Differential Experience-Dependent Plasticity of Form and Motion Mechanisms in Anisometropic Amblyopia.

Purpose: We measure neural responses associated with form and motion processing in children with anisometropia before and after treatment with spectacles and occlusion. Methods: In this prospective, case-control treatment study, 10 children with anisometropia and amblyopia and 16 age-matched visually normal children participated. Steady-state visual evoked potentials (VEP) were recorded from electrodes over the occipital cortex. The visual stimulus comprised a horizontal bar grating into which Vernier offsets were introduced and withdrawn periodically at 3.75 Hz. The VEP amplitude at 3.75 Hz (first harmonic [1F]) and 7.5 Hz (second harmonic [2F]) were recorded to index the sensitivity of form/position-sensitive versus motion/transient-sensitive neural populations, respectively. Response amplitude at 1F and 2F were recorded over a series of 10 logarithmically spaced offset sizes before and after treatment. Main outcome measures are VEP amplitude versus displacement functions, interocular response amplitude differences. Results: After relaxing into spectacles (minimally-treated state), form/position-sensitive responses in the dominant/less ametropic eye of the children with anisometropia were larger and responses in the more ametropic eye were smaller than those of controls. Motion-transient responses were equal to those of controls in the less ametropic eye, but were smaller than controls in the more ametropic eye. After treatment, responses did not differ from those of controls. Conclusions: Form and motion responses are differentially susceptible to neural deprivation via optical blur. Form responses are more plastic than motion responses in minimally-treated children with anisometropic amblyopia. Most treatment effects occurred above threshold range, suggesting some treatment effects are not detected clinically.

Short-term effects of vision trainer rehabilitation in patients affected by anisometropic amblyopia: electrofunctional evaluation.

PURPOSE: The aim of the present study was to evaluate the short-term effects of the vision trainer rehabilitation technique on retinal and post-retinal function in young amblyopic patients outside the critical visual developmental period. METHODS: Twenty-one patients (mean age 12.2 ± 2.7 years, ranging from 9.1 to 18 years) affected by unilateral anisometropic amblyopia were studied, providing 21 amblyopic eyes (AE) and 21 sound eyes (SE). Thirty eyes from 15 age-similar normal subjects served as controls. All subjects underwent extensive ophthalmologic characterization to exclude any disease not related to amblyopia. All AE were subjected to rehabilitation sessions performed by the Retimax vision trainer (VT) program. The protocol consisted of 2 sessions per week, each lasting 10 min, for 10 consecutive weeks. Before and after the rehabilitation, electrophysiological [pattern electroretinogram (PERG) and visual evoked potential (VEP)] and psychophysical [best corrected visual acuity (BCVA) and microperimetry] data were collected from AE and SE. RESULTS: When comparing baseline data with those collected at the end of the study, PERG P50-N95 amplitude and BCVA values from AE had improved significantly by the end of the study (p < 0.05). Our electrophysiological findings also showed some abnormalities in SE when the data were compared to control eyes. We found a significant correlation (p < 0.05) between PERG amplitude and VEP implicit time in SE after visual rehabilitation. CONCLUSIONS: Short-term visual rehabilitation performed by the VT program ameliorated the electrofunctional and psychophysical parameters of vision in children outside the critical developmental period, thus indicating that VT might be a potential adjuvant therapy of traditional patching treatment.

Comparison of anisometropes with and without amblyopia.

BACKGROUND: To compare binocular functions in amblyopic and non-amblyopic anisometropes and to investigate the possible associated factors for amblyopia development such as type of refractive error and initial age of refractive error correction. MATERIALS AND METHODS: Prospectively anisometropic subjects with (n=42) and without amblyopia (n=33) were included in the study. Full ophthalmological examination including binocularity and motility was performed. RESULTS: There was no statistically significant difference between the ages at the time of initial refractive error correction (P =0.946). All of the anisometropes (100%) had fusion with Worth 4-dot test and Bagolini glasses. However 81% of amblyopic subjects had fusion with Worth 4 dot test and 88.1% had normal response with Bagolini glasses. Median stereopsis was 60 sec of arc in anisometropic subjects and 400 sec of arc in amblyopes. CONCLUSION: Our data support that, binocular functions are well developed in anisometropes without amblyopia and initial age at correction of refractive error has no primary effect on development of amblyopia.

