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Biomedical subjects

M Millodot

Publications and source records attributed to M Millodot.

At least 19 recordsLinked to original sources
PubMed1989

Presbyopia correction and the accommodation in reserve.

One method of determining the additional correction for presbyopia suggests leaving a percentage of the amplitude of accommodation in reserve. The rationale for this assumption seems logical because using all of the available accommodation is not sustainable without discomfort. However there is no empirical evidence indicating what percentage of the amplitude of accommodation should actually be left in reserve. Common figures adopted have been one-half and one-third. In this investigation the percentage of accommodation used is deduced mathematically after having determined the following: 1. The 'add' by the direct subjective clinical method. 2. Measured the amplitude of accommodation. 3. Measured the reading distance in 305 presbyopes ranging from 40 to 83 years of age. The results showed a small decline in the amplitude of accommodation up to the age of 52, after which age the measurements were scattered about a steady level. This finding suggests that after the age of 52 the results are based on the depth-of-focus of the eye. Females had slightly greater accommodation than males of the same age. The power of the add was significantly correlated to the age of the subject. The mean percentage of accommodation used for the 305 subjects was found to be 50.7%, thus confirming the rule of leaving half of the accommodation in reserve, although there were large variations: there were differences between males and females and with age the percentage of measured accommodation used, after having determined the correct add, diminished. Similarly the percentage of accommodation also decreased for shorter reading distances.

Accommodation, Ocular↗
PubMed1988

Differences in adaptation of tonic accommodation with refractive state.

It has recently been demonstrated that intersubject variations in tonic (dark focus) levels of accommodation are related to corrected refractive state (McBrien and Millodot, 1987). The aim of the present study was to investigate the effect of sustained visual tasks on the tonic level of accommodation in different refractive groups. Eleven hyperopes, 16 emmetropes, ten early onset myopes and ten late onset myopes had their tonic accommodation measured with the objective infrared optometer Canon Autoref R-1 before and after a 15 min sustained visual counting task. The post-task tonic accommodation level was monitored for 15 min to assess the decay rate of any observed task-induced changes in tonic accommodation. Subjects repeated the experimental procedure for four task locations (6 m, pre-task tonic position, 37 cm and 20 cm). Late onset myopes showed significant positive (myopic) changes in their tonic level of accommodation at both near viewing distances, which showed no evidence of decay during the 15 min post-task monitoring period. Hyperopes, however, underwent transient "counteradaptive" decreases in their tonic level of accommodation after sustained near viewing. Emmetropes and early onset myopes showed little change in tonic levels at the two near distances. Differences between groups were also obtained at tonic and far viewing distances. Post-task changes in tonic accommodation demonstrated only a weak negative correlation with pre-task tonic accommodation levels at each task distance. It is proposed that the observed differences in adaptation of tonic accommodation among refractive groups may be related to variations in autonomic innervation of the ciliary muscle.

Accommodation, Ocular↗
PubMed1987

A biometric investigation of late onset myopic eyes.

There is a paucity of biometric information on late onset myopia (onset after 15-years-old). The present investigation compared the ocular component dimensions of 30 late onset myopes and 30 emmetropes, who were both age and sex matched. Measurement techniques included A-scan ultrasonography and keratometry. The findings revealed that the ultimate cause of late onset myopia is vitreous chamber elongation. Late onset myopes were also found to have significantly deeper anterior chambers and thinner crystalline lenses, no differences being found in corneal curvature measures. Possible mechanisms leading to these observed biometric differences are discussed in the light of recent findings.

Adolescent↗
PubMed1987

The relationship between tonic accommodation and refractive error.

