Distribution of refractive errors in albinos and persons with idiopathic congenital nystagmus

Clinical features and imaging characteristics in achiasmia

Achiasmia is a rare visual pathway maldevelopment with reduced decussation of the axons in the optic chiasm. Our aim was to investigate clinical characteristics, macular, optic nerve and brain morphology in achiasmia. A prospective, cross-sectional, observational study of 12 participants with achiasmia [8 males and 4 females; 29.6 ± 18.4 years (mean ± standard deviation)] and 24 gender-, age-, ethnicity- and refraction-matched healthy controls was done. Full ophthalmology assessment, eye movement recording, a high-resolution spectral-domain optical coherence tomography of the macular and optic disc, five-channel visual-evoked responses, eye movement recordings and MRI scans of the brain and orbits were acquired. Achiasmia was confirmed in all 12 clinical participants by visual-evoked responses. Visual acuity in this group was 0.63 ± 0.19 and 0.53 ± 0.19 for the right and left eyes, respectively; most participants had mild refractive errors. All participants with achiasmia had see-saw nystagmus and no measurable stereo vision. Strabismus and abnormal head position were noted in 58% of participants. Optical coherence tomography showed optic nerve hypoplasia with associated foveal hypoplasia in four participants. In the remaining achiasmia participants, macular changes with significantly thinner paracentral inner segment (P = 0.002), wider pit (P = 0.04) and visual flattening of the ellipsoid line were found. MRI demonstrated chiasmatic aplasia in 3/12 (25%), chiasmatic hypoplasia in 7/12 (58%) and a subjectively normal chiasm in 2/12 (17%). Septo-optic dysplasia and severe bilateral optic nerve hypoplasia were found in three patients with chiasmic aplasia/hypoplasia on MRI. In this largest series of achiasmia patients to date, we found for the first time that neuronal abnormalities occur already at the retinal level. Foveal changes, optic nerve hypoplasia and the midline brain anomaly suggest that these abnormalities could be part of the same spectrum, with different manifestations of events during foetal development occurring with varying severity.

Perception of Coherent Motion in Infantile Nystagmus Syndrome

Purpose

Research on infantile nystagmus syndrome (INS) and motion perception is limited. We investigated how individuals with INS perform coherent motion tasks. Particularly, we assessed how the null position affects their performance.

Methods

Subjects with INS and controls identified the direction of coherent motion stimuli (22 subjects with INS and 13 controls) in a two-alternative forced-choice design. For subjects with INS, testing was done at the null position and 15 degrees away from it. If there was no null, testing was done at primary gaze position and 15 degrees away from primary. For controls, testing was done at primary gaze position and 20 degrees away from primary. Horizontal and vertical motion coherence thresholds were determined.

Results

Subjects with INS showed significantly higher horizontal and vertical motion coherence thresholds compared with controls at both gaze positions (P < 0.001). Within the INS group, for 12 subjects with INS who had an identified null position, no differences in coherence thresholds were found between their null and 15 degrees away from it (P > 0.05).

Conclusions

Coherent motion perception was impaired in subjects with INS. The null position did not significantly influence motion coherence thresholds for either horizontal or vertical motion.

Biallelic mutations in L-dopachrome tautomerase (DCT) cause infantile nystagmus and oculocutaneous albinism

Infantile nystagmus syndrome (INS) denominates early-onset, involuntary oscillatory eye movements with different etiologies. Nystagmus is also one of the symptoms in oculocutaneus albinism (OCA), a heterogeneous disease mainly caused by defects in melanin synthesis or melanosome biogenesis. Dopachrome tautomerase (DCT, also called TYRP2) together with tyrosinase (TYR) and tyrosin-related protein 1 (TYRP1) is one of the key enzymes in melanin synthesis. Although DCT´s role in pigmentation has been proven in different species, until now only mutations in TYR and TYRP1 have been found in patients with OCA. Detailed ophthalmological and orthoptic investigations identified a consanguineous family with two individuals with isolated infantile nystagmus and one family member with subtle signs of albinism. By whole-exome sequencing and segregation analysis, we identified the missense mutation c.176G > T (p.Gly59Val) in DCT in a homozygous state in all three affected family members. We show that this mutation results in incomplete protein maturation and targeting in vitro compatible with a partial or total loss of function. Subsequent screening of a cohort of patients with OCA (n = 85) and INS (n = 25) revealed two heterozygous truncating mutations, namely c.876C > A (p.Tyr292*) and c.1407G > A (p.Trp469*), in an independent patient with OCA. Taken together, our data suggest that mutations in DCT can cause a phenotypic spectrum ranging from isolated infantile nystagmus to oculocutaneous albinism.

