Albino Subjects Research Articles

Corrélation entre la réfraction et la longueur axiale du sujet Albinos

To investigate the relationship between refraction and ocular axial length in albinos. A cross-sectional, analytical study was carried out from June to November 2021 at the Central Hospital of Yaounde (Cameroon), which included consenting albino subjects aged over 15years. All subjects underwent visual acuity testing, axial length measurements and objective refraction under cycloplegia. We included 51 albino subjects. The mean age was 26.06±9.47years, and the sex ratio was 0.5. Type 2 oculocutaneous albinism (OCA2) was predominant, representing 82.4% of cases. The mean uncorrected visual acuity was 0.93±0.25 logMAR, and the most common ametropia was myopic astigmatism (52.9%). The mean axial length was 24.65±2.54mm with extremes of 21.54 and 30.33mm. Eyes with myopia and myopic astigmatism had significantly longer axial lengths than those with hyperopic and mixed astigmatism. A strong, significant negative correlation (r=-0.93; P˂0.001) between the spherical component of the refraction and axial length was found. The spherical component of the refraction decreases significantly with increasing axial length in albinos.

Refractive errors, visual impairment, and the use of low-vision devices in albinism in Malawi.

This study focuses on the refractive implications of albinism in Malawi, which is mostly associated with the burden of visual impairment. The main goal was to describe the refractive errors and to analyze whether patients with albinism in Malawi, Sub-Saharan Africa, benefit from refraction. Age, sex, refractive data, uncorrected and best-corrected visual acuity (UCVA, BCVA), colour vision, contrast sensitivity, and the prescription of sunglasses and low vision devices were collected for a group of 120 albino individuals with oculocutaneous albinism (OCA). Refractive errors were evaluated objectively and subjectively by retinoscopy, and followed by cycloplegic refraction to reconfirm the results. Best-corrected visual acuity (BCVA) was also assessed binocularly. One hundred and twenty albino subjects were examined, ranging in age from 4 to 25 years (median 12 years), 71 (59 %) boys and 49 (41 %) girls. All exhibited horizontal pendular nystagmus. Mean visual acuity improved from 0.98 (0.33) logMAR to 0.77 (0.15) logMAR after refraction (p < 0.001). The best improvement of VA was achieved in patients with mild to moderate myopia. Patients with albinism who were hyperopic more than +1.5 D hardly improved from refraction. With the rule (WTR) astigmatism was more present (37.5 %) than against the rule (ATR) astigmatism (3.8 %). Patients with astigmatism less than 1.5 D improved in 15/32 of cases (47 %) by 2 lines or more. Patients with astigmatism equal to or more than 1.5 D in any axis improved in 26/54 of cases (48 %) by 2 lines or more. Refraction improves visual acuity of children with oculocutaneous albinism in a Sub-Saharan African population in Malawi. The mean improvement was 2 logMAR units.

A comparison of clinical and eye movement characteristics between albinism and idiopathic infantile nystagmus with and without mutations in the FRMD7 gene

Abstract Purpose Nystagmus consists of involuntary to and fro oscillations of the eyes. The differences between nystagmus associated with albinism and idiopathic infantile nystagmus (IIN) are unclear. Recently mutations in a novel gene called FRMD7 have been found to underlie a significant proportion of X‐linked IIN. Phenotypic variations in eye movements between FRMD7 and non‐FRMD7 types have also been recently described. We have compared clinical and eye movement characteristics between albinism and IIN with and without mutations in the FMRD7 gene. Methods Clinical features and eye movement were recorded from 37 albino subjects, 83 subjects with the FRMD7 mutation and 45 subjects without the FRMD7 mutation. Results Mean visual acuity was significantly worse in albinos compared to IIN patients (p&lt;&lt;0.0001). Although there was no significant differences between the groups (p&gt;0.05) for nystagmus amplitude or foveation, the frequency of nystagmus was significantly slower in albinism (p&lt;&lt;0.0001). In addition, nystagmus associated with albinism was significantly more likely to be jerk nystagmus rather than pendular nystagmus compared to FRMD7 group (p&lt;&lt;0.0001). The most common waveform associated with albinism was pure jerk nystagmus, whereas non‐FRMD7 was more likely to be associated with jerk with extended foveation. Conclusion Contrary to available literature, nystagmus associated with albinism shows distinct differences to IIN both with and without FRMD7 mutations. This suggests the possibility of different underlying mechanisms to albinism and IIN in generating eye oscillations although these are yet to be elucidated

