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Biomedical subjects

J S Pointer

Publications and source records attributed to J S Pointer.

At least 19 recordsLinked to original sources
PubMed2001

The influence of level and polarity of figure-ground contrast on vision.

PURPOSE: To document the effect upon human foveal vision of changes in the level and polarity of figure-ground contrast under photopic controlled test conditions, with particular emphasis on performance at low contrast levels. METHODS: Using a forced-choice psychophysical paradigm, threshold acuity estimates were derived at 9 discrete levels over a near-3 octave contrast range for Landolt ring-type stimuli of either positive or negative polarity. Data were obtained under binocular conditions from 10 young adults, each wearing their optimum low myopic spectacle correction. RESULTS: Visual acuity declined linearly with reducing stimulus contrast, the deterioration increasing substantially at <10% figure-ground contrast regardless of stimulus polarity. Performance was slightly (but not statistically significantly) better for positive contrast stimuli. CONCLUSION: Irrespective of contrast polarity, a reduction in stimulus figure-ground contrast <10% produces an accelerated decrement in photopic foveal vision compared to the performance at levels >10%. Some clinical and practical implications of this outcome are considered with regard to the examination of patients with normal and compromised visual function.

Adult↗
PubMed2001

Sighting dominance, handedness, and visual acuity preference: three mutually exclusive modalities?

It is tempting, even perhaps for the clinician, to assume prima facie that an individual's handedness is indicative of other lateral asymmetries, including ocular (sighting) dominance and preferred monocular acuity. An analysis of new data relating to these three modalities, as collated from counter-balanced groups of normally sighted male and female children and adults examined in optometric practice, confirms the general fallacy of this assumption and considers why it is such a persistent misconception. The degree of association between the three modalities in right-preferent individuals is revealed as statistically no greater than chance. On the basis of this study, estimates of right-sided hand, eye and/or acuity congruency are derived for the information of the clinician in the prescribing environment of the consulting room.

Adolescent↗
PubMed2001

A 6-year longitudinal optometric study of the refractive trend in school-aged children.

This report describes the analysis of the refractive data of optometric patients examined annually between the ages of 7 and 13 years. The results indicate a declining hypermetropic/increasing myopic refractive trend in 73% of the 41 individuals who attended over the entire 6 years of the investigation: overall, there was a mean rate of change of -0.09 D pa. Annual myopic incidence values of between 3.5 and 12% were found, resulting in a rise in myopic prevalence in this clinical population from 5 to nearly 40% over the course of the study. For the refractive classification adopted here, the juvenile myopic patients emerged from a pool of previously emmetropic subjects: the proportion of hypermetropic patients remained approximately stable over the 6 years reviewed. The age-related annual rates of myopic prevalence are approximately a factor of two greater in this self-selected clinical population compared to those reported for investigations in a general population. The inference is that children who were classed as emmetropic at age 7 should continue to be reviewed annually by the optometrist who should be alert to the possibility of clinically significant degrees of myopia emerging later.

Adolescent↗
PubMed2000

Evidence that a gender difference in intraocular pressure is present from childhood.

Routine assessment of intraocular pressure (IOP) is usually confined to the clinical population aged over 40 years, i.e., to those individuals considered to be most at-risk of developing glaucoma. Published IOP data collected from assumed non-glaucomatous adult subjects have shown a gender difference in this parameter, with human females recording a consistently higher value than age-matched males. A recent study has also demonstrated that a diurnal variation in IOP can be recorded in adults across normal consulting hours. IOP material is presented here, as collected in the early afternoon (14.00-14.59 hours) from n = 140 school children aged > or = 9 < 12 years. It is complemented by previously published data, also recorded between 14.00-14.59, from n = 100 middle-aged adults aged 40-59 years, and n = 102 mature adults aged over 60 years. Analysis of these three data sets indicates that a non-statistically significant gender difference in mean IOP (female > male) is present from childhood; it also suggests that, for either gender, the absolute mean level of IOP remains little altered from childhood into and throughout adulthood. However the physiological basis for these observations remains obscure.

Adult↗
PubMed1999

The far interpupillary distance. A gender-specific variation with advancing age.

