Inter-relationships between DNA damage, ascorbic acid and glycaemic control in Type 2 diabetes mellitus

AIMS

The onset of complications in Type 2 diabetes mellitus (DM) patients cannot be predicted in individuals. Evidence suggests a link between complications and hyperglycaemia, oxidative stress and antioxidants, but causality is unclear. This study investigated baseline (entry) fasting plasma ascorbic acid, lymphocytic DNA damage and glycaemic control in Type 2 DM as part of a long-term study, the aim of which is to explore a biomarker profiling approach to identify and improve outcome in high-risk subjects.

METHODS

A cross-sectional study, in which DNA damage, glycated haemoglobin (HbA(1c)), fasting plasma glucose (FPG) and ascorbic acid (AA) were measured on fasting blood samples collected from 427 Type 2 DM subjects.

RESULTS

DNA damage was significantly (P < 0.0001) and directly correlated to both FPG (r = 0.540) and HbA(1c) (r = 0.282), and was significantly (P < 0.0001), independently and inversely correlated to plasma AA (r = -0.449). In those subjects with both poor glycaemic control and low AA (< 48 microm, the overall mean value for the study group), DNA damage was significantly (P < 0.005) higher compared with those subjects with a similar degree of hyperglycaemia but with AA above the mean.

CONCLUSIONS

The novel finding of a significant inverse relationship between plasma AA and DNA damage in Type 2 DM indicates that poorly controlled diabetic subjects might benefit from increased dietary vitamin C. The data also have important implications for biomarker profiling to identify those subjects who might benefit most from intensive therapy. Longer-term follow-up is underway.

The effect of conventional CR39 and Fresnel prisms on high and low contrast acuity

The effect of conventional CR39 and Fresnel prisms on high and low contrast letter acuity was studied. Visual acuity of the fully corrected better eyes of 15 subjects was measured with the high (90%) and low (10%) contrast logMAR letter charts, while they wore prisms of varying power. The results showed that when the power of the conventional CR39 prism and the Fresnel prism reached 10 prism dioptres and 5 prism dioptres, respectively, significant reduction (1 tail t-test, p < 0.05) of the high and low contrast acuity occurred. The Fresnel prism caused a significantly greater acuity reduction than the conventional CR39 prism for powers ranging from 5 to 30 prism dioptres for both contrasts. The rate of acuity reduction with increasing prism power was greater with the low contrast targets than with the high contrast targets for both prisms. In addition, the rate of acuity reduction with increasing prism power was greater with the Fresnel prism than with the conventional CR39 prism for both contrasts. The conventional CR39 prism reduced acuity by a ratio of about 0.8-0.9 of that of the Fresnel prism for powers ranging from 5 to 20 prism dioptres and by about 0.7 for 30 prism dioptres. These ratios applied for both high and low contrast acuity, and therefore were independent of the level of contrast used.

Vision of low astigmats through thick and thin lathe-cut soft contact lenses

Distance and near visual acuity of 13 low astigmats were determined in a double-masked experiment through thick and thin (centre thickness 0.12 mm and 0.06 mm, respectively) spherical lathe-cut soft lenses. For each lens type, distance and near LogMAR VA and over-refraction were assessed with different logMAR VA charts. For 70% of the subjects, the residual astigmatism was significantly lower than the refractive astigmatism with thicker lenses. No statistically significant differences in the distance and near logMAR VA was found between the two lens types using any of the charts used, though, in general, logMAR VA obtained through the thicker lens was better than logMAR VA through the thinner lens. The variabilities in distance and near logMAR VA between the two lens types increased with decreased contrast. The variabilities in distance logMAR VA were greater with Chinese charts than with English charts, and LogMAR VA with Chinese charts were significantly worse for both lens types. Based on the results of this study, we concluded that thicker spherical lathe-cut soft lenses provide better vision in low astigmats. The Snellen acuity test is inadequate for vision assessment of soft contact lens wearers. When a patient wearing thin soft contact lenses complains of poor vision in spite of 6/6 or 6/5 Snellen acuity, changing to thicker lenses may be considered.

