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PubMed2000

Power spectrum analysis and conventional electromyogram in Duchenne muscular dystrophy.

OBJECTIVE: A comparative study of automatic electromyogram analysis (power spectral analysis) and manual measurements of the individual motor units potentials parameters in normal and Duchenne muscular dystrophy patients was performed to assess the diagnostic yield of both methods. METHODS: The analysis of 20 motor unit potentials elicited at weak effort manually by visual assessment and by power spectrum analysis at 1400 Hz Haning window were performed with concentric needle electrode in the biceps brachii and tibialis anterior. The study includes 18 healthy controls and 32 Duchenne muscular dystrophy patients. The primary diagnosis of the patients was based on the clinical criteria, family history and serum creatin kinase activity estimation. Seventeen patients were biopsied for further histological and histochemical examination. RESULTS: The conventional electromyogram of the patient group characterized by condensed, low mean amplitude of the recruited pattern and an increase in the percentage of polyphasic potentials of short duration and low amplitude in comparison to the normal subjects. About 74% of the patients were identified as myopathic patients with this method. Power spectrum analysis showed significant increase (P<0.0005) in the mean power frequently and the relative power at 1400 Hz and a significant decrease (P<0.0005) in accumulated power. About 95% of the patients were identified as being myopathic patients by this method. Statistical correlation analysis revealed no relationship between the power spectrum analysis and motor unit potentials parameters. CONCLUSION: The electromyogram power spectra was shifted to the higher frequencies in the Duchenne muscular dystrophy patients as compared to the control. The diagnostic yield of the electromyogram power spectrum analysis was higher than the measurement of the motor unit potential parameters. The best parameter of the electromyogram power spectrum is the relative power at 1400 Hz than the other two parameters. The net result of this study is that the electromyogram power spectrum has diagnostic possibilities in the muscles, which showed normal, or few motor unit potential changes.

Case-Control Studies↗

PubMed2001

Comparison of upper-body strength and power between professional and college-aged rugby league players.

Levels of upper-body strength and power can distinguish between athletes of different levels in a number of sports. The purpose of this investigation was to compare the maximum upper-body strength and power of 22 professional National Rugby League (NRL) and 27 state- and city-league, college-aged (SRL) rugby league players. All players were from the same football club and had undergone the same preseason strength and power training program for the 8 weeks prior to testing. Maximum strength was assessed by a 1 repetition maximum bench press (1RM BP). Maximum power (Pmax) and power output with loads of 40, 50, 60, 70, and 80 kg (P40, P50, P60, P70, and P80) were assessed during BP throws using the plyometric power system (PPS). Despite no differences in body mass or height, the NRL players were significantly stronger and more powerful in every variable measured. Furthermore, the differences in power output between groups became more pronounced with increasing barbell loads. Overall strength and power were highly related (r = 0.82); however, the relationship between these variables was somewhat less in the stronger NRL group (NRL r = 0.58, SRL r = 0.85). The percentage 1RM which maximized power output was also significantly lower for the NRL group as well as for stronger subgroups within each group. The results suggest that maximum strength largely influences power output; however, once a strength plateau has been reached, the changing training emphasis toward power training or the negative effects of high-volume conditioning training may alter the extent of the relationship.

Adolescent↗

PubMed2006

Anaerobic power performance and the menstrual cycle: eumenorrheic and oral contraceptive users.

