|Year : 2021 | Volume
| Issue : 2 | Page : 146-150
Prevalence of subclinical keratoconus in children presenting with refractive errors: A cross-sectional study
Rani Menon1, Sharika Menon1, Thekkuttuparambil Ananthanarayanan Ajith2
1 Department of Ophthalmology, Dr. Ranimenon's Eye Care, Thrissur, Kerala, India
2 Department of Biochemistry, Amala Institute of Medical Sciences, Thrissur, Kerala, India
|Date of Submission||22-Jul-2020|
|Date of Decision||01-Sep-2020|
|Date of Acceptance||16-Sep-2020|
|Date of Web Publication||21-Aug-2021|
Dr. Rani Menon
Department of Ophthalmology, Dr. Ranimenon's Eye Care, Thrissur - 680 003, Kerala
Source of Support: None, Conflict of Interest: None
Background: Keratoconus is a progressive noninflammatory condition that often starts to develop at the age of puberty. The subclinical disease remains unexplored geographically for its prevalence in children. This study was aimed to determine the prevalence of subclinical keratoconus in children presenting with refractive errors. Methods: A cross-sectional study was conducted among children (below 14 years of age) with refractive errors. Corneal topography indices such as Belin/Ambrosio enhanced ectasia total deviation value (BAD_D), index of vertical asymmetry (IVA), and index of surface variance (ISV) of both eyes were selected from the medical records. The prevalence of subclinical keratoconus was identified using the parameters BAD_D = 1.54–2.38, IVA >0.14, and ISV >22. The incidence was calculated and statistically analyzed. Results: Total 726 eyes (354 right and 372 left eyes) from 363 children (190 males and 173 females) were included in the study. Among the total 726 eyes studied, 132/726 (18.18%) showed subclinical keratoconus with 58/132 (43.93%) in right eyes and 74/132 (53.06) in left eyes (P = 0.3411). Definite keratoconus was observed in total 37/726 eyes only (5.09%) with 23/37 in right eyes (62.16%) and 14/37 left eyes (37.83). No statistically significant (P = 0.1678) difference was found between the incidence of definite or subclinical keratoconus with cases of normal indices. Conclusion: The incidence of subclinical keratoconus among children presenting with refractive errors was 18.18%. Corneal topography and tomography may be recommended for children presenting with refractive errors for identifying subclinical keratoconus and to arrest its progression at the onset.
Keywords: Belin/Ambrosio enhanced ectasia total deviation value, corneal topography, index of surface variance, index of vertical asymmetry, keratoconus, mean keratometry
|How to cite this article:|
Menon R, Menon S, Ajith TA. Prevalence of subclinical keratoconus in children presenting with refractive errors: A cross-sectional study. Kerala J Ophthalmol 2021;33:146-50
|How to cite this URL:|
Menon R, Menon S, Ajith TA. Prevalence of subclinical keratoconus in children presenting with refractive errors: A cross-sectional study. Kerala J Ophthalmol [serial online] 2021 [cited 2021 Dec 5];33:146-50. Available from: http://www.kjophthal.com/text.asp?2021/33/2/146/324193
| Introduction|| |
Keratoconus, a bilateral noninflammatory corneal ectatic disorder, often starts to develop at the age of puberty. The condition can aggravate in the third decade of life and thus causes a heavy burden to patients. Thinning of the corneal stroma is found in this noninflammatory disease which may or may not lead to irregular astigmatism. In order to arrest its progression, corneal cross-linking, especially in the early stages, is recommended. Therefore, early diagnosis is of vital importance. When the suggestive clinical signs and symptoms of subclinical keratoconus are overlapping with normal cornea, the diagnosis will be challenging for ophthalmologists. Rabinowitz et al., defined keratoconus suspect in a progressive perspective, and their definition was independent of the status of the fellow eye as no slit-lamp findings, asymmetric bow tie pattern with a skewed radial axis on videokeratography, or no scissoring on retinoscopy.
