Iris Diameter Research Articles

Low-level exposure of guinea pigs and marmosets to sarin vapour in air: lowest-observable-adverse-effect level (LOAEL) for miosis.

The purpose of this pilot study was to indicate, for low-level exposure of conscious guinea pigs and marmoset monkeys to sarin vapour in air, the lowest-observable-adverse-effect level (LOAEL) of sarin for miosis. This is the concentration x time (C.t) value (t = 5 h) of exposure at which miosis becomes significant. The ratio of pupil and iris diameters, measured on digital photographs taken on-line during exposure, was calculated as a measure for miosis. The exposure concentrations were in the range 7-150 microg x m(-3) and the exposure times needed to achieve significant miosis were in the range 10-300 min. Both vehicle- and pyridostigmine-pretreated animals were used in the experiments. The latter pretreatment resulted in ca. 30% inhibition of erythrocyte acetylcholinesterase in both species. In vehicle-pretreated guinea pigs and marmosets the pupil size was decreased significantly (P < 0.05) at sarin doses of 1.8 +/- 0.3 and 2.5 +/- 0.8 mg x min x m(-3), respectively. In pyridostigmine-pretreated guinea pigs and marmosets the pupil size was affected significantly (P < 0.05) at 1.8 +/- 0.5 and 3.0 +/- 0.8 mg x min x m(-3), respectively. Evidently there is no significant influence of pyridostigmine pretreatment on the LOAEL. These data were addressed in light of the recommended occupational and detection limits for sarin vapour in air. It was concluded that miosis will occur during low-level sarin exposure at levels that are not detectable by the currently fielded alarm systems, assuming that humans are as sensitive for sarin vapour in air as guinea pigs and marmosets.

Pupil dilation with intracameral 1% lidocaine during glaucoma filtering surgery

PurposeTo evaluate pupil dilation from intracameral injection of nonpreserved 1% lidocaine. DesignObservational case series of 25 consecutive phakic trabeculectomies. MethodPatients were evaluated in the operating room setting and given one drop of topical tetracaine preoperatively. Nonpreserved 1% lidocaine (0.1 cc) was injected intracameraly into the anterior chamber through a paracentesis site at the corneal limbus. Pupil diameter was measured after instillation of topical tetracaine, before injection of intracameral lidocaine. Postinjection measurements were made at 1, 3, and 5 minutes. ResultsThe mean male pupil diameter was significantly greater than female dilation at every time point. The mean blue iris diameter was greater than brown at 1 and 3 minutes, but there was no difference at 5 minutes or more. There was no racial difference in the pupil dilation response to intracameral lidocaine. ConclusionsNonpreserved intracameral 1% lidocaine produces immediate pupil dilation in previously undilated phakic patients during trabeculectomy surgery.

Assessments of corneal endothelial cell density in growing children and its relationship to horizontal corneal diameter.

Few studies have been published of corneal endothelial cell density (ECD) in children, especially in relation to the age and corneal size of the individuals. The possible effect of corneal enlargement on the endothelium was studied, and the results were objectively reviewed in relation to literature reports on corneal diameter and age. ECD was assessed in 119 children aged 5 to 15 years after endothelial photography with a noncontact specular microscope (Topcon SP-1000 or SP-2000P), followed by manual digitization of cell overlays. The horizontal corneal diameter, as the visible iris diameter, was measured to 0.5-mm accuracy. The mean +/- SD value for ECD, calculated using all individual cell area values, was 3542 +/- 510 cells/mm2 (range, 2576 to 5316), whereas it was 3246 +/- 416 cells/mm2 (range, 2404 to 4817) if the mean cell area value from each image was used to calculate ECD. The mean horizontal corneal diameter was 11.48 +/- 0.58 mm (+/- SD). The corneal diameter was not obviously age-related for this group, but there were clear trends for younger children to have higher ECD values than older children (p2, depending on the method for calculating ECD. ECD values were found to be significantly correlated to corneal diameter in children aged 5 to 15 years, and this factor should be considered in comparative studies.

Clinical performance and factors affecting the physical fit of a soft toric frequent replacement contact lens