It is now well established that accommodation adopts an intermediate resting position in the absence of visual stimulation. It also has been shown that this tonic position of accommodation exhibits considerable variation among individuals (ie, 0-4 D). Previous studies have been somewhat inconclusive as to whether these individual differences in tonic accommodation are related to the refractive properties of the eye. This study investigates the relationship between tonic accommodation and refractive error with particular reference to both the value and the time course of tonic accommodation. Sixty-two subjects were used for the study, with an age range of 19-25 yr. Subjects were placed into one of four refractive groups, after considering factors pertaining to the theories of refractive development. Darkroom measures of tonic accommodation were determined using the infrared objective autorefractor, Canon Autoref R-1. Significant differences were found among the four refractive groups, with corrected hyperopes having the highest dioptric value of tonic accommodation and corrected late-onset myopes having the lowest dioptric value. The significant difference found between early- and late-onset myopes is suggested as a possible reason for the inconclusive results of some previous studies. It also was found that the time taken to reach a stable tonic position of accommodation was much slower for the hyperopic group than for the other refractive groups. The results are discussed in the light of recent findings on accommodative hysteresis and with respect to a dual innervation to the ciliary muscle.

Accommodation, Ocular↗
PubMed1986

Amplitude of accommodation and refractive error.

This paper investigates the amplitude of accommodation of early onset myopes, late onset myopes, emmetropes, and hyperopes. Eighty subjects were used, 41 women and 39 men, with an age range of 18-22 yr (mean = 19.82). All subjects wore an optimum refractive correction, giving visual acuities of 20/20 or better. Significant differences were found between the four refractive groups, with late onset myopes having the largest amplitude of accommodation, followed by early onset myopes, emmetropes, and hyperopes. The results are discussed in the light of previous findings on tonic accommodation and the accommodative response gradient and interpretated in the context of a dual innervation to the ciliary muscle.

Accommodation, Ocular↗
PubMed1986

The effect of refractive error on the accommodative response gradient.

The accommodative responses of early-onset myopes, late-onset myopes, emmetropes and hyperopes were measured over a range of 5 dioptres using an objective infra-red autorefractor. Differences were found between the four refractive groups, with hyperopes accommodating more for near targets than emmetropes, followed by early-onset myopes then late-onset myopes. Moreover a strong correlation between the accommodative response gradient and refractive error was found, suggesting that hyperopes accommodate more to a particular target than do emmetropes or myopes. The results are interpreted in the context of a dual innervation to the ciliary muscle.

Accommodation, Ocular↗
PubMed1985

Clinical evaluation of the Canon Autoref R-1.

A clinical evaluation of the Canon Autoref R-1 was carried out on 93 subjects (186 eyes). Results were compared to clinical refractive data. A measure of the R-1 reliability was obtained both for successive measurements and measurements repeated on separate occasions. The validity of the instrument was found to be similar to that found in other investigations.

Adolescent↗
PubMed1985

Variation of astigmatism with accommodation and its relationship with dark focus.

The refraction of 122 eyes was measured for five distances of fixation with an objective Canon Auto Refractor. The cylindrical component was found to vary, but by a small amount. We found no evidence of a deliberate reduction in astigmatism with accommodation, in accord with other studies. The axis was also found to vary by at least 5 degrees in about half of the subjects tested, which is also in good accord with other investigations. The dark focus of 31 eyes was not found to correlate with a minimum astigmatic distance, since this only occurred in 11 out of the 31 eyes. For these 11 eyes, the correlation of dark focus and the dioptric distance where astigmatism was minimum was equal to + 0.54. It implied that for those eyes (about one-third of all types) there was a tendency to yield the best optical quality at the dark focus.

Accommodation, Ocular↗
PubMed1984

Effect of topical anaesthesia on corneal epithelial fragility.

The effect of topical anaesthetics on human corneal integrity was assessed by measurement of the alterations they cause in corneal damage threshold. The anaesthetics investigated were 1.0% Amethocaine HCl, assessed immediately after instillation and after delays of 20 min and 60 min, and 0.5% Amethocaine HCl and 0.4% Benoxinate HCl, assessed 20 min after instillation. At 20 min after instillation of 1.0% Amethocaine HCl, the corneal damage threshold was significantly decreased. At other times for this anaesthetic, and for 0.5% Amethocaine HCl and 0.4% Benoxinate HCl, the corneal damage threshold was unaltered.

