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PubMed1998

[Transplant vertical tilt after perforating keratoplasty--comparison between non-mechanical trepanation with excimer laser and motor trepanation].

BACKGROUND: Besides decentration of the graft/host trephination and "horizontal torsion" "vertical tilt" is an important factor for reduced visual outcome after penetrating keratoplasty (PK). The purpose of this study was to evaluate the time course of vertical tilt in absolute value and direction and to correlate it with functional results after PK. PATIENTS AND METHODS: Fifty patients each (20 primary dystrophies, 30 keratoconus) underwent nonmechanical trephination (NMT) (excimer laser MEL60, Aesculap-Meditec, Heroldsberg, Germany) or mechanical motor trephination (MT) (Geuder, Heidelberg, Germany) in penetrating keratoplasty. All procedures (7.5 mm in dystrophies, 8.0 mm in keratoconus, 8 orientation teeth in NMT, double-running 10-0 nylon suture) were performed by one surgeon (GOHN). At a postoperative gate of 6 weeks, 6 months, before partial suture removal and after complete suture removal, corneal topography analysis (TMS-1, Tomey, Tennenlohe, Germany) was performed. After a Gram-Schmidt-orthogonalization corneal topography height data of 25 noncentric rings in 256 hemimeridians were decomposed into Zernike components of radial order n = 16 in the sense of minimizing the root mean square error. The tilt of the surface relative to the videokeratoscope axis was calculated from the Zernike components Z1(1) and Z1(-1). The meridional power at the cardinal meridians was derived from all parabolic Zernike terms. Tilt and the difference between both meridians of the Zernike representation (ZA) were correlated with the results of Zeiss keratometry (KA). Simulated Keratometry (SimK) of the TMS-1, subjective refraction (RZ) and best-corrected visual acuity. RESULTS: After NMT, vertical tilt of the graft was 3 degrees without significant change over time. Following MT, an equivalent time course could be observed before partial suture removal. However, after complete suture removal, a significant increase of the tilt was measured to 5 degrees (p = 0.02). No significant difference could be detected comparing keratoconus and Fuchs' dystrophy both in NMT and MT. The direction of the vertical tilt component piled up to the hemimeridian defined by the knot of the first running suture. At all postoperative follow-up examinations, the ZA of the Zernike decomposition showed a good correlation to the RZ, whereas the KA and the SimK did not. At the end of the follow-up, best-corrected visual acuity after NMT was 2 decimal lines better than after MT. CONCLUSIONS: The Zernike decomposition of topographic height data is a suitable tool for extraction and quantifying vertical tilt of the graft following penetrating keratoplasty. In contrast to conventional keratometry with its 4-point measurement, a decomposition of topographic height data into orthogonal polynomials enables a detection of both cardinal meridians even in corneas with a high degree of local irregularities.

Adolescent↗
PubMed1991

Orientation disparity, deformation, and stereoscopic slant perception.

Koenderink and van Doorn's theory, that the basis of stereoscopic slant perception is the deformation component of the disparity, field, was tested for slant around a horizontal axis, which produces images with a vertical ramp of horizontal disparity (horizontal shear) characterised by a global orientation disparity at the vertical meridian. The disparity field in this case can be parsed into two components, deformation and curl, which each contribute half of the orientation disparity. This case was compared with similar random-dot stimuli in which the deformation component was doubled and the curl component eliminated or vice versa. All three types of stimuli had identical orientation disparity at the vertical meridian. A condition in which there was no such orientation disparity, but deformation was present, was also included. It was found that perceived slant was not related to the deformation present, as Koenderink and van Doorn's theory would predict, but was predictable from the orientation disparity at the vertical meridian per se.

Depth Perception↗
PubMed1998

The representation of the ipsilateral visual field in human cerebral cortex.