Optimal amount of anisometropia for pseudophakic monovision.

PURPOSE: To determine the optimal target anisometropia for pseudophakic monovision. METHODS: Thirty-five bilaterally pseudophakic patients who received monofocal intraocular lenses were included in the study. Binocular corrected distance visual acuity (CDVA) and binocular distance-corrected near visual acuity (DCNVA) and stereoacuity were measured after simulating 1.00, 1.50, and 2.00 diopters (D) of monovision by adding the appropriate spherical lens to the nondominant eye. We presumed that mean binocular DCNVA of 20/40, binocular CDVA of 20/25, and stereoacuity <100 seconds of arc (arc sec) were necessary for successful monovision. RESULTS: With no anisometropia, mean binocular DCNVA was 20/97, binocular CDVA was 20/20, and mean stereoacuity was 71 arc sec. With 1.00 D of monovision, mean binocular DCNVA was only 20/60, although binocular CDVA and mean stereoacuity were sufficient. With 1.50 D of monovision, binocular DCNVA was 20/38, binocular CDVA at other distances exceeded 20/21, and stereoacuity was 100 arc sec, which was a 29-arc sec reduction. With 2.00 D of monovision, binocular DCNVA reached 20/31, but stereoacuity was 158 arc sec, which was an 87-arc sec reduction. The number of patients who met the criteria for successful monovision was significantly greater with 1.50 D of monovision than with 1.00 or 2.00 D of monovision (P=.0134). CONCLUSIONS: Pseudophakic monovision with anisometropia of 1.50 or 2.00 D provides useful binocular visual acuity from far to near. However, because stereopsis with 2.00 D of monovision is substantially impaired, approximately 1.50 D of anisometropia is thought to be optimal for successful monovision.

How to measure slab-off and reverse slab prism in spectacle lenses.

It is well known that new spectacle lenses for the correction of anisometropia can induce diplopia with reading. The difference in the powers of the lenses induces a net prismatic effect that can cause double vision through off-center areas of the lenses. This is particularly bothersome when patients try to read, often noting vertical double vision in attempted downgaze, especially through multifocal add segments. This induced prismatic effect can be compensated at one level of downgaze by the use of slab-off or reverse slab prism. Typically the slab-off correction is ground into the stronger minus, or weaker plus lens. Reverse slab is ground into the weaker minus, or stronger plus, lens. Unfortunately, determining the amount of slab-off prism already incorporated into spectacle lenses is nonintuitive and inconvenient. This usually requires the use of a lens clock, which is not widely accessible to many ophthalmology practices. A simple technique, described in the past but poorly known, is illustrated here for quickly measuring slab-off and reverse slab prism prescription lenses in the clinic with a common manual lens meter.

Fitting contact lenses for visual rehabilitation after penetrating keratoplasty.

PURPOSE: To determine the optical indications for contact lens wear after corneal transplantation. The type of lenses used, fitting philosophy, visual outcomes, and complications were examined. METHODS: A 4-year retrospective chart review was performed and identified 35 eyes in 30 patients wearing contact lenses for visual rehabilitation after penetrating keratoplasty. RESULTS: The optical indications for contact lens fitting after penetrating keratoplasty were multifactorial and included irregular astigmatism (62.9%), spherical anisometropia (57.1%), and astigmatic anisometropia (54.3%). The average time from surgery to initial contact lens fitting was 18.2 months. Spherical rigid gas-permeable lenses were the most common type of lens used. The mean best-corrected visual acuity improved from less than 20/40 with spectacles alone to better than 20/30 when using a contact lens. Punctal occlusion and lubrication helped to improve contact lens tolerance. Complications associated with contact lens use tended to be minor and responded generally well to conservative treatment measures. CONCLUSION: Contact lenses can improve visual function in patients with irregular astigmatism and anisometropia after penetrating keratoplasty.

Determining exact prismatic deviations in spectacle corrections.

For nearly 100 years, Prentice's rule has been used to determine the prismatic effect and prismatic differences at peripheral points in the binocular spectacle field. However, calculations show that the current application Prentice's rule is valid only for a single lens and only if that lens is considered as a thin lens approximation. When center thickness and base curves are taken into account, Prentice's rule is no longer valid. In addition, when the prismatic difference in an off-axis region of the lenses is determined with the assumption that both eyes look through the lenses at identical distances from their optical centers, the errors are further compounded. If the eyes are to maintain fusion, this assumption is optically impossible and will produce incorrect results. It is also shown that Prentice's rule cannot be applied to iseikonic corrections to find differential prismatic effects. The article demonstrates how exact prismatic effects can be determined from the spectacle-generated images and the angles they subtend at the ocular rotation centers.