AIM: The purpose of this project was to compare the impact of the menstrual cycle on short-term, high intensity (power) performance in active females who either had normal menstrual cycles (NOC) or who were using oral contraceptives (OC). METHODS: Subjects (7 NOC, 17 OC) completed a Margaria-Kalamen staircase test and a Wingate cycle test on 3 occasions: one for familiarization and the other two trials (random order) during menses (MEN) or luteal (LUT) phase. Phase was documented by urinary luteinizing hormone for the NOC. RESULTS: There were no significant differences between MEN and LUT in the NOC group on the Wingate test (n=7) for any of the following: peak power (P=0.33), peak power per kg body weight (P=0.37), anaerobic capacity (P=0.37), anaerobic capacity per kg body weight (P=0.42), power decline (P=0.36), power decline per kg body weight (P=0.35). Also there were no significant differences in power (P=0.95) for the Margaria-Kalamen test (n=6). There were no significant differences between MEN and LUT in the OC group for any of the following variables calculated from the subjects' performance on the Wingate test (n=17): peak power (P=0.39), peak power per kg body weight (P=0.36), anaerobic capacity (P=0.42), anaerobic capacity per kg body weight (P=0.36), power decline (P=0.57), power decline per kg body weight (P=0.66). Also there were no significant differences in power (P=0.44) for the Margaria-Kalamen test (n=11). CONCLUSIONS: For a moderately active group of women, anaerobic power performance was not influenced by menstrual cycle phase in either NOC or OC users.

Adult↗

PubMedDate not supplied

Corneal power correction factor for photorefractive keratectomy.

BACKGROUND: Studies of corneal power changes resulting from photorefractive keratectomy generally rely on keratometer or videokeratograph measurements. These instruments convert corneal radius of curvatures values to optical powers by means of the single refracting surface formula, which incorporates an index of refraction value of 1.3375. This index approximates that of the tears but not the 1.376 index of the corneal epithelium or stroma. A hypothetical optical model was used to determine the most appropriate index to be chosen with respect to corneal power calculations relative to photorefractive keratectomy. METHODS: The contribution of each refractive element in the tear lens-corneal surface to the total power of the eye was calculated in order to identify which index of refraction was most appropriate for the corneal power calculation. RESULTS: The outer tear surface has significant optical power but the tear layer as a whole has nearly zero power due to the offsetting negative power of the posterior test surface. There is no significant difference in the effective power of light leaving the corneal anterior surface when considered with or without the tear layer. Photorefractive keratectomy changes the epithelium and anterior surface of the corneal stroma, but does not affect the posterior stroma or other ocular media. Hence the refractive index for the corneal epithelium or stroma of 1.376 should be used in converting radius to optical power values. The error in assuming a corneal index of 1.3375 is a constant proportion equal to 11.4% of the corneal power reading. CONCLUSIONS: Photorefractive keratectomy presents a situation in which the actual corneal refractive index of 1.376 should be used for correct corneal radius to power conversions. This may be accomplished by changing the index value in the instrument algorithm for keratometry and videokeratography to 1.376 or by adding a correction factor of either 11.4% of the regular reading to its value or multiplying by the factor 1.114. In other applications of keratometry or videokeratography, the index 1.3375 may be more appropriate.

Cornea↗

PubMed2002

Respiratory complaints and spirometric parameters of the villagers living around the Seyitomer coal-fired thermal power plant in Kütahya, Turkey.

The aim of the study was to investigate the respiratory effects of the stack emissions of the Seyitömer coal-fired thermal power plant in the Kütahya Province of Turkey. The three villages that are located within 5 km around the power plant were investigated as our "Villages around Power Plant." Two villages which were similar to the Villages around Power Plant as far as climate, culture, and lifestyle were concerned and which were located more than 30 km away from the thermal power plant were investigated as our "Control Villages." The study design was based on the comparison of the respiratory complaints and the spirometric parameters of the individuals living in the two groups of villages. The study was carried out on individuals of 15 years of age and above living in these villages (277 of 302 individuals living in the Villages around Power Plant and 225 of 264 living in the Control Villages). Among the ones living in the Villages around Power Plant, 46.2% had complaints of chest tightness and 29.2% repeated coughing attacks present for more than one year, whereas these percentages were 28.0 and 20.4% in the Control Villages, the differences being statistically significant (P=0.001 and P=0.024, respectively). The complaint of productive coughing present for more than one year was not found to differ statistically significantly between the two groups of villages (P=0.0885). The means of the spirometric parameters of FEV1 and FEF25-75% were found to be statistically significantly lower in the individuals of the Villages around Power Plant compared to the individuals of the Control Villages (P=0.0001 and P=0.0001, respectively). When the spirometric parameters of nonsmokers were compared between the two groups of villages, FEV1, FVC, and FEF25-75% were found to be statistically significantly lower in the Villages around Power Plant compared to the Control Villages (P=0.0001, P=0.0001, and P=0.0001, respectively). No statistically significant differences of the spirometric measurements of current smokers were observed between the two groups of villages (P>0.05). The spirometric parameters revealed statistically significant adverse health effects of the Power Plant, this was particularly apparent v212nfor the nonsmokers. More specific tests to confirm the diagnosis of acute and chronic lung diseases can be suggested to be carried out in the area in further studies. Also follow-up studies can be recommended in the area to detect any new adverse health effects of the Power Plant.

