Refractive State and Macular Abnormalities at Oct in Albino at Chu Iota ()
1. Introduction
A rare genetic disease, albinism is characterized globally by specific deficits of the visual system associated with a variable hypopigmentation phenotype depending on the disruption of melanin production [1] . It is linked to a hereditary defect in the biosynthesis of melanin. Disease results in a generalized decrease in the pigmentation of the appendages, skin and eyes [2] . Despite the fairly advanced knowledge of the genetics of albinism, approximately 20% of affected patients currently remain without a genetic diagnosis [3] . Poor visual acuity is one of the main signs of albinism. This visual impairment is more often moderate but can be profound [4] . Ametropia, nystagmus, strabismus, photophobia and macular abnormalities including foveolar hypoplasia are the cause of visual difficulties variously associated with albinism and produce varied clinical pictures [5] . It is not specific during photophobia and oculomotor signs [6] . There are several forms of albinism including oculocutaneous albinism classified into four main forms, three minor forms and one form of ocular albinism [1] [7] . And the prevalence of all forms of albinism varies widely around the world and has been estimated at around 1/17,000 [1] . It would be the cause of 5% to 10% of visual impairment in the world [8] . Very few studies have been conducted, hence the interest of our work at the CHU-IOTA in order to determine the various refractive anomalies and OCT data in macular anomalies in albinos.
2. Patients and Method
We conducted a prospective study between July 1, 2020, and September 30, 2021, i.e. a period of 15 months. The study included any subject over 10 years old with oculocutaneous or ocular albinism who consented to participate in the study.
The subjects were contacted by telephone and invited to the CHU IOTA, they had explanations of the objectives of the study and the procedure of the examination.
All subjects underwent an ophthalmological examination including measurement of visual acuity, objective refraction, biomicroscopic examination of the anterior segment, fund us examination and macular OCT.
Classification of albinism was based on hair color at birth and after birth, skin color and iris color [4] and The grade of foveolar hypoplasia was defined by the classification of Thomas et al. in 4 grades: absence of extrusion of the plexiform layers (grade 1), absence of a foveolar depression (grade 2), widening of the outer nuclear layer (grade 3), elongation of the outer segments (grade 4). [9] .
The data studied were age, sex, type of oculocutaneous albinism, VA before correction, VA after correction, refractive values, macular thickness, and macular anomalies. The data was collected through a survey form and a medical file developed for this purpose. Data collection and analysis were done using IBM SPSS 20.0 software. Word processing and tables were carried out by Microsoft Office software version 2016.
3. Results
Over the period, 105 cases of oculocutaneous albinism were collected out of a total of 42,024 consultations, i.e. a frequency of 0.2%. There was a male predominance in the study population with an M/F sex ratio equal to 1.6. The 21 - 40 age group was the most represented at 49.2% (Table 1). Consanguinity was noted in 99.05% of cases and 89.52% of patients had family members with albinism (Table 2). The most represented VA without correction was between 1/10-3/10 in both eyes, i.e. 46.6% on the right and 50.5% of cases on the left (Table 3). The most found VA with correction was also between 1/10-3/10, i.e. respectively 59.05% in the right eye and 57.14% in the left eye (Table 3). We recorded 13.33% and 11.43% of functional amblyopia on the right and left respectively (Table 3).
4. Discussion
In albinism, all ametropias can be found. The optical correction of these refractive errors is the initial management of albino patients, it can be done by optical glasses or by contact lenses at best [10] [11] . This optical correction must be early from a young age with an annual reassessment [7] . During our study we also found all forms of ametropia with a predominance of astigmatism at 50.48%, the mean was −3.50 D; followed by myopia which represented 29.52% with an average of −8 D; farsightedness accounted for 20% with an average of +3.50 D. All our patients received optical correction and the majorities were already wearing glasses. Astigmatism is usually the most common and is often
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Table 1. Distribution of patients by history.
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Table 2. Distribution of patients according to distance VA ODG without correction.
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Table 3. Distribution of patients by distance VA ODG WITH correction.
associated with hypermetropia hyperopia or myopia [11] . S. Gargouri et al. found 59% farsightedness, 41% myopia and 100% astigmatism with also 100% consanguinity [11] . The most common universal condition of hereditary generalized hypopigmentation, oculocutaneous albinism type 2 is the most common form in the world as well as in black Africa [1] . It represented more than half of the cases in the study, i.e. 51.45%. Protection against light is essential for albinos, especially in sunny countries. It reduces associated symptoms including glare, photophobia and nystagmus due to excessive stimulation of the hypopigmented retina by light and therefore improves vision [5] . Visual improvement is significant in myopes, especially at low diopters but this is variable [10] . We then obtained 87.15% visual improvement and 23.1% functional amblyopia.
These cases of amblyopia could be explained by the delay in the initial management, in particular of photophobia, nystagmus and high myopia by optical correction [12] . Most of the improvements were achieved in myopic patients between −2.50 and −8.50 D. In Schulza S the greatest improvement was achieved in myopic patients between −1 and −7.50 D [10] . Foveolar hypoplasia is the most common macular involvement in oculocutaneous albinism, even if it is not pathognomonic. It is visible on fundus examination and easily found on OCT examination [9] . Macular optical coherence tomography (OCT) was performed in all our patients. Grade 2 hypoplasia was the most frequent macular anomaly with 41.42 on the right and 50.6% on the left, followed by grade 4 with 31.61 on the right and 34.5% on the left, followed respectively by widening of the outer nuclear layer (grade 3) with 31.61% on the right and 34.5% on the left, elongation of the outer segments (grade 4) on the right 14.17% and 23% on the left and absence of extrusion of the plexiform layers (grade I) on the right 6.54% and on the left 6.9%. We also noted less than 5% of cases of retinoschisis and more than 6% of pachychoroid, and the macula was normal in 14.17% on the right and 5.75% on the left.
Grade 2 hypoplasia, a rare complication of high myopia, corresponds to a convex protrusion of the macula within a myopic staphyloma facing an area of scleral thickening [13] . Given the high frequency of myopia in our study, this could be the case with our patients.
5. Conclusion
A rare and universal genetic disease, albinism is accompanied by ametropia, nystagmus, strabismus, photophobia and macular abnormalities including foveolar hypoplasia. Hence, the visual impairments are in cases of oculocutaneous albinism. Their detections are based on refraction and macular OCT. Early management of these fraction defects through optical correction is necessary to avoid functional amblyopia.