A combination of pachymetric, topometric, and aberrometric indices was used to differentiate subclinical from normal cases. Belin/Ambrosio Deviation Display (BAD_D), index of vertical asymmetry (IVA), and index of surface variance (ISV) were the best variables for the diagnosis of subclinical keratoconus. BAD_D and mean keratometry were the criteria for the diagnosis of definite keratoconus. Keratoconus affects all races. However, very little information is available on the relative frequency of its incidence in patients of different ethnic origins. A previous review on keratoconus by Kok et al. concluded that the prevalence of the disease among Indians is at an earlier onset. Despite the incidence of keratoconus among the Indian children, data on the subclinical form of this disease is lacking. Hence, this study was aimed to evaluate the prevalence of subclinical keratoconus among children presenting with refractive errors which may help to prevent the progression of the disease at an early stage.
| Methods|| |
A cross-sectional study was conducted in the department of ophthalmology during the period of January 2018 to February 2020. The children below the age of 14 years presenting with unilateral or bilateral refractive errors and uncorrected visual acuity of <6/6 in at least one eye were included in the study. A thorough clinical examination was done in all the children. Cases with complete details such as age, gender, and corneal topography indices were selected from medical records. Cases with astigmatism (0.5–5 diopters) were categorized as simple myopia-hypermetropia, compound myopia-hypermetropia, and mixed astigmatism. Children of age above 14 years, those with incomplete data, and cases with history of corneal surgery or corneal scarring and contact lens users were excluded from the study. Informed consent was obtained from the parent or guardian for selecting their data for the study. The study was conducted according to the Helsinki Declaration, 1975, as revised in 2000 and approved by the Institutional Ethics Committee.
Examination was conducted using WaveLight Oculyzer II and 25 single Scheimpflug images which were taken from each eye. BAD_D, IVA, and ISV were identified as the best diagnostic criteria for the diagnosis of subclinical keratoconus. The data were extracted to a Microsoft Excel sheet. The value of BAD-D ≥1.54 (but ≤2.38), IVA >0.14, and ISV >22 was used to identify the subclinical keratoconus, while BAD-D >2.38 with K mean ≥44.9 was selected to diagnose the definite keratoconus. The prevalence of subclinical keratoconus was identified among the total cases and presented as percent incidence. Furthermore, the prevalence of definite keratoconus was also analyzed.
All the parametric data were presented as mean ± standard deviation (SD). The nonparametric data were presented as a percentage. Student t-test was used to find the statistically significant difference among the parametric data (SPSS, 16 v, IBM, CA, USA (SPSS Inc. Released 2007. SPSS for Windows, Version 16.0. Chicago, SPSS Inc)), while Chi-square test was used to find the significant difference between SKC (subclinical keratoconus) and normal topographic indices. P < 0.05 was considered statistically significant.
| Results|| |
Total 726 eyes (354 right and 372 left eyes) from 363 children (190 males and 173 females) of age between 3 and 14 years were included in the study. The mean age was 9.01 ± 2.61 years, with an average age of 8.52 ± 2.52 years in male children and 8.65 ± 2.70 years in female children. No significant difference was found between the ages of male and female children (P > 0.05, Student's t-test). Simple myopic astigmatism was found in a total of 157/726 eyes (21.62%), which was the prevalent refractive error, followed by compound myopic astigmatism (71/726; 9.77%). Normal topographic indices were observed in 557 eyes (75.40%) with 273 right eyes (49.01%) and 284 left eyes (50.98%). Among the total 726 eyes studied, 132/726 (18.18%) showed subclinical keratoconus with 58/132 (43.93%) in right eyes and 74/132 (53.06) in left eyes [Table 1]. No statistically significant (Chi-square value 0.9064; P = 0.3411) difference was found between the incidence of subclinical keratoconus in right and left eyes with that of right and left eye normal topographic indices.
|Table 1: Distribution of subclinical keratoconus with various astigmatism and myopia among children with refractive errors|
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Among the total subclinical keratoconus obtained, the prevalence of simple myopic astigmatism was found in total 83/132 eyes (62.87%) with 35/83 (42.16%) in right eyes and 48/83 (57.83%) in left eyes. The simple myopic astigmatism was found in 24 eyes and compound myopic astigmatism found in 6 eyes. No cases of simple hypermetropia, simple hypermetropic astigmatism, or simple myopia were observed in these subclinical cases
Definite keratoconus was observed in total 37/726 eyes only (5.09%) with 23/37 in right eyes (62.16%) and 14/37 in left eyes (37.83). No statistically significant (Chi-square value 1.903; P = 0.1678) difference was found between the incidence of definite keratoconus in right and left eyes with that of right and left eyes of cases with normal topographic indices. Among the total definite keratoconus obtained, the prevalence of simple myopic astigmatism was found in total 24/37 (64.86%) eyes with 13/24 (54.16%) in right eyes and 11/24 (45.83%) in left eyes. No evidence of simple hypermetropia, simple hypermetropic astigmatism, or simple myopia was found among children with definite keratoconus
Among the total eyes, 557/726 (75.40%) eyes with refractive errors were found with normal indices, 273/557 (49.01%) in right eyes and 284/557 (50.98%) in left eyes. The prevalence of simple myopic astigmatism was found in total 267/557 eyes (51.54%), 141/267 (52.80%) in right eyes and 126/267 (47.19%) in left eyes. In this group with normal indices, total compound myopic astigmatism was found in 127/557 (22.80%), mixed astigmatism in 45/557 (8.07%), compound hyperopic astigmatism in 3/557 (0.53%), simple hypermetropia in 42/557 (7.54%), simple hypermetropic astigmatism in 14/557 (2.51%), simple myopia in 19/557 (3.41%), and emmetropia in 40/557 (7.18%).
