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At least 865 records · Page 48Linked to original sources
PubMed2006

The mechanical reaction of the pars flaccida of the eardrum to rapid air pressure oscillations modeling different levels of atmospheric disturbances.

Atmospheric pressure fluctuations (APF) might induce mechanical effects in the pars flaccida (PF) of the eardrum. To clarify these effects, different kinds of pressure oscillations (PO), chosen within the range of naturally occurring APF, were applied to the middle ears (ME) of gerbils. The linear displacement of the PF during a PO in the ME was measured by laser interferometry. The compliance of the PF to PO was calculated as the ratio of the amplitude of a PF oscillation to the amplitude of a PO. The displacement of the PF traced the PO in the entire range of frequencies (from 10mHz to 200mHz) and amplitudes (from 10Pa to 110Pa) applied to the ME. Moreover, the PF is found to be displaced by pressure pulses of a few pascals only using a PO with a complex shape. The differences found in the compliance of the PF due to PO with low (less than 20Pa) and high (more than 90Pa) amplitude point out that the mechanism of pressure regulation in the ME through the mechanical reaction of the PF in gerbil ears is better adapted to ordinary levels of natural APF than to extraordinary levels. The implications of these findings for the physiology of the human ME with respect to adaptation to natural APF are discussed.

Animals↗
PubMed2004

Analysis of nonlinear systems to estimate intraocular lens position after cataract surgery.

PURPOSE: To compare the performance of neural networks with that of linear regression to predict the postoperative effective lens position (ELP) from preoperative biometry measurements. SETTING: Departments of Ophthalmology, Medical Cybernetics and Artificial Intelligence, and Medical Physics, Medical University of Vienna, Vienna, Austria. METHODS: The neural-network-type multilayer perceptron (MLP) and a linear regression technique were used to predict ELP. Suitable MLP models and variable input combinations were selected by extended-feature subset selection. Apart from the usual preoperative biometric variables, anterior chamber depth and lens thickness were measured with partial coherence interferometry and white-to-white measurements were used as input variables. RESULTS: Prediction of ELP could be improved from a correlation coefficient (Pearson) of 0.54 for linear regression to a coefficient of 0.68 for the MLP; however, this difference was not statistically significant. CONCLUSION: The prediction of postoperative ACD with the MLP was not significantly better than the prediction using linear regression.

Adult↗
PubMed2005

Change in IOL position and capsular bag size with an angulated intraocular lens early after cataract surgery.

PURPOSE: To investigate the axial movement in the first postoperative week and the influence of capsular bag size with an angulated, 3-piece, open-loop, acrylic intraocular lens (IOL). SETTING: Department of Ophthalmology, Medical University of Vienna, Vienna, Austria. METHODS: Twenty-nine eyes of 29 patients with age-related cataract were included in this study. In study 1, an open-loop, 3-piece IOL (AR40e, AMO) was implanted in a standardized fashion in 15 eyes of 15 patients. In study 2, before IOL implantation, a capsular tension ring (CTR) was inserted (14 eyes of 14 patients). Anterior chamber depth (ACD) was assessed with partial coherence interferometry 2 hours; 1, 3, and 5 days; 1 week; and 1 month postoperatively. The capsular bag diameter (CBD) was assessed using gonioscopic measurement of the eyelets of the CTR 1 day, 1 week, and 1 month postoperatively. RESULTS: In the first postoperative week, there was a significant mean forward movement of -196 microm +/- 117 (SD) (P < .005) in study 1 and -139 +/- 97 microm in study 2 (P < .005). These movements correspond to refractive changes of -0.31 diopter (D) and -0.20 D, respectively. The movement was linear in the first 5 days after surgery. Different patterns of early postoperative movement were seen, illustrating interindividual variability. A significant correlation of 0.67 (P < .05) was found between the change in ACD and CBD. CONCLUSIONS: A linear forward movement of the IOL during the first postoperative week was followed by a relatively stable IOL position. Loss of haptic memory seemed to be the most likely cause. Myopic eyes with large capsular bags showed less IOL shift in the early postoperative period than hyperopic eyes with smaller capsular bags.

Adult↗
PubMed2004

Predicting postoperative intraocular lens position and refraction.

