BOLD fMRI response of early visual areas to perceived contrast in human amblyopia.
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In this study, we used a temporal two-alternative forced choice psychophysical procedure to measure the observer's perception of a 22% physical contrast grating for each eye as a function of spatial frequency in four subjects with unilateral amblyopia and in six subjects with normal vision. Contrast thresholds were also measured using a standard staircase method. Additionally, blood-oxygenation-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) was used to measure the neuronal response within early visual cortical areas to monocular presentations of the same 22% physical contrast gratings as a function of spatial frequency. For all six subjects with normal vision and for three subjects with amblyopia, the psychophysically measured perception of 22% contrast as a function of spatial frequency was the same for both eyes. Threshold contrast, however, was elevated for the amblyopic eye for all subjects, as expected. The magnitude of the fMRI response to 22% physical contrast within "activated" voxels was the same for each eye as a function of spatial frequency, regardless of the presence of amblyopia. However, there were always fewer "activated" fMRI voxels during amblyopic stimulation than during normal eye stimulation. These results are consistent with the hypotheses that contrast thresholds are elevated in amblyopia because fewer neurons are responsive during amblyopic stimulation, and that the average firing rate of the responsive neurons, which reflects the perception of contrast, is unaffected in amblyopia. (+info)
Amblyopes see true alignment where normal observers see illusory tilt.
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Amblyopia ("lazy eye") is an impairment in visual acuity resulting from abnormal neural development in the visual cortex. We tested the responses of ten amblyopic and six normal observers to illusions of perceived orientation in textures of Gabor patches: the "Fraser illusion," the "phase illusion," and a "tilted chain" illusion. The illusory tilt of the stimulus rows was matched by actual tilt in the opposite direction by using the method of constant stimuli. Amblyopes showed a significant increase in the Fraser illusion, a decrease in the phase illusion, and a reversal of the tilted chain illusion. Amblyopic performance could be simulated in normal observers by reducing the length of the rows. These results can be modeled by a theory which places the neural abnormality in amblyopia at the level of second stage grouping processes. Additionally, the illusions might be useful in the early diagnosis of amblyopia without the need for prior refractive correction. (+info)
The degree of image degradation and the depth of amblyopia.
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PURPOSE: To determine whether the depth of monocular form-deprivation amblyopia is dependent on the degree of retinal image degradation. METHODS: Chronic monocular form deprivation was produced in nine infant rhesus monkeys by securing one of three different strengths of diffuser spectacle lenses in front of the treated eye and a clear zero-powered lens in front of the fellow eye. Three infant monkeys reared with plano lenses in front of both eyes provided control data. The treatment lenses were worn continuously from approximately 3 weeks of age for periods ranging between 11 and 19 weeks. When the monkeys were approximately 18 months of age, psychophysical procedures were used to measure the effects of the rearing procedures on the spatial contrast sensitivity function for each eye. RESULTS: The treated eyes of all nine diffuser-reared monkeys showed contrast sensitivity deficits that were indicative of amblyopia. On average, the interocular grating acuity difference increased systematically from 0.6 octaves for the weakest diffuser lens to 2.3 +/- 0.7 and 3.5 +/- 0.8 octaves for the intermediate and strongest diffuser lenses, respectively. There was a close correspondence between the magnitude of the amblyopic deficits and the reduction in retinal image contrast produced by the diffuser lenses. CONCLUSIONS: The results demonstrate that the depth of monocular, nonstrabismic amblyopia is strongly influenced by the degree of retinal image degradation experienced early in life. (+info)
Contrast sensitivity in meridional amblyopia.
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Contrast (modulation) sensitivities for gratings of various spatial frequencies and orientations have been determined for meridional amblyopes. The entire contrast sensitivity function is reduced for gratings oriented in the amblyopic meridian. Therefore, neural elements that process a broad range of spatial frequencies are affected by meridional amblyopia. (+info)
The role of anisometropia in the development of accommodative esotropia.