| Discussion|| |
The diagnosis of subclinical keratoconus remains a challenge to ophthalmologists due to the overlapping of many topographic indices with the normal cases. We have taken the Pentacam indices with acceptable specificity and sensitivity to identify subclinical cases. Studies suggest that removing the data of central 3.5 mm height and the use of enhanced best fit sphere instead of the standard mode in calculating BAD_D will be a more sensitive and specific index for detecting subclinical keratoconus. Pentacam top indices are used for diagnosing subclinical and definite keratoconus.
In BAD_D, a reference surface was defined based on the individual's own cornea after excluding the conical orectactic region (keratoconus/ectasia detection with the Oculus Pentacam; Belin/Ambrosio enhanced ectasia display). The enhanced BFS, while further exaggerating the conical protrusion, closely approximates the more normal peripheral cornea. This method in calculating BAD_D is an even more sensitive and specific index to detect subclinical keratoconus. ISV is the unitless SD of individual corneal sagittal radii from the main curvature. ISV is thus an expression of the corneal surface irregularity.
It is also elevated in all types of corneal surface irregularities. In our study, corneal scars and contact lens users were excluded from the study. IVA (in mm) is the mean difference between inferior and superior corneal curvatures. IVA is thus the value of curvature symmetry with respect to the horizontal meridian as the axis of reflection. An ISV more than 22 and an IVA more than 0.14 are taken as keratoconus suspects along the lines of research by Hashemi et al. According to Hashemi et al., ISV and IVA indices had better predictive power in detecting subclinical keratoconus than other known variables like maximum/mean keratometry. The cutoff value of 45D according to their findings was taken as the cutoff point for definite keratoconus.
The results of this study revealed that 18.18% of children with refractive errors had subclinical keratoconus. The incidence was found to be varying among the population studied. The previous study indicates that keratoconus affects all races and very little information is available in South Indian patients. In this study, we found that the average age of males and females with subclinical keratoconus was 8.5 ± 2.5 and 8.6 ± 2.7 years, respectively. Among the various indices analyzed, BAD_D was found to be more reliable for differentiating subclinical from definite keratoconus; hence, it was used in this study., We found the incidence of definite keratoconus in 5.09%. This result is in consistent with the previous report from South India which showed a prevalence of 5.2%, while in Central India, it was reported as 2.3%. No gender-wise difference was noticed in this study like the previous studies., However, refractive errors were more observed in male children than female. Among the errors presented, simple myopic astigmatism was the most prevalent among the total cases.
The disease is found to be progressive until the third or fourth decade of life, and then, it usually arrests. Various risk factors for the incidence of keratoconus were reported previously. Among those, a high rate of incidence was associated with ocular rubbing, ocular allergies, Down's syndrome, and tapetoretinal degeneration, while a lower rate of incidence was found in children with retinitis pigmentosa, Leber's congenital amaurosis, congenital cataract, and diabetes mellitus. The disease showed rapid progression in cases of eye rubbing, atopic eye disease, vernal keratoconjunctivitis, pregnancy, and frequent change of glasses. Among the pediatric patients below 14 years of age with progressive keratoconus, accelerated collagen cross-linking was reported as an effective and safe procedure for the management. However, the published data on the best treatment modality for a particular stage of keratoconus are lacking. Fernández Pérez et al. concluded the effectiveness of early diagnosis of keratoconus using highly specific diagnostic equipment to halting the disease at its asymptomatic subclinical stages so as to avoid unnecessary treatments in false-positive cases. Family history of keratoconus was found to be varying. Previous study reported that progression of the disease was seen in 52% of the cases.
We did not include the family history of these children and progression of the disease. Small sample size is one of the major limitations of this study. Furthermore, BAD_D, ISV, and IVA aberrometry data were not included in this study. Hence, a multicenter study to support the conclusion is further warranted.
| Conclusion|| |
Subclinical keratoconus is a less studied subject, especially in children. As far as we know, this is the first study that shows the prevalence of subclinical keratoconus in children with refractive errors in South India. In this study, we have introduced Pentacam indices that have acceptable sensitivity and specificity to identify cases of subclinical and definite keratoconus in children with refractive errors. This study shows the importance of detecting subclinical keratoconus in young children who need to be followed up for the development of a frank keratoconus and also measures can be taken to arrest the development of keratoconus. This study also stresses the importance of close follow-up of children with refractive errors with a corneal topography and tomography.