PURPOSE: To predict the postoperative IOL position and refraction as accurately as possible independent of individualization of the parameters. SETTING: Universitats-Augenklinik, Mainz, Germany, and Vienna, Austria. METHODS: One patient cohort (189 eyes, Vienna) was used to calibrate the prediction method, which was then applied to a second cohort (65 eyes, Mainz). All calculations were based on consistent numerical ray tracing of the pseudophakic eye using the original manufacturer's intraocular lens (IOL) data (radii, thickness, refractive index). A new algorithm to predict IOL position was developed. Ultrasound (US) axial lengths were calibrated relative to partial coherence interferometry (PCI). Corneal radii extracted from topography were checked against radii measured with the IOLMaster (Zeiss) and by Littmann keratometry. RESULTS: Zero mean prediction errors for IOL position and refraction were obtained without adjusting the parameters and with PCI lengths or US lengths calibrated relative to the PCI values. There was no significant loss of accuracy of US data compared to PCI data. Corneal radii extracted from topography were slightly but statistically significantly different from the Littmann values, and they were more accurate than the latter with respect to prediction error. The measured mean central IOL position (distance from posterior corneal surface) for all IOL types was 4.580 mm, a value very close to the mean recalculated from A-constants (4.587 mm). The difference in the individual central IOL position relative to the mean value depended only linearly (ie, no higher orders such as square or cubic are needed) on axial length, with the mean central IOL position as a free parameter. This parameter should be 4.6 +/- 0.2 mm (the same value as independently measured or recalculated) to obtain zero steepness of the prediction error as a function of axial length, producing zero bias for long and short eyes. CONCLUSIONS: Calculation errors from formulas and confusing adjusting parameters can be avoided if calculations and measurements are performed on a clear and simple physical basis. Nevertheless, an individual prediction error, typically 0.5 to 1.0 diopter, seems to be unavoidable.

Adult↗
PubMed2005

Interferometric technique to measure biomechanical changes in the cornea induced by refractive surgery.

PURPOSE: To develop a technique to quantify biomechanical changes in the cornea after microkeratome incisions as would be performed in laser in situ keratomileusis. SETTING: St Thomas' Hospital, London, and the Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Loughborough, United Kingdom. METHODS: Corneal displacements of whole sheep eyes were studied under hydrostatic loading using electronic speckle pattern interferometry before and after microkeratome incisions. RESULTS: After hydrostatic loading, there was a 20.7% increase in corneal displacement in corneas with microkeratome incisions compared to unoperated corneas; this was statistically significant (P=.0068, unpaired t test). CONCLUSIONS: Results show that in the formation of the microkeratome flap, collagen fibers are severed and minimal biomechanical loading is distributed through the flap. Corneal biomechanical integrity is compromised after microkeratome incisions.

Animals↗
PubMed2005

Calibration of axial length measurements with the Zeiss IOLMaster.

PURPOSE: To study the conditions for consistent axial length measurements with partial coherence interferometry (PCI) performed with the Zeiss IOLMaster. SETTING: University Eye Clinic, Aarhus, Denmark. METHODS: A consecutive, unselected series of 1289 cataractous eyes were measured with the optical technique of PCI according to the IOLMaster as well as with conventional (contact) A-scan ultrasound (US) for the measurement of axial length. For each PCI reading, the signal-to-noise ratio (SNR) was recorded and used for comparison with the US measurement. All patients had routine phacoemulsification with implantation of an intraocular lens (IOL). In 284 cases, the patients were reexamined 2 to 3 months after surgery and the axial length was again measured using PCI. The readings of the IOLMaster, which had been calibrated against immersion US from the manufacturer, were recalculated to represent the true optical length and used in the analysis of the consistency of the measurements. RESULTS: Not all readings obtainable with the IOLMaster were of good quality, and large differences with conventional US were found. The error between US and PCI decreased significantly with increasing SNR, showing a minimum error at an SNR value above 2.1. The SNR correlated significantly with the visual acuity with considerable scatter, however. Excluding readings with a poor quality (SNR <2.1), the postoperative PCI measurements showed a high correlation with the preoperative measurement (r = 0.99), showing a mean difference of 0.08 mm +/- 0.12 (SD). The difference was highly significantly different than zero (P < .001) and may be explained by a higher refractive index of the biological lens than assumed in the original calibration of the IOLMaster. CONCLUSIONS: The quality of the axial length readings of the IOLMaster was influenced by the SNR value. However, with proper SNR evaluation and recalibration of the PCI measurements, it is possible to achieve consistent PCI readings with little variation between preoperative and postoperative measurements. These results are promising for a higher accuracy of the IOL power calculation.