Background: Differences in ocular parameters between Chinese and Caucasian eyes, may lead to differences in the success rate of soft contact lens fittings. As most disposable or frequent replacement lenses are manufactured based on data of Caucasian eyes, the aim of this study was to investigate the clinical performance and factors affecting die preliminary fitting of a ‘one‐fit’ bi‐weekly replacement soft toric lens on Hong Kong (HK)‐Chinese.Method: Forty‐one HK‐Chinese were fitted with Acuvue soft toric lenses (on one eye only). The success rate, die comfort, vision and die effects of central corneal curvature, horizontal visible iris diameter (HVID) and palpebral aperture size (PAS) on the physical fit of die toric lenses were determined.Results: Twenty‐four of 41 eyes (58.6 per cent) attained acceptable fit and satisfactory vision with these lenses. The main reason for unsuccessful lens fit was loose fitting. Only central corneal curvatures were significandy correlated (statistically) to the looseness of the lens.Discussion: The results showed diat about 40 per cent of our subjects were unable to obtain acceptable fit with this one‐fit frequent replacement lens, the main reason for which was loose fit. This was expected due to the steeper corneas of the Chinese eyes and we would expect similar results widi odier one‐fit soft lenses. Only die central corneal radii were significandy correlated widi die looseness of the lens fit. However, this factor was not die main factor affecting die contact lens fitting. HVID and PAS did not appear to play any significant role in die physical fit of diis lens. As tiiere are individual variations of lens fitting behaviour, trial lens fitting assessment is die most suitable way to select the appropriate lens.

Initial selection of soft contact lenses based on corneal characteristics.

To determine apical radius, surface asphericity, and horizontal visible iris diameters (HVID) in normal subjects and to find out which has the greatest influence on the corneal sagittal depth. Videokeratoscopic data were analyzed to determine the apical radius and the p-value of the near horizontal principal meridian for 73 right and 77 left eyes. The HVID also were measured. Scatterplots of sagittal depth versus apical radius, p-value, and HVID indicated the strongest association between the sagittal depth and the HVID. Normal variations in corneal asphericity have the least influence whereas normal variations in HVID have the greatest influence in changing the corneal sagittal depth. The most appropriate measurement to take to select the optimum soft contact lens specification may be the HVID.

The use of pupillometry in joint and connective tissue diseases.

The central and peripheral nervous systems are variably affected in the rheumatic diseases. Automated standardized infrared pupillometry allows the safe, noninvasive assessment of the pupillary innervation. Pupillometry has already been used in studying the autonomic nervous system (ANS) in various rheumatic diseases. In systemic lupus erythematosus, the irideal parasympathetic branch of ANS was more affected then the sympathetic branch. In Sjögren's syndrome, signs of pupillary parasympathetic denervation have been reported. In rheumatoid arthritis, pupil parasympathetic dysfunction has been shown to correlate with ocular dryness. In systemic sclerosis (SSc), both sympathetic and parasympathetic irideal impairment have been demonstrated. Beside providing autonomic innervation, sensory nerves fibers are able to control iris diameter. Exogenous ocular instillation of substance P (SP), a sensory neuropeptide, can determine an omathropine-resistant, non-cholinergic myosis, acting on specific receptors present on the iris sphincter muscle. We first studied pupillary SP-ergic responsiveness in SSc, evaluating substance P (SP)-stimulated pupillary diameters by pupillometry. A higher basal and SP-stimulated myosis was found in lSSc versus both dSSc and controls, whereas no differences existed between dSSc and controls. From the literature, the pupillary parasympathetic nervous system seems to be more affected than the sympathetic branch of ANS in the rheumatic diseases characterized by an inflammatory status. However, we found in SSc both sympathetic and parasympathetic pupil control to be equally impaired. From our experience, we conclude that pupillary nervous control is differently affected in the two subsets of SSc, and that the SP-ergic system seems to be impaired only in lSSc.

Clinical evaluation of a custom-made toric soft lens

Purpose. The fitting of toric soft contact lenses is often complicated by interference between the toric optics and the geometry need to stabilise the lens on the eye. The use of a spherical trial lens to determine the parameters of a toric soft contact lens can lead to unintended positioning and movement of the lens ordered. The purpose of this study was to evaluate clinically the success Purpose. The fitting of toric soft contact lenses is often complicated by interference between the toric optics and the geometry needed Method. The design of the lenses used was such that optical correction and stabilisation were separated. The lenses had a back tonic surface limited to the central optical zone and base down prism stabilisation in the periphery. The empirical system used corneal radii, spectacle refraction and horizontal visible iris diameter as lens design parameters. Results. This multi-centre trial, comprised of 105 patients (193 eyes), revealed an overall success rate of 86%. The total number of lenses ordered to achieve success was 1.46 per eye in new patients and 1.69 per eye in patients who were failures with other toric soft lenses. In 14% of the cases success could not be achieved despite ordering several lenses (up to 4 lenses/eye). Many of these patients (60%) were also failures with other toric soft lenses. Conclusion. It is concluded that in new patients successful toric soft contact lens fitting can be achieved with an empirically based method. When refitting former toric soft lens failures, we recommend discontinuation after two further unsuccessful fittings.

