Effect of age on adult stereoacuity as measured by different types of stereotest.

AIM: To examine how stereoacuity changes with age as measured by a variety of stereotests. METHODS: Stereoacuity has been measured in 60 normal subjects aged 17-83 years by a single observer using TNO, Titmus, Frisby near, and Frisby-Davis distance stereotests. Motor fusion was measured at (1/3) metre and 6 metres. RESULTS: Overall stereoacuity measured by all tests showed a mild decline with age (p<0.001 for all tests; Spearman rank correlation). A marked reduction to screening or absent levels of stereoacuity was seen in five subjects aged over 55, but only with the TNO stereotest. All these subjects were able to achieve a stereoacuity of 200 seconds of arc or better with the Titmus test and 340 seconds of arc or better using the Frisby near stereotest. There was a small decline with age in the base out motor fusion range measured at 6 metres (p<0.05; Spearman rank correlation). No subject described difficulty in judging distances for everyday tasks. CONCLUSIONS: Although subjects showed some decline in stereoacuity with age by all tests, the large drop in stereoacuity seen in some older subjects using the TNO test was probably due to difficulty overcoming the dissociative effect of the test rather than a true reduction in cortical disparity detection. Results of random dot stereotests should be interpreted with caution in older patients, particularly with respect to their ability to perform everyday visual tasks.

A prospective study of the effect of a unilateral macular hole on sensory and motor binocular function and recovery following successful surgery.

AIMS: To examine the effect of a unilateral full thickness macular hole on sensory and motor binocular function and to study recovery after successful surgical closure. METHODS: Twenty eight consecutive patients undergoing surgery for a unilateral macular hole underwent orthoptic examination, including measurements of Titmus and TNO stereoacuity and motor fusion range before surgery. Twenty three patients had successful anatomical closure. Fifteen of these patients, who had both improved acuity in the operated eye following surgery and were available for further testing, underwent repeat orthoptic assessment 2-7 months after surgery. RESULTS: In all patients stereoacuity was reduced before surgery, but few patients were subjectively aware of a deficit of depth perception affecting their everyday life. In those patients with improved Snellen acuity after surgery, stereoacuity measured by the Titmus stereotest also improved significantly, but not that measured by the TNO test. Two patients were aware of a subjective improvement in depth perception. Motor fusion was markedly reduced compared to normal before surgery, with only limited recovery after surgery. CONCLUSION: A unilateral macular hole notably reduced both stereoacuity and motor fusion. Successful closure improved the deficit in stereoacuity associated with the hole when measured by a stereotest using contoured stimuli. The majority of patients were not subjectively aware of the deficit in stereoacuity or its improvement following surgery.

Evaluation of the electrodiagnostic investigation of children using the Greenwich Grading System.

PURPOSE: To evaluate the contribution of electrodiagnostic testing (EDT) to the management of children in a paediatric ophthalmology service using the Greenwich Grading System (GGS). METHODS: A retrospective analysis was performed of the case notes of 105 of the 113 paediatric patients referred from the Strabismus and Paediatric Service at Moorfields Eye Hospital for electrophysiological testing over a 1-year period. The GGS was used to quantify the contribution of EDT to the diagnosis, overall investigation, and treatment of each patient. Patients were further subdivided into different diagnostic groups to allow comparison of the value of EDT in different conditions. RESULTS: EDT was found to be of value in 91% of the children tested and was considered an essential investigation in 71%. EDT made a new diagnosis in 7% of patients, changed it in 5%, and confirmed or excluded a diagnosis in 79%. EDT made a useful contribution to the overall investigation of 89% of the patients and was considered the only test that could provide the required information in 71%. The results of EDT allowed reassurance and/or explanation with regard to the diagnosis, prognosis, and treatment in 91% of children. In one patient, treatment was changed as a result of EDT. The clinical outcome was not adversely affected in any patient. CONCLUSIONS: EDT was of value to the clinical management of most of the children reviewed, mainly by confirming or excluding a clinical diagnosis and allowing explanation and reassurance to children and parents. Electrodiagnostic information gave a new or changed diagnosis in 12% of the children.

