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.

Posterior pole retinal thickness measurements by the retinal thickness analyzer in healthy Chinese subjects

PURPOSE

To assess retinal thickness at the posterior pole in healthy Chinese subjects with the retinal thickness analyzer (RTA).

METHODS

Retinal thicknesses at the posterior pole and fovea were measured by the RTA in 331 eyes of 178 healthy Chinese subjects. Retinal thicknesses as a function of sex, age, refractive errors, and axial length were also evaluated.

RESULTS

The average thickness of the foveal area +/- SD was 158.6 +/- 24.8 microm, the average thickness of the perifoveal region (600-2,500 microm from fovea) +/- SD was 174 +/- 25.2 microm, and the average thickness of the posterior pole region (600-6,000 microm from fovea) +/- SD was 171.9 +/- 25.3 microm. There was no significant difference in retinal thicknesses of the foveal, perifoveal, and posterior pole regions in either right or left eyes or as a function of different spherical equivalents. Moreover, there was no significant difference of foveal thickness between males and females. Greater retinal thicknesses of the foveal, perifoveal, and posterior pole regions were associated with age of older than 40 years and axial length of < 24 mm, and greater perifoveal and posterior pole thicknesses were found for females. Furthermore, there were no significant correlations between age, refractive errors, and axial lengths with retinal thicknesses.

CONCLUSION

Retinal thicknesses of the posterior pole region differed by age, axial length, and sex, but there was no effect of laterality or different spherical equivalents. The RTA is a fast and noninvasive technology to assess retinal conditions with thickening or thinning in the fovea and posterior pole.

Results of Implementation of the DigiScope for Diabetic Retinopathy Assessment in the Primary Care Environment

Approximately 50% of patients with diabetes in the United States do not undergo recommended ocular evaluations for diabetic retinopathy. The DigiScope (EyeTel Imaging, Inc., Columbia, MD) was developed as a cost-effective and practical telemedicine digital imaging system to screen for diabetic retinopathy in the primary care physician's (PCP) office. The DigiScope has been validated against seven-field stereo color fundus photography for the detection of diabetic retinopathy. This study reports on the implementation of the DigiScope for diabetic retinopathy assessment in the primary care environment. In PCP's offices, patients with diabetes who had not undergone an eye examination in the past year were imaged with the DigiScope. The images were transmitted to a reading center where the need for referral to an ophthalmologist was determined. Nonurgent referral was recommended for patients with diabetic retinopathy greater than a few micro-aneurysms, other ocular pathology, or unreadable images. Referral was deemed "urgent" for patients with sight-threatening disease and evaluation by an ophthalmologist within 72 hours was recommended. Between October 1, 2002 and March 31, 2771 patients with diabetes underwent DigiScope imaging at multiple sites. Nonurgent referral was recommended for 468 patients (17%). Urgent referral was recommended for 71 patients (3%). The images were unreadable in 295 cases (11%). This study indicates that implementation of the DigiScope in the primary care setting is practical and allows screening of patients with diabetes who are otherwise not receiving recommended eye examinations.

Comparison of the Retinal Image Quality with a Hartmann-Shack Wavefront Sensor and a Double-Pass Instrument

PURPOSE

Wavefront sensors provide quite useful information on the optical quality of the eye. However, in eyes where very high-order aberrations and scattered light are prominent, wavefront sensors may overestimate retinal image quality. This study showed that, in those cases, the double-pass technique is a complementary tool for better estimation of ocular optical quality.

METHODS

A double-pass (DP) instrument was used, based on recording images of a point source in near-infrared light after reflection in the retina and double-pass through the ocular media. The aberrations were also measured with a prototype of near-infrared Hartmann-Shack (HS) wavefront sensor adapted to the clinical environment. From the wave aberrations, the modulation transfer function (MTF) was calculated (MTF_HS). The MTF was also obtained from the double-pass images (MTF_DP). Both techniques were applied in normal young subjects as the control and in three other groups of eyes: older subjects, after LASIK refractive surgery, and after IOL implantation.

