IJCRR

IJCRR - 5(13), July, 2013

Pages: 19-24

Date of Publication: 17-Jul-2013

CORRELATION BETWEEN REFRACTIVE ERROR AND EYE MOVEMENT PATTERNS DURING READING

Author: Noor-Suhailly Saiman, Ai-Hong Chen

Category: Healthcare

Abstract:Purpose: The purpose of this study was to investigate the correlation between refractive error and eye movement patterns. Methods: Fifty young adults aged between 19 and 27 years were recruited. The refractive errors ranged between +0.50D and -6.0D (mean = -1.77D, standard deviation = \? 1.97). Subjects were required to read the 200-word text at 40 cm on a reading stand while the eye movement was recorded using video oculography (VOG). Results: There was no association between refractive error and total count of saccades during reading (Spearman correlation coefficient, r = -0.2, p > 0.05). There was anegligible correlation between refractive error and total count of fixations during reading (Spearman correlation coefficient, r = -0.3, p = 0.051).However, a moderate negative correlation was found (Spearman correlation coefficient, r = -0.5, p< 0.05) between refractive error andtotal count of regressions during reading. Conclusion: Eye movement patterns in term of the total count of the saccade and fixation remained relatively stable between the refractive range of +0.50 to -6.0 D. However, the total count of regression type of eye movement pattern decreased with increasing refractive error. This might imply that subjects with more myopic refractive power might be a better reader.

Keywords: Refractive error, eye movement patterns, video oculography

Full Text:

INTRODUCTION
Reading involves corresponding visual-motor system which also involves the combination of eye movements with the physiological process of memory, concentration and visual information employment (Garzia et al, 1990). Three common eye movements executed during reading are saccades, fixation and regression. Saccades is a short rapid, abrupt eye movement fixating from one point to another while obtaining fixation on an object which normally took nearly 10% of reading time, with average saccade was about eight to nine character spaces (2-degree visual angle). The peak velocity of 10° amplitude saccades could exceed 300°/s and be accomplished in 40ms (Millodot, 2007; Rowe, 2003; Rayner, 1998; Tinker, 1947). Fixation referred to a number of eye stopped or paused during reading for information processing (Ciuffreda et al, 1995). Regressions were saccades that were directed from right to left, occurred when eyes overshot the target, misapprehend the text and reflexed on comprehension problems for reconfirmation during reading (Rowe, 2003). Reading eye movements were connected to visual–spatial shifts in attention and children with visualperceptual-motor delays were in peril of for reading underachievement especially among hyperopes (Rosner, 1982; 1987). Approximately 90% of reading time was on fixation in which during each fixation foveal information was processed (Solan, 1985). Visual sensitivity was recovered partially at the instigation of fixation and wholly after 70 ms, subsequently at the beginning of fixation (Isheda and Ikeda,1989).Visual information did not derived from fixation but incorporatedspatially and temporally by the movement of saccades in order to form visual perception (Schutz et al, 2011). For the direct connection between the degree of refractive error and fixation during reading, McConkie and Zola (1979) theorized that although rapid decreased visual acuity from the central fovea might affect fixation at the center of wordsbut the influence of refractive error on fixation during reading remained unclear. There was no mention of how was the regression during reading being affected by refractive error as regression represented 14% of saccades among adult and 25% among children (Starrand Rayner, 2001). Understanding the mechanism of the eye movements and the ability to sustain focus while reading is important, therefore the relationship between reading eye movement and refractive error needs to be established. Most common ways ofeye movement assessment in optometric practice includedsubjective observation of the smoothness and precisionof fixation ability, saccadic eye movement and pursuit eye movement. Visagraph III Eye movement recording system (Taylor Associate,NY) and Developmental Eye movement Test (DEM) were used as alternatives of eye movement assessment.The correlation between refractive error and eye movement during reading was investigated using Video-oculography (VOG) techniques in this study, which was introduced as one of the precise techniques to monitor the eye movement (Van der Geest and Frens, 2002). The instrument did not only record eye movement and reading duration precisely, but was also capable of tracking the center of pupil and the location of the eye which enabled the clinician to visualize linear and torsional eye movement while theeye moved (Gans, 2001).

