Straatsma syndrome

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Straatsma syndrome

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Disease Entity

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Disease

Straatsma syndrome is a rare disease entity consisting of the traditional triad of unilateral myelinated retinal nerve fibers, myopia, and amblyopia.[1] Variations of the triad include a “reverse Straatsma syndrome ”, in which patients exhibit hyperopia instead of myopia.[1] Even though nystagmus and strabismus have not been prominently associated with Stratsma syndrome, either may be present as complimentary findings without precluding one from the diagnosis. [1] Even though Straatsma syndrome has traditionally been considered a unilateral disorder, a small number of clinical cases with bilateral Straatsma syndrome[2] and a case of bilateral reverse Straatsma syndrome have been reported.[3]

Etiology

Myelination of retinal nerve fibres (MRNF) is rare, with an estimated occurrence of approximately 0.54% in all eyes, with bilateral involvement in only 7,7% of cases and with no gender predominance[4]. MRNF can be associated with multiple clinical pathology, such as myopia, amblyopia, and strabismus, as well as other systemic conditions, however, the majority of patients with incidental stagnant findings of MRNF remaining asymptomatic, an only a few cases have reported progression of the disease in childhood and adolescence. The pathogenesis of this condition is not fully understood: myelination starts at the 5th month of pregnancy, and it is complete 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 possible scenarios have been suggested in literature, such as migration of heteropic cells to the retina during in intrauterine development, but there is no consensus until today.[1]

however, it is believed to involve the actions of oligodendrocytes in the human central nervous system, which are responsible for the myelination of nerve fibres.7 Myelination of the visual pathway commences at the fifth month of gestation until just after birth, where it comes to a halt at the lamina cribrosa (LC), which behaves as a barrier to oligodendrocytic myelination of retinal nerve fibres.8,  9,  10 Thus, MRNF is believed to occur due to a compromise of the LC barrier and the subsequent myelination of retinal nerve fibres by oligodendrocyte-like cells.11 Furthermore, progression of the condition is believed to be extremely rare. Reported sources of LC disruption include optic nerve gliomas or optic nerve sheath fenestrations.12,  13

However, the association between the progression of MRNF and optic nerve head drusen has previously been reported by Jean-Louis et al.1 They described bilateral optic nerve head drusen, with one demonstrating an “acquisition” of MRNF and the other demonstrating “progression” of MRNF in an adolescent 14-year-old male, although this was believed to be fortuitous. In contrast to our case, the progression of the MRNF was associated with optic nerve head drusen; this was unilateral and progressed beyond adolescence into adulthood.

History

Straatsma et al1 first described Straatsma syndrome in 1979 in a case series of 4 patients exhibiting unilateral myelinated retinal nerve fibers in association with myopia, amblyopia, and strabismus.

Risk Factors

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General Pathology

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Pathophysiology

There has also been speculation regarding what role each component within the Straatsma syndrome triad has in the development of the syndrome, particularly in myopia and myelination.7 A common theory claims that myelination induces myopia by blurring retinal images and causing visual deprivation. This deficit ultimately contributes to myopia by inducing axial enlargement. Another theory is myopia induces myelination by delaying lamina cribrosa development, which serves as a critical stopping point for myelination during intrauterine life, and if not fully mature at a given time, myelination could theoretically proceed through the lamina cribrosa and infiltrate the nerve fiber layer. Sensory deprivation could then lead to amblyopia and strabismus. However, the existence of reverse Straatsma syndrome (hyperopia with amblyopia and myelinated nerve fibers) weakens both hypotheses and suggests that the etiological relationship between aberrant myelination and myopia may not be as strongly associated with each other.2 Although current literature shows myelinated nerve fibers occurring more frequently in myopes than hyperopes, the precise relationship between the two still needs further exploration.1–7

In summary, although nystagmus has not prominently been associated with Straatsma syndrome, it

should be considered as a complementary finding in

the setting of bilateral myelination.

Primary prevention

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Diagnosis

Despite some controversy in its diagnostic features, it should be included in the differential diagnosis of leukocoria and must be suspected in the presence of refractive errors with anisometropia[5]

History

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Physical examination

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Signs

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Symptoms

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Clinical diagnosis

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Diagnostic procedures

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Laboratory test

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Differential diagnosis

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Management

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General treatment

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Medical therapy

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Medical follow up

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Surgery

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Surgical follow up

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Complications

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Prognosis

Visual prognosis of amblyopia associated with myelination of retinal nerve fibres and anisometropia is poorer than anisometropic amblyopia without myelination. It is well known that the former is refractory to occlusive therapy. Despite having a poor prognosis, visual rehabilitation should be attempted

Additional Resources

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References

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  1. 1.0 1.1 1.2 1.3 Juhn, A. T., Houston, S. K., & Mehta, S. (2015). BILATERAL STRAATSMA SYNDROME WITH NYSTAGMUS. Retinal Cases & Brief Reports, 9(3), 198–200. doi:10.1097/icb.0000000000000137 
  2. Shenoy R, Bialasiewicz AA, Al Barwani B. Bilateral hypermetropia, myelinated retinal nerve fibers, and amblyopia. Middle East Afr J Ophthalmol 2011;18:65–66
  3. Levy NS, Ernest JT. Retinal medullated nerve fibers. Arch Ophthalmol 1974;91:330–331
  4. Duru I, Savides RP. Unilateral progressive myelinated retinal nerve fibres in an asymptomatic adult with optic nerve head drusen. Can J Ophthalmol. 2018 Aug;53(4):e136-e138. doi: 10.1016/j.jcjo.2017.10.023. Epub 2017 Dec 16. PMID: 30119805.
  5. Quezada-Del Cid NC, Zimmermann-Paiz MA, Ordoñez-Rivas AM, Burgos-Elías VY, Marroquin-Sarti MJ. Straatsma syndrome: Satisfactory amblyopia treatment. Report of two cases. Arch Soc Esp Oftalmol. 2018 Jun;93(6):300-302. English, Spanish. doi: 10.1016/j.oftal.2017.12.010. Epub 2018 Feb 15. PMID: 29398227.