April 2013
Volume 54, Issue 4
Free
Letters to the Editor  |   April 2013
Is Impaired Emmetropization Related to Foveal Hypoplasia or Is It Specific to Albinism?
Author Notes
  • Ophthalmology Group, University of Leicester, Leicester Royal Infirmary, Leicester, United Kingdom. 
Investigative Ophthalmology & Visual Science April 2013, Vol.54, 2940. doi:10.1167/iovs.13-12097
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      Irene Gottlob; Is Impaired Emmetropization Related to Foveal Hypoplasia or Is It Specific to Albinism?. Invest. Ophthalmol. Vis. Sci. 2013;54(4):2940. doi: 10.1167/iovs.13-12097.

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      © ARVO (1962-2015); The Authors (2016-present)

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I read the paper by Healy et al., which appears in the March 2013 issue, 1 with great interest. The authors describe a relationship between refractive error and the grade of foveal hypoplasia in patients with nystagmus. This finding is novel and interesting. However, the authors also conclude that their results suggest that impaired emmetropization is likely to be attributed to the whole eye effect in albinism and suggest that the fovea does not have a role in the emmetropization process. 
The authors included 23 patients with albinism, all of whom had severe foveal hypoplasia (grade 3 or 4), 2 while only 3 out of 17 patients with other forms of nystagmus had severe foveal hypoplasia (grade 3). The remaining patients with nystagmus without albinism had no foveal hypoplasia (n = 8) or mild foveal hypoplasia (n = 6; grade 1). 2 The authors found a significant correlation only when statistics included all patients (with and without albinism). As the group without albinism, consisting of only three patients with severe foveal hypoplasia, showed no correlation, the authors concluded that impaired emmetropization may be related to albinism. Statistics based on only three subjects with severe foveal hypoplasia without albinism are unlikely to be sufficiently powered to support this conclusion. No power calculation was included in the paper. 1 In this paper, of the three subjects with grade 3 foveal hypoplasia without albinism, one had a refractive error as high as +5.88 diopters spherical equivalent, suggesting an emmetropization defect in foveal hypoplasia in the absence of albinism. 
The conclusion that the fovea does not have a central role in emmetropization is surprising given that numerous retinal diseases, including foveal hypoplasia associated with PAX6 mutations 3,4 or diseases specifically affecting cone function such as blue cone monochromatism 5 or cone dysfunction syndrome, 6 are described in the literature as having high refractive errors. 
References
Healey N McLoone E Mahon G Jackson AJ Saunders KJ McClelland JF. Investigating the relationship between foveal morphology and refractive error in a population with infantile nystagmus syndrome. Invest Ophthalmol Vis Sci . 2013; 54: 2934–2939. [CrossRef] [PubMed]
Thomas MG Kumar A Mohammad S Structural grading of foveal hypoplasia using spectral-domain optical coherence tomography a predictor for visual acuity? Ophthalmology . 2011; 118: 1653–1660. [CrossRef] [PubMed]
Hingorani M Williamson KA Moore AT van Heyningen V. Detailed ophthalmological evaluation of 43 individuals with PAX6 mutations. Invest Ophthalmol Vis Sci . 2009; 50: 2581–2590. [CrossRef] [PubMed]
Hewitt AW Kearns LS Jamieson RV PAX6 mutations may be associated with high myopia. Ophthalmic Genet . 2007; 28: 179–182. [CrossRef] [PubMed]
Kellner U Wissinger B Tippmann S Blue cone monochromatism: clinical findings in patients with mutations in the red/green opsin gene cluster. Graefes Arch Clin Exp Ophthalmol . 2004; 242: 729–735. [CrossRef] [PubMed]
Michaelides M Johnson S Bradshaw K X-linked cone dysfunction syndrome with myopia and protanopia. Ophthalmology . 2005; 112: 1448–1454. [CrossRef] [PubMed]
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