Visual rehabilitation of people with oculocutaneous albinism in a tertiary clinical setting in Pakistan

PURPOSE:

All people with oculocutaneous albinism (OCA) have reduced vision. This study aimed to assess the benefits of low vision aids for people with OCA.

METHODS:

Seventy-seven consecutive people with OCA age 4 years and above examined in a low vision clinic were included in the study. Uncorrected and best-corrected visual acuity (VA), VA with low vision devices, types of low vision aids, and refractive errors data were analyzed.

RESULTS:

Of the 77 people with OCA, 57% were in the age group between 4 and 15 years and 43% in the age group of 16 years and above. At the time of presentation, the percentages of visually impaired, severe visually impaired, and blind (using WHO low vision criteria) were 52%, 22%, and 25%. Among them, 39% has near VA of 1 M or better. Difference in the means of the spherical equivalent refractive error in the right eyes and left eyes was −0.494 diopters (−01.686, 0.699; 95% confidence interval). VA improved significantly after adequate refractive correction by more than one log MAR lines in 38.6% (P < 0.01). With low vision devices, in 85.7% (n = 66) participants, VA was enhanced to normal level (6/18 or better) in the better eye while 7.8% still remained in the blind category. Telescopes were prescribed to 61% people for the enhancement of distance VA and hand hold magnifiers were prescribed to 22% people to meet their needs.

CONCLUSION:

Low vision aids can be successfully used in visual rehabilitation of people with OCA to meet their needs.

High- and Low-contrast Letter Acuity during Image Motion in Normal Observers and Observers with Infantile Nystagmus Syndrome

SIGNIFICANCE

High-contrast acuity in individuals with infantile nystagmus syndrome (INS) is poorer than expected from their ongoing retinal image motion, indicating a sensory loss. Conversely, acuity for larger low-contrast letters in these observers may be limited by image motion alone.

PURPOSE

The aim of this study was to assess visual acuity for letters of different contrast in normal observers and individuals with idiopathic INS under conditions of comparable retinal image motion.

METHODS

Visual acuity was measured using projected Landolt C charts in 3 normal observers and 11 observers with presumed idiopathic INS. Normal observers viewed each chart after reflection from a front-surface mirror that underwent continuous 4-Hz ramp motion with amplitudes ranging from 4 to 9.6° and simulated foveation durations of 20 to 80 milliseconds. Observers with INS viewed the charts directly. By reciprocally varying the luminance of the projected charts and a superimposed veiling source, Landolt C's were presented on a background luminance of 43 cd/m2 with Weber contrasts between -12 and -89%.

RESULTS

Whereas normal observers' high-contrast acuity during imposed image motion depends only on the duration of the simulated foveation periods, acuity for low-contrast optotypes also worsens systematically as motion intensity (frequency × amplitude) increases. For comparable parameters of retinal image motion, high-contrast acuity in all but one of the observers with INS was poorer than in normal observers. On the other hand, low-contrast acuity in the two groups of observers was similar when the retinal image motion was comparable.

CONCLUSIONS

Reduced high-contrast acuity in observers with INS appears to be attributable primarily to a sensory deficit. On the other hand, the reduction of low-contrast acuity in observers with INS may be accounted for on the basis of retinal image motion.

Ametropia and Emmetropization in CNGB3 Achromatopsia

Purpose

Emmetropization is the process of adjusting ocular growth to the focal plane in order to achieve a clear image. Chromatic light may be involved as a cue to guide this process. Achromats are color blind and lack normal cone function; they are often described as being hyperopic, indicating a failure to emmetropize. We aim to describe the refraction and refractive development in a population of genetically characterized achromats.

Methods

Refractive error data were collected retrospectively from 28 medical records of CNGB3 c.1148delC homozygous achromats. The distribution of spherical equivalent refractive error (SER) and spherical error was analyzed in adults. The refractive development in children was analyzed by documenting astigmatic refractive error and calculating median SER in 1-year age groups and by analyzing the individual development when possible.

Results

The distribution of SER and spherical error resembled a Gaussian distribution, indicating that emmetropization was disturbed in achromats, but we found indication of some decrease in SER during the first years of childhood. The prevalence of refractive errors was high and broadly distributed. Astigmatic refractive errors were frequent but did not seem to increase with age.

Conclusions

Refractive development in achromats is more complicated than a complete failure to emmetropize. The spread of refractive errors is larger than previously documented. Results presented here support the theory that chromatic cues and cone photoreceptors may play a role in emmetropization in humans but that it is not essential.

