Straatsma syndrome Síndrome de Straatsma

The presence of retinal myelinated nerve fibers is not a rare finding during routine examinations, and it is usually a benign and isolated finding. However, in some rare cases, it can be associated with other ophthalmological conditions. We describe a case of a patient with the triad myelin nerve fibers, myopia and ambliopia, which configures the Straatsma Syndrome.


F
irst described by Virchow in 1856, (1) myelinated nerve fiber appears at fundoscopy as white striated opacities, following the distribution of retinal nerve fibers. They are usually benign (2) and diagnosis is usually made by chance. In some cases it can be associated with other conditions, such as neurofibromatosis and vitreoretinal disorders. (3) Patients are usually asymptomatic, but a few cases can present significant visual abnormalities, in special axial myopia and amblyopia, configuring the Straatsma Syndrome. We report a case of a 60 years old female patient with this rare syndrome.
cAse RepoRt 60 years old female patient, attended at our Ophthalmology ambulatory referred by her endocrinologist for fundoscopy for diabetic retinopathy screening. Patient referred low visual acuity on her left eye (OS) since her childhood, and denied any other complaints. She had well controlled type 2 diabetes for 12 years, high blood pressure for 49 years and history of a treated breast cancer 10 years before.
On exam: best corrected visual acuity (BCVA) of 20/20 in her right eye (OR) (+0.75 = -1.25 x 95º) and 20/60 in her left eye (OS) (-6.00 = -1.75 x 40º). Biomicroscopy showed nuclear cataract (1/4+) in both eyes. At fundoscopy: OR was normal and OS showed white striated opacities emerging from the optic disk, following the distribution of retinal nerve fibers ( Figure 1). Fundus autofluorescence showed hyperautofluorescence ( Figure 2). The axial length of her eyes was 22,39mm in OR and 26,48mm in OS. OCT (optical coherence tomography) showed presence of myelin at the same topography in OS.

dIscussIon
Straatsma estimates that only 0,54% of the eyes have some sort of myelin fibers, with bilateral involvement in just 7,7% of cases (4) and with no gender predominance. The pathogenesis of this condition isn't fully well known: myelination starts at the 5th month of pregnancy, and it is over before birth. The lamina cribosa acts as a barrier for the myelination. Parulekar (5) believes that the presence of myelin in some eyes occurs as a result of a disruption of this lamina. Other possibilities were suggested in literature, such as heteropic cells migrating to retina during in utero development, (6) but there is no consensus until today.
Usually this condition is asymptomatic, and it is discovered during routine examinations. Howbeit, in some cases, it can be associated with other conditions, such as retinal telangiectasia, neurofibromatosis, Down syndrome, vitreoretinal degenerations, familiar myelinated retinal fibers, Straatsma syndrome, coloboma, keratoconus, craniosynostosis, hydrocephalus, Gorlin syndrome, and others. Myelin fibers are more frequent in the superior temporal quadrant, followed by the inferior temporal quadrant. It is typically stationary, but regression was previously reported in the literature: after Leber neuropathy, arterial occlusions, radiotherapy, and others. (3,7,8,9) Straatsma Syndrome was described initially in 1979, and it is responsible for only 0.3-10% of all cases of eyes with myelin fibers. It is characterized by the association of myelin fibers, axial myopia and amblyopia. Some authors also describe the association of strabismus with this syndrome, which is not a sine qua non condition for this syndrome.
The mechanism for development of myopia in these cases is also obscure. Some theories were previously suggested: Moradian believes that an eye with a largest axial length would present a slowly development of the lamina cribosa, which could generate an anomalous functional barrier, allowing a transitory myelination. (3) On the other side, Straatsma suggests that the presence of myelin fibers in a crucial phase on ocular development would interfere in image acquisition, generating a visual privation, and consequently an increase in axial length. (4) Amblyopia can occur for 3 main reasons: a Structural defect, in which the presence of myelin would change the normal light transmission, and also the conduction of the luminous stimulus; (3) a Refractive defect, in which anisometropia as a result of the unilateral presence of myelin fibers would be responsible for amblyopia; and last, but not least a Strabismus component could also be responsible for amblyopia. Because of this multifactorial etiology, occlusion and other common therapies do not have satisfactory results in these cases. (3) The treatment for this syndrome is usually made by the use of glasses or contact lenses, as well as occlusion for the amblyopia, if is the case. However, even with the correct treatment, only one third of patients will have a final visual acuity better than 20/30. (10) conclusIon Although Ophthalmologists are familiar with of the presence of myelin fibers, a benign and innocuous condition, which is usually detected incidentally during ocular examination, it is important to also know about ocular associations and differential diagnosis of this condition, such as Straatsma Syndrome.