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Biomedical subjects

A Chandna

Publications and source records attributed to A Chandna.

At least 19 recordsLinked to original sources
PubMed2001

Contour integration deficits in anisometropic amblyopia.

PURPOSE: Previous retrospective studies have found that integration of orientation information along contours defined by Gabor patches is abnormal in strabismic, but not in anisometropic, amblyopia. This study was conducted to reexamine the question of whether anisometropic amblyopes have contour integration deficits prospectively in an untreated sample, to isolate the effects of the disease from the effects of prior treatment-factors that may have confounded the results in previous retrospective studies. METHODS: Contour detection thresholds, optotype acuity, and stereoacuity were measured in a group of 19 newly diagnosed anisometropic amblyopes before initiation of occlusion therapy. Contour detection thresholds were measured using a card-based procedure. RESULTS: Significant interocular differences in contour detection thresholds were present in 14 of the 19 patients with anisometropic amblyopia. CONCLUSIONS: Contour integration deficits are a common, but not universal, finding in untreated anisometropic amblyopia. Differences in the prevalence of contour integration deficits between the present study and that of another study may lie in differences in treatment history and/or in the sensitivity of the two different contour integration tasks.

Adolescent↗
PubMed2000

A new test of contour integration deficits in patients with a history of disrupted binocular experience during visual development.

Previous studies have suggested that the integration of orientation information across space is impaired in amblyopia. We developed a method for quantifying orientation-domain processing using a test format that is suitable for clinical application. The test comprises a graded series of cards where each card includes a closed path (contour) of high contrast Gabor signals embedded in a random background of Gabor signals. Contour visibility in both normals and patients with histories of abnormal binocular vision depends jointly on the spacing of elements on the contour as well as background element density. Strabismic amblyopes show significant degradation of performance compared to normals. Small but significant losses in sensitivity were also observed in a group of non-amblyopic strabismus patients. Threshold measurements made with contrast reducing diffusers indicated that the amblyopic loss is not due to the reduced contrast sensitivity of the amblyopic eye. An abnormal pattern of long-range connectivity between spatial filters or a loss of such connectivity appears to be the primary source of contour integration deficits in amblyopia and strabismus.

Adolescent↗
PubMed2000

Orbital abscess masquerading as a rhabdomyosarcoma.

Although orbital cellulitis is the most common cause of acute-onset proptosis with inflammatory signs in a child, the clinician should always be alert to the possibility of rhabdomyosarcoma. We describe an unusual presentation of acute-onset nonaxial proptosis of the left orbit without sinus disease or systemic toxicity in a 6-year-old boy. Our clinical differential diagnosis included orbital cellulitis, metastatic disease, capillary haemangioma, lymphangioma with cyst, ruptured dermoid cyst, and orbital rhabdomyosarcoma. Only after orbital biopsy and subsequent microbiologic confirmation were obtained was a diagnosis of chronic orbital abscess tenable. Features in our patient included paucity of symptoms and signs of inflammation. This case illustrates the difficulty in differentiating a chronic orbital infection from orbital rhabdomyosarcoma on the basis of clinical, laboratory, and orbital imaging findings. Possible causes of this unusual presentation are discussed.

Abscess↗
PubMed1999

Oscillatory motion but not pattern reversal elicits monocular motion VEP biases in infantile esotropia.

Patients with early disruptions of binocularity show cortical directional asymmetries in their steady state monocular VEP response to oscillatory motion. The VEP directional asymmetry is characterized by significant first harmonic components that show a 180 degrees difference in the response phase between the two eyes. By contrast, the normal response is dominated by even-order response harmonics, although some normal observers also have measurable responses at the first harmonic. Experiments and simulations were conducted to determine if the first harmonic in patients could reasonably be attributed to direction selective mechanisms. A secondary goal was to determine whether the first harmonic response of normals was also due to imbalances in direction selective mechanisms. Monocular steady state VEPs were elicited by oscillating 3 c/deg gratings presented at 6 and 10 Hz in normal observers and observers with infantile esotropia. Responses were also obtained to phase-reversing gratings of the same spatial and temporal frequencies. Phase reversal eliminated the majority of first harmonic responses which were recorded for normal observers to oscillatory motion. However, phase reversal did not elicit the cortical motion asymmetry in infantile esotropia. Modeling results suggest that the first harmonic response to oscillatory motion arises due to non-linearities in both direction selective and non-direction-selective mechanisms, with the latter being dominant in patients with early onset strabismus.