Adolescent↗

PubMed2005

Possible genetic damage in the Czech nuclear power plant workers.

The aim of our study was to identify occupational risk of irradiation exposure in the Czech nuclear power plant workers. We analyzed levels of chromosomal aberrations, a well-known biomarker of early biological effects and a predictor of cancer risk. We applied the conventional method of cytogenetic analysis and fluorescence in situ hybridization (FISH, whole chromosome painting for chromosomes 1 and 4, combined with a pancentromeric probe) to three groups: 123 subjects in the Temelin nuclear power plant (2 years in use), 114 subjects in the Dukovany nuclear power plant (20 years in use), and 53 matched controls from Ceske Budejovice. Nuclear power plant workers were divided into two groups: subjects with admittance into the monitored zone, and others. Following factors were also analyzed: GSTM1, GSTT1, GSTP1, XPD, XRCC1, hOGG1, p53, MTHFR, and MS gene polymorphisms, levels of vitamins A, C, E, and folate in plasma, and level of cotinine in urine. Long-term exposure to ionizing radiation in the monitored zone was 0.47+/-1.50 mSv (miliSievert) in the Temelin nuclear power plant and 5.74+/-9.57 mSv in the Dukovany nuclear power plant. Using the conventional cytogenetic analysis, we observed 1.90+/-0.95 and 1.82+/-1.19% AB.C. (percent of aberrant cells) in the Temelin nuclear power plant, and 2.39+/-1.01 and 2.33+/-1.04% AB.C. in the Dukovany nuclear power plant, for monitored zone workers and others, respectively. In the control group, we found 2.25+/-0.82% AB.C. Genomic frequency of translocations F(G)/100 measured by FISH was 1.89+/-1.40 and 2.01+/-1.68 in the Temelin nuclear power plant, and 2.48+/-1.93 and 2.14+/-1.62 in the Dukovany nuclear power plant for monitored zone workers and others, respectively. In the control group, F(G)/100 was 1.83+/-1.19. Following factors were identified as potential confounders by the conventional cytogenetic analysis: XPD-6, by the FISH: age, GSTP1 and p53Bst genotypes, long-term use of medication, alcohol consumption, and smoking. No association between the dose of irradiation and the level of chromosomal aberrations in any nuclear power plant was detected either by the conventional cytogenetic analysis or by FISH.

Case-Control Studies↗

PubMed2000

The role of referent and expert power in mutual help.

This study explored the roles of referent power (i.e., influence based on sense of identification) and expert power (i.e., influence based on knowledge and expertise) in Schizophrenics Anonymous (SA), a mutual-help group for persons experiencing a schizophrenia-related illness. The study describes SA participants' experience of referent and expert power with SA members, SA leaders, and with mental health professionals. It also examines whether or not referent and expert power ascribed to fellow SA participants predicts the perceived helpfulness of the group. One hundred fifty-six SA participants were surveyed. Participants reported experiencing higher levels of referent power with fellow SA members and leaders than with mental health professionals. They reported higher levels of expert power for mental health professionals and SA leaders than for SA members. The respondents' ratings of their SA group's helpfulness was significantly correlated with ratings of referent and expert power. Although expert power was the best independent predictor of helpfulness, a significant interaction between referent and expert power indicated that when members reported high referent power, expert power was not related to helpfulness. These results are interpreted to suggest that there are multiple forms of social influence at work in mutual help.