RESULTS

The MTFs obtained from DP and HS techniques were compared. In the group of normal eyes with low levels of intraocular scattering, these estimates were quite similar, indicating that both techniques captured well most of the optical degradation. However, in eyes where scatter was more predominant (e.g., early cataract, posterior capsular opacification after IOL implantation) the MTF provided by the HS sensor was always higher than the MTF obtained from DP. A single parameter was used to indicate the differences.

CONCLUSIONS

In eyes with low scattering, DP and HS techniques provided similar estimates of the retinal image quality. However, in a patient's eye with mild to severe amount of scatter, wavefront sensors might overestimate image quality, whereas the DP technique produces a more accurate description of the optical quality, better correlated with the quality of vision.

Intérêt de l’auto-réfractomètre et de l’orbscan pour la mesure du diamètre pupillaire

PURPOSE

We compared pupil size measurements obtained with the Orbscan and autorefractometer to the Colvard Infrared pupillometer in order to determine their respective clinical advantages.

MATERIAL AND METHODS

We prospectively measured the pupil diameter in 94 eyes of 47 normal patients using the Colvard device, the Nikon NKR 8000 autorefractometer, and the Orbscan device. For each device, two successive measurements were taken to determine its reproducibility. We also studied the relationship with the contralateral eye (i.e., difference and correlation). The measurements obtained with the different devices in different light intensities were compared and studied using regression analysis.

RESULTS

Pupil diameter measured using the Orbscan had the highest reproducibility (mean difference between the two successive measurements: 3.8% or 0.15mm) and showed the smallest difference between the two eyes (5.0% or 0.19mm) and the strongest correlation with the contralateral eye (r=0.93; p<0.001). Scotopic Colvard measurements and autorefractometer measurements with low light settings were not significantly different (5.86mm versus 5.86mm; p=0.48). Autorefractometer measurements with low light settings showed the strongest correlation with the scotopic Colvard measurements (r=0.84; p<0.001). The Orbscan measurements were less correlated with the scotopic or photopic Colvard measurements (r=0.73; p<0.001 and r=0.51; p=0.003, respectively). For the Colvard pupillometer, the correlation between photopic measurements and scotopic measurements was also poor (r=0.51; p<0.001).

CONCLUSION

Pupil size measurements with the autorefractometer may be advantageous before refractive surgery. Measuring pupil size in photopic conditions, as with the Orbscan, cannot screen people with large pupils in mesopic conditions.

Scanning laser polarimetry for measurement of retinal nerve fiber layer in absolute, advanced and early glaucoma

BACKGROUND

To detect differences in retinal nerve fiber layer (RNFL) measurements in absolute, advanced and early glaucoma with scanning laser polarimetry (The Nerve Fiber Analyzer GDx), and to assess the usefulness and limitations of this technique for longitudinal follow-up of glaucoma patients.

METHODS

This is a prospective, cross-sectional study. Twenty-one eyes of 21 patients with absolute glaucoma, twenty-six eyes of 26 patients with advanced glaucoma and twenty-four eyes of 24 patients with early glaucoma were imaged using scanning laser polarimetry. The twelve standard GDx measurement parameters were compared using ANOVA (analysis of variance) and the Tukey test.

RESULTS

No significant differences were demonstrated for any of the twelve GDx measurement parameters between absolute and advanced glaucoma cases. There were significant differences for some GDx parameters, including the GDx number (p < 0.0001) superior ratio (p < 0.0001), inferior ratio (p < 0.0001), superior/nasal ratio (p < 0.0001), maximum modulation (p < 0.0001), ellipse modulation (p < 0.0001) and inferior average (p = 0.001) between early and advanced glaucoma, and, between early and absolute glaucoma. Significant differences were demonstrated for the superior average (p = 0.01) parameter between early and absolute glaucoma, but not between early and advanced glaucoma.

CONCLUSIONS

For follow-up of glaucoma progression, RNFL measurements using scanning laser polarimetry are more useful in the early stage than in the advanced stage.

Accuracy of the WASCA Aberrometer Refraction Compared to Manifest Refraction in Myopia

PURPOSE

To evaluate the accuracy of myopic refraction by a single measurement using the Wavefront Supported Custom Ablation (WASCA) aberrometer (Carl Zeiss Meditec AG, Jena, Germany).