Visual function and visual ability in adolescents with oculocutaneous albinism

Individuals with ocular and oculocutaneous albinism (OCA) have significantly reduced visual acuity (VA) resulting in visual impairment (VI). The aim is to report on the visual function of adolescents with OCA and their quality of life (QoL) in terms of their visual ability. A total of 28 adolescents with OCA participated in this study. Tests of visual function included distance VA, refractive error, contrast sensitivity (CS), and colour vision. The Cardiff Visual Ability Questionnaire for Children (CVAQC) was used to assess visual ability. All participants presented with cutaneous hypopigmentation and nystagmus, while only two had strabismus. A mean myopic refractive error was found, and with-the-rule (WTR) astigmatism was most common. The mean best-corrected VA was 0.81 ± 0.17 logMAR and 0.81 ± 0.18 logMAR in the right and left eyes, respectively. The mean CS with the best refractive correction was 1.23 ± 0.33 log CS in the right eye and 1.29 ± 0.33 log CS in the left eye. The mean Cardiff visual ability score was −0.37 ± 0.79 log units. The variation of refractive errors and the magnitude thereof underscores the need for regular eye examinations in individuals with OCA. The majority of participants had moderate VI, and these participants had a better mean Cardiff visual ability score than those with severe VI. Similarly, participants with normal binocular CS had a better Cardiff visual ability score than those with a loss of CS.

SLC38A8 mutations result in arrested retinal development with loss of cone photoreceptor specialization

Foveal hypoplasia, optic nerve decussation defects and anterior segment dysgenesis is an autosomal recessive disorder arising from SLC38A8 mutations. SLC38A8 is a putative glutamine transporter with strong expression within the photoreceptor layer in the retina. Previous studies have been limited due to lack of quantitative data on retinal development and nystagmus characteristics. In this multi-centre study, a custom-targeted next generation sequencing (NGS) gene panel was used to identify SLC38A8 mutations from a cohort of 511 nystagmus patients. We report 16 novel SLC38A8 mutations. The sixth transmembrane domain is most frequently disrupted by missense SLC38A8 mutations. Ninety percent of our cases were initially misdiagnosed as PAX6-related phenotype or ocular albinism prior to NGS. We characterized the retinal development in vivo in patients with SLC38A8 mutations using high-resolution optical coherence tomography. All patients had severe grades of arrested retinal development with lack of a foveal pit and no cone photoreceptor outer segment lengthening. Loss of foveal specialization features such as outer segment lengthening implies reduced foveal cone density, which contributes to reduced visual acuity. Unlike other disorders (such as albinism or PAX6 mutations) which exhibit a spectrum of foveal hypoplasia, SLC38A8 mutations have arrest of retinal development at an earlier stage resulting in a more under-developed retina and severe phenotype.

Changes in refractive errors in albinism: a longitudinal study over the first decade of life

PURPOSE

To analyze longitudinal changes in refraction in patients with albinism.

METHODS

The medical records of 481 patients were reviewed retrospectively to identify patients who had cycloplegic refractions at three ages: visit A, 0-18 months old; visit B, 4-6 years old; visit C, 8-10 years old. We recorded refraction, type of albinism, glasses wear, and best-corrected visual acuity at visit C. Only right eyes were analyzed.

RESULTS

A total of 75 patients were included. Of these, 73 wore glasses. Mean best-corrected visual acuity at visit C was 20/72 (range, 20/25-20/200). Mean spherical equivalent was 2.81 ± 2.4 D at visit A, 2.53 ± 3.4 D at visit B, and 2.15 ± 4.0 D at visit C. These values did not differ significantly from visits A to C (P = 0.0578). Mean astigmatism for the three time points was 1.60 ± 1.00 D, 2.50 ± 1.14 D, and 2.87 ± 1.45 D; these values did differ significantly from A to C (P < 0.0001). Subgroup analysis for OCA1A (16 eyes), OCA1B (20 eyes), and OCA2 (30 eyes) showed an increase in astigmatism from A to C, with a significant difference in means (P < 0.0001, P < 0.0001, and P = 0.0001, resp.). Worse best-corrected visual acuity and higher mean astigmatism at visit C were found for OCA1A (20/104 and +4.08 ± 1.34) compared to OCA1B (20/59 and +2.30 ± 1.36; P < 0.0001) and OCA2 (20/66 and +2.53 ±1.21; P < 0.0001).

CONCLUSIONS

Children with albinism require periodic cycloplegic refraction, because astigmatism often increases within the first 10 years of life.

Phacoemulsification and intraocular lens implantation in patients with oculocutaneous albinism

PURPOSE

To evaluate the benefits of phacoemulsification and intraocular lens implantation in patients with oculocutaneous albinism (OCA).

METHOD

The charts of 195 patients with OCA who visited a local eye clinic were reviewed. All of these patients had genetic linkage analysis to establish OCA type. Frequencies and Paired t-test analysis were determined.

