicroscopy (UBM), in terms of accuracy of measurement of peripheral anterior chamber depth (ACD).

METHODS

The subjects were well-controlled glaucoma patients who were being treated at the University of Yamanashi Hospital. Ten eyes from each of the 4 groups classified as Shaffer grades 1 to 4 were evaluated by SPAC, the Van Herick technique, and UBM. All measurements were performed independently on the temporal side in a masked fashion. SPAC evaluated ACD consecutively from the pupil center to the limbus at 0.4 mm intervals. UBM measurements were carried out at a depth of 500 mum (angle-opening distance 500) from the scleral spur. A dummy eye was used for evaluating SPAC measurement accuracy.

RESULTS

The results of SPAC measurement were well correlated with those of the Van Herick technique and the Shaffer grading system. The SPAC measurement results were also significantly correlated with angle-opening distance 500. The correlation coefficients at distances of 2, 4, 4.8, and 5.6 mm from the pupil center were r=0.68, 0.69, 0.69, and 0.61, respectively, and the P values of all the correlations were less than 0.0001. Study of the dummy eye revealed that SPAC has high accuracy for measuring ACD and that the coefficient variances were less than 1.0% at all measured points.

CONCLUSIONS

The results of SPAC measurement correlate well with those of the conventional methods.

Comparison of polarimetric retinal nerve fiber analyzer parameters for a single high quality image and the mean image from three high quality images

BACKGROUND

To find the correlations and differences between the nerve fiber layer parameters of a GDx (polarimetric retinal nerve fiber analyzer) in single high quality images and those in the mean image from three high quality images.

METHODS

The results of scanning laser polarimetry were selected from 63 eyes of 63 patients (31 male and 32 female). Complete ophthalmic examinations included slit-lamp biomicroscopy, dilated pupil for vitreous and ocular fundus examination, applanation tonometry, and subjective or objective refraction. There were no significant ophthalmic disorders other than glaucoma and mild lens opacity. Nerve fiber layer thickness of each eye was measured with GDx and at least three high quality images (passing the software's quality criteria) were obtained. The best of these three high quality images was selected as a single high quality image (Group One). The mean image (Group Two) was calculated from the same three high quality images.

RESULTS

We found that there was a high correlation in all nerve fiber layer parameters between Group One and Group Two. There was no significant difference in the seven relative values of nerve fiber layer parameters (Number, Ellipse Modulation, Symmetry, Superior Ratio, Inferior Ratio, Superior/Nasal and Maximal Modulation) between Group One and Group Two. Group One had significantly higher values compared with Group Two in the other seven absolute values of nerve fiber layer parameters (Average Thickness, Ellipse Average, Superior Average, Inferior Average, Superior Integral, Superior Maximal and Inferior Maximal).

CONCLUSION

It is reasonable to take a mean image from three good quality images from a cooperative patient. If only one high quality image can be obtained in repeated acquisition of GDx, the seven relative values of nerve fiber layer parameters in this high quality image can be used as a base-line image for detecting retinal nerve fiber layer defects and for determining changes of retinal nerve fiber layer thickness in sequential images of GDx.

Issues in quantifying atrophic macular disease using retinal autofluorescence

PURPOSE

To demonstrate the potential and limits of autofluorescence imaging in identifying and delineating areas of atrophy.

METHODS

Fundus photographs and infrared scanning laser ophthalmoscope (SLO) imaging, SLO macular perimetry, and SLO autofluorescence imaging results were compared for two patients with geographic atrophy (GA) from age-related macular degeneration, one patient with pigmentary alteration of the retina, and two patients with Stargardt disease. The main outcome measure in this case series was the presence of reduced autofluorescence.

RESULTS

Drusen may become undetectable during autofluorescence imaging for some patients, allowing simple identification of areas of GA with areas of reduced autofluorescence. In other patients, drusen themselves have decreased autofluorescence, despite having intact retinal function in the retina overlying them. Some patients may have areas of reduced autofluorescence that persist for many years, without evidence of the development of atrophy. In Stargardt disease, decreased autofluorescence can easily detect and delineate areas of scotoma. Areas with mottled autofluorescence may have overlying function, but the function may not be adequate to support a fixation locus in that area.

