Suma Ganesh

Development of pattern vision following early and extended blindness

Significance Deprivation of vision during typical age-defined critical periods results in seemingly irreversible changes in neural organization and behavior in animals and humans. We describe visual development in a unique population of patients who were blind during typical critical periods before removal of bilateral cataracts. The rarity of such cases has previously limited empirical investigations of this issue. Surprisingly, we find substantial improvement after sight onset in contrast sensitivity, a basic visual function that has well-understood neural underpinnings. Our results show that the human visual system can retain plasticity beyond critical periods, even after early and extended blindness. Visual plasticity peaks during early critical periods of normal visual development. Studies in animals and humans provide converging evidence that gains in visual function are minimal and deficits are most severe when visual deprivation persists beyond the critical period. Here we demonstrate visual development in a unique sample of patients who experienced extended early-onset blindness (beginning before 1 y of age and lasting 8–17 y) before removal of bilateral cataracts. These patients show surprising improvements in contrast sensitivity, an assay of basic spatial vision. We find that contrast sensitivity development is independent of the age of sight onset and that individual rates of improvement can exceed those exhibited by normally developing infants. These results reveal that the visual system can retain considerable plasticity, even after early blindness that extends beyond critical periods.

Results of late surgical intervention in children with early-onset bilateral cataracts.

Background Cataracts are a major cause of childhood blindness globally. Although surgically treatable, it is unclear whether children would benefit from such interventions beyond the first few years of life, which are believed to constitute ‘critical’ periods for visual development. Aims To study visual acuity outcomes after late treatment of early-onset cataracts and also to determine whether there are longitudinal changes in postoperative acuity. Methods We identified 53 children with dense cataracts with an onset within the first half-year after birth through a survey of over 20 000 rural children in India. All had accompanying nystagmus and were older than 8 years of age at the time of treatment. They underwent bilateral cataract surgery and intraocular lens implantation. We then assessed their best-corrected visual acuity 6 weeks and 6 months after surgery. Results 48 children from the pool of 53 showed improvement in their visual acuity after surgery. Our longitudinal assessments demonstrated further improvements in visual acuity for the majority of these children proceeding from the 6-week to 6-month assessment. Interestingly, older children in our subject pool did not differ significantly from the younger ones in the extent of improvement they exhibit. Conclusions and relevance Our results demonstrate that not only can significant vision be acquired until late in childhood, but that neural processes underlying even basic aspects of vision like resolution acuity remain malleable until at least adolescence. These data argue for the provision of cataract treatment to all children, irrespective of their age.

Immediate susceptibility to visual illusions after sight onset

The dominant accounts of many visual illusions are based on experience-driven development of sensitivity to certain visual cues. According to such accounts, learned associations between observed two-dimensional cues (say, converging lines) and the real three-dimensional structures they represent (a surface receding in depth) render us susceptible to misperceiving some images that are cleverly contrived to contain those two-dimensional cues. While this explanation appears reasonable, it lacks direct experimental validation. To contrast it with an account that dispenses with the need for visual experience, it is necessary to determine whether susceptibility to the illusion is present immediately after birth; however, eliciting reliable responses from newborns is fraught with operational difficulties, and studies with older infants are incapable of resolving this issue. Our work with children who gain sight after extended early-onset blindness, as part of Project Prakash, provides a potential way forward. We report here that the newly sighted children, ranging in age from 8 through 16 years, exhibit susceptibility to two well-known geometrical visual illusions, Ponzo [1] and Müller-Lyer [2], immediately after the onset of sight. This finding has implications not only for the likely explanations of these illusions, but more generally, for the nature-nurture argument as it relates to some key aspects of visual processing.

Improvement in Spatial Imagery Following Sight Onset Late in Childhood

The factors contributing to the development of spatial imagery skills are not well understood. Here, we consider whether visual experience shapes these skills. Although differences in spatial imagery between sighted and blind individuals have been reported, it is unclear whether these differences are truly due to visual deprivation or instead are due to extraneous factors, such as reduced opportunities for the blind to interact with their environment. A direct way of assessing vision’s contribution to the development of spatial imagery is to determine whether spatial imagery skills change soon after the onset of sight in congenitally blind individuals. We tested 10 children who gained sight after several years of congenital blindness and found significant improvements in their spatial imagery skills following sight-restoring surgeries. These results provide evidence of vision’s contribution to spatial imagery and also have implications for the nature of internal spatial representations.