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PURPOSE: To determine if anisometropia increases the risk for the development of accommodative esotropia in hypermetropia. METHODS: Records of all new patients with a refractive error of > or = +2.00 (mean spherical equivalent [SE] of both eyes) over a 42-month period were reviewed. Three hundred forty-five (345) patients were thus analyzed to determine the effect of anisometropia (> or = 1 diopter [D]) on the relative risk of developing esodeviation and of requiring surgical correction once esodeviation was present (uncontrolled deviation). RESULTS: Anisometropia (> or = 1 D) increased the relative risk of developing accommodative esodeviation to 1.68 (P < .05). Anisometropia (> or = 1 D) increased the relative risk for esodeviation to 7.8 (P < .05) in patients with a mean SE of < 3 D and to 1.49 (P < .05) in patients with SE of > or = 3 D. This difference was significant (P = .016). In patients with esotropia and anisometropia (> or = 1 D), the relative risk for an uncontrolled deviation was 1.72 (P < .05) compared with nonanisometropic esotropic patients. Uncontrolled esodeviation was present in 33% of anisometropic patients versus 0% of nonanisometropic patients with a mean hypermetropic SE of < 3 D (P = .003); however, anisometropia did not increase the relative risk of uncontrolled esotropia in patients with SE of > or = 3 D. Although amblyopia and anisometropia were closely associated, anisometropia increased the relative risk of esodeviation to 2.14 (P < .05) even in the absence of amblyopia. CONCLUSIONS: Anisometropia (> 1 D) is a significant risk factor for the development of accommodative esodeviation, especially in patients with lower overall hypermetropia (< 3 D). Anisometropia also increases the risk that an accommodative esodeviation will not be fully eliminated with hypermetropic correction. (+info)
Management of anterior segment penetrating injuries with traumatic cataract by Pentagon approach in paediatric age group: constraints and outcome.
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PURPOSE: To evaluate the efficacy of multiple combined procedure (Pentagon approach) as single-step secondary repair in cases of extensive keratolenticular trauma in paediatric age group. METHODS: Retrospective evaluation of 18 patients of penetrating injuries with sclerokeratolenticular trauma, who underwent multiple procedure as single-step secondary repair by a single team of two surgeons during a 4 year period. Surgical procedure included reconstruction of anterior segment, synechiolysis, excision of membrane, lensectomy, open sky vitrectomy, PC IOL implantation over frill and penetrating keratoplasty. Meticulous antiamblyopia measures were applied in all cases. RESULTS: Extensive vasoproliferative membrane, complicated cataract and anterior vitreous condensation were significant intra-operative hurdles. Moderate uveitis, secondary glaucoma, persistent epithelial defects were problems noted. Eleven (61.22%) patients attained good visual outcome. Regrafting was required in remaining cases due to delayed graft failure. CONCLUSION: Despite being a highly complex technique, Pentagon approach provides effective management profile in terms of graft success and functional outcome, especially in keratolenticular trauma, in children. (+info)
Results of cataract surgery in young children in east Africa.
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BACKGROUND: Cataract is the leading cause of blindness in children in east Africa. The results of surgery are poor, partly because of inadequate correction of aphakia. METHODS: A retrospective survey of 118 eyes in 71 children with bilateral cataract. All eyes had implantation of an IOL at the time of cataract surgery. The average age at surgery was 3.5 years. 28 patients(39%) were less than 2 years old at the time of surgery on their first eye. RESULTS: Preoperatively, 75.4% of eyes and 76.1% of patients were blind. A follow up of at least 3 months was available in 91 (77.1%) eyes. In these eyes, 44% had a latest corrected vision of 6/18 or better and 91.2% had a latest corrected vision of 6/60 or better. Eyes with zonular cataract, and eyes operated after the age of 2 years were more likely to obtain a vision of 6/18 or better. 3.3% of eyes and 1.8% of patients had an acuity of less than 3/60. Nystagmus was present in 42.3% of patients before surgery. In those patients followed up for a minimum of 6 months, 10.2% still had nystagmus. The most frequent complication was severe fibrinous uveitis, which occurred in 36 (30.5%) eyes. 62 (52.5%) eyes had a posterior capsulotomy at the time of cataract extraction. Of the remaining 56 eyes, 20 (35.7%) had so far required a posterior capsulotomy. The leading cause of poor visual outcome was amblyopia. Two patients developed severe complications related to the intraocular lens. CONCLUSIONS: Insertion of a lens implant at the time of cataract extraction appears to be well tolerated in the short term, and may offer significant advantages in an African setting. (+info)
Intensive occlusion therapy for amblyopia.
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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. (+info)