Previous studies of cortical retinotopy focused on influences from the contralateral visual field, because ascending inputs to cortex are known to be crossed. Here, functional magnetic resonance imaging was used to demonstrate and analyze an ipsilateral representation in human visual cortex. Moving stimuli, in a range of ipsilateral visual field locations, revealed activity: (i) along the vertical meridian in retinotopic (presumably lower-tier) areas; and (ii) in two large branches anterior to that, in presumptive higher-tier areas. One branch shares the anterior vertical meridian representation in human V3A, extending superiorly toward parietal cortex. The second branch runs antero-posteriorly along lateral visual cortex, overlying motion-selective area MT. Ipsilateral stimuli sparing the region around the vertical meridian representation also produced signal reductions (perhaps reflecting neural inhibition) in areas showing contralaterally driven retinotopy. Systematic sampling across a range of ipsilateral visual field extents revealed significant increases in ipsilateral activation in V3A and V4v, compared with immediately posterior areas V3 and VP. Finally, comparisons between ipsilateral stimuli of different types but equal retinotopic extent showed clear stimulus specificity, consistent with earlier suggestions of a functional segregation of motion vs. form processing in parietal vs. temporal cortex, respectively.

Brain Mapping↗
PubMed1996

Comparison of two commercial enzyme immunoassays with cytotoxicity assay and culture for the diagnosis of Clostridium difficile related diarrhea.

184 stool samples were analysed for the presence of Clostridium difficile and toxins using the Meridian Premier Toxin A and TechLab Tox-A EIA kits, selective culture and cytotoxin assay. Of the 184 samples 36 stools tested positive for cytotoxin. In comparison the sensitivity and specificity of the EIAs and culture were as follows: Meridian, 72 and 87, TechLab, 64 and 95, and selective culture, 83 and 96%, respectively. The positive predictive values and negative predictive values for the various methods were: Meridian, 58 and 93, TechLab, 77 and 92, and selective culture, 83 and 96%, respectively. Discrepant results to those obtained by cytotoxicity assay were encountered with both EIA kits evaluated and less so by culture. In this study direct isolation of Clostridium difficile from stool samples most closely paralleled the findings of the "gold standard" cell line cytotoxicity assay. It appears that a single test for the determination of Clostridium difficile disease is adequate, although a second method improves the predictability of the diagnosis. Direct culture of feces provided a reliable secondary procedure to cytotoxicity assay. The EIAs were simple to use, labour efficient and provided a rapid result. However the lack of sensitivity and relative expense did not justify their routine use in our laboratory.

Bacteriological Techniques↗
PubMed2006

Biofilm formation on hydrophilic intraocular lens material.

PURPOSE: To estimate bacterial biofilm formation on the hydrophilic acrylic (hydrogel) intraocular lens (IOL) Meridian (HP60M, Baush & Lomb) and to investigate a preventive effect against biofilm formation of hydrogel IOLs presoaked in antibiotics. METHODS: Two Staphylococcus epidermidis strains, ATCC 12228 and ATCC 35984 (biofilm-producer), and an Enterococcus faecalis strain (KOS1, clinical isolate from an endophthalmitis patient) were used. Biofilms were cultivated on disks of different IOL materials: hydrogel, PMMA (polymethylmethacrylate), and acrylic. Biofilms were stained with crystal violet (CV), which served as an index of biofilm formation. The bacterial population was enumerated after biofilm homogenization. Biofilms were also examined by scanning electron microscopy (SEM). IOLs were presoaked in two antibiotics, levofloxacin (LVFX) and gatifloxacin (GFLX), and then the bacterial population was enumerated. As in vivo experiment, antibiotics-treated and nontreated Meridian IOLs were implanted in rabbit eyes, which served as an endophthalmitis model, and the bacterial population was enumerated. RESULTS: The amount of biofilm formed was the least on hydrogel from among the three materials tested after 48- and 72-hr incubation (p < 0.05 to 0.01). The bacterial population was the least on hydrogel from among the three materials with ATCC 12228 (p < 0.05 to 0.01), and the bacterial population was significantly different between hydrogel and acrylic after 72-hr incubation with ATCC 35984 (p < 0.05). Biofilm by the two S. epidermidis strains were recognized after 24-hr incubation. Rates of biofilm-positive SEM fields, which were defined as being occupied by biofilm over at least half of the area, were increased through 72 hr with ATCC 35984. While the E. faecalis strain showed no bacterial adherence on the antibiotics-treated hydrogel IOLs, adherence of the S. epidermidis strain, ATCC 35984 was recognized on the LVFX-treated IOLs after 48-hr incubation (103 to 104 CFU/ml). In the rabbit in vivo model, the bacterial populations in eyes with an antibiotics-treated Meridian IOL were significantly smaller than in eyes with a nontreated IOL for 72 hr after surgery (p < 0.05 to 0.01). CONCLUSIONS: The biofilm formation was less on hydrogel than on other two materials tested. Hydrogel presoaked in antibiotics exhibited a preventive effect against biofilm formation at least for 24 hr in vitro and against bacterial proliferation in the rabbit in vivo endophthalmitis model.