CONCLUSIONS

Using decreased autofluorescence to delineate areas of atrophy may be helpful in atrophic macular disorders. For GA, correlation with fundus photographs or macular perimetry findings may be necessary to differentiate between drusen and atrophy. For Stargardt disease, the nature of areas of decreased autofluorescence may help explain visual function of those areas.

Cellular retention on diagnostic contact lenses: an evaluation of current cleaning protocol

AIMS

To compare cellular contamination of diagnostic contact lenses after two different cleaning methods.

METHODS

Twenty-five used diagnostic contact lenses were cleaned by two different methods and the material retained on their contact surface examined for cells. Two diagnostic contact lenses were examined using electron microscopy and surface debris was subjected to x-ray photoelectron spectroscopy.

RESULTS

Significantly more cells were present on used lenses compared with controls (P<0.001). There was no significant difference in total cell count between the lenses subjected to the two cleaning strategies but the lenses simply wiped clean retained marginally more nucleated cells than controls (P=0.039). Electron microscopy showed the majority of the debris on or close to the rim of the lens. X-ray photoelectron spectroscopy confirmed the presence of proteinaceous material.

CONCLUSIONS

Regardless of cleaning method, significant cellular debris is retained on the surface of diagnostic contact lenses after use.

The use of information technologies for diagnosis in ophthalmology

In 2003, a health IT programme for clinical decision support started in Lithuania. An initial goal was to create databases for ophthalmology images and to develop processing algorithms to extract diagnostically valuable information from images. We have investigated how vectors, consisting of the parameters derived from fundus images, are distributed and whether they form specific groups. When analysing the multidimensional patient data vectors, comprising all the 27 image parameters, it was impossible to separate the healthy eyes from the diseased ones. However, it was possible to simplify the system by eliminating redundant parameters and introducing new ones that represent a subset of parameters from the initial group. Thus it may prove possible to identify glaucoma using this system of parameters.

[Clinical analysis of measuring corneal thickness with non-contact method]

OBJECTIVE

To compare accuracy of the Pentacam with A-ultrasonoscope in the measurement of central corneal thickness.

METHODS

According to the degree of myopia, 107 myopic patients (211 eyes) were divided into four groups. The central corneal thickness was measured with the Pentacam system and A-ultrasonoscope. The results were compared statistically and the differences between these two methods were analyzed.

RESULTS

Mean values of central corneal thickness measured by the Pentacam system and A-ultrasonoscope was (535.58 +/- 36.34) microm and (536.73 +/- 37.18) microm, respectively. There was no difference in the results obtained by these two methods in each myopia group (P > 0.05). The 95% limits of agreement were (-1.88, -0.42).

CONCLUSIONS

The data shows that the results obtained by Pentacam system do not have significant difference as compared with that from the A-ultrasonoscope. The Pentacam system can provide precise results and has the advantage of simplicity and non-contact. Therefore, it would be a promising instrument for the evaluation of central corneal thickness before the cornea refractive surgery.

Reproducibility of ultrasound pachymetry using the Sonogage Corneo-Gage Plus 2

PURPOSE

The aim of this study was to determine the reproducibility of measurements made using the Sonogage Corneo-Gage Plus 2 (Cleveland, Ohio) ultrasound pachymeter of total corneal and corneal epithelial thickness in 5 different regions of the cornea.

METHODS

Twenty-seven subjects at the New England College of Optometry (NECO) and 20 subjects at the Southern College of Optometry (SCO) were enrolled in this study. Measurements were taken of the central cornea as well as the nasal and temporal regions of the midperipheral and peripheral regions of the right cornea of each subject. Identical measurements were again taken in these subjects 1 week later at approximately the same time of day. Within-subject variations were then assessed using paired t tests.

RESULTS

The only significant measurement differences that were found between visits were for full corneal thickness at both the nasal and temporal midperipheral locations. The mean differences for these locations were 13.5 microm and 13.7 microm, respectively.

CONCLUSIONS

Epithelial corneal thickness and central and peripheral total corneal thickness measurements using the Corneo-Gage Plus 2 pachymeter were reproducible; however, midperipheral total corneal thickness measurements showed poor reproducibility.

Intersession reproducibility of retinal nerve fiber layer thickness measurements by GDx-VCC in healthy and glaucomatous eyes

BACKGROUND

To assess intersession reproducibility of retinal nerve fiber layer (RNFL) thickness measurements on scanning laser polarimetry with variable corneal compensation (GDx-VCC) in a sample of healthy subjects and glaucoma patients.

