2004 Abstracts
British and Irish Orthoptic Journal 2004 Volume 1
The development of convergence and accommodation
Anna M. Horwood and Patricia M. Riddell
Aim: To review current literature on the development of convergence and accommodation. The accommodation and vergence systems provide the foundation upon which bifoveal binocular single vision develops. Deviations from their normal development not only are implicated in the aetiology of convergence anomalies, accommodative anomalies and strabismus, but may also be implicated in failure of the emmetropisation process.
Method: This review considers the problems of researching the development of accommodation and vergence in infants and how infant research has had to differ from adult methods. It then reviews and discusses the implications of current research into the development of both systems and their linkages.
Results: Vergence and accommodation develop rapidly in the first months of life, with accommodation changing from relatively fixed myopic focus in the neonatal period to adult-like responses by 4 months of age. Vergence develops gradually and becomes more accurate after 4 months of age, but has been demonstrated in infants well before the age that binocular disparity detection mechanisms are thought to develop. Hypotheses for this early vergence mechanism are discussed. The relationship between accommodation and vergence shows much more variability in infants than adult literature has found, but this apparent adult/infant difference may be partly attributed to methodological differences rather than maturational change alone.
Conclusions: Variability and flexibility characterise infant responses. This variability may enable infants to develop a flexible and robust binocular system for later life. Studies of infant visual cue use may give clues to the aetiology of strabismus and refractive error.
Ocular sequelae from the illicit use of class A drugs
Alison Y. Firth
Aim: To highlight the changes that may take place in the visual system of the class A drug abuser.
Methods: A literature review was carried out of ocular/visual sequelae of the more common class A drugs. These include stimulants (cocaine and crack cocaine), narcotics (heroin, morphine, methadone) and hallucinogenics (ecstasy, lysergic acid diethylamide, magic mushrooms, mescaline, phencyclidine).
Results: Ocular sequelae affecting visual acuity, the eye and its adnexa, ocular posture and ocular motility can result from recreational use of these drug(s).
Conclusions: Awareness of the consequences of illicit drug use should lead to more pertinent questioning during history-taking.
Traumatic oculomotor nerve palsy: a literature review
Sarah Christie
Aim: To review traumatic oculomotor nerve (IIIN) palsy, looking at the prognosis, site of lesion and mechanism of recovery.
Methods: A literature review was undertaken in order to research opinions on the prognosis following a traumatic IIIN palsy. The nuclear, fascicular, midbrain, subarachnoid, cavernous sinus and orbital portions were investigated and the prognosis discussed.
Results: Trauma affecting the nuclear region alone is rare, but IIIN palsy can occur indirectly as a result of haemorrhage, and spontaneous recovery may be expected. Direct nuclear palsy following trauma is not prone to recovery. The midbrain is highly vulnerable to damage caused by rootlet avulsion and recovery may be further limited by post-traumatic fusion deficiency. The cavernous sinus is particularly prone to damage but the prognosis is generally good, as is that for trauma affecting the region of the superior orbital fissure.
Conclusion: IIIN palsy as a result of trauma is not a common finding and the extent of the trauma and the site of the lesion will, in part, determine the prognosis for recovery. The mechanism of recovery is by axonal regeneration and new cellular cord formation. Prognosis is unaffected by age. Consideration should be given to aetiology and the site of the traumatic lesion in the management of traumatic IIIN palsy.
Neuroimaging in amblyopia: a literature review
Catherine A. Jukes
Aim: To review imaging techniques available for examining cortical responses to visual stimuli, with a view to selecting an objective method suitable for measuring amblyopia in children.
Methods: A literature review was carried out to explore current and developing methods of imaging visual cortical stimulation, concentrating more specifically on amblyopia research.
Results: Visually evoked potentials (VEP), magnetoencephalography (MEG), positron emission tomography (PET), single photon emission computed tomography (SPECT) and functional magnetic resonance imaging (fMRI) have all been found to detect amblyopia to some degree. Functional MRI stands out as the most suitable method for detecting amblyopia, and is capable of producing images at the level of the ocular dominance columns with no adverse effects.