Acrylic Resins↗
PubMedDate not supplied

Acupuncture reduces experimental renovascular hypertension through mechanisms involving nitric oxide synthases.

OBJECTIVE: To test the hypothesis that acupuncture on stomach 36 point (ST-36) reduces hypertension by activating nitric oxide synthase signaling mechanisms. METHODS: The authors used the two-kidney, one-clip renal hypertension (2K1C) hamster model with electroacupuncture treatment. RESULTS: Thirty-minute daily electroacupuncture treatment for 5 days reduced mean arterial pressure from 160.0 +/- 7.6 to 128.0 +/- 4.3 mmHg (mean +/- SEM), compared to 115.0 +/- 7.2 mmHg in sham-operated hamsters. Electroacupuncture increased periarteriolar NO concentration from 309.0 +/- 21.7 nM to 417.9 +/- 20.9 nM in the 2K1C hamster cheek pouch microcirculation when measured with NO-sensitive microelectrodes. Hypertension reduced endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) proteins relative to the sham-operated control, as measured by Western blotting. Electroacupuncture prevented the reduction of eNOS and nNOS associated with hypertension and showed even higher eNOS and nNOS expressions than sham-operated control in stomach and cheek pouch tissues, which are on the stomach meridian. Analysis of liver tissue, a non-stomach-meridian organ, indicated that electroacupuncture did not have a significant benefit in terms of enhanced expressions of eNOS and nNOS in the treated 2K1C hypertensive group. CONCLUSIONS: Activation of eNOS and nNOS is one of the mechanisms through which ST-36 electroacupuncture reduces blood pressure; this reduction works through the stomach meridian.

Acupuncture Points↗
PubMed2003

Enhanced nitric oxide concentrations and expression of nitric oxide synthase in acupuncture points/meridians.

OBJECTIVES: The objectives of this study were to examine the distributions of nitric oxide (NO) in the skin points (acupoints)/meridian regions and determine whether neuronal nitric oxide synthase (nNOS) protein levels were associated with NO concentrations in the areas. DESIGN: Low skin resistance points (LSRP) on the skin surface in response to electrical stimuli were performed in anesthetized adult rats. The skin together with subcutaneous tissue was isolated in meridian regions from PC 2 to 6, BL 36 to 57, CV 3 to 22, and GV 2 to 14. Control skin tissues were obtained in the areas close to related meridians without containing LSRP. Concentrations of nitrite (NO(2)(-)), nitrate (NO(3)(-)), and total NO(2)(-) plus NO(3)(-) (NO(x)(-)) were quantified in the skin tissues, micropunches of brain nuclei, and blood vessels in a blinded fashion. Western blots were also conducted using polyclonal anti-nNOS and anti-endothelial nitric oxide synthase (eNOS) antibody in the skin tissues. RESULTS: NO(x)(-) and NO(3)(-) concentrations were higher (45 +/- 8% and 43 +/- 7% in the CV, 47 +/- 7% and 51 +/- 9% in the BL, and 47 +/- 8% and 45 +/- 6% in the PC) than those in control regions (p < 0.05, n = 6). NO(x)(-) concentrations are 2- to 3-fold greater in skin tissues than those in brain regions and blood vessels (p < 0.05, n = 6-8). nNOS protein levels were consistently increased in the skin regions of BL, PC, and GV meridians compared with their controls (p < 0.05, n = 5-7) but endothelial NO synthase expression was not changed. CONCLUSION: This is the first evidence showing that NO contents and nNOS expression are consistently higher in the skin acupoints/meridians associated with low electric resistance. The results suggest that enhanced NO in the acupoints/meridians is generated from multiple resources including neuronal NOergic system, and NO might be associated with acupoint/meridian functions including low electric resistance.

Acupuncture Points↗
PubMed2002

The representation of the visual field in three extrastriate areas of the ferret (Mustela putorius) and the relationship of retinotopy and field boundaries to callosal connectivity.