MATERIALS AND METHODS
Fifty young adults (17 male and 33 female) ranged between 19 and 32 years were recruited. Spherical equivalent refractive error of subjects ranged from +0.50 to -6.0 D with astigmatism less than -1.00D. Subjects were fitted with spherical soft contact lenses (O2Optix Contact Lenses, Iotrafilcon B, 33% water content, Ciba Vision, USA) to permit best on-axis distance vision. Exclusion criteria included any ocular disease or binocular anomalies. The study was reviewed and approved by the Universiti Teknologi MARA research ethics committee. Eye movements were recorded using Video oculography or VOG (Sensomotoric Instrument version 5, Berlin, Germany) binocularly through the use of digital video camera which mounted on the goggles for tracking the center of pupil and the location of the eye (Gans, 2001; Van Der Geest and Frens, 2002). For safety and comfortable precaution, the VOG goggle was carefully adjusted. The eye position was adjusted based on iris image and the reference point was identified by capturing the eye image. The head position angle was set up based on habitual head postures. Calibration was made by using 9 reference points at 40cm working distance. Before any measurement was taken, screening as a base line was performed to ensure that all subjects could clearly see at least N6 [2 times smaller than the actual size of the character used (N8)]. Eye movement data was presented in graphic output, similar to the characteristic of eye movement presented by Eye Trac recording (Taylor, 2000). Thetotal numbers of saccades, fixations and regressions were calculated. The text used in the experiment was justified in upper case, black-to-white contrast and using Times Roman font style of N8 character size on A4 white paper (210 x 297 mm) covered 20’ of arc at 40cm. The text selected using the readability Malay language was based on local Malay newspaper consist of 200 words of 16 sentences in single paragraph with each sentence was ranged between 11 to 14 words (Khadijah Rohani, 1989). The subjects were instructed to read silently the text at 40 cm on reading stand while using VOG goggle in a good room illumination reading station which was constantly rechecked in each session.The eye movement recording was from first word until the last word. To avoid non-compliance, subjects were given oral comprehension test after assessment. None have failed during oral comprehension test, thus all data was successfully explored for statistical interpretation.Only data derived from right eyes were used during this experiment. The total number of saccades, fixation and regression during each session were statistically analyzed using SPSS 19.0 (SPSS Inc., Chicago, IL, USA). The overall refractive error was arranged in the manner of highest minus power to the most plus power in diopter (D) according to their spherical equivalent refraction (SER). Non- parametric statistical tests were employed (Shapiro Wilk:p < 0.05). Wilcoxon signed rank test was additionally used to investigate any changes of each reading eye movement among refractive error. Spearman correlation coefficient and linear regression were executed to find any relationship between each reading eye movement and refractive error. The differences in result obtained with p0.05). Linear regression analysis demonstrated insignificant relationship between refractive error and the total count of saccadesduring reading(F1, 48 = 0.479, p>0.05). There was a negligible correlation between refractive error and the total count of fixation (mean = 141.3 ± 35.9)during reading (Spearman correlation coefficient, r = -0.3, p > 0.05). Linearregression analysis showed no significant relationship between total count of fixation and refractive error (F1,48 = 1.16, p > 0.05). However, a moderate negative correlation was found between refractive error and the total count of regressions (mean = 43.4 ± 12.2)during reading(Spearman correlation coefficient, r = - 0.5, p<0.05). Linear regression analysis demonstrated a significant negative relationship (F1, 48 = 5.1, p<0.05). Regression type of eye movement increased with decreasing refractive power.

DISCUSSION
The total count of saccades remained unchanged in the refractive range between +0.50D and – 6.00D. This finding was consistent with the pattern reported in a previous study on amblyopia, eye movement, and hyperopic refractive error (Webberet al., 2009; Stifteret al., 2005). Fixationindicated reading difficulty and information processing strategy. Our finding revealed that the total counts of fixations did not correlate with refractive error ranged from +0.50 to -6.0 D. This might due to fixation was moreinfluenced by text concerning tonumber of meanings in a text,age-of-acquisition, morphology, wordoccurrence andfluency, contextual constraint and plausibility (Johnson et al., 2007). A similar trend was also reported in a study by Radakrishnan et al.(2007). There was a negative correlation between the refractive error and the total count of regressions. Regressionswere reported toimprovewhen the target words havea higher regularityof the adjacent words (Perea and Pollatsek, 1998; Pollatseket al., 1999). With regard to the text used in this study, there was a possibility of repeatable words in few sentences therefore the tendency of subjects to regress during reading was unavoidable. Another possible explanation was that readers perform an explicit reanalysis procedure(Mesegueret al., 2002). A suggestion by Kennedy et al. (2003) that some readers astutelyredirected the regression process to specific and critical part of the sentence might be one of the explanation of our study.

CONCLUSION
Our findings contributed to the knowledge on the influence of refractive error on reading performance that waseventually crucial in the overall understanding about children with vision related reading difficulty to enhance patient management in term of thequality of life.We concluded that saccades and fixation remained unchanged but regression varied with the range of refractive power between +0.50D and -6.00D.

ACKNOWLEDGEMENT
Authors acknowledge the great help received from the scholars whose articles cited and included in references of this manuscript. The authors are also grateful to authors / editors / publishers of all those articles, journals and books from where the literature for this article has been reviewed and discussed. Authors are grateful to IJCRR editorial board members and IJCRR team of reviewers who have helped to bring quality to this manuscript. Funding support:Universiti TeknologiMARA Excellence Fund [(600-RMI/ST/DANA 5/3/Dst(171/2009)].

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