RESULTS

Of the 195 patients, nine (4.6%) underwent clear cornea phacoemulsification with intraocular lens implantation. Seven of the nine patients with OCA had the Hermansky-Pudlak (HPS) type 1; two had OCA type 1. Pre-operative BCVA of all eyes ranged from 1.0 to 2.3 logMAR with a mean of 1.42 logMAR and a standard deviation of 0.41 logMAR. Post-operative BCVA of all eyes ranged from 1.0 to 1.30 logMAR with a mean of 1.04 logMAR and a standard deviation of 0.10 logMAR. BCVA improved after phacoemulsification surgery and intraocular lens implantation (p = 0.002). Pre-operative astigmatism of all eyes ranged from +0.50 to +5.75 with a mean of +2.25 and a standard deviation of +2.40. Post-operative astigmatism of all eyes ranged from +0.50 to +2.00 with a mean of +1.23 and a standard deviation of +0.42. Astigmatism improved after phacoemulsification surgery and intraocular lens implantation (p = 0.05).

CONCLUSION

Nine patients with OCA who underwent phacoemulsification and intraocular lens implant experienced improved visual acuity and reduced astigmatism post-operatively. These results suggest cataract surgery may improve vision and refractive errors, and thus quality of life, in patients with albinism.

Visual deficits in Nepalese patients with oculocutaneous albinism

BACKGROUND

Albinism poses a significant threat to visual functions and causes remarkable ocular morbidity often resulting in visual disabilities. The study aimed at describing the visual status in patients with diagnosed cases of complete oculocutaneous albinism (OCA) attending to a tertiary eye hospital in Nepal.

METHODS

This was a cross-sectional descriptive hospital-based study of all diagnosed oculocutaneous albinotic cases (16 males and 9 females; mean age of 16 years) who visited the Department of Ophthalmology at the Institute of Medicine, for ocular consultation between September 1, 2011 and December 1, 2013.

RESULTS

Twenty-five cases (50 eyes) with OCA were enrolled in the study. All the participants had maximally reduced visual acuity (mean: 1.24±0.50logMAR). Myopic astigmatism was the most common refractive error (n=17; 34%). 58% of all participants had with-the-rule astigmatism. Considering the spherical equivalent power, most of the eyes (n=30; 60%) had myopia, with overall mean SE refractive error of -1.59±5.39D. Visual acuity improved significantly with refractive correction in place (paired sample t-test, p<0.05). Horizontal pendular nystagmus was the most common nystagmus (n=34 eyes; 68%). Alternating esotropia and alternating exotropia each were observed in 16% of participants who had strabismus (40% of all cases). The diaphanous iris, foveal hypoplasia and poliosis were the most consistent clinical features.

CONCLUSION

Patients with OCA present with a broad spectrum of visual deficits that impair the visual functions. Significant improvement in visual acuity following optical correction serves as an impetus to the reduction of visual disabilities in individuals with albinism.

Characterization of Abnormal Optic Nerve Head Morphology in Albinism Using Optical Coherence Tomography

PURPOSE

To characterize abnormalities in three-dimensional optic nerve head (ONH) morphology in people with albinism (PWA) using spectral-domain optical coherence tomography (SD-OCT) and to determine whether ONH abnormalities relate to other retinal and clinical abnormalities.

METHODS

Spectral-domain OCT was used to obtain three-dimensional images from 56 PWA and 60 age- and sex-matched control subjects. B-scans were corrected for nystagmus-associated motion artefacts. Disc, cup, and rim ONH dimensions and peripapillary retinal nerve fiber layer (ppRNFL) thickness were calculated using Copernicus and ImageJ software.

RESULTS

Median disc areas were similar in PWA (median = 1.65 mm2) and controls (1.71 mm2, P = 0.128), although discs were significantly elongated horizontally in PWA (P < 0.001). In contrast, median optic cup area in PWA (0.088 mm2) was 23.7% of that in controls (0.373 mm2, P < 0.001), with 39.4% of eyes in PWA not demonstrating a measurable optic cup. This led to significantly smaller cup to disc ratios in PWA (P < 0.001). Median rim volume in PWA (0.273 mm3) was 136.6% of that in controls (0.200 mm3). The ppRNFL was significantly thinner in PWA compared with controls (P < 0.001), especially in the temporal quadrant. In PWA, ppRNFL thickness was correlated to ganglion cell thickness at the central fovea (P = 0.007). Several ONH abnormalities, such as cup to disc ratio, were related to higher refractive errors in PWA.