The clinical features of albinism and their correlation with visual evoked potentials.

AIM: To investigate the relation between the clinical and electrophysiological abnormalities of patients undergoing visual evoked potential investigation for albinism. METHODS: 40 subjects with a probable or possible clinical diagnosis of albinism underwent pattern appearance and/or flash visual evoked potential (VEP) examination. The VEP findings are correlated with the clinical features of albinism determined by clinical examination and orthoptic assessment. RESULTS: The majority of patients with clinical evidence of albinism showed a contralateral predominance in the VEPs. There was close correlation between the clinical signs of albinism and the degree of contralateral VEP predominance. This manifested as an interhemispheric latency asymmetry to monocular pattern appearance stimulation but amplitude asymmetry to flash stimulation. The strongest correlation for pattern appearance interhemispheric latency difference was with foveal hypoplasia (rho = 0.58; p = 0.0003) followed by nystagmus (rho = 0.48; p = 0.0027) and iris transillumination (rho = 0.33; p = 0.039). The VEP abnormalities were of greater magnitude in those patients with most features of albinism. Several patients with apparently mild disorders of ocular pigmentation had small but significantly abnormal VEP latency asymmetries. CONCLUSION: There is a strong association between the magnitude of the interhemispheric latency asymmetry of the pattern appearance VEP, and of amplitude asymmetry of the flash VEP, with the clinical signs of albinism. The data are consistent with a spectrum of abnormalities in albinism involving both clinical expression and electrophysiological misrouting, which is wider than previously recognised.

Increased binocular enhancement of contrast sensitivity and reduced stereoacuity in Duane syndrome.

PURPOSE: To compare the binocular enhancement of contrast sensitivity and stereoacuity in patients with Duane syndrome and normal subjects. METHODS: Monocular and binocular contrast sensitivity functions were determined using a two-alternative, forced-choice method in 14 patients with Duane syndrome and 14 normal subjects. Monocular and binocular log minimum angle of resolution (logMAR) acuities were measured, and stereoacuity was determined using the Titmus and TNO stereotests. RESULTS: In the patients with Duane syndrome, the binocular enhancement of contrast sensitivity was increased across all spatial frequencies, although stereoacuity was reduced compared to that of the normal subjects. The increased enhancement was caused by a reduction in monocular contrast sensitivity rather than an increase in binocular contrast sensitivity. The patients with Duane syndrome also showed a generalized reduction of contrast sensitivity at high spatial frequencies. CONCLUSIONS: It is suggested that the combination of reduced stereoacuity and increased binocular enhancement of contrast sensitivity seen in Duane syndrome can be explained by a partial loss of binocular cortical cells, caused by intermittent misalignment of the eyes during early visual development.

Reduced binocular beat visual evoked responses and stereoacuity in patients with Duane syndrome.

PURPOSE: To study the effects that the abnormal eye movements of patients with Duane retraction syndrome have on the development of binocular function. METHODS: Pattern reversal visual evoked responses (VEPs) to 15-minutes-of-arc and 60-minutes-of-arc checks and binocular beat VEPs to diffuse sinusoidally modulated 18- and 20-Hz stimuli were recorded in 10 patients with Duane retraction syndrome who maintain binocular function by using an abnormal head posture. Visual acuity, stereoacuity, and eye movements were measured. The results have been compared to those from 10 normal subjects. RESULTS: The patients with Duane retraction syndrome had reduced stereoacuity compared to the normal control group (TNO mean, 82.5 seconds of arc compared to 37.5 seconds of arc; Titmus mean, 143 seconds of arc compared to 44 seconds of arc). The binocular beat VEPs showed a significantly reduced difference beat response at 2 Hz in the patients with Duane syndrome compared to normal subjects (mean signal-to-noise ratio 2.40 +/- 1.05 compared to 4.30 +/- 2.66; t = 2.21, df = 18, P < 0.05). Binocular enhancement of the P100 pattern reversal amplitude to 15-minute checks was increased in these patients, because of a reduction of the monocular P100 amplitudes compared to the normal group. CONCLUSIONS: Patients with Duane syndrome who maintain binocular function using an abnormal head posture have reduced stereoacuity and show electrophysiological evidence of reduced cortical binocular interaction.