The calibration of a 2.5x Galilean focusable telescope as an optometer for refraction

A 2.5x Selsi achromatic Galilean focusable telescope was calibrated for refraction at 6 m. In its calibration, minus power trial lens was placed at the objective of the telescope to simulate vergence of a target at a finite distance, before the back vertex power (BVP) of the telescope at each setting (telescope length) was measured by a focimeter. By using a graphical presentation of the results, the BVP of the telescope at each setting could be determined at different selected target distances. For a target vergence of -0.167 D or a distance of 6 m, the common testing distance in clinical practice, this calibrated telescope had a BVP or refraction measuring range of -7.27(-)+7.52 D. When this telescope was used to measure simulated manifest refractive errors at 6 m, it yielded a mean error of +0.13 D with a 95% confidence limit of agreement of -0.38(-)+0.64 D. These results indicated that the accuracy and precision of telescopic refraction were comparable to that of retinoscopy. Therefore, the calibrated telescope could be considered as a reliable and inexpensive instrument for determining spherical refractive errors. Telescopic refraction is applicable in refracting economically disadvantaged population in underserved areas where modern equipment and electricity are not available. In addition, it provides an alternative subjective refraction method for low vision population because the magnification of this calibrated telescope has the advantage of allowing low vision patients to be refracted at the common 6 m testing distance in clinical practice.

Scattering properties of Bagolini lenses and their effects on spatial vision

The effect of a Bagolini lens on spatial vision was investigated by studying its far-field diffraction pattern as produced by a coherent beam of laser light, and its effect on the contrast sensitivity function (CSF) in human subjects. For lenses of the main type studied, which were crossed by a series of slightly-irregular striated bands, each consisting of fine, parallel, etched lines of various widths and separations, the diffraction pattern consisted of undiffracted light giving a bright central spot and wide-angle, diffracted light giving a dim streak. The latter was due to the sum of the diffraction patterns associated by the irregular fine etched lines. The streak produced by a single striated band was modulated by a series of regular maxima and minima related to the width of the band. Analysis of this pattern gave the width of the band as 0.6 mm, in close agreement with direct microscopical measurements. When four bands were illuminated by a beam of about 3 mm diameter, similar to the diameter of the photopic pupil, the diffraction pattern showed no obvious maxima and minima, due to irregularity in the width and separation of the bands. The central spot contained more than 90% of the total light in the diffraction pattern. Thus the Bagolini lens, with its relatively weak far-field diffraction pattern lacking regular maxima and minima when areas > or = 3 mm in diameter were used, was expected to have only a small effect on the apparent contrast of the targets in CSF experiments. This was confirmed by the measurements: Bagolini lenses showed no significant effect on either the monocular or binocular CSF. Further similar measurements with lenses of slightly different design from another manufacturer confirmed these findings. Therefore Bagolini lenses do not disrupt vision when they are used to determine the presence of suppression and anomalous retinal correspondence.

The validity of current clinical tests of contrast sensitivity and their ability to predict reading speed in low vision

PURPOSE

Contrast sensitivity (CS) testing using chart tests of CS is becoming increasingly common in low vision assessment. Yet we know little about the validity of these charts, i.e. which region of the spatial frequency spectrum is being measured. In this study we aimed to determine the validity of currently available CS charts by comparison against oscilloscope-based CS. We also determined their relative ability to predict reading speed.

METHODS

CS was measured with five commercially available charts and the contrast sensitivity function was determined with sinusoidal gratings presented on a Joyce screen using a two-alternative forced choice staircase technique in 36 observers with low vision and 3 with normal vision. Reading rate was also measured with the subject reading with his or her own optical low vision aid.

RESULTS

The results show that the Pelli-Robson chart and the Cambridge gratings are good measures of medium to low spatial frequencies, as would be predicted from their design, while the Regan and UW charts correlated with medium to high frequencies. The Vistech chart was a good predictor of CS at each spatial frequency.

CONCLUSIONS

The best chart test of CS depends on which region of the CS curve is of interest. All the charts were good predictors of reading rate.