Adolescent↗
PubMed2006

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

PURPOSE: To compare central corneal thickness (CCT) values obtained with ultrasonic pachymetry and a new optical method using partial coherence interferometry (PCI). SETTING: Department of Ophthalmology, Medical Health and Science Center, University of Debrecen, Debrecen, Hungary. METHODS: The study comprised 136 eyes of 70 patients whose spherical refractive error was not greater than +/-6.0 diopters (D) and whose keratometric astigmatism was not greater than 2.0 D. Central corneal thickness was measured 5 times with a new optical device (ACMaster, Zeiss) and with an ultrasonic pachymeter (AL-2000, Tomey). All measurements were obtained by the same investigator. RESULTS: Mean CCT was 531.2 microm +/- 3.9 (SD) with PCI and 547.8 +/- 36.0 microm with the ultrasonic device. The difference between groups was significant (P = .001). There was no difference between CCT values measured in right and left eyes (P = .55) with ultrasonography and PCI (P = .67). The coefficient variation was 0.73% for PCI and 6.5% for ultrasonography. Correlation between the CCT measurements with both devices was strong and statistically significant (Spearman correlation = .91, P = .001). CONCLUSIONS: Mean CCT values measured by the PCI method were significantly smaller than those measured by the ultrasonic device. Central corneal thickness measured with PCI is more reproducible and seems to be more reliable than that measured by ultrasonography.

Adult↗
PubMed2006

Local corneal thickness changes after small-incision cataract surgery.

PURPOSE: To assess whether a temporal limbal-corneal incision approach for phacoemulsification cataract surgery induces a gradient in corneal thickening along the horizontal meridian. SETTING: Department of Ophthalmology, Medical University of Vienna, Vienna, Austria. METHODS: Corneal thickness in 21 eyes of 21 patients was measured preoperatively as well as 1 day, 1 week, and 1 and 3 months after phacoemulsification through a temporal limbal-corneal incision. Measurements were performed using partial coherence interferometry (PCI) with a commercial instrument, the ACMaster (Carl Zeiss Meditec, Jena). Measurements were taken along the horizontal meridian centrally along the visual axis at 1.5 mm, 3.0 mm, and 4.5 mm eccentricity. RESULTS: Preoperatively, there were slight nasal-temporal differences in corneal thickness at all eccentricities. The mean thickness was 522 microm +/- 34 (SD) at 1.5 mm nasally and 513 +/- 36 microm at 1.5 mm temporally (P<.01). On day 1, there was a significant mean increase in corneal thickness (38 +/- 43 microm) along all locations. The thickening was slightly more pronounced in the periphery than in the center, a difference not reaching statistical significance. At 1 week, corneal thickness returned almost to baseline at all locations except for 3.0 mm temporally, where it was slightly, but not significantly, thicker (mean 8 +/- 14 mum). At 1 month, corneal thickness at the 3.0 mm temporal location returned to baseline. CONCLUSIONS: A nasal-temporal difference in corneal thickness was found preoperatively in all patients. Phacoemulsification through a temporal limbal-corneal incision caused an increase in corneal thickness along the horizontal meridian 1 day after surgery. The prolonged corneal thickening at 3.0 mm eccentricity temporally could be a result of the proximity to the incision site.

Aged↗
PubMed2005

Two-dimensional and 3-dimensional optical coherence tomographic imaging of the airway, lung, and pleura.