Conclusion: New avenues of investigating amblyopia have recently opened and have proved to be sensitive in its detection and sometimes in measuring its extent. Further research needs to be carried out to determine the sensitivity in detecting degrees of amblyopia and the practicalities of testing children. In the future these methods may allow us to understand amblyopia more fully and to progress further with treatment methods.
Attentional visual field analysis amongst stroke survivors
I. Cunningham; F.J.Rowe; P.C. Knox; A.C. Fisher and C.Jack.
Aim: To investigate the effect of a modified attentional visual field test in subjects who had returned to independent living after surviving a cerebrovascular accident (CVA) and compare these stroke survivors with a group of age-matched control subjects.
Methods: A Humphrey Visual Field Analyser was modified by the addition of external lasers which introduced a task additional to a standard threshold field task by presenting central red targets at fixation. Standard and modified visual fields were assessed in 4 stroke survivors and 4 age-matched control subjects. Visual field sensitivity, manual response times to central laser targets and duration were compared.
Results: Stroke survivors had depressed visual field sensitivity compared with controls. Sensitivity was further reduced when the stroke survivors were exposed to the modified field test. Manual response times to central targets increased for both groups when combined with the field test; stroke survivors had longer response times.
Conclusion: Subjects considered to have recovered from a CVA and who have returned to independent living may still have visual problems which are manifest only when they have to divide their attention. These problems may therefore not be detected using standard clinical tests.
The Effect Of Diabetes And Ageing On The Initiation Of Smooth Pursuit Eye Movement
Jillian H. Davidson and Paul C. Knox
Aim: To examine the initiation of smooth pursuit in a group of elderly, diabetic subjects, and to compare their performance with a group of age-matched non-diabetic subjects and a group of healthy young subjects.
Methods: Smooth pursuit was assessed quantitatively in ten diabetic subjects (mean age 69.2±6.8; range 58-80 years), ten age-matched non-diabetic subjects (mean age 69.8±5.2; range 64-81 years) and ten healthy young subjects (mean age 21±2.3; range 19-26 years), using infra-red oculography.
Results: Qualitatively, pursuit performance was similar between healthy elderly, diabetic and young subjects. However, quantitatively statistical analysis indicated smooth pursuit latency was significantly higher in both elderly diabetic and age-matched, healthy individuals when compared to healthy young individuals (p<0.0001). Diabetes itself did not affect smooth pursuit latency for either leftward or rightward pursuit (p>0.05).
Conclusion: Given that we have demonstrated there is no statistically significant difference in smooth pursuit latency between healthy elderly and diabetic elderly subjects, systemic disease in general does not appear to exacerbate the age-related alteration in pursuit we have previously reported. This result suggests that quantitative assessment of smooth pursuit might provide a means of assessing the general state of the cortex in elderly subjects.
Quantifying the vertical fusion range at four distances of fixation in a normal population
Katie Ulyat, Alison Y. Firth and Helen J. Griffiths
Aim: To compare the vertical fusional amplitudes in isometropic participants with normal binocular single vision at four distances of fixation: 33cm, 1m, 4m 6m.
Methods: Vertical fusion ranges (break point and recovery point) were measured with a Gulden vertical prism bar with the participant fixing a 6/12 Snellen equivalent letter, twice at each distance. Order effects were controlled with randomisation of both fixation distance and prism direction.
Results: Twenty-seven participants were examined (aged 20.4 ± 1.05 years). Base up and base down measurements were similar, therefore measurements were combined to give a total vertical range. Median values for break points were: 33cm, 6Ä; 1m, 6Ä; 4m, 5.5 Ä; 6m, 5.5 Ä; and for the recovery points were: 33cm, 4Ä; 1m, 4Ä; 4m, 3.5 Ä; 6m, 3.5 Ä. The difference was significant between either of the near measures i.e. 33cm and 1 m) and either of the far measures (i.e. 4m and 6m).