International cooperative exchange programs in clinical optometry

A reciprocal exchange program between the University of Waterloo and the Hong Kong Polytechnic in clinical optometry is presented. Costs and benefits are described.

Normal values of eye position and head size in Chinese children from Hong Kong

We measured the eye position and head dimensions of Chinese children in Hong Kong. Values for exophthalmos, interpupillary distance (IPD), interorbital distance (IOD), distance between medial canthi, and head dimensions were found to be larger than those for Caucasian, Black, or other Chinese groups.

Notch in contrast sensitivity function of optical origin: diffraction effects of acrylic filters

A series of retinal image degrading filters was evaluated by measuring the contrast sensitivity function of four human subjects through the filters (residual CSF). The acrylic filters, with regularly spaced cross-hatches, produced progressively more reduction in the residual CSF as the density of the cross hatching increased. For some of the filters there was a selective loss of a narrow band of spatial frequencies as a result of diffraction effects. This experiment serves to further emphasize the need to rule out optical causes of such notches in the CSF before making a diagnosis of neurological dysfunction.

Eye position and head size in the Chinese population: a comparison of the Chinese from Hong Kong with the Chinese from Guangdong Province

Measurements obtained in this study include facial and head dimensions. From our findings, it would appear that the Chinese population in Hong Kong have not become different in the two or three generations that separate them from those living in Guangdong province of China.

Normal values of eye position in the Chinese population of Hong Kong

Exophthalmos, interpupillary distance (IPD), interobital distance (IOD), and inner intercanthal distance (ICD) were measured in an adult Chinese population from Hong Kong (HKC). Mean values and normal range for 95% of the population were determined and the relation with head size and body height examined. Values of exophthalmos and IPD in our Chinese population were similar to those given for Caucasian groups. IOD and ICD were larger in the Chinese than in adult Caucasians. Our findings show generally larger values in the HKC than has been found for other populations in mainland China.

Current methods of treating and preventing myopia

In this review, we discuss and compare current methods of treating and preventing myopia including radial keratotomy, keratomileusis, keratophakia, epikeratoplasty, keratokyphosis, scleral reinforcement, phakoemulsification, and heat application. Among the visual training methods are such procedures as biofeedback and behavior modification. The use of drugs, orthokeratology, spectacles, bifocals, prisms, intraocular lenses, contact lenses, and ultrasound are described.

Effect of magnification and field of view on reading speed using a CCTV

Reading speeds were measured in 18 subjects with normal vision and 10 with low vision for each of 20 experimental conditions with different magnifications and field sizes on the Closed Circuit Television System (CCTV). There was a significant difference between the results for the two groups of subjects. These results suggested that in low-vision patients with faster reading speeds, minimum magnification for maximum field size on the CCTV would be valid advice. For low-vision patients who read more slowly, reading speed may improve at higher magnifications despite reduced field size.

Telescopic scanning and age-related maculopathy

We report the management of various aspects of the care provided over a span of 12 years for a patient with age-related maculopathy (ARM). The use of a low-power telescope proved to be particularly helpful because, with it, she learned eccentric viewing and made best use of her remaining vision.

Optical management of posterior chamber lens tilt

A pseudophakic patient reported blurred vision and diplopia one year after the surgery. We suspected that the origin of both these problems was subluxation of the intraocular lens. His blurred vision was eliminated by a cylindrical spectacle lens at an oblique axis. Monocular diplopia could only be eliminated occasionally. The displacement of the IOL is shown photographically in this report.