METHODS

One eye each from 29 healthy and 29 glaucomatous subjects was selected and underwent RNFL scanning by the same operator at baseline and 1 week later. Glaucoma diagnosis relied on the presence of a reproducible defect on automated perimetry. GDx-VCC parameters considered were those available on page 1 of the printout [TSNIT average and standard deviation (SD), superior and inferior average (SA, IA), Nerve Fiber Indicator]. Reproducibility was assessed by calculating coefficient of variation and intraclass correlation coefficient separately for the two groups and for each parameter. The percentage of eyes with an intersession difference in thickness parameters of more than 5% was also calculated.

RESULTS

Coefficient of variation was <6% for TSNIT average, SA and IA in both groups. Corresponding values for TSNIT SD in healthy subjects and in glaucoma patients were 13.7 and 11.4%, respectively, whereas for Nerve Fiber Indicator they were 82.9 and 13.3%. Intraclass correlation coefficient ranged from 0.794 to 0.907 in healthy subjects and from 0.924 to 0.972 in glaucoma patients. In healthy subjects, TSNIT average, SA and IA intersession difference was 5% or less in 55-69% of eyes, whereas the value for TSNIT SD was 34.5%. Corresponding values in glaucomatous eyes ranged from 69 to 79.3% for TSNIT average, SA and IA and was 37.9% for TSNIT SD.

CONCLUSIONS

Intersession reproducibility of RNFL thickness measurements on GDx-VCC is high, both in healthy and in glaucomatous eyes. In a few cases, however, intersession variation may be larger than 10%. Caution is necessary while interpreting these changes during follow-up, in order to separate physiological variability from real RNFL thickness variations.

Quantification of Refractive Error: Comparison of Autorefractor and Focometer

PURPOSE

The advantages of a focometer (FOCOMETER) over other methods of refraction for use in developing countries are that it is lightweight, compact, relatively inexpensive, fairly quick, and easy to use with minimal training. This clinical trial compared the repeatability, validity, and ease of use of the focometer with an autorefractor.

METHODS

The refractive status of the right eye of 80 participants was determined with an autorefractor (Canon RK3). Three measurements were also taken with the focometer.

RESULTS

The spherical equivalent (M) of the focometer was 0.25 D more positive than the autorefractor (p < 0.001) and 84% of measurements were within 0.75 D of the autorefractor. The autorefractor detected astigmatism in 91% (73) of the eyes, whereas the focometer identified only 32% (26). The design of the clock target restricts cylinder axis accuracy to the nearest 15 degrees . There was evidence of a learning effect for the focometer: the second and third measurements were more repeatable in the untrained group. There were no differences between the mean (1.03 +/- 2.28) and third focometer (-1.05 +/- 2.32) measurements (p = 0.34). However, using the third focometer measurement, 94% of participants had visual acuities of at least 6/12(-2).

CONCLUSIONS

This study highlighted the focometer's restricted power range, inaccuracy of astigmatism and axis determination, and dependence on subject understanding and compliance. Therefore, in most clinical settings, the focometer would not be adequate for quantifying refractive error, but the focometer spherical equivalent was within acceptable limits of the autorefractor, and the visual acuity with lenses determined by the focometer indicates its potential usefulness in public health settings, especially where only spherical ready-made spectacles are dispensed. There may be more cost-effective ways to determine refractive error in these circumstances. A potentially important enhancement in focometer methodology that improves its ease of use was identified: use only the third measurement for each eye.

Shooting a Film Photo Slit Lamp Into the Digital Age

PURPOSE

The purpose of this study is to describe a method of taking a slit lamp initially designed for film photography and updating it to provide digital photographs.

METHODS

A "how-to" guide is provided.

RESULTS

Updating a Nikon FS-2 slit lamp is more economic than many practitioners may realize. By using what is already available on the market, a few steps can make a would-be dated instrument useful for many years to come.

CONCLUSIONS

The upgrade to the Nikon FS-2 slit lamp is not only possible, but is able to functional well in the clinical setting and capture high-resolution photographs.

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.