Adolescent↗
PubMed1999

Contour detection threshold: repeatability and learning with 'contour cards'.

Human observers are able to locate contours that are defined solely on the basis of long-range, orientation-domain correlations. The integrity of the mechanisms responsible for second-order contour detection is disrupted by amblyopia (Kovacs et al., 1996; Hess et al., 1997) and it is therefore of interest to develop methods for assessing pediatric patients undergoing treatment for amblyopia. In this study, we have determined the inter-observer and test-retest reliability of a card-based test of second-order contour integration. The magnitude of practice effects was also assessed in both adult and pediatric patient groups. Contour detection thresholds were measured for a closed contour, defined by Gabor patches, embedded in a randomly oriented Gabor-patch background. The visibility of the contour was controlled by varying the density of the background elements. Thresholds, defined in terms of the ratio of contour element spacing to average background spacing were measured with a clinical staircase procedure. Thresholds measured by two observers differed on average by 0.023 +/- 0.075 or about one half the increment between cards. Children and adults showed only small practice effects (0.022 +/- 0.051 vs 0.053 +/- 0.077, respectively) and average unsigned differences between repeated measures were equivalent to approximately 1 card across groups. A card-based test of second-order contour integration produces reliable estimates of contour integration performance in normal and amblyopic observers, including children.

Adult↗
PubMed1998

Validation of a handheld automated keratometer in adults.

PURPOSE: To evaluate the Nidek handheld automated keratometer and compare it with the manual Zeiss keratometer. SETTING: St. Paul's Eye Unit, Royal Liverpool University Hospital, Liverpool, United Kingdom. METHODS: Forty-five normal adult volunteers were included in the study. Three sets of randomized keratometry measurements were taken from both eyes of each adult, with both instruments by two independent observers. Readings included powers of the steep and flat meridians and axis of the flat meridian. The mean difference between the two instruments was calculated. The variance of each instrument was calculated for the axis, the steep and flat meridians, and the mean of the two meridians. RESULTS: There was no significant difference between the mean Nidek and Zeiss keratometry readings for the steep (0.015 mm; P = .167) or flat (0.054 mm; P = .069) meridian or axis measurements (P = .172). On repeated measurements, the within-subject and within-group variabilities, calculated separately for each instrument, were significantly less for the Nidek automated keratometer than the Zeiss keratometer (P < .01) when measuring the steep and flat meridians. There was however, a significant increase in axis variability using the Nidek keratometer (range 20 degrees; P < .01). CONCLUSION: The Nidek automated keratometer was accurate, reliable, and easy to use and compared favorably with the manual Zeiss keratometer when measuring corneal curvature. In the handheld mode, the Nidek is not suitable for axis measurements. It has the additional advantage of portability.

Adult↗
PubMed1998

Repeatability of the hand-held Nidek auto-keratometer in children.

Measurement of the anterior corneal radius of curvature is important in the pediatric population for proper fitting of contact lenses, calculation of intraocular lens power in patients undergoing cataract surgery, and monitoring changes in shape of the cornea in keratoconus. Because astigmatism in preschool children is mainly the result of corneal asphericity, measurement of the anterior corneal radius of curvature may also be used in screening in children at risk for amblyopia. The aim of this study was to determine the repeatability of the hand-held automated Nidek keratometer (Nidek Co. Ltd, Tokyo, Japan) and its ease of use in children.

Adolescent↗
PubMed1996

Downgaze paresis following severe head trauma in a child.

A 4 1/2-year-old girl developed a downgaze paresis following severe head trauma. Magnetic resonance imaging showed evidence of peri-aqueductal lesions in the rostral midbrain in the region of the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF). Twenty five weeks following the injury, the downgaze paresis remained unchanged but she developed convergence retraction nystagmus on attempted upgaze. Repeat imaging did not show any change in the lesions in the rostral midbrain. This report provides further evidence for the riMLF in the control of downgaze, and a synkinesis is postulated for the development of the convergence retraction nystagmus.

