Abstract
Purpose: :
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.
Methods: :
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.
Results: :
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.
Conclusions: :
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.
Keywords: reading • eye movements • quality of life