The Scotopic Sensitivity Tester-1 and the detection of early age-related macular degeneration1

PURPOSE

Previous research shows that dark adaptation is a marker of early age-related macular degeneration (ARMD), even when visual acuity remains good. This study evaluates whether a commercially available, off-the-shelf device for measuring dark adaptation, the Scotopic Sensitivity Tester-1 (SST-1), which uses a full-field stimulus, detects early ARMD as defined by fundus appearance. Fundus appearance is the gold standard method for defining the presence of ARMD.

METHODS

Dark adaptation was measured using the SST-1 in 12 young adults (mean age 23 years), 17 old adults with normal retinal health (mean age 69) and 19 old adults with early ARMD (mean age 74). Normal retinal health and presence of early ARMD were defined by masked grading of dilated fundus photographs using the Wisconsin Age-Related Maculopathy Grading System.

RESULTS

Older adults in normal retinal health exhibited slower dark adaptation as compared with young adults. No difference in the rate of dark adaptation was found between early ARMD patients and older adults in normal retinal health.

CONCLUSIONS

Although the SST-1 differentiated between young and older adults, it failed to detect dark adaptation abnormalities in early ARMD when referenced against older adults in normal retinal health. This may be attributable to the full-field stimulation used by the SST-1, which may be better suited for characterizing retinal degenerations affecting large retinal areas than for focal macular diseases like ARMD.

The effect of pupil dilation on scanning laser polarimetry with variable corneal compensation

BACKGROUND AND OBJECTIVE

The feasibility and reproducibility of scanning laser polarimetry performed through dilated pupils rather than through non-dilated pupils was tested.

PATIENTS AND METHODS

One eye each of 36 subjects (12 normal, 12 suspected glaucoma, and 12 glaucoma) was scanned using a single GDx unit with variable corneal compensator (GDx-VCC; Laser Diagnostic Technologies, Inc., San Diego, CA). Two scans prior to and two scans after dilation were performed on each study eye, resetting the cornea compensation prior to each scan. The dilated eye was viewed off-center, such that the whitish focusing patch was projected on the 9-o'clock peripheral iris. After adequate anteroposterior focus, the pupil was centered and a scan was acquired. Each of 5 GDx parameters was evaluated comparing the pre-dilation and post-dilation scans.

RESULTS

No statistically significant difference was found between pre-dilation and post-dilation measurements. There was a high pre-dilation to post-dilation correlation of 98%, 98%, 98%, 93%, and 95% for nerve fiber indicator, TSNIT average, TSNIT standard deviation, superior average, and inferior average, respectively. Less than 5% of the measurement variability was attributed to changes in pupil size (R2 ranging from 0.024 to 0.047). Stratifying the data by diagnostic groups yielded similar results.

CONCLUSIONS

Pharmacologic mydriasis was not found to influence the retinal nerve fiber layer measurements acquired using the GDx-VCC. Results were comparable to scans achieved in the same eyes prior to dilation.

Assessment of pupil size under different light intensities using the Procyon pupillometer

PURPOSE

To study the relationship between pupil size and light intensity using the Procyon pupillometer.

SETTING

University based clinic.

METHODS

In this retrospective study, 20 consecutive patients had pupil size assessment with the Procyon pupillometer under 3 different light conditions--4, 0.4, and 0.04 lux. Correlation was established using the log unit of the light intensity and pupil size.

RESULTS

The correlation coefficient for the association between pupil size and log unit of light intensity in all eyes was significant (P<.001). The mean correlation coefficient for the association between pupil size and log unit of light intensity in all patients was 0.968 +/- 0.089 (SD) in the right eye and 0.970 +/- 0.031 in the left eye.

CONCLUSION

The linear relationship between the pupil size and the log unit of the light intensity showed a tight correlation in all cases. These results can be useful in the comparing pupil size with pupillometers that work under different light conditions.

Comparative higher-order aberration measurement of the LADARWave and Visx WaveScan aberrometers at varying pupil sizes and after pharmacologic dilation and cycloplegia

PURPOSE

To compare higher-order aberration (HOA) measurements of LADARWave and Visx WaveScan aberrometers, to test the validity of the peripheral wavefront data, and to evaluate the effect of pharmacologic dilation and mild cycloplegia.

METHODS

Thirty-three myopic eyes of 17 volunteers were enrolled and had the ocular HOAs measured and analyzed with varying pupil diameters (PD) controlled by a tunable light intensity source and after instillation of tropicamide 1% and phenylephrine 2.5%.