BACKGROUND: Methods for obtaining real-time in vivo histologic resolution by means of noninvasive endoscopic optical imaging would be a major advance for thoracic surgical diagnostics and treatment. Optical coherence tomography is a rapidly evolving technology based on near-infrared interferometry that might provide these capabilities. The purpose of this study is to investigate the feasibility of real-time 2- and 3-dimensional optical coherence tomographic imaging of airway, pleural, and subpleural lung tissues in normal, inflammatory, and malignant animal models and patients with known or suspected airway malignancy. METHODS: Freshly excised lungs and pleural tissue obtained from rabbits with inhalation lung injury and induced empyema, metastatic sarcomas, and pleural sarcomas and from patients with airway disease were imaged by using 2- and 3-dimensional optical coherence tomography with a prototype superluminescent diode optical coherence tomographic system constructed in our laboratory. Lungs and pleural tissue were subsequently processed for standard hematoxylin and eosin histology for comparison with optical coherence tomography. RESULTS: Optical coherence tomographic imaging achieved an ex vivo resolution of 10 microm and an in vivo resolution of about 30 microm with a depth penetration of 1 to 2 mm with 2- and 3- dimensional reconstruction capabilities. Tumors as small as 500 microm were detectable with optical coherence tomography. The acquired images closely matched histologic images, demonstrating details at the level of mucosal layers, glands, alveoli, and respiratory bronchioles. CONCLUSIONS: Optical coherence tomography with near-infrared interferometric methods enables near real-time in vivo near-histologic resolution optical imaging. With further advances, optical coherence tomography has the potential for real-time accurate and early pleural and subpleural diagnostics by using small-diameter flexible fiberoptic endoscopic probes for a wide range of thoracic surgical applications.

Animals↗
PubMed2004

Laserinterferometric assessment of pilocarpine-induced movement of an accommodating intraocular lens: a randomized trial.

PURPOSE: To measure the axial movement of an accommodating intraocular lens (IOL) induced by ciliary muscle contraction after application of pilocarpine. DESIGN: Randomized, controlled, patient- and examiner-masked trial with intrapatient comparison. PARTICIPANTS AND CONTROLS: One hundred ten eyes of 55 patients with age-related bilateral cataract. METHODS: This study was divided into 3 parts. In the first, the accommodating IOL (1CU) was compared with a 3-piece open-loop acrylic IOL that served as the control. In the second, to assess the effect of capsule fibrosis on the potential accommodating performance of the accommodating IOL, extensive polishing of the anterior capsule with a slit cannula was compared with standard surgery. In the third, the effect of a posterior capsulorhexis was compared with that of standard surgery. Anterior chamber depth (ACD) was assessed with partial coherence interferometry, measured before and after topical application of pilocarpine 2%, and near visual acuity (VA) was evaluated 3 months after surgery. MAIN OUTCOME MEASURE: Pilocarpine-induced change in ACD. RESULTS: The accommodating IOL showed a forward movement under pilocarpine with a median amplitude of movement of -314 microm (95% confidence interval [CI]: -148 to -592), compared with the backward movement of 63 microm (95% CI: 161 to -41) for the open-loop control IOL (P = 0.001). Capsule polishing and a posterior capsulorhexis had no effect on IOL movement with the accommodating IOL. The median near VA with distance correction was 20/60. CONCLUSION: Pilocarpine induced a small but significant forward movement of the accommodating IOL. However, the amount of movement was calculated to result in a refractive change of <0.5 diopters (D) in most patients, reaching 1 D or slightly more in only single cases, with a large variability of movement. Neither polishing of the capsule bag nor a posterior capsulorhexis could enhance the accommodative ability.

Accommodation, Ocular↗
PubMed2005

Stimulus-driven versus pilocarpine-induced biometric changes in pseudophakic eyes.

PURPOSE: Most trials that study the lens movement of accommodative intraocular lens (IOLs) use pilocarpine to stimulate ciliary muscle contraction. The aim of this study is to assess in vivo whether a more physiologic, stimulus-driven accommodation is comparable to pilocarpine-induced IOL movement. DESIGN: Controlled patient- and examiner-masked clinical trial. PARTICIPANTS: The study population included 38 eyes with accommodative IOL implants (1CU) and a control group of 28 eyes with conventional open-loop IOLs. METHODS: A high-precision biometry technique, partial coherence interferometry, was used to measure IOL position. Anterior chamber depth was measured during physiologic (near point) and pharmacological (pilocarpine 2%) stimulation. In a subgroup of 14 1CU eyes, IOL position was determined repeatedly within 90 minutes after pilocarpine administration. A different subgroup was investigated as to the effect of cyclopentolate on IOL position. Best-corrected distance visual acuity (VA), best-corrected near VA, and distance-corrected near VA (DCNVA) were assessed using logarithm of the minimum angle of resolution charts. MAIN OUTCOME MEASURES: Anterior chamber depth change under pilocarpine and near-point-driven accommodation. RESULTS: Near-point accommodation did not induce movement of either the accommodating 1CU or the control IOLs. Pilocarpine induced a 201+/-0.137-mm anterior movement of the 1CU IOL (P<0.001), compared with no movement within the control IOL groups (P>0.05). There was no significant (P>0.05) difference in DCNVA between the accommodative and open-loop IOLs. No correlation between near point- or pilocarpine-stimulated IOL movement and DCNVA was found. Concerning the time course of movement after pilocarpine administration, most of the 1CU IOLs showed some movement 30 minutes after application. Cyclopentolate-induced ciliary muscle relaxation caused a posterior IOL movement, as compared with the relaxed state, when focusing on a distant target. CONCLUSION: Pilocarpine-induced ciliary muscle contraction seems to overestimate IOL movement relative to a monocular near-driven stimulus. Therefore, concerning IOL movement, pilocarpine may act as a superstimulus and may not adequately simulate daily life performance of accommodative IOLs. However, it may be helpful to evaluate the maximum potential of an accommodating IOL.

