Dr.Nisha Yadav, Prof.Zia Chaudhuri
Abstract(Nisha Yadav, MS 1, Zia Chaudhuri, MS, FRCS (Glasg), FICO, PhD1,2, Rajiv Garg, MD 1)
Aim– To assess speed of reading in normal and amblyopic eyes in children and adults
Method– Speed of reading (SOR) was assessed with the National Institute of Health (NIH) MN Read charts in 36 amblyopic eyes of children (mean age 9.52±2.57 years)with non-strabismic refractive amblyopia and compared to 62 age matched normal eyes(mean age 9.67±3.16 years). Similarly, 18 adult amblyopic eyes (mean age 28.41±9.33 years) with non-strabismic refractive amblyopia were compared to 56 age matched adult normal eyes (mean age 28.80±9.95 years). All recruited subjects were proficient in the English language in which this test is conducted.
Results– While there was no significant difference in SOR between amblyopic (69.03±30.59 words per minute [wpm]) and normal (88.45±59.19 wpm) eyes in children (p value =0.101), in adult amblyopic eyes the SOR (98.61±50.05 wpm) was significantly lower than that in normal eyes (156.68±60.67 wpm) (p value<0.0001).
Conclusion- This study suggested that there is decrease in functional visual plasticity in adult amblyopes with time, which often precludes long-term post-amblyopia treatment gains in this cohort.
Department of Ophthalmology, Lady Hardinge Medical College (LHMC) and associated Kalawati Saran Children’s Hospital (KSCH), University of Delhi1, PGIMER & Dr RML Hospital, New Delhi, India2 (Study conducted at LHMC, New Delhi, India)
Key words– Amblyopia, Speed of reading (SOR), MN read chart
Key message: SOR, a very important functional visual parameter is more affected in adult amblyopes as compared to that in children irrespective of the levels of distance visual acuity present in the amblyopic eyes versus the fellow eye.
Introduction
Amblyopia results from abnormal development of the visual system.[1] Clinically, amblyopia is diagnosed when there is a difference in visual acuity (VA) between the eyes of two lines or more, a pre-disposing amblyogenic condition is present, and there is no sign of visible ocular or visual pathway disease.[1]The most common pre-disposing conditions for amblyopia are strabismus (causing disruption of binocular vision development), refractive error (particularly anisometropia or hyperopia), or, more rarely, media opacification (such as congenital cataracts) causing reduction in image quality.[2]Amblyopia results in varied numberof functional visual deficits.[3] In this study, it was aimed to evaluate an important functional parameter, speed of reading [SOR] in children and adults with non strabismic refractive amblyopia, with strabismus as exclusion, thus eliminating other disparate situations that ocular misalignment brings forth into the genesis of amblyopia.
Subjects and Methods
This was a hospital based, observational, case-control study. Recruitmentwas done of consecutive children (6-18 years) and adults (> 18 years) diagnosed with non–strabismic refractive amblyopia. An age matched control group without amblyopia was also recruited for the study. Ethical clearance for the study was taken from the Institutional Ethics Committee (IEC). An informed consent was obtained from patients or the parents / guardian of the children accompanied.
Each subject of study population underwent through a complete standard ophthalmological evaluation, including the following. Assessment of best corrected visual acuity (BCVA) for distance and near was done by using Snellen’s chart. Complete cycloplegic refraction was done by using eye ointment atropine of a rice grain size amount was prescribed 3 times a day for 3 days in children of age group 6-7 years and 2% homatropinedrop was used for rest of the age groups of ≥8 years age.Complete anterior segment evaluation was done by using torch light and slit lamp.Posterior segment was evaluated with direct and indirect ophthalmoscopy. Other parameters including axial length, keratometry, fundus photography, speed of reading, colour vision,contrastsensitivity, stereopsis and pattern-reversal visually evoked potential (VEP) were recorded of all subjects.
All subjects with refractive errors in the case and control groups were prescribed their appropriate power of glasses as per standards of practice (SOP). Occlusion therapy was started after refractive adaptation for at least a month in subjects with anisometropic amblyopia conforming to current SOPs.