METHODS

We retrospectively compared the refractive errors obtained by manifest refraction and wavefront refraction (WASCA) in 50 eyes of 25 consecutive myopic patients undergoing laser refractive surgery. The sphere ranged from -1.00 to -8.25 diopters (D) and cylinder from 0 to -3.75 D. WASCA measurements under cycloplegia were made and WASCA refractions calculated for a 6-mm analysis zone using the Seidel method within the WASCA. We used the manifest refraction as our best estimate of the true refractive error, therefore accuracy was defined as the difference between manifest refraction and that of the WASCA. Correlation coefficients and mean vector errors between manifest and WASCA refraction were calculated.

RESULTS

High correlation was shown between manifest and WASCA refractions, with correlation coefficients (R2) of 0.97, 0.85, and 0.79 for M, J180, and J45, respectively. Mean power vector error (standard deviation) was 0.22 D (0.39), +0.03 D (0.21), and +0.03 D (0.13) for M, J180, and J45, respectively. Total dioptric power vector error was 0.43 D with 74% eyes within 0.50 D.

CONCLUSIONS

When measuring normal myopic eyes, the concordance between manifest and WASCA refractions was found on average to be high; however, outlier measurements occurred.

The power of a cylinder in an oblique meridian: revisiting an old controversy*

The sine-squared correlation states that the cylinder power in an oblique meridian forming an angle beta with the axis of the cylinder is reduced to sin(2)beta of the maximal power. The sine-squared relationship is fundamental in paraxial optics, but its validity has repeatedly been questioned during the last century. It appears that two powers are operative in an oblique meridian, curvital and torsional. Curvital power is responsible for refraction in the plane of the meridian, while the torsional component twists the light out of that plane. Curvital power is the traditional power concept, while torsional power has only recently been described. The long-standing criticism of the sine-squared correlation is based on the erroneous assumption that only curvital power is operational in paraxial imagery. Curvital and torsional power are both derived from the sine-squared correlation. The concept of these dual powers repudiates the criticism and is in complete accordance with paraxial optics.

Comparison of central corneal thickness measurements with a new optical device and a standard ultrasonic pachymeter

PURPOSE

To compare central corneal thickness (CCT) values obtained with ultrasonic pachymetry and a new optical method using partial coherence interferometry (PCI).

SETTING

Department of Ophthalmology, Medical Health and Science Center, University of Debrecen, Debrecen, Hungary.

METHODS

The study comprised 136 eyes of 70 patients whose spherical refractive error was not greater than +/-6.0 diopters (D) and whose keratometric astigmatism was not greater than 2.0 D. Central corneal thickness was measured 5 times with a new optical device (ACMaster, Zeiss) and with an ultrasonic pachymeter (AL-2000, Tomey). All measurements were obtained by the same investigator.

RESULTS

Mean CCT was 531.2 microm +/- 3.9 (SD) with PCI and 547.8 +/- 36.0 microm with the ultrasonic device. The difference between groups was significant (P = .001). There was no difference between CCT values measured in right and left eyes (P = .55) with ultrasonography and PCI (P = .67). The coefficient variation was 0.73% for PCI and 6.5% for ultrasonography. Correlation between the CCT measurements with both devices was strong and statistically significant (Spearman correlation = .91, P = .001).

CONCLUSIONS

Mean CCT values measured by the PCI method were significantly smaller than those measured by the ultrasonic device. Central corneal thickness measured with PCI is more reproducible and seems to be more reliable than that measured by ultrasonography.

Validity of Pachymetric Measurements by Manipulating the Acoustic Factor of Orbscan II

PURPOSE

To assess the validity of pachymetric measurements by examining the constancy of the acoustic factor (AF) of the Orbscan II (Orbtek, Bausch & Lomb, Rochester, NY) after overnight rigid gas-permeable (RGP) contact lens wear.

METHODS

Twenty participants wore CRT (Paragon Vision Sciences, Mesa, AZ) HDS 100 contact lenses on one eye and control lenses on the contralateral eye for one night while sleeping. Another 24 participants wore CRT lenses on both eyes for one night. Central corneal thickness was measured using optical coherence tomography and Orbscan II on the night before lens use, immediately after lens removal on the following morning, and 1, 3, 6, and 12 hours later. By using optical coherence tomography as a reference, the adjusted AF was calculated by using a least squares method over time.

