Patterns of posterior ocular complications in myopic eyes of Indian population

This is a retrospective study aimed to investigate the patterns of myopic fundus complications in Indian children and young adults. Electronic medical records of 29,592 patients, aged 10–40 years, who visited L V Prasad Eye Institute between 1st January to 31st December 2016 were analysed in the study. Data such as age, gender, refractive error and various pathologic lesions of posterior globe were considered for analysis. Among all the patients with different types of refractive errors, myopia was found in 47.4%, high myopia in 6.8% and pathologic myopia in 2.2%. There was no trend of the increased prevalence of pathologic myopia with increasing age, except for a significant difference between the children aged 10–15 years (2.7%) and those aged more than 15 years (>4%). . Although, the overall pattern of pathologic lesions was similar across different grades of myopia (2.5% in low myopes vs. 2.2% in severe myopes), lesions like staphyloma and retinal detachment increased with increasing degree of myopia. The proportion of pathologic lesions across different grades of myopia suggests the necessity for careful peripheral fundus examinations irrespective of the degree of myopia for better management and prognostic purposes.

Single eye analysis (only right eye analysed of the two eyes) showed 2.5% of myopes to have pathologic myopia. Whilst tessellation of fundus and lattice were observed in majority of patients, the occurrence of CNVM was much lower, a trend similar to what observed when both eyes were considered for analysis. Retinal holes, CRA, staphyloma and RD were present even in mild and moderate myopia groups as shown in Table 3. However, proportion of myopes having staphyloma and RD increased with the degree of myopia. Staphyloma was four times more common in severe myopes (0.4%) than in mild myopes (0.1%).

Discussion
Among different types of refractive errors, we found myopia in 47.4% of patients, high myopia in 6.8% and pathologic myopia in 2.2%. However, among only myopes, high myopia was found in 14.4% and pathologic myopia in 4.3%. Children between 10-15 years of age group had lowest proportion (2.7%) while adults between age group 25-30 years had highest proportion (4.9%) of pathologic myopia. Various pathologic lesions associated with myopia were found across all grades of myopia indicating that pathologic myopia lesions also exist in low grades    12 ). The Shihpai Eye Study conducted in Taiwan has defined the pathologic myopia taking into account both refractive error and axial length whereas our study has defined pathologic myopia based on fundus findings only. Direct comparison of our study results with Beijing, Shihpai, Hisayama and Blue Mountain studies may not be appropriate because of the following two reasons: Our study is a hospital based study while the other studies were population based study. Secondly, population included in these studies were elderly (≥49 years in Blue Mountain Eye Study, ≥65 years in Shihpai Eye Study, >40 years in Hisayama study and >40 years in Beijing Eye Study) while the current study included individuals within the age group of 10-40 years. In our study, the overall number of individuals with high myopia (<−5.0 D to −10.0 D) were found to be 6.8% which is higher than prevalence reported in Beijing Eye Study (3.3%), Hisayama study (5.7%) and Blue Mountain Eye Study (2.2%). In patients between 11-20 years of age, the prevalence of high myopia was found to be 2.15% which is significantly lower than the results reported by the study done in Singapore (7.3%) 29 in adolescent children of age 14 years.
Beijing Eye Study showed the prevalence of staphyloma to be 1.6% and chorio-retinal atrophy to be 3.1%. In 2008, Lai et al. 30 reported the prevalence of staphyloma to be 7.7%, chorio-retinal atrophy to be 2.7%, Lacquer crack to be 1.8% and Fuch's spot to be 0.3% in the posterior pole. In the similar age group among myopic patients, the pattern of these pathologic lesion in our study is quite low, 0.15% of staphyloma and 1.1% of chorio-retinal   Unlike other studies (Beijing, Shihpai and Blue Mountain Eye Study), the current study does not show a trend of increased prevalence of pathologic myopia with age, except for a significant difference between the ones aged 11-15 years and the remaining (2.7% in younger children vs. >4% in those aged >15 years). With the increasing age, several structural and functional changes occur in the posterior part of the eye 31,32 . A study conducted with OCT has shown thinning of retina with ageing 33 . As the age advances, lacquer cracks extend, increasing the area of atrophy in the macular area 34 . This could be the reason for increased prevalence of myopic maculopathy with age. In our study, the upper age limit is 40 years and this might have delivered lesser difference in proportion of patterns of various myopia complications between younger and older age group within 10-40 years. The results of current study also show no difference in the pattern of pathologic lesions with increase in grades of myopic refractive error. Beijing Eye Study had found prevalence of myopic retinopathy significantly increased with increasing refractive error, from 3.8% in eyes with <−4.0 D to 89.6% in eyes with at least −10.0 D. The Hisayama study also reported an increase in prevelence of pathologic lesions with increase in degree of myopia (myopic retinopathy increased from 0.3% in eyes with refractive error <−6.0 D to 36.8% in eyes with refractive error of at least −10.0 D). However, on analysing each pathologic lesion independently, we found that the proportion of staphyloma and RD increased with grades of myopia.
There was no difference in the pattern of pathologic myopia between male and female in our study, similar to the results from Blue Mountains and Beijing Eye Study. However, Hisayama study in Japanese elderly population reported female to have higher prevalence than males (2.2% vs. 1.2%). Similar outcomes were reported by Ito-Ohara et al. and Gozum et al. from Japan and Turkey respectively 35,36 .
The current study included 29,592 myopes for the analysis, which is so far, the highest number of patients enrolled for a study on patterns of pathologic myopia. This is one of the biggest strength of this study. In most of the East Asian and Caucasian studies, prevalence of pathologic myopia was seen in elderly population but we reported its prevalence in children and young adults. This study has some limitations. Firstly, our study is hospital based study where most of the patients' visit only if they have some vision related problem. Secondly, the pattern of pathologic lesions were reported only among myopes. Thus, the results obtained in this specific age group may be an overestimated value i.e. proportion of people with myopia lesions. Considering that the few changes associated with pathologic myopia such as chorio-retinal atrophy and myopic CNV usually develop later in life, the use of data from 10 to 40 years age in this study does not give insights on overall proportion of myopia lesions in elderly population. Due to retrospective nature of the study, our study failed to analyse the axial length measurements and retinal Optical Coherence Tomography findings and classify the severity of the fundus changes based on the META-PM (META-analysis for Pathologic Myopia) study. Hence comparison of the results from this study with other studies and the generalisability of the outcomes of this study should be made with caution. Further population based studies are needed to understand the actual prevalence of pathologic myopia and its association with axial length. The relationship between various lesions of posterior globe with visual acuity and describing lesions based on its location were beyond the scope of this paper.
In conclusion, various pathologic lesions of myopia were found in 4.3% of myopes in our database. Although, the overall proportion of pathologic myopia was similar among all degrees of myopia, lesions like staphyloma and retinal detachment increased with increasing degree of myopia. The results from this study indicates the necessity for careful peripheral fundus examinations irrespective of degree of myopia for better management and prognostic purposes. Future studies are needed to understand the age appropriate strategies for management of pathologic myopia so that visually debilitating lesions like retinal detachment and CNVM/CNV can be prevented or strategically managed.