Inclusion criteria:
Cases:
Children (6-18 years) and adults (> 18 years) with unilateral and bilateral non-strabismic refractive amblyopia conforming to the criteria for diagnosis of amblyopia as mentioned below.
Controls:
Children (6-18 years) and adults (> 18 years) without any organic pathology decreasing vision, without strabismus and refractive amblyopia.Amblyopia was defined as: [4]
BCVA less than -0.3 log MAR (6/12 Snellen) in both eyes in bilateral amblyopia. A patient with a difference of 2 or more lines between both eyes with the better eye having BCVA less than -0.3 logMAR was recruited as a case of bilateral amblyopia.
A difference of 2 or more lines between both eyes with the better eye having BCVA more than -0.3 logMAR (6/12 Snellen) was recruited as a case of unilateral amblyopia.
The non-amblyopic control group comprised:
BCVA more than- 0.3 logMAR (6/12 Snellen) bilaterally.
A difference of less than 2 lines between both eyes with both eyes having BCVA more than -0.3 logMAR (6/12 Snellen).
Subjects recruited under the control group may have refractive errors but the BCVA has to conform to criteria under points 1 and 2 above. Any presence of an obvious organic pathology was an exclusion criterion for this group, similar to the group with amblyopia.
Exclusion criteria:Strabismus, intellectual disability, presence of any organic pathology decreasing BCVA in both cases and controls.
Total 42 children (mean age 9.52± 2.57 years) in case group comprised of 36 cases (36 eyes) of unilateral and 6 cases (12 eyes) of bilateral amblyopia and were compared to31 children (62 eyes) (mean age 9.67±3.16 years)inthe control group. Similarly 31 adults (mean age 28.41± 9.33years) in the case group comprised of 29 cases (29 eyes) of unilateral and 2 cases (4 eyes) of bilateral amblyopia and were compared with 30 adults (60 eyes) (mean age 28.80±9.95 years)in the control group. (Table 1&2)
| Table 1. Age and sex distribution of subjectsin the case and control groups | |||
| Mean age | Total number | Average Age±SD | |
| Children (case group) | Mean overall (in years) | 42 | 9.52± 2.57 |
| Males (in years) | 22 | 9.81± 2.80 | |
| Females (in years) | 20 | 9.20± 2.33 | |
| Children (control group)
|
Mean overall (in years) | 31 | 9.67±3.16 |
| Males (in years) | 10 | 10.10±2.92 | |
| Females (in years) | 21 | 9.47± 2.33 | |
| Adults (case group) | Mean overall (in years) | 31 | 28.41± 9.33 |
| Males (in years) | 17 | 28.41±10.27 | |
| Females (in years) | 14 | 28.42±8.44 | |
| Adults (control group)
|
Mean overall (in years) | 30 | 28.80±9.95 |
| Males (in years) | 16 | 31.62±12.57 | |
| Females (in years) | 14 | 25.57 ± 4.21 | |
| Table 2: Distribution of unilateral and bilateral amblyopia cases | |||
| Amblyopia Case group | Unilateral | Bilateral | Total |
| Children | 36 | 6 | 42 |
| Adult | 29 | 2 | 31 |
Visual acuity for distance (logMAR) was assessed in all subjects and compared between cases and control. Speed of reading (SOR) was assessed with the NIH MN Read charts in amblyopic eyes of children and adults who were able to read sentences and compared to age matched normal eyes (Table 3&4). In the children group, 29 out of 36 eyes of case group and 60 out of 62 eyes of control group was able to read. Similarly, in adults, 18 out of 29 eyes of case group and 56 out of 60 eyes of control group were able to read. SOR assessed in both sets and was compared with each other.
Statistical analysis done by using the SPSS 19.0 software package (SPSS Inc., Chicago, IL). A value of p<0.05 was considered statistically significant.