CONCLUSIONS

In PWA, ocular maldevelopment is not just limited to the retina but also involves the ONH. Reduced ppRNFL thickness is consistent with previous reports of reduced ganglion cell numbers in PWA. The thicker rim volumes may be a result of incomplete maturation of the ONH.

Human parallels to experimental myopia? A literature review on visual deprivation

Raviola and Wiesel's monkey eyelid suture studies of the 1970s laid the cornerstone for the experimental myopia science undertaken since then. The aim has been to clarify the basic humoral and neuronal mechanisms behind induced myopization, its eye tissue transmitters in particular. Besides acquiring new and basic knowledge, the practical object of the research is to reduce the burden of human myopia around the world. Acquisition and cost of optical correction is one issue, but associated morbidity counts more, with its global load of myopia-associated visual loss and blindness. The object of the present PubMed literature-based review is to evaluate apparent similarities between experience from disturbed imaging in experimental laboratory science and varieties within the spectrum of childhood human myopia. So far, the main impression is that macroscopical optical deprivation appears absent in the prevalent types of human myopia, nor is myopia a regular sequel where early eye pathology has led to poor imaging and optical deprivation. Optical aberrations of a higher order are a relatively new issue in myopia research, and microstructural deprivation is only marginally dealt within the survey. Links between experimental and human myopia appear mainly occasional, and with only few examples in humans where factual parallels appear credible. Clinical and epidemiological data on refraction remain important, in particular with a view to life style and environmental factors. Such knowledge may further serve as inspiration to the laboratory research, which aims at solving the basic enigmas on a tissue level.

Ocular Findings in Patients with the Hermansky-Pudlak Syndrome (Types 1 and 3)

PURPOSE

To describe and compare ocular findings in patients with Hermansky-Pudlak syndrome (HPS) type 1 and 3.

METHODS

This is a retrospective case series of 64 patients with HPS from 1999 to 2009 evaluated at an outpatient private ophthalmologic clinic. Patients underwent genetic analysis of selected albinism (Tyrosine and P gene) and HPS genes (HPS-1 and HPS-3) by screening for common mutations and exon sequencing with DNA screening. Descriptive and non-parametric statistical analyses were carried out.

RESULTS

Nearly 70% of the patients were homozygous for common Puerto Rican mutations leading to the HPS1 gene (16-BP DUP, 53.6%), while 30% had the 3904-BP DEL HPS3 gene mutation. Best corrected visual acuity (BCVA) was poorer in patients with type 1 HPS than in patients with type 3 HPS (p < 0.001), esotropia was more common among type 1 HPS patients (p < 0.018), while exotropia was more common among patients with type 3 HPS. Total iris transillumination was more common in patients with type 1 HPS and minimal iris transillumination in patients with type 3 HPS (p < 0.001). The maculae were translucent in patients with type 1 HPS, while patients with type 3 HPS had opaque maculae (p < 0.001).

CONCLUSIONS

Patients with type 1 HPS had poorer BCVA, increased incidence of esotropia, lighter iris and macular appearance. In contrast, patients with type 3 HPS had more exotropia. In addition, to our knowledge this is the largest series type 3 HPS ever reported.

Longitudinal study of spherical refractive error in infantile nystagmus syndrome

PURPOSE

To explore the onset and progression of spherical refractive error in a population with infantile nystagmus syndrome.

METHODS

Retrospective refractive error data were obtained from 147 medical records of children with infantile nystagmus syndrome (albinism n = 98; idiopathic infantile nystagmus n = 49), attending a low vision clinic in Northern Ireland, over a 24 year period (1986-2010). Data were categorised by age to allow for comparisons with published studies. A prospective group of participants with Infantile nystagmus syndrome (INS) [n = 22 (albinism n = 18, idiopathic infantile nystagmus n = 4)] (aged 0-4) were also recruited. Cycloplegic streak retinoscopy was performed biannually, over a 3 year period. Spherical equivalent refractive error and most ametropic meridian were analysed.

RESULTS

The mean spherical equivalent refractive errors for albinism and idiopathic infantile nystagmus groups (across all age categories) were hypermetropic, with highest levels demonstrated by the participants with albinism aged 1 ≤ 4 years (Mann-Whitney U test, p = 0.013). Mean most ametropic meridian was highest in the albinism group aged 1 ≤ 12 years (Mann-Whitney U test, p < 0.05). Individual data demonstrated relatively static spherical equivalent refractive errors over time. Prospective participants were hypermetropic at all visits and those with albinism had, on average, higher refractive errors than those with idiopathic infantile nystagmus (IIN). No significant correlations were noted between visual acuity and spherical equivalent refractive errors or most ametropic meridian.

CONCLUSIONS

Hypermetropia is the most prevalent spherical refractive error in the INS population, irrespective of level of visual acuity. Individuals with infantile nystagmus syndrome fail to demonstrate typical patterns of emmetropisation, particularly in the presence of albinism.