Child, Preschool↗
PubMed1995

Intraocular pressure after peribulbar anaesthesia: is the Honan balloon necessary?

Peribulbar anaesthetic blocks were administered to 70 patients and the intraocular pressure (IOP) measured immediately before and within 1 minute of the injections. In 10 patients IOPs were recorded at 1 minute intervals for 15 minutes after injection and then compared with the IOPs recorded in 60 patients after 5 or 10 minutes of Honan balloon ocular compression. The IOP rose significantly after injection in all patient groups and in some cases this increase was marked (over 50 mm Hg in 10 patients). The IOP showed an equivalent drop after 5 or 10 minutes of ocular compression when compared with eyes that did not receive ocular compression. The Honan balloon does not appear to be necessary to reduce IOP in the 10 minutes following peribulbar injection. Furthermore, the occurrence of IOP peaks after peribulbar anaesthesia suggests that the balloon should be used with caution in eyes in which the ocular circulation may be compromised.

Aged↗
PubMed1992

Results of intraocular lens implantation in paediatric aphakia.

Intraocular lenses were implanted in 16 eyes of 13 patients with congenital cataract, and visual progress was plotted using a preferential-looking technique. Initial surgery was by lens aspiration with preservation of the posterior capsule, and subsequent posterior capsulotomy without anterior vitrectomy. Poly-HEMA posterior chamber lenses were used, usually as a primary procedure but in four cases as a secondary procedure after contact lens failure. No serious complications were encountered. Most eyes achieved a very significant visual improvement, and none were worse than preoperatively. Residual refractive error was highly unpredictable, but did not exceed 6 dioptres. The importance of rigorous occlusion therapy is stressed. With close follow-up, this procedure offers an effective and safe method for the correction of unilateral paediatric aphakia, and, in selected cases only, for bilateral aphakia.

Cataract↗
PubMed1991

Natural history of the development of visual acuity in infants.

A selective review of the contemporary understanding of development of infant visual acuity is presented together with recent developments in methodology to detect this change. References are confined, wherever possible, to human infant studies relating to factors explaining the development of acuity. Results obtained from a two year study of the development of grating acuity in normal infants are discussed briefly. The findings indicate the importance of establishing acuity norms and sensitivity of interocular acuity difference as an important parameter in the detection of monocular visual deficit in clinical practice.

Child Development↗
PubMed1991

Tranexamic acid-associated ligneous conjunctivitis with gingival and peritoneal lesions.

A considerable number of agents have been proposed as causing ligneous conjunctivitis. We report the first case to arise as a side effect of tranexamic acid (Cyclokapron), an anti-fibrinolytic drug used in the treatment of menorrhagia. In addition to the typical conjunctival changes our patient had lesions affecting the gingiva and the peritoneum the last causing considerable protein loss into the peritoneal cavity.

Adult↗
PubMed1989

Preferential looking in the mentally handicapped.

We have assessed the feasibility of Preferential Looking (PL), using Teller Acuity Cards, for the estimation of binocular and monocular visual acuities in a group of mentally handicapped adults. Our results show the comparison between grating and recognition acuities, inter-observer variation, success rate, time taken and the sensitivity of this method in identifying monocular visual deficit in this group of subjects. The reasons for success or failure with PL methods in relation to criteria for mental handicap are discussed.

Adult↗
PubMed1988

Preferential looking in clinical practice: a year's experience.

Preferential Looking (PL) is now a well established laboratory method of measuring visual acuity in preverbal children. We have evaluated the feasibility of its routine use in clinical practice. We present our methods and results obtained in 80 normal children and 36 children with visual disorder and discuss the problems encountered in applying this test.

Aging↗
PubMed1986

Aluminium phosphide poisoning: a prospective study of 16 cases in one year.

Sixteen patients suffering from aluminium phosphide poisoning were treated during the year from January 1985 to December 1985. These accounted for approximately half the total number of cases of acute poisoning. Profuse vomiting, pain in the upper abdomen and shock were the most common presenting features. Six patients succumbed to their illness. Analysis of various prognostic factors revealed that ingestion of 'unexposed' tablets of aluminium phosphide taken from a freshly opened bottle was associated with a greater risk of fatal outcome. Aluminium phosphide poisoning has become an important matter of public health in parts of India.

Abdomen↗