Anomalies of binocular function in patients with longstanding asymmetric keratoconus.

AIMS: To study binocular function in patients with longstanding asymmetric keratoconus. METHODS: In 20 adult patients with longstanding asymmetric keratoconus managed with a scleral contact lens a full clinical and orthoptic assessment was performed with and without the scleral contact lens in the poorer eye. RESULTS: All 20 patients had a corrected acuity of at least 6/9 in their better eye. With the scleral lens in situ the acuity of the poorer eye ranged from 6/6 to 6/60 and without the lens from 6/18 to hand movements. Patients were aged from 18 to 68 years and had worn a scleral contact lens for between 3 and 106 months. Without the contact lens in their poorer eye all patients had a small exotropia and all showed suppression, with the exception of one patient who had a right hypertropia with diplopia. With the scleral lens in situ 12 patients had an exophoria or esophoria, six a microexotropia, and two a manifest exotropia with suppression. CONCLUSIONS: Binocular function breaks down in some adult patients with longstanding asymmetric keratoconus. This is probably caused by longstanding unilateral visual deprivation. There are similarities to the breakdown of binocular function seen in some patients with a longstanding dense unilateral adult onset cataract who can develop intractable diplopia following cataract surgery.

Intensive occlusion therapy for amblyopia.

AIM: To study the effects of supervised inpatient occlusion treatment for amblyopia in children who had failed to respond to outpatient treatment. METHODS: A retrospective study of 39 children admitted to a paediatric ophthalmic ward for 5 days of supervised intensive occlusion therapy having previously failed to respond to outpatient occlusion. Visual acuity of amblyopic and fellow eyes was recorded at each clinic visit before admission, daily during admission, and at each outpatient visit after discharge. RESULTS: There was no significant overall improvement in visual acuity during a mean of 9 months of attempted outpatient occlusion before admission. During the 5 days of admission 26 children (67%) gained at least one line of acuity in their amblyopic eye and five (13%) gained three or more lines (mean gain 1.03 Snellen lines). The acuities of both the amblyopic and fellow eyes subsequently improved with continuing part time patching as an outpatient, including in nine of the children who did not respond during admission. At the last recorded visit, at a median time of 14 months after discharge, 13 (33%) of the patients had an acuity of at least 6/12 in their amblyopic eye. CONCLUSIONS: The acuity of amblyopic eyes did not improve without effective treatment. Subsequent supervised inpatient occlusion therapy was effective in the majority of the children.

Reduction in binocular enhancement of the visual-evoked potential during development accompanies increasing stereoacuity.

PURPOSE: To study the maturation of normal binocular vision. METHODS: Binocular visual function has been studied and monocular and binocular pattern reversal visual-evoked potentials (VEP) recorded in 20 normal subjects aged 5 to 43 years. RESULTS: Stereoacuity improved significantly between the age of 5 and adulthood. Mean stereoacuity for eight children measured by the Titmus test was 61 seconds of arc and 56 seconds of arc by the TNO test. For the 12 adults in the study, corresponding mean stereoacuities were 45 and 31 seconds of arc. Over the same timespan, binocular enhancement of the VEP P100 amplitude decreased. For the children aged 5 to 10 years, the mean binocular VEP enhancement to 20' checks was 1.60, whereas for young adults it was 1.19. There was no comparable change in the binocular enhancement to 40' checks, with mean binocular enhancement of 1.31 in the children and 1.26 in the young adults. Over the same age range, VEP latency also decreased. CONCLUSION: During visual maturation, improvement in stereoacuity is accompanied by a fall in binocular enhancement of the P100 amplitude of the VEP to small checks and a reduction in the P100 latency.

Delayed visual evoked potentials in adults after monocular visual deprivation by a dense cataract.