RESULTS

The adjusted AF depended on the corneal thickness in normally hydrated corneas. The adjusted AF and the percentage change of the adjusted AF varied before and after overnight lens wear. There was a strong and significant correlation between the corneal swelling and the percentage change of the adjusted AF (all r at least 0.91, P<0.05).

CONCLUSIONS

The adjusted AF is a variable, not a constant. The AF is a function of the corneal thickness and its alteration with, for example, corneal swelling. The validity of the adjusted Orbscan II pachymetric measures using a single AF is untenable.

A New Calibration Set of Phase Plates for Ocular Aberrometers

PURPOSE

To manufacture and test a set of phase plates for the calibration of ocular aberrometers and apply it to the calibration of an ocular laser ray tracing aberrometer.

METHODS

The set of phase plates is made by a greyscale single-mask photosculpture in photoresist method. Each plate induces a given amount of a particular aberration (Zernike) mode. The set contains two subsets: 1) pure Zernike modes to test the accuracy among different orders (from 3rd to 7th, approximately 0.3 to 0.4 microm); and 2) plates having different amounts of the same mode, 3rd order coma ranging from 0.11 to 0.47 microm. After manufacturing, the plates were tested twice, as a crosscheck, measuring the aberration pattern of each plate with a Mach-Zehnder interferometer and a single-pass Hartmann-Shack wavefront sensor. The set was then applied to the calibration of an ocular double-pass laser ray tracing aberrometer.

RESULTS

Close agreement was found between the three types of measurement. The maximum difference between Hartmann-Shack and laser ray tracing measurements was 0.032 microm (ie, approximately lambda/20, half of the typical measuring error in human eyes). This permitted detection of a small bias in the ocular laser ray tracing aberrometer.

CONCLUSIONS

The calibration set may be a powerful tool for the assessment of accuracy and reliability in ocular aberrometry. It discovered a small bias, which is almost impossible to detect when working with human eyes or trial lenses. This type of calibration tool is especially important in clinical environments.

Anterior chamber depth measurement by optical pachymetry: systematic difference using the Haag-Streit attachments

BACKGROUND/AIM

Haag-Streit recommends that for the most accurate anterior chamber depth (ACD) results, the corneal thickness, as determined with attachment No I, should be deducted from a measurement from corneal epithelium to the anterior lens surface, made with attachment No II (method A). Often ophthalmologists use the measurement made from the corneal endothelium to the anterior lens surface, using only attachment No II (method B), which is a simpler and faster method. This study examined agreement between methods A and B.

METHODS

Two studies were conducted independently by each author. PHA measured 127 (27 men, 100 women; mean age, 66.9 years) consecutive Danish patients referred for evaluation because of possible angle closure. RRB measured 109 subjects (30 men, 79 women; mean age, 61.3 years) consecutively from a population based glaucoma survey in Rom Klao, Thailand.

RESULTS

Using method A, mean ACD was 1.97 mm (SD 0.29) in the Danish study and 2.59 mm (SD 0.27) in the Thai study. ACD measured with method B was significantly (p<0.001) deeper than method A in both studies (Danes: difference = 0.118 (95% CI: 0.109 to 0.127); Thais: difference = 0.166 mm (95% CI: 0.158 to 0.174)). With an increase in ACD of 1 mm, the methodological difference increased by 0.052 mm (regression formula: difference (B - A) = 0.0667 x mean ACD - 0.0148; R(2) = 0.31). This positive correlation did not differ significantly between the two studies.

CONCLUSIONS

The relevance and importance of estimating ACD as a risk factor in primary angle closure glaucoma suspects and patients has been repeatedly emphasised. This is the first empirical study to quantify the difference in ACD using these two methods in two samples, one clinic based (angle closure suspects) and the other population based. The size of the methodological difference has a level that corresponds to the age reduction of ACD per decade, or to about 6% of ACD in a given eye. These findings highlight the importance of clinicians recognising that these two methods will give different results and recommend that one should standardise ACD measurements using the Haag-Streit optical pachymeter.