Methodology.
A retrospective analysis of patient's electronic medical record (EMR), who visited any of the four tertiary centres of the L V Prasad Eye Institute (LVPEI), between 1 st January 2016 to 31 st December 2016, was conducted. Although, the four tertiary centres are located in four different geographical location of India, viz Bhubaneswar, Orissa; Visakhapatnam, Andhra Pradesh; Vijayawada, Andhra Pradesh; and Hyderabad, Telangana, the involved 29,592 patients came from different states panning from east to west and north to south India. Every single patient had signed informed general consent form prior to routine clinical examinations approving the use of their data for research purposes. The study was approved by institutional ethics committee of LVPEI, Hyderabad and procedures were in accordance to the tenets of the Declaration of Helsinki.
A total of 233,575 patients visited for the first time during the chosen one-year study time period. To avoid the effect of any age-related changes on the refractive error like emmetropization or cataract, only patients above 10 years and below 40 years of age were included in the study. Any patients who either had media opacity or underwent any form of ocular surgery that could influence the refractive error were excluded from the study (N = 171,155) leaving behind 62,420 patients of which 29,592 were myopes. Figure 2 represents the flowchart of patient's data pool at different level of inclusion and exclusion stages.
Demographic data such as age and gender, and clinical data such as refractive error and retinal signs as documented in EMR by treating ophthalmologist using indirect ophthalmoscope and slit lamp biomicroscope were collected. Medical records were reviewed to identify various pathologic myopia lesions, namely tessellation of fundus, white without pressure (WWOP), white with pressure (WWP), lattice degeneration, chorio-retinal atrophy (CRA), retinal holes, choroidal neovascularisation (CNVM/CNV), posterior staphyloma and retinal detachment (RD). Considering that the CNVM/CNV can also occur due to causes other than myopia, viz. idiopathic CNVM and punctate inner choroidopathy, care was taken to exclude such findings. Pathologic myopia was defined as the presence of any one of the following retinal signs: lattice degeneration, CRA, retinal holes, CNVM/ CNV, posterior staphyloma or RD 16 . The prevalence of high myopia and pathologic myopia based on age, gender and grades of myopia was expressed in percentage (%). Data of both the eyes were collected and if above mentioned signs were present in at least one of the eye, then patient was labelled to have pathologic myopia lesion. To understand the patterns of pathologic lesions based on refractive error, data of only right eye were analysed. Myopia was divided into 4 categories i.e. mild, moderate, high and sever where mild myopia was defined as spherical equivalent (SE) of <−0.50 D to −3.00 D, moderate myopia as <−3.00 D to −5.00 D, high myopia as <−5.00 D to −10.00 D and severe myopia as <−10.00 D and above 5 .