Conclusions: The vertical fusion range appears to be slightly greater at near than distance. However, the difference is not clinically significant. Measurements for distance, in a normal population, appear to be the same whether a fixation distance of 4m or 6m is used.
Do We Really Need Binocular Single Vision?
Kathryn C. Brown and David Buckley
Aim: To investigate whether or not we need binocular single vision (BSV) for successful depth perception.
Methods: A mixed-measures design was used to compare monocular subjects and binocular subjects in their ability to judge depth. Experimental stimuli were images resembling large drawing pins that were displayed on a computer screen. Subjects had to adjust the spike of the drawing pin, by means of a keypad, until it appeared to be at an angle of 90° to the head of the pin. The head of the drawing pin was at a slant of 30° from the frontal plane, around either the horizontal or vertical axis. The computer recorded the number of degrees away from the 90° position that the spike was set, the time taken and the standard deviation of the settings. A three-factor mixed measures ANOVA was used to analyse the results.
Results: Overall, binocular subjects were more accurate than monocular subjects (F=13.894, df=1, 14, p<0.01) in judging when the spike was set at an angle of 90° to the head of the pin. There was no significant difference between the horizontal or vertical orientations of stimuli in terms of accuracy (F=1.250, n.s.), or between the two groups in the time it took them to complete the task.
Conclusion: BSV is advantageous and the time and resources spent on restoring and maintaining BSV are worthwhile.
Paediatric Idiopathic Intracranial Hypertension
Fiona J. Rowe and Carmel P. Noonan
Aim: Idiopathic intracranial hypertension usually occurs in adults. The purpose of this study was to review paediatric idiopathic intracranial hypertension and determine the specific characteristics and outcome of the paediatric condition compared to adult idiopathic intracranial hypertension.
Methods: Thirteen case notes were retrospectively reviewed (11 females, two males). The average presenting age was 13 ½ years (10-17 years). Diagnosis of idiopathic intracranial hypertension followed exclusion of other neurological causes. Each patient underwent full ophthalmic, orthoptic and neurological evaluation.
Results: Three patients were asymptomatic whereas the remainder presented with symptoms including headaches, visual disturbances, lethargy, vomiting and nausea. Each patient had papilloedema. Initial lumbar puncture opening pressures ranged from 160-790mmH2O. Orthoptic findings included concomitant esotropia, sixth, third and fourth nerve palsies. Visual fields were impaired in 9 cases. Treatment included prednisolone, acetazolamide, lumbar peritoneal shunting and optic nerve sheath fenestration.
Conclusions: Visual fields were impaired in 9 patients despite absence of visual symptoms in 3. Medical treatment was usual although 3 patients required lumbar peritoneal shunting and 1 required optic nerve sheath fenestration to arrest visual deterioration. The paediatric visual outcome of idiopathic intracranial hypertension reflects the adult condition. Paediatric patients require the same evaluation, follow-up and treatment regimes to optimise outcome.
Transient extraocular muscle palsy following dental anaesthesia
Jayshree Dhanji and Deborah Lysons
Aim: To present 3 unusual cases of transient extraocular muscle palsy following local dental anaesthesia for fillings or extraction of the upper fifth, sixth and/or seventh molars.
Methods: Three cases are reported that presented to the Orthoptic Department with extraocular muscle palsy which occurred immediately following local anaesthesia for dental treatment.
Results: Two patients subsequently fully recovered and one was left with a slight superior oblique weakness. The result in this last case is thought not to have been caused by the local dental anaesthesia but by a longstanding weakness which seems to have been decompensated by the injection of the anaesthetic.
Conclusion: Tranisent muscle palsies linked to local dental anaesthesia may be common, but as they are so short-lived they do not present to the Orthoptic Department. Possible causes for the findings in these cases are discussed and the favoured aetiological hypothesis is stated.