Adult↗

PubMed2001

Power and gender influences on responsibility attributions: the case of disagreements in relationships.

In a sample of 156 college students (74 men and 82 women), the authors examined the influences of power status and gender on responsibility attributions and resolution choices during disagreements in personal relationships. The participants read vignettes in which relationship partners disagreed; then the participants placed themselves in the situations depicted and reported their perceived responsibility and resolution choices. The participants were randomly assigned to 1 of 2 power-status conditions (you have/your partner has greater power in the situation). Power status was based on resource power (i.e., a monetary inheritance) or on perceived power (i.e., financial knowledge). The authors tested 2 alternative power-status hypotheses (justified benefits/rights and ability/accountability) and 1 gender hypothesis. The results supported both power-status hypotheses. In addition, the men's and the women's responsibility attributions and resolution choices (i.e., adhering to their own wishes or deferring to their partner's wishes) revealed differential dependence on the type of power held by the person with greater situational power. The authors suggest issues further research concerning how situational differences in socially based expectations (e.g., power status and gender) may affect conflicts within relationships.

Adolescent↗

PubMed2002

Relationship power, sexual decision making and condom use among women at risk for HIV/STDS.

This study examines the associations among relationship power, sexual decision-making dominance, and condom use within a sample of women at risk of HIV/STDs. Data from face-to-face interviews with 112 women were analyzed to (a) describe who women perceive as more powerful and who makes sexual decisions within their heterosexual relationships, (b) explore the association between relationship power and sexual decision-making dominance, and (c) examine the relationship of power and decision making regarding condom use to condom use behavior. Women were recruited from clinics and community locations in Atlanta, Los Angeles, Oklahoma City and Portland, OR. Participants were 18-25 years of age and were primarily Hispanic and African American. Over half (58.2%) reported that they share power with their partner, 25.5% said they have more power, and 16.4% reported that their partner has more power in their relationship. For the five domains of sexual decision-making examined, over half (50.5%-75.7%) of the women reported that they and their partners make decisions together. A higher percentage of women who perceived that they have more power or share power, as compared to those who perceived that their partners have more power, reported that "I/We" make decisions about birth control use, condom use, whether to have sex, and type of sexual activity. Relationship power was not associated with condom use. Condom use was, however, significantly higher among women who reported that they make decisions about using condoms alone or with their partner as compared to those who reported that their partner makes those decisions.

Adolescent↗

PubMed2006

Lessons in power: Lyndon Johnson revealed. A conversation with historian Robert A. Caro.

No one can lead who does not first acquire power, and no leader can be great who does not know how to use that power. The trouble is that the combination of the two skills is rare. Amassing power requires ambition, a focused pragmatism, and a certain ruthlessness that is often at odds with the daring, idealistic vision needed to achieve great things with that power. The tension is as real in business as it is in politics. This magazine is replete with examples of successful senior managers who could not make the switch from ambitious executive to corporate leader because they did not know what to do with the power they had so expertly accumulated. Robert Caro is a student of power. For the past 27 years, the two-time Pulitzer prize-winning biographer of Robert Moses and Lyndon Johnson has focused on the question of how Johnson amassed and wielded power. Caro's deep understanding of the inner workings of power offers senior executives a nuanced picture of leadership at the highest level. In this wide-ranging conversation, Caro shares his insights about the nature of power, the complexity of ambition, and the role that the greater good can play in the making of a leader. Power doesn't always corrupt, he insists. But what it invariably does is reveal a leader's true nature. "Today, when CEOs have acquired more and more power to change our lives," Caro says,"they have become like presidents in their own right, and they, too, need to align themselves with something greater than themselves if they hope to become truly great leaders."

