Astigmatism

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Retrieved

2019-09-22

Source

Omim

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Genes

TYR, CASC15, CACNA1F, ARCN1, PRRX2, ANKRD11, SLC25A24, VSX1, SMARCAL1, WAC, MBTPS2, P4HTM, PRMT7, TRAF3IP1, PHIP, FANCL, RFWD3, SETD5, UBE2T, NIPBL, AUTS2, NPLOC4, VAX2, ADNP, PACS2, POGZ, EMC1, ARSG, KDM5B, CLDN16, MAD2L2, ECEL1, ARHGEF2, AP3D1, CDK13, FANCI, MBD5, RNF113A, CHRDL1, PROX1-AS1, RNU4ATAC, MIR184, GTF2H5, BLOC1S3, ZDHHC24, EBF3, LVRN, KCNV2, SPATA5, CLDN19, MPLKIP, DNAJC21, SGSM1, UBE3B, MFF, LOXL3, SLX4, CHD6, CEP78, BRIP1, TRIM8, PALB2, CCDC28B, SLC39A8, PIEZO2, FANCM, CC2D2A, KIDINS220, ARID1B, USP9X, HERC2, XRCC2, ERCC4, H3-3A, VARS1, GTF2E2, GRIN2B, GNAQ, GLRB, FBN1, FANCG, FANCF, FANCB, FANCE, FANCD2, FANCC, FANCA, ERCC3, MAG, ERCC2, EGFR, DPYD, DNAH5, COL11A1, COL9A3, COL9A2, COL9A1, CHD4, CHD3, C1QBP, BRCA2, BRCA1, BBS1, HARS1, H1-4, MECP2, CHMP1A, CLRN1, TUB, TEAD1, TCF4, TBCE, RAD51C, RAD51, PTPN11, PDGFRA, PCYT1A, LINC02422, TRNS2, TRIM37, NEUROD2, GPR143, NFIX, MFT2, TNMD, CYLD, CCT, MT1L, OCA2, TWIST1, THOP1, ART1, LINC00273, MELTF, ATR, TYMS, TMTC3, TGFB2, STAR, SFPQ, FTMT, CCL21, IGFBP7, CREBZF, PLXNA2, PYCARD, APH1A, CCL1

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Description

Astigmatism (from the Greek 'a' meaning absence and 'stigma' meaning point) is a condition in which the parallel rays of light entering the eye through the refractive media are not focused on a single point. Both corneal and noncorneal factors contribute to refractive astigmatism. Corneal astigmatism is mainly the result of an aspheric anterior surface of the cornea, which can be measured readily by means of a keratometer; in a small fraction of cases (approximately 1 in 10) the effect is neutralized by the back surface. The curvature of the back surface of the cornea is not considered in most studies, because it is more difficult to measure; moreover, in the case of severe corneal astigmatism, there is evidence that both surfaces have the same configuration. Noncorneal factors are errors in the curvature of the 2 surfaces of the crystalline lens, irregularity in the refractive index of the lens, and an eccentric lens position. Since the cornea is the dominant component of the eye's refracting system, a highly astigmatic cornea is likely to result in a similarly astigmatic ocular refraction (summary by Clementi et al., 1998).

Inheritance

Clementi et al. (1998) reviewed studies beginning early in the 20th century, demonstrating familial aggregation of astigmatism but coming to various conclusions as to mode of inheritance.

Mash et al. (1975) concluded from study of the families of affected subjects that heritability is low; Teikari and O'Donnell (1989) suggested that genetic factors did not contribute to astigmatism, leaving environmental causes as the major contributors.

In a geographically well-defined sample of 125 nuclear families of individuals affected by astigmatism, Clementi et al. (1998) performed complex segregation analysis by the POINTER and COMDS programs. POINTER could not distinguish between alternative genetic models, and only the hypothesis of no familial transmission could be rejected. After inclusion of the severity parameter, COMDS results defined a genetic model for corneal astigmatism and provided evidence for single-major-locus inheritance. These results suggested that genetic linkage studies might be feasible and that they should be limited to multiplex families with severely affected individuals. Autosomal dominant inheritance was favored.