A knowledge of the magnitude of the far interpupillary distance (FIPD) in relation to a specific population is of clinical, practical and theoretical interest. A FIPD database is presented here, comprising material collated from the spectacle dispensing records of n = 1800 subjects seen in routine optometric practice. All measurements were taken by the author on healthy Caucasian (white, Northern European) males and females. The data were equi-partitioned either across three age bands (16-25, 26-40, 41-65 years: mixed refractive types, total n = 900) or between the three distance refractive types (emmetropia, hypermetropia, myopia: all subjects aged between 41-65 years, total n = 900). A consistent gender difference (male > female) was confirmed throughout this material, irrespective of age group; refractive type, however, had no influence on the magnitude of this facial parameter. Summary results of this anthropometric survey are presented in tabular form, facilitating reference by ophthalmic and dental clinicians and by the designers of binocular optical instruments. There was also revealed evidence of a gender-specific pattern of change in the FIPD variable with advancing age. An approximately 3% increase in the magnitude of the human FIPD from the mid-teens to later middle age was attained in males by early middle age, being little altered thereafter: in contrast females continued to record an increase in this facial parameter into later middle age. An explanation for this hitherto unremarked feature of human facial anthropometry might be sought in the gender-specific changes post-puberty of the cranial skeletal anatomy and in the soft tissues of the orbital region.

Adolescent↗
PubMed1998

The influence of eye movement on soft contact lens visual performance.

An apparently undocumented aspect of the correction provided by soft hydrophilic contact lenses, either at the fitting stage or in wear, is the influence of eye movement on visual performance. Using a televised visual discrimination task both spectacle (control) and soft contact lens (experimental) monocular visual performance was assessed in a group of human subjects (N = 5) under conditions of stationary fixation and subsequent to a defined 15 deg ocular excursion. For this subject group, analysis of variance revealed no statistically significant difference (P > 0.9) between visual performance under the control and any of the experimental conditions: the group psychometric functions were similar in all cases, regardless of the direction--or absence--of a deliberate eye movement. It is concluded that even in new and inexperienced soft contact lens wearers, provided that the lens fit is optimum, eye movement does not have a significant influence on the visual performance of the eye/lens system.

Journal Article↗
PubMed1998

The Kettering Diabetic Monitoring Programme: twelve months experience of an optometric practice-based scheme.

Over recent years the British Government has pursued a policy encouraging the integration of primary and secondary health care. This drive to promote the efficient delivery of primary care at local centres has seen the forging of co-operative alliances between various healthcare practitioners. A notable development has been the growth of optometric practice-based schemes for monitoring the eyecare of diabetic patients. This paper reports on the first twelve months operation (April 1995-March 1996, inclusive) of such a 'collaborative care' scheme operating in the Kettering Health Area of Northamptonshire. With the co-operation of their general medical practitioner (GMP) and under the case-review of the hospital-based specialist, diabetic patients attended participating optometric practices for an annual sight test and eye examination including mandatory fundus assessment under mydriasis. A brief 'ticked menu' report was subsequently forwarded to the patient's GMP for filing or action as necessary. A copy was also sent to the hospital clinic to enable updating of the diabetic patient database and for the authorisation of the supplementary fee payable to the examining optometrist. An audit of the first year of operation has indicated that those 92% of optometrists in the locality who participated in the programme logged 34% of the projected diabetic population of the Kettering Health Area. Of these individuals, 10.8% were identified as requiring referral for ophthalmological assessment, including 0.7% who needed urgent intervention. Approximately 80% of the referrals were assessed in the Ophthalmology Clinic within the twelve month timeframe of this first year audit; one-third of these patients received treatment and/or a second review over this period, the net outcome being that one-half of the original referrals were returned to the programme for continued routine annual screening. The scheme has received a funding allocation for a further financial year, with the possibility of its extension county-wide being kept under review.

Adolescent↗
PubMed1998

The burgeoning presbyopic population: an emerging 20th century phenomenon.