We describe representations of the visual field in areas 18, 19 and 21 of the ferret using standard microelectrode mapping techniques. In all areas the azimuths are represented as islands of peripheral visual field surrounded by central visual field representation. The zero meridian was found at the 17/18 and 19/21 borders; at the 18/19 and anterior border of 21 the relative periphery of the visual field was found. In areas 18 and 19, elevations are represented in a smooth medio-lateral progression from lower to upper visual field. In several cases the elevations in area 21 evidenced a similar medio-lateral progression; however, in others the elevations exhibited a split representation of the horizontal meridian. Anatomically determined callosal connections coincided with the representation of azimuths near the zero meridian. Medio-lateral bands of callosal connectivity that straddle the 17/18 and 19/21 borders are connected by bridges of callosally projecting cells. Acallosal cortical islands corresponded to the peripheral visual field and were found straddling the 18/19 border and the anterior border of area 21. The results are discussed in relation to callosal connectivity and retinotopy in extrastriate visual cortex and to proposed homologies of carnivore and primate visual cortex.

Animals↗
PubMed1977

Visual response time to colored stimuli in peripheral retina: evidence for binocular summation.

Simple onset response time (RT) experiments, previously shown to exhibit binocular summation effects for white stimuli along the horizontal meridian, were performed for red and green stimuli along 5 oblique meridians. Binocular RT was significantly shorter than monocular RT for a 45-min-diameter spot of red, green, or white light within eccentricites of about 50 deg from the fovea. Relatively large meridian differences were noted that appear to be due to the degree which the images fall on corresponding retinal areas.

Adolescent↗
PubMed1985

Sector pupil dilation with phenylephrine and tropicamide.

A comparison of sector pupil dilation produced with 2.5% phenylephrine and 1.0% tropicamide was carried out on nine subjects. We found that 2.5% phenylephrine produced a significant increase in the vertical as compared to the horizontal diameter at 10, 20, 30, 40, and 50 min after instillation of the drug with the maximum vertical diameter occurring at 40 min. The pupil diameter in the vertical and horizontal meridians before drug instillation was 3.7 mm +/- 0.2 (mean +/- SE) whereas at 40 min the vertical and horizontal diameters were 6.7 mm +/- 0.4 and 5.2 mm +/- 0.3, respectively. Instillation of 1% tropicamide produced equal dilation of the vertical and horizontal diameters, which was maximum at 40 min. Before drug instillation, the pupils were 3.7 mm +/- 0.2 (mean +/- SE) in both the horizontal and vertical meridians. At 50 min the pupil diameter was 7.0 mm +/- 0.2 in both meridians in the eye that received tropicamide.

Adult↗
PubMed1987

Location of the corneal apex and its influence on the stability of the central corneal curvature. A photokeratoscopy study.

A new photokeratoscopic method is presented for the determination of the corneal apex. Any asymmetry of photokeratoscopic data is interpreted as an apex displacement xa, defined as the chord distance between the visual axis and the corneal apex. I find the normal corneal apex to be displaced about 0.5 mm temporally and upward. In the area around the visual axis the corneal shape as well as xa influence the constancy of the radius of the corneal curvature. Quantitatively this curvature stability is depicted by an apex factor (AF) in a given meridian defined as the change in the corneal refractive power per millimeter chord distance in the corneal intersection point of the visual axis. The magnitude of AF is found to be about 0.3 D/mm in both the horizontal and the vertical meridians. The term central corneal cap (CCC) is defined as an area, symmetric around the visual axis, in which the change in the corneal refractive power is less than 0.5 D in a given meridian. CCC is calculated to have an area of 2.4 mm2.

Adolescent↗
PubMed1988

Effect of induced aniseikonia on fixation performance.

The purpose of the study was to determine to what extent induced aniseikonia affects fixation performance. Aniseikonia was induced in the vertical meridian only, whereas fixation alignment was monitored in the horizontal meridian. A previously developed technique based on the dependency of border enhancement bandwidth on fixation eccentricity was used to monitor deviations from central fixation during fusion. Stress on the fusion mechanism was supplied by controlled increments of forced horizontal vergence. It was found that deviation from central fixation in the horizontal meridian generally increases with increasing amounts of vertical aniseikonia. The effect is particularly pronounced for small amounts of aniseikonia.

Aniseikonia↗
PubMed1994

Accommodation in astigmatic eyes.