Impact of low vision rehabilitation on functional vision performance of children with visual impairment

Purpose: To evaluate the impact of low vision rehabilitation on functional vision of children with visual impairment. Materials and Methods: The LV Prasad–Functional Vision Questionnaire, designed specifically to measure functional performance of visually impaired children of developing countries, was used to assess the level of difficulty in performing various tasks pre and post visual rehabilitation in children with documented visual impairment. Chi-square test was used to assess the impact of rehabilitation intervention on functional vision performance; a P < 0.05 was considered significant. Results: LogMAR visual acuity prior to the introduction of low vision devices (LVDs) was 0.90 ± 0.05 for distance and for near it was 0.61 ± 0.05. After the intervention, the acuities improved significantly for distance (0.2 ± 0.27; P < 0.0001) and near (0.42 ± 0.17; P = 0.001). The most common reported difficulties were related to their academic activities like copying from the blackboard (80%), reading textbook at arms length (77.2%), and writing along a straight line (77.2%). Absolute raw score of disability pre-LVD was 15.05 which improved to 7.58 post-LVD. An improvement in functional vision post visual rehabilitation was especially found in those activities related to their studying lifestyle like copying from the blackboard (P < 0.0001), reading textbook at arms length (P < 0.0001), and writing along a straight line (P = 0.003). Conclusions: In our study group, there was a significant improvement in functional vision post visual rehabilitation, especially with those activities which are related to their academic output. It is important for these children to have an early visual rehabilitation to decrease the impairment associated with these decreased visual output and to enhance their learning abilities.

Hyperopic corneal refractive surgery in patients with accommodative esotropia and amblyopia: comment.

To the Editor: We commend the authors of “Hyperopic corneal refractive surgery in patients with accommodative esotropia and amblyopia” for addressing very important issue of concurrent amblyopia in patients with accommodative esotropia and exploring the possibility of hyperopic refractive surgery in such patients. We would like to comment on the study’s methodology and results. Esodeviation was apparently measured with respect to near fixation alone; we failed to find any information regarding deviation for distance, presence of any near distance disparity, and high ratio of accommodative convergence to accommodation. All of these findings are extremely important in the ultimate response to any type of optical or surgical correction in patients with accommodative esotropia; therefore, the motor alignment results would have been more appropriate and complete had these factors also been studied. The authors found that most of their amblyopic patients (70% in synoptophore tests and 50% in Titmus fly test) showed improvement in gross stereopsis following surgery. This result is much better than previous studies, which noted only a modest improvement or no improvement, in spite of the fact that most of these studies involved nonamblyopic subjects. We would like to ask the authors whether a masked evaluation of the postoperative visual acuity, alignment, and stereopsis was performed to neutralize observer bias. The data on patient no. 3 in Table 2 shows that the spectacle-corrected esotropia of 40 improved to unaided 10 after refractive surgery. Such large improvements in

Pseudomyopia in intermittent exodeviation: Comment

Dear Editor, We have read with great interest an article by Jayakumar et al., on Pseudomyopia in intermittent exodeviation.[1] The authors have described a young patient with intermittent exodeviation (IXT) who was operated for bilateral lateral rectus weakening and thereafter diagnosed as a case of pseudomyopia which was well managed with cycloplegics. We commend the authors for addressing a very important problem in strabismology practice and would like to add a few comments. Large exophoria or intermittent exotropia has been described as an aetiological factor for accommodative spasm.[2] We agree with the authors that patients with IXT could make use of accommodative convergence to control the exodeviation, thereby resulting in accommodative spasm over a period of time. We have recently published our experience with diagnosis and role of vision therapy exercises in a young patient with accommodative spasm secondary to long standing intermittent exotropia.[3] In contrast to the patient described by Jayakumar M, our patient presented with severe asthenopic symptoms, an intractable spasm of accommodation, high pseudomyopia, and a variable angle of deviation. It was only after management with cycloplegia and normalizing the accommodative amplitudes by vision therapy exercises that IXT as the aetiology was diagnosed; there was complete resolution of symptoms after squint surgery. We also agree with the authors that post-surgery residual angle could lead to persistence of pseudomyopia. In this group of patients, we therefore undertake a prolonged prism adaptation to uncover the full amount of deviation before planning surgery. We appreciate the authors’ effort to make the ophthalmologists aware of occurrence of pseudomyopia in patients with IXT. Since the presentation in such cases may be myriad, a detailed orthoptic evaluation is warranted to reach a proper diagnosis. We would also like to emphasize the role of vision therapy exercises to normalize the accommodative amplitude as an important adjunct in management of such cases.