Tolerance to visual defocus

Low-resolution optical systems are more tolerant to defocus than are high-resolution systems. We wished to determine whether this principle applies to human vision. We used psychophysical methods to measure the effects of defocus in normal eyes under low-resolution conditions. Modulation transfer of sine-wave gratings was measured as a function of dioptric defocus at low and medium spatial frequencies. We defined the depth of focus at a given spatial frequency to be the dioptric range for which the modulation transfer exceeds 50% of its peak value. For dilated pupils, depth of focus increased from about 2.5 diopters (D) at 3.5 cycles/deg to about 17 D at 0.25 cycles/deg. From our results we predicted that tasks requiring only low spatial frequencies will be more tolerant to defocus than tasks requiring higher spatial frequencies. This prediction was confirmed in a letter-recognition experiment. The increasing tolerance to defocus at low spatial frequencies also implies that individuals with low acuity will be more tolerant to defocus than people with normal vision. We confirmed this prediction by measuring tolerance to defocus in 30 low-vision eyes.

Effect of Fresnel prism dispersion on contrast sensitivity function

Fresnel prisms are often used in orthoptics for binocular anomalies and in low vision for visual field defects. These prisms are made of optical polyvinyl chloride (PVC) and this material increases chromatic dispersion and produces a loss of contrast. In this study, the effect of chromatic dispersion on contrast sensitivity is determined. Contrast thresholds over a wide range of spatial frequencies are obtained on a number of subjects with the use of Fresnel prisms ranging from 5 to 30 prism dioptres. As predicted there is a decrease in visual acuity and cut-off spatial frequency threshold as prism power increases. Similarly, a decrease in contrast sensitivity at high and medium spatial frequencies is recorded.

Effect of hemodialysis on contrast sensitivity in renal failure

After a brief review of the ocular aspects of hemodialysis treatment for renal failure, we report on 10 patients who underwent this treatment. Contrast thresholds over a wide range of spatial frequencies and Snellen visual acuities were measured before and after treatment. Subtle changes in vision can be monitored by the contrast sensitivity function (CSF) technique. We conclude that there are measurable changes in contrast sensitivity after hemodialysis treatment for each of the 10 patients (20 eyes).

Contrast sensitivity function as a diagnostic tool in low vision

In this case report, a patient's visual loss associated with both cataract and senile macular degeneration is described. The contrast sensitivity function (CSF) as well as Retinometer and Visometer findings indicate that the additional visual loss over a year's time was lenticular, rather than retinal, in origin.

Contrast attenuation characteristics of iris clipped intraocular lens implants in situ

In this study contrast thresholds were monitored over a wide range of spatial frequencies for patients with iris clipped implants or Fyodorov and Binkhorst types. These results were compared with those of an age matched normal group and attenuation characteristics derived for the implants and media environment alone. These results show that lenticular implants of this type can produce large reductions in contrast with a wide variety of transfer functions, for example, low pass, band reject, and band pass. These findings highlight the potential inadequacies of the assessment of the visual capabilities of these devices by acuity measures alone. We suggest that a more realistic and abbreviated approach should be based upon supplementing acuity assessment with monitoring of threshold sensitivity for a low, medium, and high spatial frequency sinewave grating.

The Refractive State of the Eye of the Kangaroos Macropus giganteus and M. rufus

Refractive findings were determined with a retinoscope for two species of kangaroos. The 10 eyes studied were found to be hyperopic between 1.5 and 2.0 dioptres, with and without cycloplegia. Due to the large size of the eye, the hyperopia cannot be explained on the basis of retinoscopic reflection from the vitreous-retina border. The hyperopia may be due to an as yet unexplained artefact or it may reflect indifference to optical quality.

A distance visual acuity chart incorporating some new design features

Standardized visual acuity assessments are possible when consideration is given to legibility, acuity row legibility, letter spacing, optotype, row arrangement, and letter size gradation. The relative optotype legibilities reported by Sloan were verified experimentally under simulated conditions of optical defocus. Acuity row component letters were selected to equalize aggregate row legibilities and were arranged to minimize contaminative sequencing dependency. We describe a new acuity chart format with vertical acuity row presentations to eliminate bias from previous reading experience, and testing procedures using this chart.

Effect of target configuration on the measurement of astigmatism

In this study, five dissimilar crossed cylinder targets were used to determine the cylindrical component of the refractive error of 30 subjects. Our purpose is to see if variations in target configuration affect the results of the test. Although there are statistical differences when targets with different configurations are used in determining astigmatism subjectively, these differences are not clinically significant if we assume that the least amount of error required for clinical significance is +/- 0.25 D. We conclude that dissimilar crossed cylinder targets yield similar astigmatic findings clinically.