Humans↗

PubMed1985

Estimating radiofrequency power deposition in body NMR imaging.

Simple theoretical estimates of the average, maximum, and spatial variation of the radiofrequency power deposition (specific absorption rate) during hydrogen nuclear magnetic resonance imaging are deduced for homogeneous spheres and for cylinders of biological tissue with a uniformly penetrating linear rf field directed axially and transverse to the cylindrical axis. These are all simple scalar multiples of the expression for the cylinder in an axial field published earlier (Med. Phys. 8, 510 (1981]. Exact solutions for the power deposition in the cylinder with axial (Phys. Med. Biol. 23, 630 (1978] and transversely directed rf field are also presented, and the spatial variation of power deposition in head and body models is examined. In the exact models, the specific absorption rates decrease rapidly and monotonically with decreasing radius despite local increases in rf field amplitude. Conversion factors are provided for calculating the power deposited by Gaussian and sinc-modulated rf pulses used for slice selection in NMR imaging, relative to rectangular profiled pulses. Theoretical estimates are compared with direct measurements of the total power deposited in the bodies of nine adult males by a 63-MHz body-imaging system with transversely directed field, taking account of cable and NMR coil losses. The results for the average power deposition agree within about 20% for the exact model of the cylinder with axial field, when applied to the exposed torso volume enclosed by the rf coil. The average values predicted by the simple spherical and cylindrical models with axial fields, the exact cylindrical model with transverse field, and the simple truncated cylinder model with transverse field were about two to three times that measured, while the simple model consisting of an infinitely long cylinder with transverse field gave results about six times that measured. The surface power deposition measured by observing the incremental power as a function of external torso radius was comparable to the average value. This is consistent with the presence of a variable thickness peripheral adipose layer which does not substantially increase surface power deposition with increasing torso radius. The absence of highly localized intensity artifacts in 63-MHz body images does not suggest anomalously intense power deposition at localized internal sites, although peak power is difficult to measure.

Humans↗

PubMed1995

Non-invasive prediction of blood lactate response to constant power outputs from incremental exercise tests.

We determined the ability of gas exchange analyses during incremental exercise tests (IXT) to predict blood lactate levels associated with a range of constant power output cycle ergometer tests. Twenty-seven healthy young men performed duplicate IXT and four 15-min constant power output tests at intensities ranging from moderate to very severe, before and after a training program. End-exercise blood lactate levels were approximated from superficial venous samples obtained 60 s after each constant power output test. From IXT, the power outputs corresponding to peak oxygen uptake (Wmax) and lactic acidosis threshold (WLAT), were determined. We examined the ability of four measures of exercise intensity to predict blood lactate levels for power outputs above the LAT: (1) power output (W), (2) power difference (W-WLAT), (3) power fraction (W/Wmax) and (4) power difference to delta ratio [(W-WLAT)/(Wmax-WLAT)]. Correlation coefficients were r = 0.38, 0.69, 0.75, and 0.81, respectively. The best linear regression prediction equation was: lactate (mmol.l-1) = 12.2[(W-WLAT)/(Wmax-WLAT)] + 0.7 mmol.l-1. This relationship was not significantly affected by training, despite increased values of LAT and peak oxygen uptake. Normalizing exercise intensity to the range of power outputs between WLAT and Wmax provided an estimate of blood lactate response to constant power outputs with a standard error of the estimate of 1.66 mmol.l-1.

Adult↗

PubMed2006

Interactions between cadence and power output effects on mechanical efficiency during sub maximal cycling exercises.