RESULTS

Higher-order aberrations increased with PD and optical zone (OZ), especially an OZ between 6.0 mm and 6.5 mm. Spherical aberration increased the most, followed by coma, then trefoil and secondary astigmatism. Measurement differences were observed between LADARWave and WaveScan at an OZ of 6.0 mm, although measurement correlations between the 2 machines were high. In the case of the WaveScan, when PD = OZ (6.0 mm), the spherical aberration and, to a less extent, the coma data differed from those obtained with larger PDs and the same OZ. In the case of the LADARWave, at an OZ of 6.0 mm, the HOAs measured in eyes with physiologic pupils were similar to those in pharmacologically dilated pupils when the physiologic pupil center was taken as the reference.

CONCLUSIONS

There were detectable measurement differences between LADARWave and Visx WaveScan. Ensuring that the PD is at least 0.5 mm larger than the desired OZ is very important. Dilation and mild cycloplegia did not clinically affect the wave measurement magnitude or pattern.

Anterior chamber measurements using Pentacam rotating Scheimpflug camera

PURPOSE

To investigate the mean values and standard deviations according to age, reliability, and correlation between different parameters of anterior chamber measurements using the Pentacam rotating Scheimpflug camera.

SETTING

Heidelberg IOL and Refractive Surgery Research Group, Department of Ophthalmology, University of Heidelberg, Heidelberg, Germany.

METHODS

This prospective clinical study comprised 76 healthy volunteers (mean age 46.6 years +/- 16.8 [SD]). Three consecutive measurements were made of only 1 eye and anterior chamber depth (ACD), mean and minimum anterior chamber angle (ACA), and anterior chamber volume (ACV) were evaluated.

RESULTS

Mean ACD was 2.93 +/- 0.36 mm, mean ACA was 34.81 +/- 5.05 degrees, minimum ACA was 29.99 +/- 5.53 degrees, and mean ACV was 160.3 +/- 36.81 mm3. Increasing age was associated with reduced ACD and ACV; however, mean and minimum ACAs were lowest in patients aged 40 to 59 years. Excellent correlation was found between ACD and ACV (R = 0.92). Anterior chamber depth and mean ACA correlated only moderately (R = 0.65). The correlation coefficient between ACD and minimum ACA was smaller (R = 0.58). There was no correlation between ACV and ACA (R = 0.37). Minor standard deviations were noted (ACD 0.02 +/- 0.02 mm, mean ACA 1.12 +/- 0.94 degrees, minimum ACA 2.04 +/- 2.67 degrees, and ACV 2.48 +/- 1.65 mm3).

CONCLUSIONS

Using the Pentacam, it was possible to examine different parameters of the anterior chamber within a short period and with good reliability. The evaluation of the ACA in different positions can help to classify the potential risk for angle-closure glaucoma.

Optical biometry of the anterior eye segment: interexaminer and intraexaminer reliability of ACMaster

PURPOSE

To evaluate the interexaminer and intraexaminer reliability of corneal thickness, anterior chamber depth (ACD), and crystalline lens thickness measurements using a commercially available anterior segment optical biometry instrument (ACMaster, Carl Zeiss Meditec) based on partial coherence interferometry (PCI).

SETTING

Medical University of Vienna, Vienna, Austria.

METHODS

Interexaminer reliability and intraexaminer reliability were evaluated in 10 eyes of 10 young volunteers and 11 eyes of 11 cataract patients. The measurements of the interexaminer reliability were taken by 3 examiners. Corneal thickness, ACD, and lens thickness of the intraexaminer reliability were measured twice in all eyes by 1 examiner. To evaluate the effect of cycloplegia on the variability, the measurements were performed on 5 volunteers under cyclopentolate 1%. Measurements were performed using the prototype of the ACMaster based on PCI.

RESULTS

The interexaminer/intraexaminer reliabilities were 99.9% for corneal thickness and ACD. The reliability of lens thickness could not be estimated because of a large number of missing values in the cataract patient group. The median interexaminer variability (SD) was 1.9 microm for corneal thickness, 7.5 microm for ACD, and 10.6 microm for lens thickness. The median intraexaminer variability (SD) was 1.6 microm for corneal thickness, 10.8 microm for ACD, and 8.7 microm for lens thickness. With cycloplegia, both the interexaminer variability and intraexaminer variability were smaller than without cycloplegia.

