Myopic related retinal changes among the Hong Kong Chinese high myopes

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Myopic related retinal changes among the Hong Kong Chinese high myopes

 

Author: Cheng, Chi Kwan
Title: Myopic related retinal changes among the Hong Kong Chinese high myopes
Degree: Ph.D.
Year: 2012
Subject: Myopia -- China -- Hong Kong.
Retina -- Physiology.
Hong Kong Polytechnic University -- Dissertations
Department: School of Optometry
Pages: 227 leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2551244
URI: http://theses.lib.polyu.edu.hk/handle/200/6771
Abstract: It has been often reported that sight threatening retinal complications are associated with high myopia more than -6 D in the adult population. High myopia is a leading cause of irreversible blindness, contributing around 6% to 13% of blindness as reported in previous worldwide studies. In cities like Hong Kong where the prevalence of myopia is in the range of 70% to 80%; myopia starts as early as the start of schooling and progresses steadily throughout the schooling age. Prevalence of high myopia presents a threat to the visual quality of this population. There was little information on the early changes in the retina, as well as the consequence of high myopia among schoolchildren and adolescents that would lead to retinal complications or other ocular pathologies. This study aims to indentify the early changes in the retina among school children and adolescents with high myopia and whether these retinal changes are any different from those of the adult population. This information may help to identify the possible risk factors including biometric and demographic characteristics for children or adolescents having high myopia ocular complications in their later years. In identifying an efficient and effective method in the detection of early retinal changes among the adolescent group, the latest available technology and instrumentation were explored. The Optomap was selected for the investigation of sensitivity and specificity in fundus screening. To further understand on how the retina changes in a myopic bigger eye, as a result of myopia progression and axial elongation, retinal thickness variation along the horizontal meridian was also investigated. This may shed lights on the relationship between anatomical variations and retinal complications. This study has three main objectives: 1. Identify an effective and efficient screening methodology 2. Determine the prevalence of retinal features for the 12 to 18 years high myopic adolescent and risk factors 3. Relate retinal thickness profile with the myopic retinal changes 1. Identify an effective and efficient screening methodology: To identify an efficient method in retinal screening / examination, the ultra wide field scanning laser ophthalmoscope was investigated. Fifty-four eyes identified with retinal / choroidal signs and eight normal eyes were recruited from 31 Hong Kong Chinese subjects to evaluate the use of Optomap on detecting retinal signs under non-mydriatic condition with standard procedure. Photodocumentation of fundal changes were taken by the Optomap under undilated conditions before a dilated fundus examination by a clinician. To combat the problem caused by the eyelid blocking the image, a cotton bud was used to retract the eyelid. Optomap images were evaluated by four other investigators for identifying retinal features under a masked condition. Results were compared with those obtained using a dilated fundus examination as the gold standard. The sensitivity and specificity of the Optomap averaged 76.4% and 71.9% respectively, which was similar to a previous report by other researchers. The fundal signs commonly missed by all observers were lattice degeneration (2 cases), white-without-pressure (1 case), paramacular drusen (1 case), and pigmentary change (1 case). Paramacular drusen were detected by contrasting the red laser channel and green laser channel, while other missed fundal signs were located in the far peripheral retina apparently outside the field of the Optomap. The Optos non-mydriatic fundus imaging system offers high sensitivity and specificity in fundus screening. Using a cotton bud to retract eyelid may be a useful modification especially for droopy eyelid patients. Optomap has certain advantages; however, there are limitations especially in some areas of the peripheral fundus may not be accessible. As a screening tool, the Optomap permits fundus examination without the use of a mydriatic agent, which is more comfortable for the patients, and that a permanent digital record of the findings can be kept. However, the colours of the Optomap are the artificial combination of two laser channels, resulting in a distorted image. Retinal lesions at the outside edges of the retina might not be detected. The Optomap is a complementary method to the standard dilated fundus examination but not as a substitute, especially with a high myopic population with a high risk of having retinal lesions.