PURPOSE: To study the effect of monocular visual deprivation caused by dense unilateral cataracts in adults. METHODS: Visual evoked potentials have been recorded in 11 patients after removal of a dense unilateral cataract acquired in adulthood. These were compared with those from 8 control patients after removal of a mild lens opacity. RESULTS: Visual evoked potentials recorded on the first day after removal of a longstanding, dense, unilateral cataract showed a marked delay to stimulation of the operated eye compared to the unoperated eye. No delay was found in the operated or unoperated eye of control patients. Delays in the visual evoked potential returned to normal within approximately 3 months after surgery, with the exception of the two patients with the most longstanding cataracts in whom the delays persisted much longer. CONCLUSIONS: The adult central visual system is sensitive to visual deprivation caused by a longstanding, dense, unilateral cataract. The changes found may be important in understanding the causes of intractable diplopia, which sometimes occurs after the removal of such cataracts.

Binocular enhancement of the visual evoked potential in patients with Duane's syndrome.

Monocular and binocular visual evoked potentials were recorded in eight patients with Duane's syndrome who used an abnormal head posture to maintain binocular single vision. With their abnormal head posture, all patients had stereoscopic vision, although with mildly reduced stereoacuity, and the visual evoked potential showed binocular enhancement (mean binocular to monocular ratio, 1.44). Without their head posture, the patients experienced diplopia or suppressed vision in one eye. Binocular visual evoked potentials recorded under these conditions were of lower amplitude (mean binocular to monocular ratio, 1.05). However, without the abnormal head posture, a manifest strabismus was present and the deviating eye was not fixating the stimulus screen. Monocular visual evoked potentials recorded with the eye fixating just to one side of the screen gave little or no response, and this lack of fixation may account for the loss of binocular enhancement of the visual evoked potential in strabismus.

Edridge-Green Lecture. Competition and cooperation in visual development.

Studies of the effect of visual deprivation on cells in the lateral geniculate nucleus (LGN) show that there are two distinct sensitive periods in the monkey during which different reactions between the visual pathways related to the two eyes predominate and requirements for recovery from deprivation differ. The first extends from birth to about 8 weeks of age. The main interaction between the pathways from the two eyes is competitive, segregation of cortical ocular dominance columns occurs during this early period and monocular deprivation results initially in hypertrophy of undeprived LGN cells, with later parallel shrinkage of both deprived and undeprived parvocellular cells. Simply reopening the closed eye produces no recovery but reverse suture is effective in reversing some of the changes. The second sensitive period starts from about 8 weeks of age, although the peak of the later sensitivity appears to be at 7-9 months of age and some effect is still present at 12-18 months. During this later phase a cooperative interaction between the pathways related to the two eyes is necessary for normal development and in the absence of this selective shrinkage of both deprived and undeprived parvocellular LGN cells occurs. Simply reopening an eye during this late sensitive period allows recovery of these cells to normal size.

Lipid-containing cells in brains of normal and hypoxic infant monkeys: a quantitative and ultrastructural study.

The significance of lipid-containing cells found at autopsy in the white matter of infant brains is controversial, particularly with respect to their postulated role as markers of the "sudden infant death syndrome." To determine whether such cells are indicative of prior nonlethal hypoxic insult, we quantitated them in the brains of control infant monkeys and in two groups of infant monkeys that were subjected to 30 minutes of hypoxic insult. One group consisting of monkeys that died less than 48 hours after the hypoxia, and the other of those that survived 7 to 13 days following the insult. The quantification of lipid-containing cells was undertaken in frozen brain sections stained with Oil red O; sections of brains from 4 perfusion-fixed animals were evaluated by electron microscopy. Lipid-containing cells were found in the corpus callosum, in the septum, and in periventricular white matter in both posthypoxic and control animals. There was a relationship between numbers of lipid-containing cells and the age of the animal; animals with large numbers were less than 28 days old. Decreases in numbers of lipid-containing cells correlated with advancing myelination as well as with age. Electron microscopic evaluation revealed lipid droplets in the cytoplasm of cells with irregularly shaped nuclei, densely clumped chromatin, occasional microtubules, and narrow cytoplasmic processes. We suggest that lipid-containing cells in the white matter of the brains of infants are related to age and to maturational factors and, in the absence of other pathologic signs, are not related to prior hypoxic injury.

Experiments to study recovery of lateral geniculate nucleus cell size following monocular lid closure and reverse suture in infant monkeys.