The purpose of this study was to investigate the interactions between cadence and power output effects on cycling efficiency. Fourteen healthy subjects performed four constant power output-tests (40, 80, 120 and 160 W) in which the cadence varied in five bouts from 40 to 120 rpm. Gross efficiency (GE) was determined over the last ten respiratory cycles of each bout and was calculated as the ratio of mechanical energy to energy expenditure. Results showed that (1) GE-cadence relationships reached a maximum at each power output corresponding to the cadence maximising efficiency (CAeff) and (2) GE increased with power output whatever the cadence until a maximal theoretical value. Moreover, interactions were found between these two factors: the cadence effect decreased linearly with power output and the power output effect increased exponentially with cadence. Consequently, cycling efficiency decreased more when cadence differed from CAeff at low than at high power output, and increased more with power output at high cadence than at low cadence. These interactions between cadence and power output effects on GE were mainly due to cadence and power output effects on the energy expenditure shares not contributing to power production.

Adult↗

PubMed1995

Delta (0.5-1.5 Hz) and sigma (11.5-15.5 Hz) EEG power dynamics throughout quiet sleep in infants.

Twenty-eight healthy infants, split into 3 groups according to age (group 1: 2-6 weeks, n = 10; group 2: 7-14 weeks, n = 10; and group 3: 4-12 months, n = 8), were recorded during the whole night. For each infant, the longest quiet sleep (QS) phase occurring between 8 p.m. and midnight was selected for EEG power spectral analysis. The power in the frequency band related to low-frequency delta waves (0.5-1.5 Hz, "delta band") and the power in the frequency band related to sigma spindles (11.5-15.5 Hz, "sigma band") were analyzed. Group 1 infants showed no significant modification of the power in the sigma band in the course of the QS phase; the power in the delta band showed a significant increase between the second and the third 5 min segment and a decrease thereafter. Group 2 infants showed a progressive reduction of the power in the sigma band, whereas the power in the delta band increased during the first 15 min. In group 3 infants, the sigma band power significantly decreased between the third and the fifth 5 min segment without further changes. The power in the delta band, on the contrary, increased progressively for the first 20 min and showed a second progressive increase beyond 35 min. For both group 2 and group 3 infants, it appeared that the change in delta power preceded the change in sigma power. The above results provide quantitative evidence that a well-defined temporal inhomogeneity pattern in the EEG of the QS phase may appear between 7 and 14 weeks of age and continues from the fourth month on.

Age Factors↗

PubMed1982

Left ventricular work and power: circumferential, radial and longitudinal components. Mathematical derivation and characteristic variation with left ventricular dysfunction.

Cardiac work and power, defined as the wall stress-velocity product per unit volume, have been derived with respect to a circumferential, radial and longitudinal component for the human left ventricle during a complete cardiac cycle. Thirty-nine patients, comprising five clinical groups, were evaluated using pressure and volume data acquired from single-plane cineangiography. The results indicate that work and power are divided into approximately 60% circumferential, 23% radial and 17% longitudinal components for normals. Characteristic variations from normal are presented for selected pathological case studies. With a compensated volume overload patient, diastolic work and power are uniformly reduced in all three directions and systolic radial power approximately equals longitudinal power. With a decompensated volume overload patient, systolic radial power is greater than longitudinal power. With a compensated pressure overload patient, systolic radial work and power are greatly elevated as compared to the normals and represent about 30% of the total work and power, while longitudinal work and power represent only about 8% of the total. With a congestive cardiomyopathy patient, systolic work and power are greatly reduced in all three directions as compared to normals.

Adult↗

PubMed2006

Muscle function and power output during suction feeding in largemouth bass, Micropterus salmoides.