A correçäo da anisometropia quando sobrevem a presbiopia / The correction of anisometropia when presbyopia starts

Os autores preconizam o emprego de lentes progressivas nos casos de presbiopia com anisometropia para eliminar a diplopia e o salto da imagem. Após o cálculo da diferença dióptrica no meridiano vertical de ambos os olhos, utilizando-se a fórmula de Prentice, produz-se na lente mais fraca um prisma com a metade do valor encontrado. Säo apresentados 90 casos, todos bem sucedidos

[Pleoptic therapy in anisometropic and strabismic amblyopia]. / Pleoptyczne leczenie niedowidzenia spowodowanego róznowzrocznoscia i niedowidzenia zezowego.

The study aims at describing the current trends in pleoptic treatment with a special attention paid to the practised exercises. On the basis of literature a short review of the pathogenesis of amblyopia with or without strabismus is presented. The need for careful choice of the treatment according to specific conditions in each subject is emphasised. The importance of active pleoptic therapy in cases with or without strabismus is particularly pointed out. In anisometropia contrast sensitivity is decreased, differentiation of optotypes put in line and shape differentiation are worsened, ability to discern figures and to accommodation are impaired. Amblyopia with strabismus leads to decrease in space orientation ability, impairment in following movement, prolongation of saccadic movement and of eye-hand coordination time. The types of visual dysfunction mentioned above determine the exercises which should be recommended in a given case. Examples of exercises are presented and the range of improvement possible to achieve is documented.

Técnica cirúrgica para correçäo de miopia. Anel corneano intra-estromal / Myopia correction with intrastromal corneal ring

Os implantes intracorneanos para correçäo de ametropias vêm sendo pesquisados desde a década de 50. Os anéis corneanos intra estromais, por serem bem tolerados, vêm se destacando como um técnica alternativa segura para tratamento daas ametropias. Após prolongados estudos em animais, utilizando anéis com 5,00 mm de diâmetro e espessuras variáveis, reslizamos um implante em paciente míope e amblíope, no terço anterios do estroma corneano, utilizando a técnica de ceratectomia parcial. Após 3 anos de observaçäo clínica ficaram evidenciados e perfeita tolerância da córnea à prótese e a estabilidade do resultado refracional. Desenvolvemos a partir daí, uma técnica para implante do anel através de tunelizaçäo do estroma. Selecionamos um paciente míope, anisométrope e amblíope e realizamos a cirurgia. O resultado, após o primeiro mês de observaçäo, mostrou boa tolerância além de um aplanamento central da córnea de 3,00 dioptrias confirmado tanto pela ceratometria quanto pelo topografia corneana computadorizada. Embora o período de observaçäo seja muito pequeno, podemos afirmar, embasados em nossos estudos preliminares, que esta técnica representa uma alternativa promissora para o tratamento dos erros refracionais

[The prevalence of refractive, anisometropic amblyopia in adults without strabismus and with contact lens correction]. / Rasprostranennost' refraktsionnoi, anizometropicheskoi ambliopii u vzroslykh bez kosoglaziia na fone kontaktnoi korrektsii.

The paper presents results after examination of 1260 adults (2547 eyes), aged from 18 to 55 years, for the period from 1982 to 1988. The examination was carried out in order to reveal the incidence of refractive, anisometropic amblyopia without strabismus in persons using glasses (a control group) and contact lenses as well as to determine a degree of spheric, astigmatic refraction in development of amblyopia on the background of contact lenses. It was found that amblyopia on the background of contact correction, as compared with glass correction, develops rarer making up 22.03% of them low degree of amblyopia is recorded in 51,16%, moderate--in 35,65% high--in 13,19% to the total number of amblyopic eyes examined. Direct relationship between the number of amblyopic eyes and degree of astigmatism and anisometropia is revealed. Detection of amblyopia in adults without strabismus with subsequent contact correction and treatment is considered to be necessary for medical and labour rehabilitation of such patients.