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Robyn Burton, David P. Crabb, Nicholas D. Smith, Fiona C. Glen, David F. Garway-Heath; Reading Speed, Eye Movements And Visual Field Defects In Glaucoma. Invest. Ophthalmol. Vis. Sci. 2012;53(14):175.
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To explore reading speed (RS) and eye movements in patients with bilateral glaucomatous visual field (VF) defects and compare these to age-similar people with normal vision.
Forty nine glaucoma patients (mean age:69 [SD:8] years) with bilateral VF defects and 38 age-similar visually healthy controls (mean age:67 [SD:8] years) were recruited. Silent reading speeds were measured for eight sets of fixed size, non-scrolling texts, on a computer monitor at 100% contrast. Eye movements (EMs) were simultaneously monitored using the EyeLink 1000 (SR Research). All participants had visual acuity better than 6/9 and underwent standard tests of visual function, including Humphrey 24-2 & 10-2 VFs, along with other non-sensory tests including cognitive (Middlesex Elderly Assessment of Mental Status Test [MEAMS]) and reading ability. Patients had no other ocular morbidity and were classified as having ‘mild’ (mean deviation [MD] >-5dB), ‘moderate’ (MD -5 to -10dB), or ‘advanced’ (MD <-10dB) glaucomatous VF defects in their ‘better’ eye. Median RS(words per minute; wpm) from 8 trials (different passages of text) and EM data were analysed.
Patients and controls were similar in average performance on MEAMS, Burt’s Reading test, a lexical decision task and had similar self reported reading frequency (all P>0.05). Average RS in the patient group with more advanced VF defects (MD< -10dB) was 280 [SD: 82] wpm and this was significantly different to the average in controls (215 [SD: 84] wpm; p=0.03). Average RS for the other patient groups did not differ from the controls. There was no evidence of a univariate association between 24-2 VF MD in the better eye and RS (Spearman’s rho=0.24) in the patient group as a whole (n=49). However, EM analysis revealed that patients with more advanced VF defects fixated, on average, for longer than controls, 145(SD: 19) and 124 (SD: 13) ms, respectively (P=0.001). Also, average left to right saccade amplitude was significantly smaller in patients with advanced VF defects compared to controls, 2.9 (SD: 0.8) and 3.6 degrees (SD: 0.6) respectively (P=0.03). Individual saccade scanpaths revealed idiosyncratic EM behaviour in some patients with more advanced VF defects.
There is little direct association between RS and clinically used summary measures of VF defect severity, although patients with MD worse than -10dB in their ‘better’ eye were slower than age-similar people with healthy vision. A combination of smaller saccade amplitude and increased fixation duration are likely to account for slower RS in these patients. RS is a highly variable measure but analysis of eye movements and examination of specific types of VF defects might reveal more about predicting individual patient’s reading impairment.
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