McMaster University, Hamilton, Ont.
McGill Vision Research, Department of Ophthalmology, McGill University, Montreal, Que.
Can J Ophthalmol. 2018 Dec;53(6):609-613. doi: 10.1016/j.jcjo.2018.01.032. Epub 2018 Apr 7.
Both genetic and environmental factors are thought to play a role in the pathogenesis of strabismus and subsequent ocular dominance and amblyopia. Our purpose was to compare the characteristics of sensory visual function in 2 adult monozygotic (genetically identical) twins who presented with esotropia at different ages.
Monocular and binocular visual function was measured in the twins. Contrast sensitivity was used to assess monocular function. Suppressive and stereoscopic measurements were undertaken to assess binocular function. All tests were run using a 2-alternative forced choice psychophysical procedure. Eighteen short tandem repeats (STR) were genotyped across the genome in both twins to determine their exact relationship.
Twin 1 (nondominant eye OD) was diagnosed with esotropia at 6 months of age, whereas twin 2 (nondominant eye OS) was diagnosed with esotropia at 5 years of age. They underwent a similar corrective surgical intervention soon after diagnosis to correct their esodeviations. Monocular contrast sensitivity was poorer for twin 1, particularly at intermediate spatial frequencies. In addition, twin 1 demonstrated complete suppression and unmeasurable stereoscopic function (>300 seconds). On the other hand, twin 2 demonstrated fusion, exhibited only mild suppression, and had near-normal (28 seconds) stereoscopic function. All STR alleles were identical in the twins, proving monozygosity.
Sensory measurements of monocular and binocular visual function in these genetically proven monozygotic twins were significantly different, with the earlier onset of esotropia associated with reduced visual function. Twin 2, whose esotropia was diagnosed at the age of 5 years, had near-normal visual function, both monocularly and binocularly. To the best of our knowledge, this represents the first study of a genetically identical sibling pair with strabismus. By eliminating the genetic differences between these patients, we are able to make powerful observations about the effect of environment on visual function in strabismus.
遗传和环境因素被认为在斜视的发病机制以及随后的眼优势和弱视中起作用。我们的目的是比较 2 名年龄不同的患有内斜视的同卵双胞胎（遗传上完全相同）的感觉视觉功能特征。
对双胞胎的单眼和双眼视觉功能进行了测量。使用对比敏感度评估单眼功能。进行抑制和立体测量以评估双眼功能。所有测试均使用 2 种替代强制选择心理物理程序进行。在双胞胎中横跨基因组共对 18 个短串联重复序列（STR）进行了基因分型，以确定他们的确切关系。
双胞胎 1（非优势眼 OD）在 6 个月大时被诊断出患有内斜视，而双胞胎 2（非优势眼 OS）在 5 岁时被诊断出患有内斜视。他们在诊断后不久就接受了类似的矫正手术干预，以纠正他们的内斜视。双胞胎 1 的单眼对比敏感度较差，特别是在中间空间频率。此外，双胞胎 1 表现出完全抑制和无法测量的立体功能（>300 秒）。另一方面，双胞胎 2 表现出融合，仅表现出轻微的抑制，并且具有接近正常的（28 秒）立体功能。双胞胎的所有 STR 等位基因都相同，证明是同卵双胞胎。
通过消除这些患者之间的遗传差异，我们能够对斜视中环境对视觉功能的影响做出有力的观察。在这些经过基因证实的同卵双胞胎中，单眼和双眼视觉功能的感觉测量结果明显不同，内斜视的早期发病与视觉功能降低有关。双胞胎 2 的内斜视在 5 岁时被诊断出，其单眼和双眼的视觉功能均接近正常。据我们所知，这是首例关于斜视的遗传相同的兄弟姐妹对的研究。