Results–
Analysis of unilateral amblyopesshowed that the VA for distance (logMAR) amblyopic (worse) eyes was very less in both children and adults when compared with respective controls. In children,meanBCVAin the worse eyes was 0.56±0.19 logMAR while that in control eyes was 0.14±0.12 logMAR(p <0.0001, t test).In adults mean VA of worse eyes was 0.66±0.22logMAR while that in control eyes was 0.08±0.12 logMAR (p <0.0001, t test). While speed of reading was almost same in amblyopic eyes (69.03±30.59wpm) of children and control (88.45±59.19wpm) (p=0.101, t test), but this was significantly less in the adult amblyopic eyes (98.61±50.05wpm) as compared to controls (156.68±60.67wpm) (p<0.0001, t test). (Table3 &4)
| Table 3 Children unilateral amblyopia: worse eyes versus control eyes | |||||
| Total number | Mean | Std. Deviation | P value (difference between worse and control eyes) | ||
| VA Distance(logMAR) | amblyopic eyes | 36 | 0.56 | 0.19 | 0.000 |
| control eyes | 62 | 0.14 | 0.12 | ||
| Reading speed (wpm) | amblyopic eyes | 29 | 69.03 | 30.59 | 0.101 |
| control eyes | 60 | 88.45 | 59.19 | ||
| Table 4 Adult unilateral amblyopia: worse eyes versus control eyes | |||||
| Total number | Mean | Std. Deviation | P value (difference between worse and control eyes) | ||
| VA Distance (log) | amblyopic eyes | 29 | 0.66 | 0.22 | 0.000 |
| control eyes | 60 | 0.08 | 0.12 | ||
| Reading speed (wpm) | amblyopic eyes | 18 | 98.61 | 50.05 | 0.000 |
| control eyes | 56 | 156.68 | 60.67 | ||
On the other hand, when unilateral amblyopic eye was compared with the fellow eye (better eye), in children mean VA of worse eyes was (0.56±0.19 logMAR) which significantly lower than the VA of better eyes (0.14±0.13logMAR) (p <0.0001, t test) but the SOR was almost similar amongst the worse (69.03±30.59wpm) and better eyes (80.10±31.66wpm) (p= 0.175, t test). (Table 5)
Similarly, in adults mean VA of worse eyes was 0.66±0.22logMAR while of better eyes was 0.10±0.20logMAR (p <0.0001, t test) and there was no significant difference in SOR between worse (98.61±50.05wpm) and better eyes (106.00±50.35wpm)) (p= 0.634, t test). (Table 6)
| Table 5 Children unilateral amblyopia: Worse Eyes versus Better eyes | |||||
| Total number | Mean | Std. Deviation | P value (difference between better and worse eyes) | ||
| VA Distance (logMAR) | worse eyes | 36 | 0.56 | 0.19 | 0.000 |
| better eyes | 36 | 0.14 | 0.13 | ||
| Reading speed (wpm) | worse eyes | 29 | 69.03 | 30.59 | 0.175 |
| better eyes | 31 | 80.10 | 31.66 | ||
| Table 6 Adult unilateral amblyopia: Worse Eyes versus Better eyes | |||||
| Total number | Mean | Std. Deviation | P value (difference between better and worse eyes) | ||
| VA Distance (logMAR) | worse eyes | 29 | 0.66 | 0.22 | 0.000 |
| better eyes | 29 | 0.10 | 0.20 | ||
| Reading speed (wpm) | worse eyes | 18 | 98.61 | 50.05 | 0.634 |
| better eyes | 26 | 106.00 | 50.35 | ||
Bilateral amblyopic eyes were also compared with their respective control eyes in both children and adults. In both the groups, VA for distance was significantly lower in children (0.56±0.12logMAR) and adults (0.14±0.12logMAR) when compared with the BCVA in age matched control eyes of children (0.60±0.14logMAR) and adults (0.08±0.12logMAR) (p <0.0001, t test), but there was no significant difference in SOR in both children (45±23.24 wpm)(p =0.081, t test), and adults (150±00 wpm)(p =0.878, t test) groups when compared to their age matched controls(88.45±59.19 wpm), (156.68±60.67 wpm) respectively. (Although, the bilateral amblyopes were very less in number as compare to controls)(Table 7)
| Table 7Children Bilateral amblyopia: BAE (Bilateral amblyopic eyes) versus control eyes | ||||||||
| Total number | Mean | Std. Deviation | P value (difference between BAE and control eyes) | |||||
| VA Distance (logMAR) | BAE | 12 | 0.56 | 0.12 | 0.000 | |||
