Comparison of objective and subjective refraction before and after laser in situ keratomileusis

PURPOSE

To compare the accuracy and reliability of objective and subjective refractions before and after laser in situ keratomileusis (LASIK) for myopia, hyperopia, and astigmatism.

SETTING

Augenchirurgie und Laserzentrum Hochrum, Innsbruck, Austria.

METHODS

In this prospective study, the objective refraction obtained with the Nidek AR-K 900 autorefractor was compared with the subjective refraction in 159 eyes (125 with myopia and 34 with hyperopia) operated on with 2 different lasers. Refractions were done before and 6 months after LASIK.

RESULTS

Preoperatively, the objective and subjective refractions correlated better in eyes with low myopia than in those with high myopia (P < .01). Postoperatively, objective refraction was less accurate and reliable than preoperatively. The difference between the objective and subjective spherical refractions was statistically significant (P < .0001) after LASIK in eyes with hyperopia. The correlation between the objective and subjective cylindrical refractions was stronger preoperatively. Especially after LASIK for hyperopia, the objective refraction did not reliably assess the magnitude and axis of the cylinder. The preoperative refractive error did not significantly affect the preoperative and postoperative difference between the objective and subjective refractions or the change between the preoperative and postoperative mean differences. The type of excimer laser used significantly affected the difference between the objective and subjective refractions.

CONCLUSIONS

Especially after LASIK for hyperopia, the objective refraction determined with the Nidek AR-K 900 autorefractor delivered erroneous results, which have implications for postoperative care and preoperative measurements for ocular surgery such as enhancement procedures or cataract surgery.

Retinal nerve fiber layer measurement by nerve fiber analyzer in normal subjects and patients with glaucoma

OBJECTIVE

To identify the pattern of retinal nerve fiber layer (RNFL) loss in glaucoma using the Nerve Fiber Analyzer (NFA).

DESIGN

Case-control study.

PARTICIPANTS

A total of 80 normal and 75 age- and race-matched chronic open-angle glaucoma subjects were recruited.

INTERVENTION

The RNFL thickness was assessed with a scanning laser polarimeter (Nerve Fiber Analyzer GDX, Laser Diagnostic Technologies Inc., San Diego, CA). Analysis of variance was used to compare the corresponding RNFL measurement indices of the different groups.

MAIN OUTCOME MEASURES

Superior/nasal (S/N) and inferior/nasal (I/N) ratios of NFA are sensitive parameters to differentiate between glaucoma and nonglaucoma subjects.

RESULTS

Peripapillary RNFL measurements at the superior and inferior regions were significantly lower in the glaucoma group (P<0.001) but were similar in temporal and nasal regions (P>0.05). Using nasal value as reference, S/N and I/N ratios were significantly lower in the glaucoma groups (P<0.001) and also decreased with increasing severity of glaucoma.

CONCLUSIONS

In glaucoma, RNFL was more susceptible to loss in the superior and inferior regions than in the nasal and temporal regions. The S/N and I/N ratio parameters provided by the NFA appeared to give further discriminating ability in early glaucoma.

The effect of excimer laser photorefractive keratectomy for myopia on nerve fiber layer thickness measurements as determined by scanning laser polarimetry

OBJECTIVE

Scanning laser polarimetry measures the retardation of polarized laser light as it passes through the birefringent retinal nerve fiber layer (RNFL). Because retardation is directly proportional to the number of retinal nerve fibers, indirect measurements of the RNFL thickness are obtained. A fixed compensatory mechanism is used to correct for retardation attributed to birefringence in the cornea and anterior segment. Excimer laser photorefractive keratectomy (PRK) corrects myopia by ablating tissue from the cornea. This study was conducted to determine the effect of this ablation on RNFL measurements.

DESIGN

Prospective comparative case series.

PARTICIPANTS

Eighteen patients.

METHODS

Patients undergoing PRK had RNFL measurements performed with the GDx Nerve Fiber Analyzer (Laser Diagnostic Technologies, San Diego, CA), a scanning laser polarimeter, in both eyes before and 90 days after PRK in the first eye.

MAIN OUTCOME MEASURES

Fourteen different GDx parameters were analyzed for statistically significant differences preoperatively and 3 months postoperatively in the treated and untreated eye using Hotelling's T-squared generalized means test.