Muscle power output is thought to limit suction feeding performance, yet muscle power output during suction feeding has never been directly measured. In this study, epaxial activation and strain, hyoid depression, and intra-oral pressure were simultaneously measured during suction feeding in the largemouth bass (Micropterus salmoides). A mechanical model of muscle force transmission between the neurocranium and oral cavity was used to estimate muscle stress, work, and power. The epaxials shortened from rest an average of 9% of their length, with the highest efforts producing greater than 20% strain. Onset of shortening was simultaneous with or shortly after (< 10 ms) onset of activation. Maximal net power for individual fish ranged from 17 to 137 W kg(-1). Muscle power was significantly correlated with rectified EMG area (r = 0.80; p < 0.0001). The power required for cranial expansion was significantly correlated with epaxial power (r = 0.81; p < 0.0001), and the power exponent of this relationship ( approximately 1 for 3 of the 4 fish) implies that epaxial power accounts for most of the power of cranial expansion. The limitations imposed by the kinematic requirements and loading environment of suction feeding (short delay between activation and strain, maximal stress occurring after shortening, operation at lengths shorter than resting length) may prevent maximal muscular power production.

Animals↗

PubMed2006

Effect of augmented plantarflexion power on preferred walking speed and economy in young and older adults.

With age, loss of skeletal muscle mass (sarcopenia) results in decreased muscle strength and power. Decreased strength and power, in turn, are closely linked with declines in physical function. Preferred walking speed, a marker of physical function, is slower in older adults compared to young adults. Research suggests that older adults may walk slower as a consequence of decreased plantarflexor power at push-off. In this study, we hypothesized that providing additional plantarflexion (PF) power during push-off would (1) increase preferred walking speed, and (2) reduce metabolic cost of transport (MCOT), in young and older adults. PF power was augmented using powered ankle-foot orthoses (PAFOs). The PAFOs, which use pneumatic actuators to provide an additional PF moment, were based on a design by Ferris et al. [Ferris DP, Czerniecki JM, Hannaford B. An ankle-foot orthosis powered by artificial pneumatic muscles. J Appl Biomech 2005;21:189-97.]. Nine young (23.3+/-1.6 years) and seven older (74.6+/-6.6 years) adults participated. For the young adults, eight out of nine increased their preferred walking speed when push-off power was augmented (1.18+/-0.16 to 1.25+/-0.16m/s, p=0.03). A similar, but non-significant, trend in preferred walking speed was observed for the older adults. With augmented push-off power, MCOT for young adults decreased from 0.395+/-0.057 to 0.343+/-0.047 (p=0.008); indicating that the neuromuscular system was able to adapt to use external energy to reduce metabolic cost. Only three older adults were tested but MCOT values showed a similar trend. Augmenting PF power increases gait speed and reduces MCOT in young adults. Older adults may need a longer period to take advantage of additional push-off power.

Adult↗

PubMed1995

Assessment of the power and height of radial aspheres reported by a computer-assisted keratoscope.

PURPOSE: The two purposes of this study were (a) to assess the accuracy with which a keratoscope, the Topographic Modeling System (TMS-1), calculated the heights and powers of rotationally symmetric, radially aspheric test surfaces and (b) to determine whether the TMS-1 used an axial solution for radius of curvature to determine the power of a sphere that would produce the same semichord as would the test surface on a keratograph. METHODS: The TMS-1 heights and powers were studied for four test surfaces that had radial profiles similar to those of normal corneas. The powers of the surfaces were calculated from the local radius of curvature derived from the surfaces' manufacturing formulas. The heights and powers that would result from an axial solution were calculated in a TMS-1 simulator. TMS-1 data were compared with data from the surfaces' formulas and with data from the simulation. RESULTS: The TMS-1 data were almost identical to the heights and powers calculated from the simulated axial solution. The TMS-1 data were similar to the heights and powers calculated from the mathematical formulas from the apex to 2 mm from the apex but differed by up to 85 microns of height and 10 diopters of power in the periphery. CONCLUSIONS: The TMS-1 appeared to use the axial solution that does not calculate power from local radius of curvature. Clinicians should use caution when inferring corneal shape from power maps based on an axial solution, especially outside the central 2-mm radius of a normal cornea, because such power does not depict corneal curvature.

Cornea↗