2. Determine the prevalence of retinal features for the 12 to 18 years high myopic adolescent and risk factors: To determine the prevalence and risk factors of myopic related retinal changes in young Hong Kong Chinese eyes with high myopia, 120 eyes were examined among school children with over -6 D myopia aged between 12 to 18 years. The eye with higher spherical equivalent error (SER) was used for analysis for each subject. Personal data collection, history related to myopia progression, biometry and documentation of retinal characteristics were performed with informed consent. Mean age of the subjects was 14.83 ± 1.58 years. Among the subjects, 50.8% were boys. The mean SER of the eyes was -8.41 ± 1.60 D. The five most frequent retinal lesions found were optic nerve crescents (52.5%), white-without-pressure (51.7%), lattice degeneration (5.8%) microcystoid degeneration (5%) and pigmentary degeneration (4.2%). Multiple logistic regressions showed axial length longer than 26.5 mm was a significant risk factor for peripheral lesions (p = 0.008, odd ratio 3.37), optic nerve crescents (p = 0.019, odd ratio 2.80) and white-without-pressure (p = 0.017, odd ratio 2.93). Peripheral retinal degenerative lesions and optic nerve crescent were found in a significant proportion of high myopic teenage subjects. There was a positive relationship between axial length and peripheral retinal lesions. There is a higher chance of having retinal lesions in eyes with axial length exceeding 26.5 mm in the age between 12 -18 years. Myopic related fundus changes could appear in early life in high myopic eyes. 3. Relate retinal thickness profile with the myopic retinal changes: The third study established the retinal thickness profiles in the central horizontal eighty degrees and relates retinal thickness profile with myopic retinal changes by comparing the profile between myopic and non-myopic eyes. The retinal thickness profiles of 30 myopic eyes (spherical equivalent error (SER) between -6.00 D and -13.63 D) and 31 non-myopic eyes (SER between +2.75 D and -0.50 D) were measured using the StratusOCT (Carl Zeiss Meditec, Dublin, CA). Two scan types were used: the Macular Thickness Map and the Customized Line Scan for a central 80 degrees horizontal retinal thickness profile. Myopic eyes have a thicker retina at the foveal center and fovea (p = 0.002 and 0.044 respectively), and thinner retina at other regions, compared to non-myopic eyes (p < 0.01, unpaired t-test). At other zones of the macula, the retina was significantly thinner in myopic eyes compared to non-myopic eyes (p < 0.01, unpaired t-test). From 40 degree nasal to 40 degree temporal retina, a general reduction of retinal thickness was observed across the myopic retina compared to the non-myopic retina, except at 20 degrees nasal to fixation. The peripheral retinal thickness was approximately 7% thinner in myopic eyes compared to the non-myopic eyes. General conclusions: Based on the results of the investigation with ultra wide field scanning laser ophthalmoscope, the Optos non-mydriatic fundus imaging system offers high sensitivity and specificity in fundus screening. The cotton bud eyelid retraction method may be a useful modification especially for droopy eyelid patients. However, there is still a chance that certain area of the fundus might not be identified. The Optomap is a complementary method to the standard dilated fundus examination but not a substitute, especially in a group with a high risk of retinal lesions, such as the high myopic population. The results of this prevalence study point out that myopic related fundus changes could appear in early life in high myopic eyes. There was a positive relationship between axial length and peripheral retinal lesions. There is a higher chance of having retinal lesions in eyes with axial length exceeding 26.5 mm in the age between 12 -18 years. As the myopic related retinal changes are present among this age group, though there are no urgent types of retinal lesion counted in our study, lesions like lattice degeneration is a predisposing factor of retinal detachment. Thus the early detection and assessment of fundal changes among young high myopes is important. An investigation of anatomatical retinal variation related to myopia, retinal thickness profiles have been established in the central horizontal eighty degrees in myopic and non-myopic eyes. This study found that myopic eyes have a thicker retina at the fovea and thinner retina at other regions compared to non-myopic eyes. From 40-degree nasal to 40-degree temporal retina, the peripheral retinal thickness was approximately 7% less in myopic eyes compared to the non-myopic eyes. We found retinal thickness reduction associates with high myopia in our study. There is a lot more to be done, such as correlating retinal changes with visual changes, and longitudinal monitoring to observe the changes over time.

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