RESULTS

Eighteen patients underwent PRK in the nondominant eye first. Preoperative refractions averaged -3.8+/-1.6 diopters (D), with an average correction of 3.4+/-1.9 D, corresponding to 49.7+/-20.5 microns of ablation. There were no statistically significant preoperative differences between the fellow eyes in refractive error (P = 0.65). Postoperatively, there were no statistically significant changes in any GDx parameter in the treated eye compared with the untreated control eye (P = 0.21).

CONCLUSIONS

Excimer laser PRK for moderate myopia has no significant effect on RNFL thickness measurements as determined by scanning laser polarimetry.

Corneal surface temperature change as the mode of stimulation of the non-contact corneal aesthesiometer

PURPOSE

The non-contact corneal aesthesiometer (NCCA) assesses corneal sensitivity by using a controlled pulse of air, directed at the corneal surface. The purpose of this paper was to investigate whether corneal surface temperature change was a component in the mode of stimulation.

METHODS

Thermocouple experiment: A simple model corneal surface was developed that was composed of a moistened circle of filter paper placed on a thermocouple and mounted on a glass slide. The temperature change produced by different stimulus pressures was measured for five different ambient temperatures. Thermal camera experiment: Using a thermal camera, the corneal surface temperature change was measured in nine young, healthy subjects after exposure to different stimulus air pulses. Pulse duration was set at 0.9 s but was varied in pressure from 0.5 to 3.5 millibars.

RESULTS

Thermocouple experiment: An immediate drop in temperature was detected by the thermocouple as soon as the air flow was incident on the filter paper. A greater temperature change was produced by increasing the pressure of the incident air flow. A relationship was found and a calibration curve plotted. Thermal camera experiment: For each subject, a drop in surface temperature was detected at each stimulus pressure. Furthermore, as the stimulus pressure increased, the induced reduction in temperature also increased. A relationship was found and a calibration curve plotted.

CONCLUSION

The NCCA air-pulse stimulus was capable of producing a localized temperature change on the corneal surface. The principal mode of corneal nerve stimulation, by the NCCA air pulse, was the rate of temperature change of the corneal surface.

Quantitative comparison of Zeiss-Humphrey model 840 and Rion UX-02 systems of ultrasound biomicroscopy

BACKGROUND

Our objective was to estimate the agreement between two different ultrasound biomicroscopes (UBMs) and to evaluate the clinical implications of the measurements obtained.

METHODS

We measured the anterior chamber depth, trabecular-iris angle, angle opening distance at 250 and 500 microm from the scleral spur, iris thickness and scleral-iris angle using the Humphrey UBM model 840 and Rion UBM UX-02 in 25 eyes of 25 normal volunteers.

RESULTS

No significant difference was found in the mean values of any parameters measured by the Humphrey and Rion systems. Correlation coefficients of greater than 90% were observed for the parameters studied. Each system showed high reproducibility for all measured parameters. There were significant differences between the two systems in coefficients of variation for all parameters measured except the anterior chamber depth.

CONCLUSIONS

The parameters measured with the Humphrey and Rion systems showed correlation coefficients of greater than 90%. The Humphrey system showed better reproducibility than the Rion system.

Noninvasive measurement of the Bayliss effect in retinal autoregulation

PURPOSE

The Bayliss effect describes the reaction of smooth muscle cells in the arterial wall to changes in blood pressure. A rise in mean arterial blood pressure (MAP) causes an autoregulatory myogenic vessel constriction by smooth muscle cells in the arterial wall. The responsiveness of retinal vessels to changes in MAP were analyzed using the Retinal Vessel Analyzer (RVA).

METHODS

Continuous measurement of retinal arterial vessels was performed in 40 healthy volunteers (age 18-56 years.) over a 9-min period. After a 3-min baseline measurement (phase I), isometric exercise caused a rise in MAP over the next 3 min (phase II). During the last 3 min (phase III) recovery was observed. Blood pressure and ECG were documented simultaneously throughout the experiment.

RESULTS

Exercise caused a significant rise of 22.8 (+/-6.0) mm Hg in MAP (phase II vs. phase I: P<0.001). Retinal arterioles showed 5.5% (+/-2.8%) vasoconstriction (P<0.001). During phase III vessel diameters returned to normal, with no difference from phase I (P = 0.179).

CONCLUSION

Noninvasive measurement and quantitative analysis of the Bayliss effect in human retinal vessels by means of the RVA is possible. Analysis of retinal arterial autoregulation may provide valuable insight into pathologic conditions such as diabetic or hypertensive retinopathy.