Improved social welfare in the wake of the 'industrial revolution' set in train in mid-18th century Britain an escalation in population numbers which has been sustained through to the end of the 20th century--and is projected to continue into the 21st century. However, within the total population envelope the percentage-contribution of certain age groupings shows a striking pattern when viewed across nearly five centuries. For 350 years, up to the end of the 19th century, the over--40 year old section of the population comprised a steady 25% of the total population count of England (latterly England and Wales): over the same period the 60-plus section contributed nearly 10% of the total. Throughout the ten decades of the 20th century these proportions have both increased, such that with the arrival of the next millennium a two-fold increase in the percentage-contribution of both age groups will have occurred: nearly one-half (over 24 million) of the population of England and Wales will be aged over 40, or more than one-fifth (around 11 million) will be aged over 60 years. This 'ageing' of the general population will have economic and socio-medical implications both at home and abroad, since this is a demographic trend which is present/projected in all countries of the European Union (as presently constituted). The future practise of optometry will certainly be touched by these changes. Naturally a potential increase in demand for presbyopic refractive corrections from the growing volume of aged 40-plus individuals is possible. However of greater significance is the certain increase in age-related oculo-visual problems arising from within the growing aged 60-plus population. Greater acknowledgement and utilisation of the optometrist's skills, currently being reappraised through the profession's participation in 'collaborative care' schemes, may indicate the direction in which optometry should move in the early 21st century to remain a valuable--and valued--health care profession.

Age Distribution↗
PubMed1997

Intraocular pressure asymmetry is not a clinically-significant feature when using the PULSAIR non-contact tonometer.

This report describes the results of a retrospective analysis of intraocular pressure (i.o.p.) values recorded from the right (R) and left (L) eyes of middle-aged and elderly at-risk but assumed non-glaucomatous subjects. The tensions had been measured using the Keeler PULSAIR non-contact tonometer (NCT) in the course of routine optometric practice when individuals attended for a sight test. These bilateral IOP data were collated on the basis of each subject's gender, (male/female), age (40-59 years/60+ years) and the time of the tonometry assessment (a.m./p.m.). Wherever possible material was equi-partitioned across these three bipartite variables producing balanced data groupings. Pair-wise testing of R versus L absolute values of pneumo-applanation pressures across any of the balanced data groupings failed to reveal a statistically-significant difference between the paired IOP distributions. There was a consistent but small relative IOP asymmetry (L > R) in these data. Further analysis indicated that this asymmetry only attained borderline statistical significance with respect to subject's age: neither gender nor the time of assessment were statistically significant features, and there were no statistically-significant interactions between any of the three variables. In conclusion, provided that the manufacturer's operating instructions are adhered to, IOP asymmetry is not a clinically-significant feature when using the PULSAIR NCT on a clinical population at risk of developing glaucoma.

Adult↗
PubMed1997

The diurnal variation of intraocular pressure in non-glaucomatous subjects: relevance in a clinical context.

Although it has been recognised for a century that an individual's intraocular pressure (i.o.p.) varies over a 24 hr period, the implications for the clinician of this physiological characteristic remain uncertain. While financial constraints nowadays prohibit in-patient assessment of suspect ocular hypertensive cases, the U.K. has witnessed a concurrent increase in the monitoring of at-risk subjects at local centres, including optometric practices. Consequently a description of the pattern of variation of IOP in the at-risk population during normal consulting hours, assessed using a popular model of pneumo-applanation tonometer, could assist the clinician in establishing management and referral protocols. This report describes the results of a single-centre study based on the retrospective analysis of the records of over 1,500 age-matched male and female at-risk but assumed non-glaucomatous subjects. Statistical analysis of the collated data indicated that subject age group was not a major variable: however gender and the time of IOP assessment were both significant features. For recordings between the hours of 09.00 and 18.00 human non-glaucomatous males and females registered an IOP peak in the late morning, succeeded by a lowered value from mid-afternoon. For both male age groups (40-59 and 60+ years) the afternoon mean IOP values were significantly lower than the male morning values and significantly different to the female morning and afternoon means. On the basis of these results it is suggested that male subjects who record borderline or high pressures at an afternoon appointment should be reassessed the following (mid-)morning; also that subsequent reviews of such cases should be scheduled for morning visits. By adopting this approach the likelihood of recording an elevated IOP value is increased and true-positive cases of raised IOP identified. However, during normal consulting hours the present evidence suggests that this temporal precaution need not be observed in female subjects.

Adult↗
PubMed1996

Evidence of a global oblique effect in human extrafoveal vision.