Following monocular eyelid closure at birth in macaque monkeys, reverse suture at 3 weeks of age cancels the difference in size between deprived and undeprived parvocellular lateral geniculate nucleus (LGN) cells by causing hypertrophy of the initially deprived cells. This means that two weeks after reversal cells in both initially deprived and initially undeprived parvocellular laminae are approximately 15% larger than normal. However, long term survival shows that there is a second phase of change during which all parvocellular cells shrink, but particularly the initially undeprived cells which become considerably smaller than the initially deprived cells. Reopening the secondarily closed eye after a short period of reversal resulted in normal cell sizes in one animal, but two animals developed marked squints and had very small parvocellular cells in all laminae, and one animal developed bilateral amblyopia. Simply reopening the eye of two animals after two months of late closure started at 7 months of age reversed the shrinkage of all parvocellular cells which is caused by late closure.

A comparison of cell size changes in central and pericentral representations within the primate lateral geniculate nucleus following early monocular deprivation.

Mean cell areas have been measured in the most posterior part of the lateral geniculate nucleus containing the representation of central retina in 8 normal monkeys (Macaca mulatta) and in 5 monkeys following monocular closure from birth. Comparisons with cell size changes at a more anterior level, where pericentral retina is represented, show that size changes of parvocellular cells at the posterior level are significantly less, being only between half and two-thirds of those more anteriorly. The undeprived cells undergo less initial hypertrophy than cells at a more anterior level and subsequently the deprived cells show less shrinkage. There is no comparable difference for magnocellular cells.

Effects of enucleation at different ages on the sizes of neurons in the lateral geniculate nucleus of infant and adult monkeys.

Cell areas have been measured in the lateral geniculate nucleus following enucleation in 7 infant and 3 adult monkeys. Deafferented cells showed rapid transneuronal degeneration. Following enucleation at birth non-deafferented parvocellular LGN cells underwent hypertrophy which was followed by a delayed return to normal size. Enucleation at 7 months of age caused marked shrinkage of non-deafferented parvocellular cells. These changes in the non-deafferented cells are similar to those following monocular lid closure at the same ages. Sizes of non-deafferented cells were unchanged following enucleation of adult monkeys.

Changes in the size of cells in the monocular segment of the primate lateral geniculate nucleus during normal development and following visual deprivation.

Cell areas have been measured in the monocular segment of the lateral geniculate nucleus in a series of 18 normal rhesus monkeys and in 27 following monocular or binocular lid closure or monocular enucleation. Cells in the parvocellular monocular segment shrank by 16% during the later period of normal development, between about 3 and 18 months of age, in contrasts to cells in the binocular segment which did not. Monocular closure at birth caused hypertrophy of cells in the undeprived monocular segment whereas long-term closure started later caused shrinkage of both deprived and undeprived parvocellular cells additional to that occurring during normal development. In both these instances cells in the monocular segment related to the undeprived eye are undergoing changes indicating some form of binocular interactions even in the monocular segment, but these interactions are considerably weaker than in the binocular part of the nucleus. Enucleation caused marked transneuronal degeneration of cells in the contralateral monocular segment of both infant and adult monkeys.

Abnormal tubular structures associated with the granular endoplasmic reticulum of neocortical neurons in a biopsy from a patient with Alzheimer's disease.

The electron microscope has been used to examine a diagnostic biopsy of frontal neocortex which showed the light microscopic features of Alzheimer's disease. In addition to plaques and tangles, the biopsy showed some neurons which contained abnormal tubular profiles specifically associated with their granular endoplasmic reticulum. In transverse section the profiles consisted of two concentric layers of trilaminar unit membrane with an overall diameter of approximately 75 nm and they appeared to lie within the cisternae of granular endoplasmic reticulum. When cut longitudinally, the structures appeared as elongated tubes lying within the endoplasmic reticulum, but a number of ends were found where the inner membrane formed a closed tube and the outer membrane folded back and was continuous with the membrane forming the outer layer of the sac of endoplasmic reticulum. These profiles do not appear to have been described previously although similarities between their ultrastructure and that of the coat of certain unusual forms of Rhabdovirus are noted.