| control eyes | 62 | 0.14 | 0.12 | |||||
| Reading speed (wpm) | BAE | 6 | 45.00 | 23.24 | 0.081 | |||
| control eyes | 60 | 88.45 | 59.19 | |||||
| Adult Bilateral amblyopia: BAE versus control eyes | ||||||||
| VA Distance(logMAR) | BAE | 4 | 0.60 | 0.14 | 0.000 | |||
| control eyes | 60 | 0.08 | 0.12 | |||||
| Reading speed (wpm) | BAE | 2 | 150.00 | 0.00 | 0.878 | |||
| control eyes | 56 | 156.68 | 60.67 | |||||
Discussion-
Amblyopia is the consequence of the disruption of the normal neurological development of the visual system and can occur with varying degree of severity.[5] Characteristics of amblyopic vision are decreased visual acuity, abnormal binocular function, reduced stereopsis, reduced contrast sensitivity, crowding, reduced Vernier and spatial acuity.[3, 6] However, conventionally, improvement in distance BCVA is taken as the only parameter for diagnosing as well as treating amblyopia. Speed of reading is a very important functional visual parameter that determines the capacity of an individual with amblyopia to cope up with routine work. It is expected to be less in amblyopia as compared to normal students because it incorporates the physiological principles of lateral inhibition.[7]
The present study was undertaken to see how much is the speed of reading (SOR) truly affected by decrease in visual acuity in nonstrabismic refractive amblyopia in both children and adults.
Previous studies have reported that amblyopes have better letter acuity for an isolated letter than when this letter appears in a line.[5,8,9] We observed significantly reduced speed of reading in the amblyopic eye in adult amblyopes as compared to adult controls. In children, however, the speed of reading in the amblyopic and the non-amblyopic eye were similar to each other and to the controls.
On evaluation of literature on this subject, it was observed that in a study performed on 20patients with strabismic amblyopia and compared with age matched 20 controls, it was observed that reading is impaired, not only during monocular viewing with the amblyopic eye, but also with the non-amblyopic eye and binocularly.[10] It was observed that these deficits in the speed of reading persisted even when single letters was used, suggesting that these abnormalities were not related to crowding.[11]
Microstrabismic amblyopia has been found to be associated with significant impairment of reading acuity and speed in treated amblyopes, even in those with no persistent acuity deficit. The genesis of this reading impairment has been largely attributed to the crowding phenomena seen in amblyopia.[12]
Other studies on speed of reading had demonstrated mechanism of lateral suppression in amblyopes, however its relation with crowding is not fully understood till yet. But there is very scarce literature on non strabismic refractive amblyopia which suggests these reading impairments in adult amblyopes.
In our study, we conclude that thefunctional visual parameter like speed of reading is less affected in initial stages of amblyopia that is the reason children are able to achieve maximum functional outcomes when diagnosed and treated on time. This also suggests that adult brain has lesser degree neural plasticity as compare to the children, which leads to more suppression of few visual functions with prolonged course of time.
Acknowledgement:
We are thankful for the humble support and cooperation of our patients and colleagues. We would specifically like to thankDr Sunita Mondol, MD, Director Professor and Head of Physiology, Lady Hardinge Medical College, New Delhi and Dr Madhulika Monga, MD, Professor of Physiology, Lady Hardinge Medical College, New Delhi for their contribution towards conceptualization and actualiation of the study.
Conflicts of interest-
There are no conflicts of interest
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