Analysis of recently published human contrast-sensitivity data obtained along the cardinal and major oblique visual-field meridians of a single subject has demonstrated a consistently greater sensitivity at a given eccentricity to horizontally oriented as compared with obliquely oriented gratings. This difference was evident not only at foveal but also at several eccentric loci over a range of low to medium spatial frequencies. This observation is to be distinguished in extrafoveal fixation from the well-documented oblique effect, which describes the variation in sensitivity with orientation at a single visual-field locus. With periodic stimuli which were well localised in space and frequency, and had comparable spatial-summation properties, a spatial-frequency dependency of what could be termed the global oblique effect could be demonstrated along isoeccentric contours centred on the fovea (eccentricity 0 deg) out to an eccentricity of at least 40 deg.

Contrast Sensitivity↗
PubMed1995

The presbyopic add. I. Magnitude and distribution in a historical context.

The presbyopic addition or 'add' is the (binocular) spherical positive power supplement superimposed on any distance refractive correction to counter near vision difficulties associated with the physiological age-related loss of accommodation and consequent recession of the near point: its necessity is first encountered in middle age. The continuous (linear) ascending trend in near lens power versus increasing age advocated since the seventeenth century is at odds with the twentieth-century clinical observation that there is a deceleration in add requirement beyond an individual's mid-fifties. It is shown here that this difference is reconciled--in broadly qualitative terms if not in magnitude-when typical clinical near addition data are superimposed on the accepted distance hypermetropic refractive base recorded from early middle age onwards: a continuous rising function is produced spanning most of the three decades beyond 40 years of age. This result is considered in the context of the age markings found on certain eighteenth-century antique near vision glasses and the recommendations attached to the self-selection of ready-made reading glasses in the late twentieth century.

Adult↗
PubMed1995

The presbyopic add. II. Age-related trend and a gender difference.

New transverse clinical data are presented which confirm and extend earlier results to be found in the literature describing the time course of presbyopia-as indicated by the magnitude of the binocular spectacle add--in normally sighted male and and female Caucasian subjects. An initial steep increase in add requirement beginning in the early forties becomes relatively slower but still of significance beyond the mid-fifties. This observation is correlated with the age-related progressive decline in the amplitude of accommodation, itself a consequence of physiological changes in the crystalline lens and capsule. The continuing need for an increase, albeit at a reduced rate, in the positive near supplement beyond the mid-to-late fifties-by which time little or no useful accommodation is available-is now attributed to the visually disruptive effects within the high spatial frequency domain of progressive age-related lenticular changes. The magnification afforded by the positive add increases spatial grain and thereby enhances visibility of detail in an ageing visual system free of any gross senile visual pathology. A small but consistent gender difference is revealed in presbyopic corrections: physiological and physical bases are suggested for the observation that females require an add of greater magnitude than their age-matched male counterparts.

Adult↗
PubMed1995

The presbyopic add. III. Influence of the distance refractive type.

The possibility of the distance refractive type-emmetropia, hypermetropia or myopia-influencing the magnitude and rate of change of the presbyopic add does not seem to have received systematic consideration. To address this possibility a further series of transverse clinical data on the progression of the presbyopic add is presented. Analysis of these data reveals the influence of the distance refractive type on the presbyopic progression. Hypermetropes appear to show a two-phase rise in add requirement whereas emmetropes follow a linear and myopes a curvilinear path over the four decades between 41 and 80 years of age. Nevertheless the magnitude of the binocular add requirement at a given age for each of the three refractive types is very similar and all three classes maintain an increasing requirement with advancing age.

Adult↗
PubMed1995

Broken down by age and sex. The optical correction of presbyopia revisited.

New transverse clinical data are presented which describe the time course of presbyopia, as indicated by the temporal change in magnitude of the binocular spectacle add, in normally sighted male and female Caucasian subjects. An initial steep increase in add requirement beginning in the early forties becomes relatively slower but still of significance beyond the mid-fifties. This observation is correlated with the age-related progressive decline in the amplitude of accommodation, itself a consequence of physiological changes in the crystalline lens and capsule. The continuing need for an increase, albeit at a reduced rate, in the positive near supplement beyond the mid-to-late fifties (by which time little or no useful accommodation is available), is now attributed to the visually disruptive effects within the high spatial frequency domain of progressive age-related lenticular changes. The magnification afforded by the positive add increases spatial grain and thereby enhances visibility of detail in an ageing visual system free of any gross senile pathology. A small but consistent gender difference (congruent to 0.1 D) is revealed in presbyopic corrections: physiological and (more probable) physical bases are suggested for the observation that females require an add of greater magnitude than their age-matched male counterparts.

Accommodation, Ocular↗