Differentiation of degenerative retinoschisis from retinal detachment using optical coherence tomography

OBJECTIVE

To assess the potential of optical coherence tomography (OCT) to differentiate retinoschisis from retinal detachment. Optical coherence tomography is a noninvasive, noncontact imaging method that produces high-resolution, cross-sectional images of ocular tissue.

DESIGN

Retrospective case series.

PARTICIPANTS

Thirteen eyes of 12 patients with the differential diagnosis of retinoschisis versus retinal detachment.

METHODS

Differentiation between retinoschisis and retinal detachment was established from both ophthalmoscopic and OCT examinations.

MAIN OUTCOME MEASURE

Ability of OCT to differentiate retinoschisis from retinal detachment was measured.

RESULTS

Thirteen eyes of 12 patients with retinal elevation were examined with OCT. The cross-sectional view produced by OCT was effective in distinguishing retinoschisis from retinal detachment. Optical coherence tomography images of retinoschisis show a splitting of the neurosensory retina. The OCT images of retinal detachment show separation of full-thickness neurosensory retina from the retinal pigment epithelium band. The OCT images correlated with the clinical impression in all 13 cases.

CONCLUSIONS

Based on this series of cases, OCT is a potentially useful new test that may be used to distinguish retinoschisis from rhegmatogenous retinal detachment.

Corneal indentation during ultrasonic pachometry

PURPOSE

This study attempted to determine whether the indentation of the cornea with an ultrasonic probe affects the corneal-thickness measurement.

METHODS

A solid-tip ultrasonic transducer was mounted into the spring arm of a standard Goldmann Applanation Tonometer. Five human subjects were studied. The visual axis of each cornea was marked with a corneal marker, and the ultrasonic transducer was placed on the visual axis. Corneal-thickness measurements were made during five tension settings of the tonometer: 0, 10, 20, 40, and 80. The R-F signals were received by using a 475 Textronix oscilloscope, and the thicknesses were digitally measured.

RESULTS

There was no trend for decreasing or increasing thickness measurements with increasing tension settings.

CONCLUSION

Corneal-thickness measurements by ultrasonic pachometry are not significantly affected by corneal indentation with the ultrasonic probe.

Brightness alters Heidelberg retinal flowmeter measurements in an in vitro model

PURPOSE

The Heidelberg Retinal Flowmeter (HRF), a laser Doppler flowmetry device, has captured interest as a research and clinical tool for measurement of ocular blood flow. Concerns remain about the range and accuracy of the values that it reports.

METHODS

An in vitro blood-flow model was constructed to provide well-controlled laminar flow through a glass capillary for assessment by HRF. A change in material behind the glass capillary was used to simulate changing brightness conditions between eyes.

RESULTS

Velocities reported by the HRF correlated linearly to true velocities below 8.8 mm/sec. Beyond 8.8 mm/sec, HRF readings fluctuated randomly. True velocity and HRF reported velocities were highly correlated, with r = 0.967 (P < 0.001) from 0.0 mm/sec to 2.7 mm/sec mean velocity using a light background, and r = 0.900 (P < 0.001) from 2.7 mm/sec to 8.8 mm/sec using a darker background. However, a large change in the y-intercept occurred in the calibration curve with the background change.

CONCLUSIONS

The HRF may report velocities inaccurately because of varying brightness in the fundus. In the present experiment, a darker background produced an overreporting of velocities. An offset, possibly introduced by a noise correction routine, apparently contributed to the inaccuracies of the HRF measurements. Such offsets vary with local and global brightness. Therefore, HRF measurements may be error prone when comparing eyes. When used to track perfusion in a single eye over time, meaningful comparison may be possible if meticulous care is taken to align vessels and intensity controls to achieve a similar level of noise correction between measurements.

Evaluation of focal defects of the nerve fiber layer using optical coherence tomography

OBJECTIVE

To analyze glaucomatous eyes with known focal defects of the nerve fiber layer (NFL), relating optical coherence tomography (OCT) findings to clinical examination, NFL and stereoscopic optic nerve head (ONH) photography, and Humphrey 24-2 visual fields.

DESIGN

Cross-sectional prevalence study.

PARTICIPANTS

The authors followed 19 patients in the study group and 14 patients in the control group.

INTERVENTION

Imaging with OCT was performed circumferentially around the ONH with a circle diameter of 3.4 mm using an internal fixation technique. One hundred OCT scan points taken within 2.5 seconds were analyzed.