Emmetropisation and the aetiology of refractive errors

The distribution of human refractive errors displays features that are not commonly seen in other biological variables. Compared with the more typical Gaussian distribution, adult refraction within a population typically has a negative skew and increased kurtosis (ie is leptokurtotic). This distribution arises from two apparently conflicting tendencies, first, the existence of a mechanism to control eye growth during infancy so as to bring refraction towards emmetropia/low hyperopia (ie emmetropisation) and second, the tendency of many human populations to develop myopia during later childhood and into adulthood. The distribution of refraction therefore changes significantly with age. Analysis of the processes involved in shaping refractive development allows for the creation of a life course model of refractive development. Monte Carlo simulations based on such a model can recreate the variation of refractive distributions seen from birth to adulthood and the impact of increasing myopia prevalence on refractive error distributions in Asia.

Infantile nystagmus and visual deprivation: foveal instability and refractive development in a low vision register series

PURPOSE

To evaluate whether effects of early foveal motor instability due to infantile nystagmus might compare to those of experimental visual deprivation on refraction in a childhood series.

METHODS

This was a retrospective analysis of data from the Danish Register for Blind and Weaksighted Children with infantile nystagmus recorded as prime diagnosis. We perused 90 records of children now aged 10-17 years, some of whom eventually exceeded the register borderline of 0.3 as best-corrected visual acuity. Spherical equivalent refraction was the primary outcome parameter, but visual acuity, astigmatism, and age were further considered. The series comprised 48 children with nystagmus as single diagnosis, whereas 42 had clinical colabels (Down syndrome [13], dysmaturity [9], and mental retardation, encephalopathy [20]).

RESULTS

Median binocular visual acuity was 0.3 in the full series, and median refraction was emmetropia in all subgroups. Compared with Danish control data, myopia was over-represented, and generally of juvenile onset. The Down syndrome subgroup was separated from the remainder by an even higher myopia prevalence. Astigmatism above 1 D cylinder value was recorded in 52% of all cases.

CONCLUSIONS

The prevalence of myopia and astigmatism was higher among children with nystagmus than in controls. Myopia was mainly juvenile, and not related to the period of infancy when the motor foveal smear is considered most disturbing and possibly influencing visual development.

Onset and progression of with-the-rule astigmatism in children with infantile nystagmus syndrome

PURPOSE

The purpose of this study was to examine the onset and progression of with-the-rule (WTR) astigmatism during the first 8 years of life in children with idiopathic infantile nystagmus syndrome (INS) or INS associated with albinism and to compare their development with that of normal children. Also explored was whether early WTR astigmatism influences emmetropization in children with INS and whether there is evidence of meridional emmetropization.

METHODS

Cycloplegic refractions culled from medical records were converted into power vector components: M (spherical equivalent), J(0) (positive J(0) indicates WTR astigmatism), and J(45) (oblique astigmatism). Two diagnostic groups (idiopathic, n = 106; albinism, n = 95) were evaluated and compared with a reference normal group (n = 495). Four age subgroups were evaluated: age< or =0.5 year, 0.5<age< or =1 year, 1<age< or =4 year, and 4<age< or =8 year; in the normal group, no data were available for 4- to 8-year-olds. In addition, two longitudinal groups of children with INS (idiopathic, n = 22; albinism, n = 27) were studied.

RESULTS

WTR astigmatism was prevalent among children with INS, even during infancy. Both the prevalence and magnitude of WTR astigmatism increased with age in both INS groups. Predicted J(0) from the fitted longitudinal data agreed with cross-sectional data. Moreover, the spherical equivalent of children with INS demonstrated little emmetropization during the first 8 years of life.

CONCLUSIONS

Both the cross-sectional and longitudinal data showed that WTR astigmatism was common among children with INS and increased in magnitude with age during the first 8 years of life. Changes observed in meridional refractive error with age were consistent with meridional emmetropization in children with INS and WTR astigmatism.

A review of astigmatism and its possible genesis

Astigmatism is a refractive condition encountered commonly in clinical practice. This review presents an overview of research that has been carried out examining various aspects of this refractive error. We examine the components of astigmatism and the research into the prevalence and natural course of astigmatic refractive errors throughout life. The prevalence of astigmatism in various ethnic groups and diseases and syndromes is also discussed. We highlight the extensive investigations that have been conducted into the possible aetiology of astigmatism, however, no single model or theory of the development of astigmatism has been proven conclusively. Theories of the development of astigmatism based on genetics, extraocular muscle tension, visual feedback and eyelid pressure are considered. Observations and evidence from the literature supporting and contradicting these hypotheses are presented. Recent advances in technology such as wavefront sensors and videokeratoscopes have led to an increased understanding of ocular astigmatism and with continued improvements in technology, our knowledge of astigmatism and its genesis should continue to grow.