Accommodation, Ocular↗
PubMed2000

Assessment of optic disk blood flow in patients with open-angle glaucoma.

PURPOSE: To characterize optic disk blood flow in patients with open-angle glaucoma compared with age-matched healthy control subjects. METHODS: In this prospective cross-sectional study, 90 eyes of 90 patients with open-angle glaucoma and 61 eyes of 61 age-matched healthy control subjects were evaluated. Flow in the optic disk cup and the neuroretinal rim were assessed with scanning laser Doppler flowmetry. Fundus pulsation amplitude in the cup and the macula were assessed with laser interferometry. Visual field mean deviation was measured with the Humphrey 30 to 2 program. RESULTS: Flow in the neuroretinal rim (-18%, P =.002), and in the cup (-46%, P <.001) and fundus pulsation amplitude in the cup (-33%, P <.001) and in the macula (-24%, P <.001) were significantly lower in patients with open-angle glaucoma compared with healthy control subjects. A significant association between blood flow measurements in the cup and fundus pulsation amplitudes in the cup was observed in both study cohorts. A significant association was also observed between the mean defect from visual field testing and ocular hemodynamic parameters. CONCLUSIONS: Reduced optic disk perfusion in patients with open-angle glaucoma is evidenced from two independent methods in the present study. Moreover, our data indicate that reduced ocular blood flow in these patients is linked to visual field changes. It remains to be established whether compromised optic disk and choroidal blood flow contributes to optic disk damage in glaucomatous eyes or is a secondary functional phenomenon.

Aged↗
PubMed1994

Interferometric measurement of corneal thickness with micrometer precision.

The recently developed partial coherence laser Doppler interferometry technique was improved to measure central and peripheral corneal thickness with high precision. Corneal thickness profiles were measured on 18 eyes of health, volunteer subjects. All of these eyes were measurable at angles (between visual axis and measuring direction) ranging from 20 degrees nasal to 25 degrees temporal. At larger angles (up to 35 degrees) only part of the eyes was measurable. The thickness profiles of the 18 corneas have a nearly perfectly parabolic shape within the measured region. The precision (standard deviation) was 1.6 microns for central measurements and decreased somewhat to about 3.5 microns at measuring angles in the range of 25 to 30 degrees. No significant interobserver variability was found on 14 eyes measured by three different observers. This study indicates that the new technique is likely to be superior to currently used ultrasound and conventional optical pachymetry techniques, especially for refractive procedures.

Cornea↗
PubMedDate not supplied

Wall shear stress in backward-facing step flow of a red blood cell suspension.

An experimental investigation of the wall shear stress distribution downstream of a backward-facing step is carried out. The wall shear stress distribution was determined by measuring the deformation of a gel layer, attached to the wall downstream of the step. Speckle pattern interferometry was applied to measure the deformation of the gel layer. The measured deformation, combined with the properties of the gel layer, served as an input for a finite element solid mechanics computation to determine the stress distribution in the gel layer. The wall shear stress, required to generate the measured deformation of the gel layer, was determined from these computations. A Newtonian buffer solution and a non-Newtonian red blood cell suspension were used as measuring fluids. The deformation of the gel layer was determined for a Newtonian buffer solution to evaluate the method and to obtain the properties of the gel layer. Subsequently, the wall shear stress distribution for the non-Newtonian red blood cell suspension was determined for three different flow rates. The inelastic non-Newtonian Carreau-Yasuda model served as constitutive model for the red blood cell suspension. Using this model, the velocity and wall shear stress distribution were computed by means of a finite element fluid mechanics computation. From the comparison between the numerical and the experimental results, it can be concluded that wall shear stresses, induced by the red blood cell suspension, can be modeled accurately by employing a Carreau-Yasuda model.