CONCLUSIONS

Partial coherence interferometry measurements of anterior chamber distances (corneal thickness, ACD, lens thickness) using the prototype of ACMaster were highly reliable, allowing examiner-independent measurements. However, lens thickness measurements in cataract eyes were often difficult.

[Clinical study of anterior ocular segment topography in angle-closure glaucoma using the three-dimensional anterior segment analyzer Pentacam]

PURPOSE

The anterior ocular segment topography in angle-closure glaucoma was studied using the non-contact three-dimensional anterior segment analyzer Pentacam.

SUBJECTS AND METHODS

The central anterior chamber (AC) depth, mid-peripheral AC depth, peripheral AC depth, AC volume, central AC depth/ocular axial length ratio and angles of a narrow angle group (47 eyes of 29 patients), a post laser iridotomy (LI) group (43 eyes of 30 patients), and an open-angle glaucoma (OAG) group (37 eyes of 21 patients) were measured and compared. In addition, changes in the parameters before and after LI (13 eyes of 9 patients) were investigated.

RESULTS

The AC volume for the narrow angle group (74.5 +/- 21.1 microl) was significantly smaller than for the other groups (post LI group: 96.4 +/- 21.4 microl; OAG group: 144.2 +/- 31.6 microl, p<0.001). The most significant association was detected between AC volume and the peripheral AC depth. Only two parameters, AC volume and peripheral AC depth, increased significantly after LI (p< 0.001).

DISCUSSION

Measurement of the AC volume and the peripheral AC depth using Pentacam is useful for evaluating the anterior ocular segment topography in narrow angle eyes.

Adaptive optics system for investigation of the effect of the aberration dynamics of the human eye on steady-state accommodation control

It is now known that defocus is not the only aberration in the eye that exhibits dynamic behavior during fixation. It is currently unknown what effects, if any, the dynamics of these other aberrations have on steady-state accommodation control. We constructed an adaptive optics system to serve as a tool for future investigations in this area. The system has several design features of interest, including automated precompensation of defocus and astigmatism and a method to bypass a scanner used to reduce speckle. It also has the facility to measure the eye's aberrations independent of the aberration manipulation device-a 37-actuator membrane deformable mirror. Coherence function analysis was used to assess the deformable mirror performance in terms of coupling between Zernike modes. Modes beyond third radial order showed severe coupling. Pilot data were collected on one subject to demonstrate the utility of this system in steady-state accommodation studies. The value of the system for future work in this area is discussed.

An Evaluation of Keratometry in 6-Year-Old Children

PURPOSE

To evaluate the repeatability and comparability of keratometry measured by both the IOLMaster and RK-F1 AutoRef-Keratometer in children.

METHODS

Keratometry results from a sample (n = 447) of 6-year-old children who were examined in the Sydney Myopia Study were analyzed. Corneal power was analyzed along the flattest and steepest meridians to determine if there were any systematic differences between repeat measurements or between the two instruments. The 95% limits of repeatability (LR) and 95% limits of agreement (LA) (mean difference +/- 1.96 x standard deviation of differences) were calculated.

RESULTS

There were no systematic differences in repeat measurements for each instrument. For the IOLMaster, mean difference of the flattest corneal meridian was -0.01 (D) (P = 0.3, 95% LR, -0.22, 0.21 D) and of the steepest corneal meridian, 0.01 D (P = 0.3, 95% LR, -0.35, 0.38 D). For the RK-F1, mean difference of the flattest corneal meridian was -0.02 D (P = 0.3, 95% LR, -0.25, 0.21 D); and of the steepest corneal meridian, 0.00 D (P = 0.9, 95% LR, -0.39, 0.39 D). Systematic differences, however, were found between the two instruments. The IOLMaster gave significantly (P < 0.0001) steeper readings than the RK-F1 for both the flattest corneal meridian, 0.29 D (95% LA, -0.08, 0.66 D), and the steepest corneal meridian, 0.18 D (95% LA, -0.29, 0.65 D).

CONCLUSIONS

Keratometry was highly repeatable for both the IOLMaster and RK-F1 instruments when used in young children. These instruments would be suitable for use in monitoring changes of corneal curvature over time. Small significant systematic differences in keratometry between the two instruments were also found.