Opposing Cycloplegic Refractions And Intraocular Lens Power Calculations For Identical Female Twins With Rpgr-Related X-Linked Retinitis Pigmentosa.

To report non-identical refractions, axial lengths, and intraocular lens power calculations in monozygotic, monochorionic female twins with X-linked retinitis pigmentosa.

Cataracts are a significant secondary cause of visual impairment in X-linked retinitis pigmentosa. They are characterized by an early onset, and the most common morphological type is posterior subcapsular lens opacities. Cataracts have a significant effect on patients' quality of life and economic productivity. Despite X-linked inheritance, females can demonstrate a carrier phenotype (a radial sheen seen on autofluorescence imaging) with variable effects on visual function.

Female twins attending Oxford Eye Hospital underwent a full ophthalmological examination, fundus autofluorescence, optical coherence tomography, and intraocular lens power calculations (ZEISS IOLMaster^® 500).  Blood and salivary samples were taken for genetic analysis and X-inactivation testing.

Monozygotic, monochorionic female twins with X-linked retinitis pigmentosa were found to be heterozygous for the pathogenic c.1047delT, p.(Phe349fs) mutation in the Retinitis Pigmentosa GTPase regulator (RPGR) gene. Cycloplegic refraction and intraocular lens power calculations demonstrated longer axial lengths (Right eye: 24.63mm; Left eye: 24.79mm) and myopia (Right eye: -1.75/ -3.25 x 15; Left eye: -3.00/-2.75 x 162) in twin one compared to twin two (Right eye: 22.59mm; Left eye: 23.04mm) who was hypermetropic (Right eye: +3.00/-3.00 x 005 degrees; Left eye: +3.00/-3.25 x 165 degrees). Axes of refraction are similar in both twins.

Variation in skewed ocular X-inactivation may underlie post-fertilization phenotypic discrepancy resulting in a more severe X-linked retinitis pigmentosa in twin one leading to blurred vision, defective emmetropization, lengthening of axial length, and myopia. Intraocular lens power calculations are not interchangeable for identical female twins with X-linked retinitis pigmentosa.