Quantitative in vivo retinal thickness measurement in chinese healthy subjects with retinal thickness analyzer

PURPOSE

To measure the retinal thickness of the posterior pole in healthy Chinese subjects using a retinal thickness analyzer and to compare the retinal thicknesses between different age, gender, and refractive error groups.

METHODS

Between February 2002 and September 2004, healthy Chinese subjects (age range, 21-50 years), underwent measurements of visual acuity, refractive error, intraocular pressure, and posterior pole retinal thickness with the RTA, as well as ophthalmoscopy and slit lamp examinations. Eleven retinal thickness parameters were directly derived from the reports of the RTA measurement. The average value of each parameter was compared between the male and female groups, the emmetropia and low-myopia groups, and the three age groups (21-30, 31-40, and 41-50 years). Linear regression analysis was also applied to determine the effect of age on 11 parameters. Some participants were also enrolled in the reproducibility assessment procedure.

RESULTS

The 272 eyes of 272 subjects (mean age, 34.4 years) were included. The intraclass correlation coefficients of intravisit and intervisit reproducibility were 0.95 and 0.88, respectively. The average retinal thicknesses at the foveola and fovea are 147.6 and 160.0 microm, respectively. No significant difference was found in any of the parameters between the different gender groups, emmetropia and low-myopia groups, or age groups. Regression analysis revealed no significant negative linear correlation between any of the parameter values and age.

CONCLUSIONS

The retinal thickness of macular region in the Chinese is a little lower than in Westerners, but not statistically significant. The Chinese retinal thickness was not gender or refractive error related.

Evaluation of Optical Function Using a New Point Spread Function Analysis System in Cataractous and Pseudophakic Eyes: Preliminary Results

PURPOSE

To evaluate optical function in cataractous and pseudophakic eyes using the new point spread function (PSF) analysis system in a clinical setting.

METHODS

We applied this new analysis system in the study of two cataractous eyes and one pseudophakic eye of two patients. Using a PSF analyzer, double-pass PSF was measured directly for each subject, and the single-pass modulation transfer function (MTF) and single-pass PSF were calculated. The simulated retinal images of various sizes of Landolt's rings and their contrast characteristics were also calculated by the PSF analyzer.

RESULTS

The MTF and the contrast of the simulated retinal images degraded in cataractous eyes were compared with data for normal eyes; the degradation pattern depended on the opacification pattern. The MTF and the contrast of the simulated retinal images in the pseudophakic eye improved significantly compared with the cataractous eyes, although both values were lower in the pseudophakic eye than in young normal eyes.

CONCLUSIONS

Our data showed degradation of optical function in cataractous and pseudophakic eyes in comparison with optical function in young normal eyes. If further accumulations of PSF data are made, it may be possible to establish an objective standard by which to measure the progression of cataract, as well as an objective indication for treatment in the future.

Pupil measurement using the Colvard pupillometer and a standard pupil card with a cobalt blue filter penlight

PURPOSE

To compare scotopic pupil measurements obtained with a Colvard pupillometer with measurements taken with a printed pupil gauge and penlight with a cobalt blue filter attachment in mesopic and scotopic luminance.

SETTING

The Illinois Eye Institute, Chicago, Illinois, USA.

METHODS

Pupil measurements were taken of both eyes of 38 patients (76 eyes). Any subject presenting with anterior segment disease, fixed or dilated pupils, iris abnormalities, or a history of eye disease or eye trauma was excluded. At a mesopic luminance of 2.11 foot-candles, pupil measurements were taken with a Bernell pupil card and penlight with a cobalt blue filter attachment. At a scotopic luminance of less than 2.00 foot-candles, pupil measurements were taken with the Bernell card system and the Colvard pupillometer.

RESULTS

In mesopic luminance, the mean pupil diameter was 5.17 mm (range 3.0 to 7.5 mm) with the Bernell card method. The mean difference between the Colvard in scotopic luminance and the Bernell card system in mesopic luminance was -0.04 mm (P = .0831). In scotopic luminance, the mean pupil diameter was 6.32 mm (range 4.0 to 8.0 mm) with the Bernell card method and 5.13 mm (range 3.0 to 7.5 mm) with the Colvard pupillometer, with a mean difference of -1.18 mm (P<.0001). The limits of agreement between the mesopic Bernell card system and the Colvard pupillometer were small (-0.32 to 0.24), whereas the limits of agreement between the scotopic measurements of both techniques were large (-2.18 to -0.18).