Distance and Near Visual Acuity in Infantile Nystagmus

PURPOSE

Infantile nystagmus (IN) has been reported to decrease with convergence. However, previous studies reported equivocal results regarding a corresponding improvement in acuity with near viewing. The aim of this study was to determine whether visual acuity improves with near viewing in patients with IN.

METHODS

In the first experiment, visual acuities were measured using clinical test charts at standard test distances of 3 or 6 m and 40 cm and using S Charts at 3.75 m and 40 cm. In the second experiment, visual acuities were measured using a Bailey-Lovie chart at distance and a Lighthouse modified ETDRS near card held by each subject at his or her preferred working distance. S-chart acuities were obtained again at 3.75 m and 40 cm for comparison. Horizontal eye movements were recorded using infrared limbal reflection for 20 of the 34 subjects in the first experiment and for all 20 subjects in the second experiment.

RESULTS

The S-chart acuities measured at distance and near were almost all within 0.1 logMAR (logarithm of the minimum angle of resolution) in experiments 1 and 2. Clinically measured acuity averaged nearly one line better at 40 cm than at distance in experiment 1, but the mean difference between near acuity using the ETDRS card and distance acuity using the Bailey-Lovie chart was less than one letter in experiment 2. No consistent relationship existed between the changes in visual acuity with viewing distance and the subject's eye movements.

CONCLUSION

Despite a reduction of nystagmus at near distances in many patients with IN, the visual acuity at near does not improve significantly. These results imply that visual acuity in patients with IN is determined primarily by sensory limitations rather than by the moment-by-moment characteristics of these patients' eye movements.

Visual and perceptual consequences of congenital nystagmus

One way to assess the influence of retinal image motion on visual functioning in congenital nystagmus (CN) is to examine the effects of comparable image motion in observers with normal vision. A second approach is to evaluate visual functioning in subjects with CN when the retinal image motion is reduced. Using these approaches, we determined that spatial contrast sensitivity and visual acuity are not limited by the parameters of retinal image motion in some subjects with CN, but rather by a form of amblyopia. Clinical evidence from patients with bilateral refractive amblyopia suggests that a gradual improvement of visual acuity may be possible in persons with CN, if the optimal refractive correction is worn and parameters of the retinal image motion undergo long-term amelioration.

Infantile nystagmus: current concepts in diagnosis and management

This review examines current approaches to the diagnosis and management of congenital forms of nystagmus. Emphasis is placed on diagnostic features that are amenable to clinical identification but those issues that can be addressed only with more detailed investigations, such as eye movement recording, are indicated. Non-surgical management, including prism spectacles, contact lenses and vision therapy, is discussed, as are surgical approaches. Because many aspects of congenital forms of nystagmus, particularly as experienced by patients with the condition in their normal lives, are poorly addressed in both the clinical and research literature, these limitations are also highlighted.

Changes in astigmatism in children with congenital nystagmus

BACKGROUND

Astigmatism is commonly reported in children with and without nystagmus. In children less than 4 years of age the astigmatism changes from against the rule (ATR) to with the rule (WTR) astigmatism in children without nystagmus. However, little is known about children with congenital nystagmus. We compared astigmatism in children with congenital nystagmus below 4 years and above 4 years of age.

MATERIAL AND METHODS

Three hundred and fifty-six eyes in 178 children who satisfied the study criteria were included. The children were divided into those below 4 years of age (n of eyes = 192) and those above (n of eyes = 164). Cycloplegic refraction (with manual retinoscopy) carried out at presentation and at the last follow-up were recorded and compared. Cycloplegia was achieved using cyclopentolate eye drops. Outcome of eyes with no astigmatism at initial presentation was compared with the final refraction in both the age groups. The visual acuity at the first presentation was compared with the visual acuity at the last presentation.

RESULTS

Average follow-up duration was 3.36+/-1.59 years. On presentation, 176 (49.44%) eyes did not have any astigmatism. We found that 26 (25.2%) out of the 103 children below 4 years of age who did not have any astigmatism on presentation developed WTR astigmatism after a mean follow-up of 3.5+/-1.5 years. (p= 0.042). In children >or=4 years of age only 7 (9.6%) children out of 73 developed WTR after a mean follow-up of 3.4+/-1.4 years. The visual acuity change was not found to be significant in the two groups. The majority (90.3%) improved or had same visual acuity in group A and 88.9% improved or had the same visual acuity in group B at the last follow-up (p= 0.77).