MAIN OUTCOME MEASURES

Measurements of NFL thickness using OCT were performed.

RESULTS

In most eyes with focal NFL defects, OCTs showed significant thinning of the NFL in areas closely corresponding to focal defects visible on clinical examination, to red-free photographs, and to defects on the Humphrey visual fields. Optical coherence tomography enabled the detection of focal defects in the NFL with a sensitivity of 65% and a specificity of 81%.

CONCLUSION

Analysis of NFL thickness in eyes with focal defects showed good structural and functional correlation with clinical parameters. Optical coherence tomography contributes to the identification of focal defects in the NFL that occur in early stages of glaucoma.

Quantitative analysis of diabetic macular edema after scatter laser photocoagulation with the scanning retinal thickness analyzer

PURPOSE

To define the effect of scatter laser photocoagulation on foveal retinal thickness.

METHODS

A commercial scanning retinal thickness analyzer was used to measure retinal thickness. The foveal retinal thickness was measured at the central area of the fundus (0.4 x 0.4 mm). The method was applied to 20 consecutive patients (mean age, 52.4 +/-16.9 years) with diabetic retinopathy. Measurements were performed before and 6 weeks after scatter photocoagulation. Patients were examined by fluorescein angiography and slit-lamp biomicroscopy to detect macular edema.

RESULTS

Mean foveal thickness before scatter photocoagulation was 187+/-45 microm, increasing to 221+/-46 microm after the treatment (P = 0.0001). The foveal thickness increased in 12 eyes (60%). Laser treatment increased macular permeability in two eyes (10%). Biomicroscopic examination revealed central macular thickening in one eye (5%). Visual acuity was reduced in four eyes (20%).

CONCLUSIONS

Our results suggest that subclinical macular edema occurs after scatter laser photocoagulation. The retinal thickness analyzer is a sensitive tool for early detection of macular edema after laser treatment, because increases in retinal thickness as small as 34 microm cannot be assessed by slit-lamp biomicroscopy.

Noninvasive mapping of the normal retinal thickness at the posterior pole

OBJECTIVE

Objective and sensitive measurements of the retinal thickness at the posterior pole are useful to detect and delineate macular edema or retinal atrophy. The authors therefore developed an instrument, the Retinal Thickness Analyzer (RTA), to map the retinal thickness rapidly. The RTA was used to study the normal thickness at the posterior pole and to provide a pilot baseline.

DESIGN

Cross-sectional study.

METHODS

A green (540-nm) laser slit was focused on the retina via a scanning mirror placed at the conjugate plane of the pupil. The intersection between the laser slit and the retina was viewed at an angle and recorded by a video camera. Nine scans, each acquired in 200 to 400 msec, covered the central 20 degrees of the fundus.

PARTICIPANTS

The posterior pole was mapped in 29 normal subjects 19 to 76 years of age (mean, 48 years).

RESULTS

The thickness maps matched the posterior pole anatomy. Points with maximum thickness were located in the perifovea in a C-shaped manner extending from the disc to above and below the fovea. The local variation (standard deviation) in retinal thickness among the subjects was, on average, 15 microns. Age, gender, and race did not have a large effect (< 35 microns) on the values.

CONCLUSIONS

Rapid scanning thickness analysis with the RTA provides a detailed map of the retinal thickness. The relatively narrow range of thickness values in normal subjects indicates that the method may provide a sensitive detection of pathologic thickening or thinning of the retina.

Quantification of blood-aqueous barrier breakdown after photorefractive keratectomy for myopia

BACKGROUND

Photorefractive keratectomy (PRK) using the excimer laser is a well-established surgical technique for correction of mild to moderate myopic refraction errors in case of spectacle or contact lens incompatibility. As it is still uncertain whether this procedure causes intraocular inflammatory changes, it was the purpose of this study to quantify breakdown of the blood-aqueous barrier following PRK and to look for possible correlations with clinical parameters.

PATIENTS AND METHODS

Aqueous flare was quantified using the laser flare-cell meter after medical pupil dilation preoperatively and on days 1, 3 and 7 as well as 1 month and 3 months following PRK with a 193-nm excimer laser (MEL 60, Aesculap-Meditec) in 37 eyes of 22 patients. The preoperative spherical equivalents were -4.4 +/- 3.1 D (range -1.5 to -8.0 D). Pre-, intra- and postoperative treatment was standardized.

