poor visual acuity

Optic Nerve Hypoplasia, Bilateral

Clinical Characteristics
Ocular Features: 

The hallmark of this syndrome is bilateral optic nerve dysplasia including aplasia and hypoplasia. It may occur in isolation or as part of other syndromes, especially in those having abnormalities of the central nervous system.  All components of the nerve head are abnormally small including the entire disc area, the cup, and the neuroretinal rim. It has been reported that retinal vein tortuosity is predictive of patients with endocrinopathies.  Retinal arteries often appear straight and narrow but this may not be seen in all cases.  Visual acuity ranges from 20/50 to NLP but usually 20/200 or better.  Many patients have nystagmus and strabismus.

This disorder shares many characteristics with septooptic dysplasia (182230) but the optic nerve anomalies are usually unilateral in the latter disorder and the disc rim often has a double margin.  Mutations in different genes are responsible for the two disorders. 

Systemic Features: 

Pituitary dysfunction and endocrinopathy may lead to life-threatening illness caused by adrenal crisis or hypoglycemia.  An absent or abnormal septum pellucidum is present in 49% of patients and 64% have a hypothalamic-pituitary axis abnormality.  Among those with an abnormal septum pellucidum, 56% have some kind of endocrinopathy. Other midline brain defects and cerebral anomalies have also been reported.

 

Genetics

Bilateral optic nerve hypoplasia is inherited in an autosomal dominant pattern based on the few families reported.  Mutations in the PAX6 (11q13) gene are responsible.

A somewhat similar disease with extensive CNS and endocrinological abnormalities is septooptic dysplasia (182230) caused by mutations in the HESX1 gene. 

Pedigree: 
Autosomal dominant
Treatment
Treatment Options: 

There is no treatment for the optic nerve hypoplasia but individuals need to be monitored for endocrinopathy and treated appropriately.  Low vision aids and sometimes mobility training can be helpful for some patients. 

References
Article Title: 

Endocrine status in patients with optic nerve hypoplasia: relationship to midline central nervous system abnormalities and appearance of the hypothalamic-pituitary axis on magnetic resonance imaging

Birkebaek NH, Patel L, Wright NB, Grigg JR, Sinha S, Hall CM, Price DA, Lloyd IC, Clayton PE. Endocrine status in patients with optic nerve hypoplasia: relationship to midline central nervous system abnormalities and appearance of the hypothalamic-pituitary axis on magnetic resonance imaging. J Clin Endocrinol Metab. 2003 Nov;88(11):5281-6.

PubMed ID: 
14602752

Colorblindness-Achromatopsia 5

Clinical Characteristics
Ocular Features: 

Poor visual acuity and congenital nystagmus are characteristic of ACHM5 and may be seen in infancy.  Vision loss can be progressive for those who have a milder form of colorblindness or incomplete achromatopsia.  Such patients have a somewhat later onset and may not have nystagmus or photophobia.  Cone responses are usually absent in the ERG whereas rod responses are often normal.  However, in the incomplete form there may be reduced but measureable cone responses.  There may be some reduction in rod responses with disease progression.  Myopia has been found in some patients.  Atrophy of the RPE in the posterior pole characteristic of progressive cone dystrophies may be seen. 

Systemic Features: 

No systemic abnormalities are found in this disorder. 

Genetics

This is an autosomal recessive disorder resulting from mutations in the PDE6C gene located at 10q24.  This condition is sometimes called cone dystrophy 4.

Other forms of achromatopsia are ACHM3 caused by mutations in CNGB3 (262300), ACHM2 caused by mutations in CNGA3 (216900), and ACHM4 by mutations in GNAT2 (139340).

 

Pedigree: 
Autosomal recessive
Treatment
Treatment Options: 

There is no treatment for the cone dystrophy but dark glasses and red colored contact lenses are helpful in reducing the photophobia and can improve acuity to some extent.  Low vision aids can also be helpful. 

References
Article Title: 

A Nonsense Mutation in PDE6H Causes Autosomal-Recessive Incomplete Achromatopsia

Kohl S, Coppieters F, Meire F, Schaich S, Roosing S, Brennenstuhl C, Bolz S, van Genderen MM, Riemslag FC; the European Retinal Disease Consortium, Lukowski R, den Hollander AI, Cremers FP, De Baere E, Hoyng CB, Wissinger B. A Nonsense Mutation in PDE6H Causes Autosomal-Recessive Incomplete Achromatopsia. Am J Hum Genet. 2012 Sep 7; 91(3) :527-32.

PubMed ID: 
22901948

Homozygosity mapping reveals PDE6C mutations in patients with early-onset cone photoreceptor disorders

Thiadens AA, den Hollander AI, Roosing S, Nabuurs SB, Zekveld-Vroon RC, Collin RW, De Baere E, Koenekoop RK, van Schooneveld MJ, Strom TM, van Lith-Verhoeven JJ, Lotery AJ, van Moll-Ramirez N, Leroy BP, van den Born LI, Hoyng CB, Cremers FP, Klaver CC. Homozygosity mapping reveals PDE6C mutations in patients with early-onset cone photoreceptor disorders. Am J Hum Genet. 2009 Aug;85(2):240-7.

PubMed ID: 
19615668
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