CONCLUSIONS

Under both illuminance conditions, the Bernell card system with the cobalt filter measured a larger pupil size than the Colvard pupillometer. The measurement differences between the techniques were most pronounced at the lower illumination. The limits of agreement were larger under the lower illumination, indicating more variation between techniques. This study suggests that the Bernell card system with cobalt illumination provides a generous measurement of the pupil size compared with the Colvard pupillometer, which makes it an appropriate and cost-effective screening tool for refractive surgery evaluation.

Longitudinal changes of optical aberrations in normal and form-deprived myopic chick eyes

We performed measurements of refraction (with retinoscopy), axial length (with ultrasound biometry) and ocular aberrations (with a custom-built Hartmann-Shack aberrometer) on seven awake White-Leghorn chicks occluded monolaterally with diffusers for two weeks. Treatment started on the first day after hatching (day 0) and measurements were conducted on several days between day 0 and 13. Non-occluded eyes experienced normal emmetropization (decreasing hyperopia at 0.2 +/- 0.09 D/day and increasing axial length at 0.05 +/- 0.03 mm/day), while occluded eyes developed axial myopia (1.50 +/- 0.2 D/day and 0.12 +/- 0.02 mm/day). Interocular differences in refraction and axial length by day 13 were on average 17.43 D and 0.86 mm, respectively. Monochromatic high order aberrations decreased with age in both eyes. Average RMS (for 1.5 mm pupil diameter) decreased from 0.11 +/- 0.03 at day 0 to 0.06 +/- 0.03 microm (day 13) in occluded eyes, and from 0.12 +/- 0.05 to 0.03 +/- 0.01 microm in non-occluded eyes. MTF-based optical quality metrics also show an improvement with age. However, while this improvement occurs in both eyes, after day 8 myopic eyes tend to show significantly higher amounts of aberrations (and consequently worse best-corrected optical quality) than normal eyes. The degradation imposed by aberrations is small compared to that imposed by defocus and the diffuser. These results suggest a decrease of aberrations during development which does not seem to be visually guided. Myopic eyes showed slightly worse optical quality than normal eyes, suggesting that the geometrical changes resulting from excessive ocular axial growth also affect the optical quality of the ocular components.

Continuous Measurement of Corneal Dehydration With Online Optical Coherence Pachymetry

PURPOSE

Online optical coherence pachymetry (online OCP) allows continuous central corneal thickness measurements over time. In this study, the effect of dehydration on corneal tissue was investigated with online OCP.

METHODS

Twelve eyes of 11 patients were examined with online OCP, and the central corneal thickness was registered over 5 minutes after insertion of an eyelid speculum.

RESULTS

Online OCP measurements revealed no decrease in reproducibility after 5 minutes of dehydration. The initial mean central corneal thickness was 538 +/- 48 microm. After 5 minutes the central corneal thickness decreased to 483 +/- 43 microm (P = 0.001). This corresponded to a mean corneal thinning of 55 +/- 4 microm (10.2%) at a rate of 0.19 microm/s.

CONCLUSIONS

Online OCP was suitable for continuous measurements of corneal changes caused by dehydration. These dehydration effects should be particularly considered in refractive corneal surgery.

Quantitative pupillometry: normative data in healthy pediatric volunteers

OBJECT

The authors describe the prospective use of a new hand-held point-and-shoot pupillometer (NeurOptics) to assess pupil function quantitatively.

METHODS

Repetitive measurements were made in 90 pediatric participants ranging in age from 1 to 18 years, providing a total of 100 measurements under ambient light conditions. The participants consisted of 45 patients without known intracranial or ophthalmological pathological conditions as well as 45 volunteers in the outpatient setting. Quantitative pupil measurements were reliably replicated in the study participants. The mean resting pupil aperture was 4.11 mm and the minimal diameter after stimulation was 2.65 mm, resulting in a 36% change in pupil size. The mean constriction velocity was 2.34 mm/second, with a mean dilation velocity of 2.2 mm/second.

CONCLUSION

Pupil symmetry was impressive in the entire cohort.