A new microwave cavity resonator for determining molecular orientation and dielectric anisotropy of sheet materials

A new type of microwave instrument is developed for quick determination of the molecular orientation and dielectric anisotropy in sheet materials. Its cavity resonator differs from the conventional one in that the waveguide is separated by a narrow gap. Thus, it consists of a pair of rectangular waveguides, each partitioned by an iris plate. A given sheet is inserted into the gap, and can be rotated around the axis normal to its plane. The iris diameter and gap width are determined so as to meet the requirement that the transmitted microwave power and the Q value may not drop markedly after insertion of thick films into the gap. Polarized microwaves are irradiated perpendicularly to the sheet, and the transmitted wave intensity is measured at every 1° of rotation angle as the sheet is rotated at a speed of 6.0 s per turn. This operation quickly gives information related to the molecular orientation in the given sample. Dielectric measurements can be made at any rotation angles, allowing the angular dependence of the real and imaginary parts of the complex dielectric constant and, thus, the dielectric anisotropy of the sheet to be determined in a few minutes.

Is the Corrected QT Interval a Reliable Indicator of the Severity of Diabetic Autonomic Neuropathy?

We investigated whether the corrected QT interval correlated with two other tests for diagnosing autonomic dysfunction in 60 type I diabetic patients with proven peripheral neuropathy. The mean age +/- SD was 48.3 +/- 11.2 yr, the mean duration of diabetes was 24.9 +/- 11.4 yr, and the mean HbA1 was 9.3 +/- 2.4%. All patients underwent three autonomic function tests: 1) the standard five cardiovascular Ewing tests, each scored 0 (normal), 0.5 (borderline), or 1.0 (abnormal). We used the sum of the abnormal findings for the analysis, the cardiovascular autonomic score; 2) measurement of the corrected QT interval taken from a routine electrocardiogram recording; and 3) static and dynamic pupillometry: measurement of dark adapted pupil diameter as percentage of total iris diameter and of pupil constriction latency using an infrared light reflex technique. No significant correlation was found between age, duration of diabetes, or HbA1 and any of the autonomic function tests, except for one between age and cardiovascular autonomic score (r = 0.3202, P = 0.0126). Corrected QT interval did not correlate with cardiovascular autonomic score, pupil diameter, or constriction latency. A significant inverse correlation was found between cardiovascular autonomic score and pupil diameter (r = -0.4861, P < 0.001) and constriction latency (r = 0.3783, P < 0.001). Pupil diameter and constriction latency correlated well (r = -0.4276, P < 0.001). The corrected QT interval did not correlate with cardiovascular autonomic tests nor pupillometry results. The corrected QT interval therefore should not be used for the diagnosis of the severity of diabetic autonomic neuropathy.

Clinical Comparison of Corneal Diameter and Curvature in Asian Eyes with Those of Caucasian Eyes

Anatomical comparisons of the horizontal visible iris diameter (HVID) and the average keratometry (Kav) measurements were made between Asians and Caucasians and also between males and females. It was found that the HVID was significantly different as a function of both culture and gender. Also found was a significant difference in the Kav between males and females but not between Asians and Caucasians.

Pupillary Size in Children and Adolescents with Type 1 Diabetes

Pupillary adaptation to darkness was studied in 63 children and adolescents with Type 1 diabetes using a simple portable pupillometer. Results were compared with those in a group of age-related non-diabetic children and expressed as the ratio of the pupil diameter to the iris diameter (pupil diameter %). In the diabetic patients the pupil diameter % was 61.1 +/- 5.8 (44.4-71.9) % compared with 64.2 +/- 4.1 (53.2-72.6) % in the control subjects (p less than 0.001). Abnormal pupillary adaptation to darkness was found more commonly than abnormal heart rate variation in response to a variety of stimuli in the diabetic patients. Pupillary adaptation to darkness may be useful as an indicator of subclinical autonomic neuropathy in diabetic children.

Transverse Instabilities in the LIL

In view of a Beam Break Up (BBU) study, we have calculated and identified series of transverse deflecting modes in the S band sections of the LEP Injector Linacs (LIL). In these TW quasi-constant gradient structures with various iris diameters from 18 to 26 mm, only it-modes of the C band of the HEM11, having negative group velocities and phase velocities around c will lead to cumulative BBU. These deflecting ?-modes occur at frequencies in the range from 4558 to 4290 MHz for diameters from 18 to 26 mm. Frequency variation with iris diameter is -15 MHz for each added mm for calculated and measured 0-modes and about twice that value for ?-modes. Levels for starting transverse instabilities have been determined for various accelerated Beam Currents with different pulse widthes.

A new method for measuring the diameter of the in vivo human cornea.