RESULTS

Preoperatively, aqueous flare values were 3.9 +/- 0.8 photon counts/ms and showed no significant correlation with the spherical equivalent (p > 0.1). Postoperatively, aqueous flare rise was very small with flare values not significantly higher than preoperative values. All postoperative flare values were below the normal limit (< 8.0 photon counts/ms). Flare was highest on day 3 after PRK surgery. There was no statistically significant correlation between aqueous flare and depth of stromal ablation. The number of aqueous "cells" did not increase following PRK at any postoperative follow-up examination.

CONCLUSION

Our results indicate that PRK in mild to moderate myopia does not cause a significant breakdown of the blood-aqueous barrier.

Optical coherence tomography of macular thickness after cataract surgery

PURPOSE

To evaluate macular thickness changes after uneventful cataract surgery using optical coherence tomography (OCT) and compare the findings with those of flare and cell measurements of the anterior chamber.

SETTING

Clinique Sourdille, Nantes, France.

METHODS

In this retrospective study, 41 eyes having uneventful cataract surgery with a clear corneal small incision and intracapsular fixation of a foldable intraocular lens were evaluated by OCT and laser flare and cell measurements preoperatively and 1, 8 to 12, and 30 to 60 days postoperatively.

RESULTS

Some postoperative increase in macular thickness was noted in 11 eyes. This was not related to a higher postoperative flare. Visual consequences were proportional to the macular elevation.

CONCLUSION

Clinical and subclinical thickness changes, without breakdown of the blood-aqueous barrier, can be detected after cataract surgery. Most of these changes resolve spontaneously, but their mid- and long-term significance is unknown.

Measurement of corneal sensitivity to mechanical and chemical stimulation with a CO2 esthesiometer

PURPOSE

To develop an instrument to measure corneal sensitivity. Mechanical stimulation was performed with increasing air flow. Chemical stimulation consisted of local pH decreases induced by a mixture of air and CO2 at different concentrations.

METHODS

Air and 98.5% CO2 were mixed with an electronic, proportional-direction control valve to obtain gas mixtures from 0% to 80% CO2. The regulated outflow of gas was carried to a probe mounted on a slit lamp holder, where it was warmed and its CO2 concentration monitored. An electronic valve directed gas pulses of controlled duration to the cornea. Corneal stimulation was performed in 17 young human subjects. The intensity of the experienced sensation was recorded in a continuous visual analog scale (VAS). To obtain threshold values and intensity-response curves, 3-second pulses were applied. For mechanical stimulation, air pulses of increasing flow were used. For chemical stimulation, gas mixtures of increasing CO2 concentration at subthreshold flow and CO2 in stepped increases of 5% was applied.

RESULTS

Mechanical and chemical stimulation of the cornea evoked a brief sensation of irritation. Mechanical threshold (flow values) varied among subjects but were reproducible within each subject and were higher with warmed air. The magnitude of the sensation increased proportionally to the flow of air. The mean chemical stimulation threshold (CO2 concentration) was 25% +/- 3%. Increases in CO2 concentration from 10% to 80% augmented proportionally the intensity of the evoked sensation.

CONCLUSIONS

The gas esthesiometer, which combines variable air flow and CO2 concentrations, permits application to the cornea of mechanical stimuli of controlled force and pH reductions of increasing magnitude. This instrument may be useful in a separate exploration of mechanical and chemical sensitivity of the cornea in human subjects.

Agreement and repeatability of infrared pupillometry and the comparison method

OBJECTIVE

To evaluate the accuracy and repeatability of the widely used comparison method of measuring pupil size.

DESIGN

Cross-sectional study.

PARTICIPANTS

Fourteen eyes of seven healthy myopic subjects were examined.

INTERVENTION

Two examiners made two repeated measures of pupil diameters of 14 eyes using Rosenbaum card comparison pupillometry and infrared pupillometry. Subjects fixated on a distant visual acuity chart, and pupils were measured under three luminance conditions. The agreement and inter-rater repeatability of both methods were determined.

MAIN OUTCOME MEASURES

Outcomes were pupil diameters, limits of agreement, and coefficient of repeatability of two examiners.

RESULTS

The mean difference between the two techniques ranged from 0.3 to 0.5 mm. The limits of agreement within two standard deviations ranged from 2.4 to 2.8 mm. Coefficient of repeatability ranged from 0.6 to 1.4 mm for infrared pupillometry and 1.0 to 1.2 mm for Rosenbaum pupillometry. Inter-rater repeatability of Rosenbaum pupillometry was consistently pupil diameter biased. Pupil diameters measured with the Rosenbaum method were consistently larger than diameters measured with the infrared technique for both examiners under all luminance conditions.