It is essential to recognize that keratoconus suspect is a topographic classification of an abnormal pattern that resembles keratoconus with no definite characteristics. The study concluded that though the incidence (18.18%) of subclinical keratoconus was statistically nonsignificant, children presenting with refractive errors should be recommended for corneal topography for identification of subclinical keratoconus in order to arrest the progression of the condition at the earliest.
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Conflicts of interest
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| References|| |
Rebenitsch RL, Kymes SM, Walline JJ, Gordon MO. The lifetime economic burden of keratoconus: A decision analysis using a markov model. Am J Ophthalmol 2011;151:768-773.
Dahl BJ, Spotts E, Truong JQ. Corneal collagen cross-linking: An introduction and literature review. Optometry 2012;83:33-42.
Hashemi H, Beiranvand A, Yekta A, Maleki A, Yazdani N, Khabazkhoob M. Pentacam top indices for diagnosing subclinical and definite keratoconus. J Curr Ophthalmol 2016;28:21-6.
Rabinowitz YS, McDonnell PJ. Computer-assisted corneal topography in keratoconus. Refract Corneal Surg 1989;5:400-8.
Shi Y. Strategies for improving the early diagnosis of keratoconus. Clin Optom (Auckl) 2016;8:13-21.
Pearson AR, Soneji B, Sarvananthan N, Sandford-Smith JH. Does ethnic origin influence the incidence or severity of keratoconus? Eye (Lond) 2000;14 (Pt 4):625-8.
Kok YO, Tan GF, Loon SC. Review: Keratoconus in Asia. Cornea 2012;31:581-93.
Kanellopoulos AJ, Asimellis G. Revisiting keratoconus diagnosis and progression classification based on evaluation of corneal asymmetry indices, derived from Scheimpflug imaging in keratoconic and suspect cases. Clin Ophthalmol 2013;7:1539-48.
Jafri B, Li X, Yang H, Rabinowitz YS. Higher order wave front aberrations and topography in early and suspected keratoconus. J Refract Surg 2007;23:774-81.
Ambrosio Jr., R, Faria-Correia F, Ramos I, Valbon VF, Lopes B, Jardim D, et al
. Enhanced screening for ectasia susceptibility among refractive candidates: The role of corneal tomography and biomechanics. Curr Ophthalmol Rep 2013;1:28-38.
Ambrósio R Jr, Caiado AL, Guerra FP, Louzada R, Sinha RA, Luz A, et al
. Novel pachymetric parameters based on corneal tomography for diagnosing keratoconus. J Refract Surg 2011;27:753-8.
Shetty R, Kaweri L, Pahuja N, Nagaraja H, Wadia K, Jayadev C, et al
. Current review and a simplified “five-point management algorithm” for keratoconus. Indian J Ophthalmol 2015;63:46-53.
] [Full text]
Jonas JB, Nangia V, Matin A, Kulkarni M, Bhojwani K. Prevalence and associations of keratoconus in rural Maharashtra in central India: The central India eye and medical study. Am J Ophthalmol 2009;148:760-5.
Georgiou T, Funnell CL, Cassels-Brown A, O'Conor R. Influence of ethnic origin on the incidence of keratoconus and associated atopic disease in Asians and white patients. Eye (Lond) 2004;18:379-83.
Gorskova EN, Sevost'ianov EN. Epidemiology of keratoconus in the Urals. Vestn Oftalmol 1998;114:38-40.
Krachmer JH, Feder RS, Belin MW. Keratoconus and related noninflammatory corneal thinning disorders. Surv Ophthalmol 1984;28:293-322.
Shetty R, Nagaraja H, Jayadev C, Pahuja NK, Kurian Kummelil M, Nuijts RM. Accelerated corneal collagen cross-linking in pediatric patients: Two-year follow-up results. Biomed Res Int 2014;2014:894095.
Fernández Pérez J, Valero Marcos A, Martínez Peña FJ. Early diagnosis of keratoconus: What difference is it making? Br J Ophthalmol 2014;98:1465-6.
Zadnik K, Barr JT, Edrington TB, Everett DF, Jameson M, McMahon TT, et al
. Baseline findings in the Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study. Invest Ophthalmol Vis Sci 1998;39:2537-46.