Monte Carlo model for studying the effects of melanin concentrations on retina light absorption

We developed a Monte Carlo model to calculate light absorption in human and mouse retinas. The retina was modeled as a five-layer spherical structure. The effects of melanin concentrations in the retinal pigment epithelium (RPE) and choroid layer were studied. Variations of blood content in choroid were also considered in the simulation. Our simulation results indicated that light absorption in neural retina was at least 20% higher in albino subjects than in pigmented subjects under both photobleaching and dark-adapted conditions. It can be four times higher at optical wavelengths corresponding to minimal hemoglobin absorption. The elevated absorption at neural retina was attributed to the light backscattered from the choroid and sclera layers. This simulation model may provide useful information in studying light-induced retina damage.

Stereopsis in patients with albinism: Clinical correlates

Purpose: A hallmark of albinism is excessive decussation of retinostriate projections at the optic chiasm. This misprojection might lead to abnormalities in the retinal correspondence and may account for the usual absence of stereovision. We report on 2 groups of patients with albinism who have either fine or gross stereopsis and compare the clinical findings of these groups to other patients with albinism with similar visual acuities but no stereopsis. Methods: A retrospective chart review of patients with albinism was used to segregate those with a letter visual acuity of 20/100 or better in one eye, assessment of stereopsis, and strabismus • 10 PD. Forty-five patients were identified. Albinism type, best-corrected visual acuity, motility, Titmus vectograph stereoacuity, iris and macula transparency grades, and the presence or absence of both melanin and an annular reflex in the macula were tabulated. A comparison of the clinical characteristics of the groups with and without stereopsis was made. Results: Those albino subjects who demonstrated stereopsis had better visual acuity, less iris transillumination, more frequent presence of melanin in the macula, less nystagmus, and less marked foveal hypoplasia than the albino subjects without stereopsis. No nystagmus was clinically detected in 5 patients with fine stereopsis. All these differences were statistically significant. Macular transparency grade was not significantly different between the groups. Conclusions: Patients with albinism who demonstrate stereopsis tend to have better visual acuity, more iris pigment, and more melanin pigment in the macula than their counterparts without stereopsis. (J AAPOS 2001;5:98-104)

Metastatic melanoma of the nasal cavity in a patient with oculocutaneous albinism

The nasal cavity is a rare location for primary malignant melanoma, borne out by the few cases reported in the literature since 1940. Rarest of all is nasal melanoma in a patient with oculocutaneous albinism. An albino subject, aged 33, was referred to us with this diagnosis. Because of the numerous metastases in the liver and left lung, we did not advise radical surgical intervention and, despite hyperfractionated high dose radiotherapy and chemo-immunotherapy, the advanced stage of disease caused the death of the patient within a year. We have reviewed the diagnostic, clinical and therapeutic aspects, and the literature on melanomas of the nasal cavity in albino subjects. We performed a Medline literature search, examining only ‘extensive’ papers and excluding abstracts or case reports presenting poor data.

Assessment and educational implications of albinism

Forty-seven visually impaired albino schoolchildren were identified from the Victorian school population. 28 (aged 7-18) who had had a standard ophthalmic examination including the LH5 Visual Acuity Test for Contrast Sensitivity agreed to try a battery of educational tests in addition. The tests were the Non-Verbal Ability Test, Visual Motor Integration Test, Torch Reading, reading miscue analysis and reading of test to measure sustained near visual acuity. The most useful of these was the Non-Verbal Ability Test (NAT) which indicated that this group of albinos was of above average cognitive ability. This was independent of the findings on ophthalmic examination. The NAT is also useful in identifying relative strengths and weaknesses in information processing abilities in albino subjects.