CONCLUSIONS

Results indicate that although the mean difference in techniques was small, the range of the agreement between the Rosenbaum and the infrared techniques was large. The Rosenbaum method consistently overestimated pupil diameters and was subject to inter-rater repeatability bias. Rosenbaum pupillometry may not be appropriate when accurate pupil measurements are required. The results have implications for many clinical trials in ophthalmology, including those evaluating refractive surgery that use Rosenbaum comparison pupillometry.

Detection of glaucoma with scanning laser polarimetry

OBJECTIVE

To determine which retinal nerve fiber layer (RNFL) measures obtained with scanning laser polarimetry are most useful in detecting early to moderate glaucomatous visual field loss.

SUBJECTS AND METHODS

One eye from 84 healthy individuals and 83 patients with early to moderate glaucomatous visual field loss (167 eyes) was assessed with a scanning laser polarimeter (Laser Diagnostic Technologies, San Diego, Calif). Three separate scans were obtained, and a baseline scan was created and used in the analyses. Integrated software (program GDx, version 1.0.02; Laser Diagnostic Technologies) was evaluated by assessing its sensitivity and specificity for detecting early and moderate glaucomatous visual field loss. Fisher linear discriminant functions also were developed in this population to assess sensitivity and specificity and were compared with the GDx analyses.

RESULTS

There were statistically significant differences between the healthy and glaucomatous eyes for 14 of the 15 RNFL measures (P = .001). However, considerable overlap in measurements between groups was found. With the GDx number, the area under the receiver operator characteristic (ROC) curve was 0.78, and the sensitivity and specificity were 82% and 62%, respectively. Applying the best discriminant function using 3 variables (average thickness, ellipse modulation, and average ellipse thickness) to our study population resulted in an area under the ROC curve of 0.89 and a sensitivity and specificity of 74% and 92%, respectively.

CONCLUSIONS

A combination of RNFL measures obtained using the scanning laser polarimeter improved the ability to differentiate between healthy eyes and eyes with early and moderate glaucomatous visual field loss. Analyses using GDx software did not differentiate between healthy and glaucomatous eyes as well as the discriminant analysis function did.

A microendoscopic test card for ophthalmic endoscopes

Ophthalmic endoscopes allow examination of intraocular structures when traditional surgical microscopic visualization is limited or impossible. Periodic evaluation of the optical precision of these instruments is essential to ensure optimal intraoperative performance. A test card has been developed to aid in the calibration of ophthalmic endoscopes. Its 5 test targets assess white balance and fiberoptic bundle integrity, focus and resolution, orientation, color fidelity, and angle of view.

Preoperative measurement of scotopic pupil dilation using an office pupillometer

PURPOSE

To describe a light-amplification pupillometer designed for office evaluation of refractive surgical candidates and compare its usefulness with that of a millimeter ruler and a standard pocket-card pupillary gauge.

SETTING

Center for Ophthalmic Surgery, Encino, California, USA.

METHOD

The pupil sizes of 100 patients with a mean age of 28 years (range 18 to 50 years) were measured at 2 levels of illumination: 15 and 3 lumens. Pupil size was measured with a Rosenbaum pocket-card pupil gauge, a millimeter ruler, and the pupillometer at approximately 15 lumens. This level of illumination was chosen by 3 technicians as the lowest at which the pupil of a brown eye could be measured with confidence using the Rosenbaum card. Pupil size was then measured using the light-amplification pupillometer at approximately 3 lumens. This illumination level was chosen to simulate that of night-driving conditions.

RESULTS

At 15 lumens, mean pupil diameter was 5.1 mm (range 2.5 to 8.0 mm). There was no difference in the measurements taken with the 3 instruments at this illumination level. At 3 lumens, the pupil diameter could not be measured with confidence using the Rosenbaum card or the millimeter ruler. Using the pupillometer, mean pupil size was 6.2 mm (range 3.0 to 9.0 mm). The mean difference in pupil diameter measured at 15 and 3 lumens was 1.1 mm (range 0.0 to 3.0 mm).