An evaluation of the Arden grating test

The Arden grating test is found to be a statistically reliable tool which provides an index of contrast sensitivity. Although no statistically valid mean score can be assigned to each plate, a range of normals can be established for this particular age group. In this study, after each individual's initial scores were established for each plate they remained constant each time the test was repeated. The scores found for each plate are somewhat less than those established by Arden which may in part be related to the effect of age and to some variation in the mode of presentation by the test administrator. In summary, the Arden grating test when used properly should be a rapid and effective screener. It can reveal visual loss in instances where other clinical techniques fail to show significant findings. It is a reasonable clinical substitution of the contrast sensitivity function test in monitoring or detecting subtle changes in low and medium spatial frequency thresholds. The Arden grating test has recently been updated and is being marketed by the American Optical Company. Use of this test can add another dimension to the clinical ophthalmic examination although clinical trials should first be made against the original AGT.

Fresnel prism therapy for right hemianopia

Fresnel prisms placed on the spectacle lenses of a patient with right hemianopia provide an easier means for the patient to become aware of objects located in the blind field. Exact location of the prisms is important.

Color of visual display terminals and the eye. Green VDTs provide the optimal stimulus to accommodation

The longitudinal chromatic aberration of the human eye is substantial and therefore the color of the phosphor chosen for a visual display terminal (VDT) will affect refractive state and accommodative demand. For most working distances, green stimuli (lambda max 520 nm) are optimal.

A pilot study of contrast sensitivity assessment of the CAM treatment of amblyopia

Contrast thresholds of varying spatial frequencies were obtained on 3 amblyopic patients before and after the CAM treatment of amblyopia. Results of this study confirm previous findings that in the absence of change of visual acuity, contrast sensitivity function can be changed with the use of this technique. Improvement of contrast sensitivity can occur in older patients and that the sensitivity sometimes can deteriorate when treatment is stopped.

Measuring light levels with photographic meters

With proper conversion factors, light meters designed for photographic use may be used to measure clinical light levels. Conversion factors and use of these light meters are discussed.

Absolute stereoscopic thresholds as measured by crossed and uncrossed disparities

Stereoscopic tests of 30 subjects by means of diastereo instruments showed a lower threshold for crossed disparities than for uncrossed disparities. These findings support Richards' conclusion that crossed and uncrossed disparity limits are the result of two different mechanisms.

A comparison of three methods for determining the reading addition

Three subjective determinations of the reading addition required by each of 10 subjects were obtained in this study with the use of a cross cylinder grid target, a variable color, near-point, grid target and an ordinary reading card. All three methods gave similar results. In addition, there was no change in the measurement when the color of the horizontal and vertical lines was reversed on the variable color, near-point, grid target.

The AO SR IIItm Subjective Refraction System: comparison with Phoropter measures

Subjective measures of refractive error were obtained on 530 eyes using the AO SR III Subjective refraction System (operated by a trained secretary) and using a phoropter (operated by optometrists and optometry students) in a clinical setting. Comparison of these measures from the present study and from a previous study by Bannon leads us to conclude that the SR III instrument is capable of estimating refractive error with good agreement with conventional refractive methods. Comparison with the Acuity Systems 6600 Auto-RefractorTM was also made.

Comparison of accommodation with rigid and flexible contact lenses

Measurements were made of the amplitude of accommodation for myopes wearing spectacles, rigid contact lenses, and flexible contact lenses. Both forms of contact lenses placed greater accommodative requirements on the myope than did spectacle correction, but no significant difference was found between the 2 types of contact lenses in this respect.

The effect of hard and soft contact lenses (SoflensTM) on the spherical aberration of the human eye

An attempt was made in this study to determine experimentally the relative effects of hard and soft contact lenses on the spherical aberration of the human eye. Results of this study indicate that there is very little difference in the value of spherical aberration between wearing soft or hard contact lenses.