Red or rufous albinism in Southern Africa

Red or rufous albinism is a rare type of oculocutaneous albinism described, but not as yet fully investigated, in Africa and New Guinea. Twelve rufous albino subjects from 10 families participated in this preliminary study. The prevalence of rufous albinism was found to be approximately one in 8,580 among school children in the negroid population. The combination of the unusual red skin colour, ginger to reddish hair colour, low susceptibility to sun damage, and minimal visual problems, in affected individuals, suggested that they form a group which is distinct from the brown and other types of albinism. The mode of inheritance was found to be recessive. Tyrosinase assays showed that rufous albinos are tyrosinase positive and on electron microscopy studies normal melanosomes and melanocytes were observed in hair bulbs and skin. Visual evoked potential testing did not show the gross decussation abnormalities of the optic pathway detected in other types of albinism. Rufous albinism might be at one end of the spectrum of types of oculocutaneous albinism and, because affected people have such mild symptoms, their inclusion in this group might be debatable.

Skin color, aging, and plasma l-dopa levels

Although plasma levels of l-dopa are derived substantially from catecholamine-synthesizing tissues, melanocytes—which produce l-dopa as part of the melanin synthetic cascade—also may be a source of circulating l-dopa. We compared plasma l-dopa levels in albino subjects and in Caucasian and Black normal volunteers and patients with essential hypertension. DOPA levels were similar among the subject groups. Among Caucasian normal volunteers, l-dopa levels were negatively correlated with subject age ( r = -0.30, P < 0.05), whereas norepinephrine levels tended to increase with subject age ( r = 0.25, 0.05 < P < 0.10), so that the l-dopa: norepinephrine ratio was highly negatively correlated with subject age ( r = -0.50, P < 0.01). Skin pigmentation does not contribute importantly to plasma l-dopa levels in humans. In contrast with levels of norepinephrine, l-dopa levels appear to decrease during normal aging.

Psychological aspects of albinism: An exploratory study with Nigerian (IGBO) albino subjects

This paper reviews some studies done on the psychological aspects of albinism. Studies on the intellectual ability of albinos produce equivocal results. Results from personality studies seem more consistent and show albinos to be more emotionally unstable than non-albinos. This paper also reports a study by the author which examines the phenomenon of albinism from the albino's viewpoint. It examined the responses of three undergraduate albino subjects—one female and two males—to the author's request for each to write an essay on ‘the merits and demerits of being an albino based on personal experiences’. All consider being an albino to be more of a demerit than a merit. The demerits include conspicuous colour, delicate skin which blisters under the sun, defective sight, interpersonal, especially heterosexual, problems and society's unkind attitude. The paper ends with a discussion of possible future research in the area and a recommendation of the need for psychological rehabilitation as part of the management programme for albinos.

Human albinos can discriminate spatial frequency and phase as accurately as normal subjects

Previous experiments testing grating and vernier acuities in albino central vision are consistent with the hypothesis that the deficit in their monocular spatial processing is mainly due to the increased spacing of their foveal cones. This was tested by measuring albino spatial frequency discrimination over the range 0.25–4.0 cpd. The same experiments were performed on three normal subjects both in the fovea and at a peripheral locus at which their grating acuity was identical to that of the albino subjects. Spatial frequency discrimination thresholds averaged 3.71% for albinos, 5.18% for the normal fovea, and 8.81% for the normal periphery, the latter being over 2.3 times greater than albino thresholds. A comparable pattern of results was observed in phase discrimination experiments. These data reject the possibility that albino central vision is similar to normal peripheral vision, but the results are predictable on the hypothesis that the central retina of albinos is a spatially magnified (underdeveloped) version of the normal fovea.