PURPOSE: To investigate the effect of target chart contours and the severity of astigmatism on accommodation in astigmatic eyes. METHODS: The accommodative responses of 30 subjects were measured with an automated refractometer (Canon RK-1) using star pattern and bar pattern targets. RESULTS: The mean accommodative response was greatest when the bar pattern was parallel to the stronger principal meridian of the eye, followed by the star pattern and the bar pattern parallel to the weaker meridian on both meridians. Similar results were obtained in subjects with astigmatism greater or less than 1.25 D. The mean slopes of AR/AS plots decreased in the same order as the accommodative response and the change was significant in subjects with astigmatism exceeding 1.25 D. In addition, about one-third of the subjects showed a consistent decrease in astigmatism with accommodation. CONCLUSIONS: These results indicate that the type of target chart and the severity of astigmatism influence the accommodative response.

Accommodation, Ocular↗
PubMed1996

Oxygen transmissibility at various locations in hydrogel toric prism-ballasted contact lenses.

PURPOSE: Corneal metabolism is known to be adversely affected by anterior surface hypoxia. It has been demonstrated that contact lens (CL) oxygen transmissibility (Dk/L in cmmL O2/s mL mm Hg) is a direct function of the oxygen permeability (Dk in cm2 ml O2/mm Hg mL mm Hg) of the plastic divided by the thickness of the lens (L in cm). It has also been shown recently that the cornea should be sensitive to the Dk/L of that portion of a CL immediately overlying the tissue, in the absence of tear exchange and mixing; such is the case for all hydrogel CLs. Because hydrogel toric CLs are known to have anisomorphically variable thickness profiles, we have measured lens thickness along the vertical meridian and calculated local oxygen transmissibilities (Dk/L) for a series of hydrogel CLs. METHODS: Thickness was measured at 5 locations along the vertical meridian of 16 different prescription toric hydrogel CLs of each of 6 brands (5 prism-ballasted design and 1 double-slab off design) and 12 different prescription spherical CLs of 2 brands (controls). Dk (at 38 degrees C) was calculated for each material from the nominal water content by a known relation. RESULTS: We found that the average Dk/L for all lenses was greatest from the center (mean +/- SD of 8 +/- 4 x 10(-9)) to the superior portion (12 +/- 2 x 10(-9) at 6 mm from the CL center and 13 +/- 4 x 10(-9) at 3 mm from the CL center) of prism-ballast design toric CLs, and least in the lower portions (4 +/- 2 x 10(-9) at 6 mm from the lens center and 6 +/- 1 x 10(-9) at 3 mm from the CL center) of these CLs. Analysis of covariance showed that the effect of location for the prism-ballasted CLs is statistically significant (F = 203.11, p < 0.00005). One nonprism ballast toric CL design and the spherical designs showed minimal differences across the vertical meridian. We therefore conclude that clinicians should carefully monitor the physiological hypoxic response of the cornea, in particular the inferior area, during wear of prism-ballasted hydrogel lenses.

Contact Lenses↗
PubMed1997

Equivalent dioptric power asymmetry relations for thick astigmatic systems.

For optical systems consisting of separated obliquely crossed toric interfaces, the equivalent dioptric power has principal meridians that are not necessarily orthogonal to each other. In this case it takes four parameters to specify the equivalent power. A set of parameters convenient for ophthalmic optics consists of three traditional spherocylindrical parameters SC x theta together with a dioptric asymmetry parameter g. The parameter g has been described as "so far" being entirely mathematical in nature. The purpose of this paper is to develop further optical knowledge about the equivalent power asymmetry g. The method was a theoretical and numerical study involving optics and the dioptric power matrix theory. Among the results of this study are a number of new equations involving g that clarify the relationships between the nonorthogonal principal meridians and the power and axis meridians of SC x theta, as well as explicitly illustrating the parameters that can increase or decrease g. It is also pointed out that the asymmetry g is formally identical to the circular astigmatism that has previously been presented in discussions of ray vector deflection fields (and is used in the Humphrey Lens Analyzer measurements). In conclusions, the theoretical relations presented here provide optical insight into the equivalent dioptric power asymmetry and the parameter g. The relations and insight can assist further developments.

Astigmatism↗
PubMed1997

Repeatability and accuracy of automated refraction: a comparison of the Nikon NRK-8000, the Nidek AR-1000, and subjective refraction.