Prevalence of buried probe in complex congenital nasolacrimal duct obstruction and evaluation of its success rate post ‘probing and irrigation’: a single-centre retrospective study

ABSTRACT Introduction: The aim of this study was to determine the prevalence of buried probe variant of complex congenital nasolacrimal duct obstruction (CNLDO) and to evaluate the outcome of probing and irrigation in such cases. Institutional review board approval was taken. Material & Methods: A total of 309 eyes (258 patients) were diagnosed with CNLDO during the study period of January 2014–March 2017. A retrospective file review of 25 lacrimal systems of 20 patients diagnosed as buried probe variant of complex CNLDO was carried out during the study period. Result: Buried probe variant of complex CNLDO was found to be 8% of the total CNLDO cases during the study period. Mean age at presentation was 1.7 years (range 8–48 months). Discharge and matting of eyelashes were the presenting symptoms in 22 out of 25 (88%) cases, whereas the only epiphora was the presenting symptom in three (12%) cases. Regurgitation of mucopurulent discharge on pressure over lacrimal sac area was positive in 16 out of 25 (64%) eyes. Associated lacrimal and nasal pathologies were seen in six out of 25 cases (24%). Success rate in buried probe variant cases of CNLDO in our study at 3-month follow-up was 88% (22 of 25 cases). Conclusion: A high period prevalence of 8% out of all CNLDO cases in our study suggests that the buried probe should be considered in selective cases of CNLDO and earlier unsuccessful probing.

Ophthalmic Manifestations in Children with Periventricular Leukomalacia

To the Editor: Periventricular leukomalacia (PVL), an important neuroradiological sign of perinatal cerebral damage, causes visual impairment in children [1]. We retrospectively analysed the predisposing factors and ophthalmic manifestations in children <16 y withMRI evidence of PVL in a tertiary care centre of Northern India. Records of 32 patients with PVL were analysed. Mean presenting age was 51.2 mo. Antenatal and perinatal history was positive in 43.7% and 96.8% children respectively (preterm in 65.6%, delayed cry in 54.2%, NICU admission in 81.2%, oxygen therapy in 50%, perinatal seizures in 34.3%, feeding difficulties in 21.8% and pathological jaundice in 34.3%). Hypoglycemia, sepsis and birth asphyxia were cumulatively present in 20.6%. The major risk factor was perinatal hypoxia. The commonest presenting ocular complaint was strabismus (59.3%) [2], followed by poor eye contact, poor visual response, poor hand eye coordination, keeping eyes in upgaze and decreased vision. PVL may go undiagnosed in absence of strabismus [3]. Visual level was assessed as classified and described by Huo [4]. Vision was better than grade 3 in 62.5% children. Contrary to previous studies [4], the number of children fixing and following light (level 3) in our study were comparable to those with vision upto 20/50 (level 4, 5). Simple hyperopic astigmatism was the commonest refractive error. Myopia ranged upto −9.25DS whereas hyperopia ranged upto 4.5DS. Exotropia was seen in 12(37.5%) patients whereas 10(31.2%) children had esotropia [5]. Nystagmus was present in 13(40.6%) patients, most common being horizontal jerk nystagmus in 7 children, followed by latent nystagmus in 3 children, rotatory nystagmus in 2 children and end-gaze nystagmus in 1 child. On posterior segment evaluation, temporal disc pallor was seen in 10 patients whereas diffuse pallor was present in 5 patients. Vision and disc appearance were in concordance with each other in 10 out of 32 children. Pursuits and saccades could be recorded in 17(53.1%) patients; they were normal in 4 patients (23.5%) only. Inspite of severe ophthalmic manifestations seen in PVL, only 2 children were referred to ophthalmologists for early interventions. To conclude, increased emphasis on early visual function interventions can aid in better therapeutic recovery of children with PVL.

Accuracy of noncycloplegic refraction performed at school screening camps

Purpose: The aim of this study was to compare noncycloplegic refraction performed in school camp with that performed in eye clinic in children aged 6–16 years. Methods: A prospective study of children with unaided vision <0.2 LogMAR who underwent noncycloplegic retinoscopy (NCR) and subjective refraction (SR) in camp and subsequently in eye clinic between February and March 2017 was performed. A masked optometrist performed refractions in both settings. The agreement between refraction values obtained at both settings was compared using the Bland–Altman analysis. Results: A total of 217 eyes were included in this study. Between the school camp and eye clinic, the mean absolute error ± standard deviation in spherical equivalent (SE) of NCR was 0.33 ± 0.4D and that of SR was 0.26 ± 0.5D. The limits of agreement for NCR were +0.91D to − 1.09D and for SR was +1.15D to -1.06D. The mean absolute error in SE was ≤0.5D in 92.62% eyes (95% confidence interval 88%–95%). Conclusion: A certain degree of variability exists between noncycloplegic refraction done in school camps and eye clinic. It was found to be accurate within 0.5D of SE in 92.62% eyes for refractive errors up to 4.5D of myopia, 3D of cylinder, and 1.5D of hyperopia.