Albino spatial vision as an instance of arrested visual development

Adult albinos and human infants share a number of common visual characteristics: both have low grating acuity, both lack a foveal pit (foveal hypoplasia), and both have much lower central cone densities than in the normal adult. We have explored the consequences of these characteristics by measuring both spatial and temporal contrast sensitivity in the central retina and by comparing central and peripheral grating and vernier acuities in two young adult albino subjects. To compensate for nystagmus, horizontally oriented patterns were employed. Both subjects had normal flicker sensitivities, but their central grating and vernier acuities were approximately five times worse than normal. At 10.0° in the inferior visual field, however, vernier and grating acuities were normal for both subjects. Finally, the ratio of grating to vernier acuity in albino central vision fell within the normal foveal range, suggesting that albino central vision does not resemble the adult periphery. These results are consistent with the hypothesis that spatial processing deficiencies in albino central vision are a direct consequence of the increased spacing of their central cones. Our data are comparable to available psychophysical results obtained from infants of approx. 10 months of age, thus suggesting that the albino visual system may represent a case of arrested development.

Lateral dominance and visual evoked potentials in albinos.

Lateral preferences for the use of eye, hand, and foot were assessed in 17 male and female albino subjects, aged 15 to 52 yr. Visual evoked potential (VEP) recordings suggested that optic fibres were abnormally decussated in these subjects, as others have shown. Fewer albino subjects showed the lateral preference for the use of hand/eye and foot/eye similar to that of normals. It is postulated that the abnormal decussation of optic fibres may underlie the reduced preference for the use of the same hand and eye, and foot and eye, in albinos.

Color vision in albino subjects.

Color vision testing was performed on a group of ten black tyrosinase-positive albino patients and a group of normal subjects. Testing was accomplished by means of a Farnsworth-Munsell (F-M) 100-hue test and Nagel anomaloscope. As a group, the albino patients showed an increase in number of errors scored on the FM-100 hue test, without any specific axis in the majority of cases. Results on the Nagel anomaloscope showed a 'widening' into the red end of the Rayleigh equation. A possible explanation for this apparent widening is discussed, which emphasizes anticipated results of matching ranges obtained on extrafoveal cones.

Abnormal visual pathways in human albinos studied with visually evoked potentials

Numerous investigations in albino mammals using neurophysiological and neuroanatomical techniques report an abnormal crossing projection from the temporal retina. Recent studies in human albinos suggest a similar defect. Averaged visually evoked potentials to flashed checkerboard patterns were recorded bilaterally from the scalp overlying the occipital regions in normal and albino human subjects. Square stimulus patterns (10°) were presented to the nasal-temporal retina and hemipatterns to the nasal or temporal retina of each eye. Observations of visual fields, monocular acuities, and stereopsis were recorded. Normal left and right hemispheric responses were symmetrical to monocular nasal-temporal stimulation; in albinos the contralateral early latency responses were larger than the ipsilateral. In monocular nasal stimulation in albinos and in normals, the amplitude of contralateral evoked responses was larger than the ipsilateral; in normals the largest responses to temporal stimulation were ipsilateral. By contrast, temporal retina stimulation of albinos usually produced larger early latency components contralaterally. Temporal stimulation at 5° from the vertical meridian in albinos produced larger contralateral responses. Stimulation beyond 15° gave smaller components contralaterally; new larger amplitude components appeared ipsilaterally. At 30 and 45° eccentricity, ipsilateral responses were reduced. Albino subjects had normal monocular visual fields but failed to fuse stimuli from random dot stereograms. Results of this study provide further evidence for abnormal visual pathways and functional anomalies in human albinos.

Sex, strain, and housing: Variables influencing the effects of prior shock exposure on shock-induced aggression

A series of experiments was conducted to investigate sex, housing conditions, and strain as possible factors influencing the interference effect of prior exposure to shock on shock-induced aggression. In albino subjects, female rats and rats housed in community cages evidenced the greatest suppression in aggression following prior exposure to shock. In addition, ten sessions of prior exposure to shock produced a greater suppression in shock-induced fighting than 20 sessions of prior exposure to shock. The prior shock effect was not obtained with hooded subjects. Responsivity to shock was also investigated to determine whether the prior exposure to shock attenuation of shock-induced fighting was a consequence of reduced activity in response to shock. Responsivity to shock measured with an isometric platform accounted for less than 4% of the variance in shock-induced fighting in the single experiment that obtained a correlation between responsivity and shock-induced aggression.