DISCUSSION

Our incidence of WTR astigmatism in children with congenital nystagmus is similar to those previously reported series. Our data suggest that there is a significant chance that children under 4 years with congenital nystagmus may develop WTR astigmatism compared with children above 4 years of age.

CONCLUSION

With the rule (WTR) astigmatism is common in children with nystagmus. Children under 4 years of age presenting with no astigmatism may acquire WTR astigmatism as they grow. The amount of astigmatism increases with age in children with nystagmus. Visual acuity, however, remains stable as the age advances.

Eye movement abnormalities in hermansky-pudlak syndrome

BACKGROUND

Hermansky-Pudlak Syndrome (HPS) is a type of oculocutaneous albinism associated with a bleeding diathesis and pulmonary fibrosis. Although it is known that patients with HPS exhibit nystagmus, the nature of these abnormal eye movements has not been studied.

METHODS

Twenty-seven patients with HPS, diagnosed by platelet morphology and genetic analysis, underwent a systemic evaluation and complete eye examination. Twenty-five had eye movement recordings using magnetic search coil, infrared, or video oculography.

RESULTS

All patients had iris transillumination, foveal hypoplasia, and variable hypopigmentation in skin and eyes. All had bleeding tendencies, and 2 reported excessive bleeding during strabismus surgery. Nine patients had pulmonary fibrosis. Visual acuities ranged from 20/20- to 20/320. Twenty patients had strabismus despite 6 having strabismus surgery previously. Ocular oscillations consistent with congenital nystagmus (CN) were clinically evident in 24 of 27 patients, and half showed periodic alternating nystagmus. In 3 patients without CN, eye movement recordings revealed minimal end-gaze nystagmus, square-wave jerks, drift during fixation and saccades, and low-gain pursuit. These patients had melanin in the posterior pole and better visual acuities than the others (P = 0.002).

CONCLUSIONS

Most patients with HPS have CN, and many have periodic alternating nystagmus. Some have subtle eye movement abnormalities without clinically evident nystagmus, which can obscure the diagnosis, especially if hypopigmentation is mild. Absence of clinical nystagmus in a child with HPS suggests good vision. Patients with albinism, especially before surgery, should be evaluated for HPS to prevent life-threatening complications.

Infantile-onset nystagmus

PURPOSE OF REVIEW

Recent studies on the various forms of infantile-onset nystagmus have advanced our understanding of these disorders. The previously described waveforms of infantile nystagmus syndrome (congenital nystagmus) may be identified in infants less than 7 months of age, including the more mature forms; the visual status of these patients may be directly correlated with their mean foveation times.

RECENT FINDINGS

Refractive errors in patients with infantile nystagmus syndrome do not follow the expected trend toward emmetropization during infancy and early childhood. A study on the torsional component of nystagmus present in most patients with infantile nystagmus syndrome found it to be generated centrally and not by peripheral or mechanical dynamics. Two psychophysical studies on patients with infantile nystagmus syndrome revealed significant differences compared with control subjects. Two different animal models imply that lack of normal visual motion during a critical period of development in infancy leads to infantile nystagmus syndrome. An electron microscopic study of the enthesis site-where the extraocular muscle tendon inserts onto the sclera-in normal individuals versus patients with infantile nystagmus syndrome revealed significant abnormalities in the latter. Significant demographic and socioeconomic differences were reported between patients with infantile nystagmus syndrome and those with spasmus nutans.

SUMMARY

New evidence supports a role for sympathomimetic modulation of infantile nystagmus syndrome. Novel surgical treatments for infantile nystagmus syndrome are also discussed.

Orientation discrimination and variability of torsional eye position in congenital nystagmus

Thresholds for discriminating the orientation of unreferenced horizontal and vertical lines were measured in subjects with congenital nystagmus (CN) and normal observers and compared to the variability of torsional eye position. Orientation thresholds were determined for horizontal and vertical lines between 0.7 degrees and 5.6 degrees in length, that were presented binocularly for 20-1280 ms. The variability of torsional eye position was assessed using the magnetic search coil technique. Orientation thresholds improved with line length and stimulus duration in both groups of observers. Some of the subjects with CN exhibited poorer than normal thresholds, particularly when the length of the line was short. In addition, orientation discrimination in the subjects with CN was consistently anisotropic, with significantly lower thresholds for horizontal than vertical lines. The standard deviations of torsional eye position were larger in the subjects with CN than in normal observers. However, orientation thresholds were poorer than expected from the variability of torsional eye position in normal observers, and better than expected on the basis of torsional variability in some of the subjects with CN. These results imply that torsional variability does not limit normal orientation thresholds and that torsional eye movements in CN are compensated partially by extraretinal signals.