This study assessed the repeatability of the Nikon NRK-8000, the Nidek AR-1000, and subjective refraction. In addition, the accuracy of the Nikon and the Nidek were evaluated in comparison to subjective refraction. Measurements were taken with all 3 techniques on 2 separate occasions with a test-retest separation of at least 24 h. The right eyes of 30 normal subjects were used. Repeatability and accuracy statistics and plots were generated using matrix representations of dioptric power. Subjective refraction was the most repeatable method, with the coefficient of repeatability (COR) found to be 0.611, 0.224, and 0.490 in the vertical, torsional, and horizontal meridians. The autorefractors' COR was found to range from 0.712 to 0.826 for the vertical and horizontal meridians, whereas the torsional meridian ranged from 0.224 to 0.319.

Adult↗
PubMed1997

Infant emmetropization: longitudinal changes in refraction components from nine to twenty months of age.

Rapid emmetropization is described in pediatrically normal infants from 9 months of age during the following year. The infants, obtained from various categories of the Cambridge population screening program, provided a broad range of refractive errors. The large group of 254 nonanisometropic infants studied allowed the mean rate of change and dependence on the initial refraction value to be determined. Refraction was measured by cycloplegic retinoscopy. Rapid emmetropization changes occurred in the following refractive components: mean spherical equivalent (MSE), astigmatism magnitude, the horizontal astigmatism component, the infant's most positive meridian, and the infant's most negative meridian. The MSE and astigmatism rates of change (diopters/year), were highly dependent on their respective initial powers (r = -0.61 and r = -0.76). The percentage weighted mean proportional rate of change for MSE was -30% (SE 4%) and for astigmatism magnitude it was -59% (SE 14%). There was much individual variation, with some exhibiting fast emmetropization and others not. The MSE and astigmatism changes, however, were almost independent of each other. The refractive errors of the most positive and most negative meridians emmetropize because they are both derived from the MSE and half the astigmatism. With-the-rule astigmatism was more prevalent than against-the-rule astigmatism at 9 months of age, and with-the-rule astigmatism exhibited a significantly greater proportional rate of change. The relationship of emmetropization and refractive screening is considered. A new component "MOMS" is introduced, the maximum ocular meridional separation, when both eyes are considered. Thus incorporating astigmatism and anisometropia may be a good single indicator of conditions associated with later amblyopia. The almost independent emmetropization of the MSE and astigmatism components is an important result to consider in theories of emmetropization, refractive screening, clinical prescribing, and the evaluation of infants in treatment trials.

Accommodation, Ocular↗
PubMed1999

Short-term repeatability of hand-held keratometry measurements.

PURPOSE: The Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) Study is a multi-center, observational investigation of ocular component and refractive error development in schoolchildren. Anterior corneal curvature is one of several ocular components which influence refractive status of the eye, and the CLEERE Study uses the Alcon Auto-Keratometer to measure corneal curvature. This report assesses the repeatability of this hand-held instrument. Previous studies have demonstrated the validity of the Alcon Auto-Keratometer; however, none have assessed its repeatability. METHODS: Sixty children were recruited from clinics affiliated with the Southern California College of Optometry and the University of Houston College of Optometry. Two sets of five hand-held keratometry measurements were obtained on the right eye of each child by one investigator at each site using the Alcon Auto-Keratometer. The two sets of measurements were performed at least 10 minutes apart. RESULTS: The mean differences between the two occasions were not significantly different from zero for either the flat or steep corneal curvature measurements regardless of the number of readings taken. The largest improvement in repeatability, primarily for the steep meridian, occurred when the first two readings were averaged. The addition of readings 3, 4, and 5 to the average did not substantially improve repeatability for either meridian. The 95% limits of agreement between the average of two readings on two occasions for the flat and steep meridians were +/-0.28 and +/-0.39 D, respectively. The 95% limits of agreement after two readings were +/-0.28, +/-0.20, and +/-0.24 D for the M, J0, and J45 vectors, respectively. CONCLUSION: The Alcon hand-held keratometer provides a repeatable measure of corneal curvature as demonstrated by short-term repeat agreement within +/-0.50 D. This level of repeatability can be achieved only by manually averaging two consecutive measurements.

Adolescent↗