CONCLUSION

This evaluation suggests that it would be difficult for clinicians to reliably predict the level of pupil dilation at 3 lumens by measuring pupil size at 15 lumens. The light-amplification pupillometer provides a tool for measuring pupil size at an illumination level that simulates night-driving conditions. The use of this device may help surgeons identify refractive surgery candidates who are more likely to be dissatisfied with their postoperative vision at low illumination levels.

Slope of the peripapillary nerve fiber layer surface in glaucoma

PURPOSE

To develop structural markers of early glaucomatous optic nerve damage with confocal scanning laser ophthalmoscopy.

METHODS

Custom software was developed to analyze the images of 53 patients with open-angle glaucoma and 43 healthy subjects (matched for age, race, and refractive error), with images acquired with a confocal scanning laser ophthalmoscope. Height values were obtained along radial profiles of the peripapillary nerve fiber layer surface at 5-degree intervals around the disc edge. Two new parameters were derived: mean height and mean slope of the peripapillary nerve fiber layer surface. Mean slope was tested for its independence from a retinal reference plane. A logistic regression analysis was used to determine functions of disease probability. Receiver-operating characteristic (ROC) curves were used to evaluate sensitivity and specificity of peripapillary nerve fiber layer slope and height to discriminate normal subjects from glaucoma patients.

RESULTS

Mean (+/-SD) visual field mean deviation in the glaucoma group was -4.8 +/- 3.3 dB. Mean slope (+/-SD) of the peripapillary nerve fiber layer was significantly (P < 0.001) steeper (0.30 +/- 0.12) in glaucoma patients than in healthy subjects (0.11 +/- 0.12). Mean slope values were identical with or without the retinal reference plane. Mean height (+/-SD) values with respect to a retinal reference plane were 45.2 +/- 103 microm in healthy subjects and -65.2 +/- 105 microm in glaucoma patients, which were significantly different (P < 0.001). The differences for mean slope and for mean height between the healthy subjects and the glaucoma patients were greatest inferiorly. The diagnostic precision, sensitivity, and specificity of mean slope were 83%, 85%, and 80%, respectively. The diagnostic precision, sensitivity, and specificity of mean height were 75%, 69%, and 83%, respectively.

CONCLUSIONS

Mean peripapillary slope of the nerve fiber layer surface can be used to discriminate between healthy subjects and glaucoma patients with clinically useful diagnostic precision. This parameter is independent of a retinal reference plane and may be particularly useful to detect progressive glaucoma damage.

Differentiating patients with glaucoma from glaucoma suspects and normal subjects by nerve fiber layer assessment with scanning laser polarimetry

PURPOSE

A study was conducted to determine normative data for nerve fiber layer measurements as obtained by scanning laser polarimetry with the Laser Diagnostic Technologies Nerve Fiber Analyzer II, identify factors affecting the measurements, and identify parameters capable of differentiating normal subjects from patients with glaucoma and patients suspected of having glaucoma because of ocular hypertension or because of a large cup-to-disc ratio (GS-disc).

DESIGN

A case series.

PARTICIPANTS

Four hundred normal subjects, 35 patients with ocular hypertension, 42 patients with glaucoma, and 17 glaucoma suspects based on optic disc appearance participated.

METHODS

Nerve fiber layer thickness assessments were determined in normal subjects (with normal-appearing optic nerves and normal visual fields). The results were compared to measurements from samples of age-matched patients with ocular hypertension (with normal visual fields), patients suspected of having glaucoma based on enlarged cup-to-disc ratios, and patients with open-angle glaucoma who had visual field loss.

RESULTS

The majority of the parameters derived from the measurements showed no significant relationship to age, although some parameters tended to decrease with increasing age. Multiple parameters showed statistically significant differences between normal subjects and patients with glaucoma. In particular, the intraellipse sector variability, an indirect measure of the shape of the nerve fiber layer in an ellipse surrounding the nerve head, showed statistically significant differences between normal subjects and patients with glaucoma as well as between glaucoma suspects and normal subjects. Similar results were seen with the superior maxima, the average thickness assessment value of the 1500 thickest points in the superior bundle.

CONCLUSIONS

Assessments of nerve fiber layer thickness as determined by scanning laser polarimetry can differentiate patients with glaucoma from normal subjects and may identify otherwise undetected damage in glaucoma suspects.

Correlation of peripapillary nerve fiber layer thickness by scanning laser polarimetry with visual field defects in patients with glaucoma

PURPOSE

To assess the correlation between the results of peripapillary scanning laser polarimetry of the retinal nerve fiber layer (NFL) and automated visual field testing in patients with open-angle glaucoma.