Anesthetics, Local↗
PubMed1984

Peripheral refraction in aphakic eyes.

Peripheral refraction was measured in aphakic eyes and control eyes of approximately the same age, using a Topcon refractometer. In addition, two aphakic eyes in young patients were also measured and compared with data obtained on young patients by Millodot using the same technique. It was found that aphakic eyes have much less oblique astigmatism than phakic eyes of the same age, suggesting a large contribution to the crystalline lens. The total oblique astigmatism of the eyes increases with age but that of the cornea remains approximately the same, thus implying that this increase with age is also accounted for by the lens. Moreover, the total oblique astigmatism of old eyes is nearly the same as the theoretical value, suggesting that with age the lens becomes more spherical.

Adult↗
PubMed1984

The influence of age on the fragility of the cornea.

Corneal fragility was measured with the Cochet-Bonnet aesthesiometer on 171 eyes of various ages. It was found to remain the same until about age 40. It increased significantly and progressively afterwards. It was compared to corneal sensitivity which diminishes significantly after about the same age.

Adolescent↗
PubMed1984

Sensitivity of the cornea after exposure to ultraviolet light.

Corneal sensitivity was measured before and after exposure to an electric welding arc. The ultraviolet radiation produced in the exposed eye a rapid and large decrease in corneal sensitivity with an equally rapid recovery, all occurring within 4 h. The other eye serving as a control retained the same sensitivity throughout the same period of time.

Adult↗
PubMed1983

Sensitivity and fragility in keratoconus.

38 persons with various degrees of keratoconus were examined. Using the photokeratoscope an index of the severity of the cone was established and compared to a group of normal eyes. Sensitivity was measured in the centre and periphery of the cornea. It was found to be significantly lower than in normal eyes and those eyes wearing contact lenses exhibited the lowest sensitivity. There was no correlation between peripheral CTT (Corneal Touch Threshold) and the severity of keratoconus, but there was a significant correlation between central CTT and severity, though only for the group of eyes not wearing contact lenses. Corneal fragility was also found to be greater in keratoconus than in normal eyes and more so in those eyes wearing contact lenses. There was a significant correlation between the severity and the fragility.

Adolescent↗
PubMed1982

Electrophysiological evidence of adaptation to colored filters.

Subjects wore blue filters (Kodak Wratten 45) in front of their normal spectacle correction for a period of 4.5 hr. Visual evoked potential (VEP's) were measured (monocularly) before, in white light and through the blue filters at the start and finish of wearing the filters. Predictably, from the chromatic interval, the subjects initially showed some degree of myopia, confirmed by more negative lens power required to give maximum VEP response. However, after 4.5 hr of wear of the filters, VEP's were measured again and it was found that the maximum VEP response was obtained in each case with less negative lens power, indicating adaptation of the visual system toward emmetropia. The role of accommodation in this adaptive process is discussed.

Accommodation, Ocular↗
PubMed1981

Effect of ametropia on peripheral refraction.

Peripheral refraction was measured in 62 eyes along the horizontal meridian from 60 degrees nasally to 60 degrees temporally, using a Topcon refractometer. The amount of astigmatism was found to increase progressively, although less than predicted theoretically, toward the periphery in 91% of the eyes. Dividing the sample into myopes, hyperopes, and near-emmetropes showed that the type of astigmatism differed significantly with each group of eyes and that this factor played a most important role.

Adolescent↗
PubMed1981

VEP measurement of the amplitude of accommodation.

The amplitude of accommodation was measured in 44 subjects by visually evoked potentials (VEP) in response to negative lenses. It was found that about two-thirds of the subjects responded to the lenses by increasing their accommodation in order to minimise blur, while the other one-third accepted the blur and accommodated very little. The amplitude was also determined subjectively (push-up method) and it correlated very well with the VEP measurement (r = 0.91). It is therefore suggested that VEP constitutes a feasible method of assessing objectively the amplitude of accommodation.

Accommodation, Ocular↗