Blood Vessels↗
PubMed1986

Extracorporeal stone disintegration using chemical explosive pellets as an energy source of underwater shock waves.

Extracorporeal renal stone disintegration using a chemical explosive pellet (lead azide 10 mg.) as an energy source of underwater shock waves has been successfully performed in animals. The shock wave was observed by holographic interferometry. Shock wave generation was performed by a reflector whose configuration was part of a pseudoellipsoid. The explosions were conducted 10 to 100 times for each animal and the stone (extracted human renal calculus or model calculus of activated alumina) placed in the renal pelvis was disintegrated satisfactorily. Negative findings in explorative laparotomy and histological examination, except for minor bleeding in several tubular lumina of the kidney, indicated that the method was clinically applicable.

Animals↗
PubMed2003

New technology for the design of advanced ultrasonic transducers for high-power applications.

A new high-frequency ultrasonic transducer for wire bonding has been conceived, designed, prototyped and tested. In the design phase an advanced approach was used and established. The method is based on the two basic principles of modularity and iteration. The transducer is decomposed to its elementary components. For each component an initial design is obtained with finite elements method (FEM) simulations. The simulated ultrasonic modules are then built and characterized experimentally through laser-interferometry measurements and electrical resonance spectra. The comparison of simulation results with experimental data allows the parameters of FEM models to be iteratively adjusted and optimized. The achieved FEM simulations exhibit a remarkably high-predictive potential and allow full control on the vibration behavior of the ultrasonic modules and of the whole transducer. The new transducer is fixed on the wire bonder with a flange whose special geometry was calculated by means of FEM simulations. This flange allows the converter to be attached on the wire bonder not only in longitudinal nodes but also in radial nodes of the ultrasonic field excited in the horn. This leads to a nearly complete decoupling of the transducer to the wire bonder, which has not been previously obtained. The new approach to mount ultrasonic transducers on a welding-device is of major importance not only for wire bonding but also for all high-power ultrasound applications and has been patented.

Computer Simulation↗
PubMed2001

Unilateral light-dark transitions affect choroidal blood flow in both eyes.

There is recent evidence that the perfusion of the choroid changes during dark-light transitions. We set out to investigate this response in more detail and to elucidate possible mechanisms involved in this process. For this purpose, the effect of dark-light transitions on choroidal perfusion was studied in healthy subjects. Choroidal blood flow and ocular fundus pulsation amplitude were measured as indices of choroidal perfusion during dark-light transitions using laser Doppler flowmetry and laser interferometry, respectively. In the first experiment, subjects were first kept in room light for 20 min, then light conditions were changed to darkness for 20 min, and thereafter, subjects were exposed to room light again. Both choroidal parameters decreased (-12% to -14%) during darkness but returned to baseline after the final room light period. In the second experiment, the index eye underwent the same procedure, whereas the contralateral eye was kept in light throughout the experiment. Choroidal haemodynamic parameters in the index eye reacted in a way comparable to that seen in the first experiment. The eye that was kept in light also reacted, but the effect tended to be less pronounced than that seen in the index eye (-8% to -10%). The observation that choroidal blood flow in both eyes reacts during unilateral light-dark transitions indicates that choroidal perfusion rate is adapted to retinal illumination conditions by neural control mechanisms.

Adaptation, Ocular↗
PubMed1997

Foveal cone spacing and cone photopigment density difference: objective measurements in the same subjects.

Foveal cone spacing was measured in vivo using an objective technique: ocular speckle interferometry. Cone packing density was computed from cone spacing data. Foveal cone photopigment density difference was measured in the same subjects using retinal densitometry with a scanning laser ophthalmoscope. Both the cone packing density and cone photopigment density difference decreased sharply with increasing retinal eccentricity. From the comparison of both sets of measurements, the computed amounts of photopigment per cone increased slightly with increasing retinal eccentricity. Consistent with previous results, decreases in cone outer segment length are over-compensated by an increase in the outer segment area, at least in retinal eccentricities up to 1 deg.

Adult↗