An in vivo method of measuring the size of the human cornea by using catoptric imagery as devised for both closed-circuit television and 35-mm camera systems. The system was validated by using precision reticules and casts of eyes. The reproducibility of the closed-circuit television system was +/- 0.11 mm. The mean horizontal corneal diameter (HCD) for a sample of the right eyes of 50 subjects was 12.89 +/- 0.60 mm. The system was also used to measure horizontal visible iris diameter (HVID). The mean HVID for the same sample was 11.64 +/- 0.49 mm. Although there was a good general correlation between HCD and HVID, the HVID was found to be a poor predictor of HCD for the individual eye.

Threshold conditions for laser-initiated plasma shutters

The characteristics of laser-initiated plasma shutters used for retropulse isolation in high-power CO2 laser-fusion systems are discussed. Initiation of the plasma breakdown is shown to depend on the fluence that is incident on the edge of the iris which is employed in these shutters. A relatively simple model for the ignition process has been verified for a range of pulse durations (0.7–60 ns) and iris diameters (100–800 mm). This model provides practical design criteria for sizing plasma isolators for a variety of applications.

‘Zero 6'Extra Thin Soft Contact Lenses: Report on Clinical Trials

The development of micro‐thickness soft contact lenses to increase available oxygen to the cornea beneath the lens has exposed new problems for the patients in lens handling and lens durability. A newly designed lathe‐cut lens of only 0.06mm centre thickness, known as Zero 6, has been developed to overcome problems of shape stability and increase lens durability.The results of a clinical trial conducted on 410 patients over a period of 15 months are reported. The results showed the lens to be well tolerated by the eye and easily handled by the patient. A low breakage rate of 1.7% confirmed that the lens plastic has the durability required of micro‐thickness lenses. A new approach to the prescribing of the lens based on sagittal height showed good correlation with tolerance data from the trial. Ninety‐three percent of patients were successfully fitted with the lenses recommended by the manufacturer's Indicated Lens Table, based on mean keratometer reading and horizontal visible iris diameter. Two percent of patients were not satisfactorily fitted and 6.6% required lenses different to those recommended.

A technique for estimating the contribution of photomechanical responses to visual adaptation

This paper presents a technique for isolating and quantifying the contribution of photomechanical responses to visual adaptation. The technique is developed in the context of the pupillary mechanism that is active in the primary visual cells of the insect eye. Using a feedback-control model to represent the combination of retinular cell and pupil, it is shown that the effect of pupillary movements on retinal illumination can be inferred by analysing an intensity-response function of the pupil. When the technique is applied to the pupils of the butterfly and the fly, the results indicate that, in each case, the pupil decreases retinal illumination by approximately 0.7 log units when the ambient light level is increased from pupillary threshold to a level 2.5 log units higher. The validity of the technique is examined by applying it to the human pupil. The results predict changes of retinal illumination which are in close agreement with those expected on the basis of changes in iris diameter, including the Stiles-Crawford effect. The procedure presented here is simple and can, in principle, be applied to many forms of photomechanical adaptation.

NORMAL VALUES IN CLINICAL ELECTROOCULOGRAPHY

The following EOG potential and time parameters from 72 normal subjects were analysed: base value B, dark trough D, light peak L, light induced potential rise L-D, interval between beginning of dark adaptation and occurrence of dark through d and interval between dark trough and light peak l. Their relations to sex, age pupillary diameter, degree of iris pigmentation, refractive error, axial length, corneal curvature and diameter, ocular protrusion and interpupillary distance were assessed. Right eye and left eye samples of the EOG parameters were congruent, although individual differences were sometimes appreciable. The levels of B and D were higher in the female half of the sample. A positive correlation existed between age and D level. L-D was negatively correlated to the degree of refractive error and positively correlated to the ocular protrusion. A positive correlation was found between d and the four potential parameters, and there was a positive correlation between age and l. Practical consequences of the statistical analysis relating to the interpretation of such EOG data are discussed.

Genetic influences in drug responses of the eye and the heart.

1. Pupillary responses to locally applied phenylephrine and cardiac responses to intravenous hyoscine N-butylbromide have been studied in ten pairs each of healthy monovular and binovular twins aged between 24 and 60 years. 2. Under identical lighting conditions resting pupil diameters differed widely among individuals, being greater in female subjects and in those with larger irides and smaller with increasing age. 3. Monovular twins, but not binovular twins, showed significant concordance in iris diameter, initial pupil diameter, initial heart rate and responses to both drugs. The results suggest that these responses were dependent on the concordance of peripheral sympathetic and parasympathetic tone within each twin pair. 4. It is concluded that much of the variability in response to drugs acting on the autonomic nervous system is determined by physiological factors and that these are genetically influenced.

The interocular distance

Particulars of individuals tested. Historical remarks. Means employed. Mean and extreme values for men and women. Application of results to Galilean and prismatic binoculars. Variation of distance with width of head. Variation with height. Variation with age. Width of eye in relation to age. Colours of iris. Diameter of iris. Abnormalities.