METHODS

Visual fields from 42 patients with varying stages of glaucoma were scored using Collaborative Initial Glaucoma Treatment Study (CIGTS) criteria. Mean deviation, pattern standard deviation, and CIGTS total and hemifield visual field scores were correlated with peripapillary NFL thickness measured by scanning laser polarimetry using summed, ratio-based, and modulation parameters.

RESULTS

Mean deviation and CIGTS total and upper hemifield score were significantly correlated with NFL retardation values using summed, ratio-based, or modulation parameters. The CIGTS lower hemifield score was significantly correlated with modulation parameter values only. Correlation of CIGTS scores was significantly stronger with modulation parameters than with summed parameters (total and lower hemifield scores) and ratio-based parameters (lower hemifield only) by the Hotelling t test.

CONCLUSION

Relative NFL thickness measured by scanning laser polarimetry correlates well with visual field defects seen on Humphrey perimetry of patients with open-angle glaucoma. Modulation parameters, in which the superior and inferior peak NFL thickness (as measured by scanning laser polarimetry) are adjusted for the patient's average minimum NFL thickness in the nasal and temporal quadrants, provided stronger correlation than summed parameters and ratio-based parameters.

Retinal nerve fiber layer thickness within the area of apparently normal visual field in normal-tension glaucoma with hemifield defect

PURPOSE

To evaluate changes in nerve fiber layer (NFL) thickness in areas with apparently normal retinal sensitivity in eyes with normal-tension glaucoma (NTG) with hemifield dominant visual field defects.

METHODS

The prospective clinical study consisted of 17 eyes from 17 patients with NTG in whom superior or inferior hemifield dominant defects based on the Humphrey visual field of central 30 degrees were present, and 10 normal eyes from 10 control subjects matched in age and refractive error. The retinal NFL thickness was evaluated with a scanning laser polarimeter. Mean NFL thickness measurements in the defined ring in four quadrants (superior, inferior, nasal, and temporal) were obtained. To facilitate visual field and NFL thickness correspondence, the total deviation (TD) plot of the visual field was divided into four 90 degrees quadrants, using Wirtschafter's scheme to match the four quadrants examined by laser polarimetry.

RESULTS

The mean NFL thickness in the unaffected quadrant, i.e., the quadrant within the area corresponding to the hemifield with apparently normal visual field in eyes with NTG, was significantly thinner than the average NFL thickness of the superior and inferior quadrants in the normal eyes. In eyes with NTG, the NFL thickness in the affected quadrant also was significantly thinner than that in the unaffected quadrant. In the unaffected quadrant, visual field TD (the sum of the TD values within this quadrant) showed a significant correlation with the ratio of NFL thickness in the unaffected quadrant to that in the nasal quadrant.

CONCLUSION

Early changes in the retinal nerve fiber layer may already exist even in the unaffected area of the visual field in eyes with NTG with hemifield dominant visual field defects.

Disinfection of eyelid speculums for retinopathy of prematurity examination

OBJECTIVE

To evaluate the effectiveness of 70% isopropyl alcohol swabs in disinfecting eyelid speculums after examination for retinopathy of prematurity.

METHODS

Two phases. Phase 1: 46 autoclave-sterilized eyelid speculums randomized into either a cleaned or control group following examination for retinopathy of prematurity. Speculums in the cleaned group were disinfected with a 70% isopropyl alcohol swab while control speculums were not cleaned. Bacterial and fungal cultures were then obtained. Phase 2: 20 autoclave-sterilized eyelid speculums inoculated with a clinically relevant dilution of adenovirus serotype 5 or herpes simplex virus type 2. Inoculated speculums were randomized into either a cleaned or control group.

RESULTS

Phase 1: 17 (70.8%) of 24 cultures from the cleaned group yielded bacteria compared with 21 (95.5%) of 22 controls. Fungi were isolated from only 1 control and from no cleaned speculums. Phase 2: all speculums inoculated with adenovirus supported growth of the organism irrespective of cleaning with 70% isopropyl alcohol swabs. None of 5 cleaned speculums inoculated with herpes simplex virus type 2 supported viral growth, compared with 3 (60%) of 5 cultures positive for growth in the control group.

CONCLUSION

Cleaning eyelid speculums with 70% isopropyl alcohol swabs provided inadequate disinfection against bacteria following examination for retinopathy of prematurity and against adenovirus in a laboratory simulation.