الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Summary
Nowadays several devices are available to measure the ocular anterior segment parameters. These instruments depend on different technical principles and different assumptions underlying these principles to measure these parameters. Evaluation of the precision and the accuracy of these devices is crucial before they become widely used in clinical practice and research settings.
This study aimed to evaluate and compare anterior segment measurements including the white-to-white (WTW) corneal diameter, central corneal thickness (CCT) and keratometry readings obtained with the optic low-coherent reflectometer (LENSTAR LS 900) and the Scheimpflug topography (TOMEY TMS-5). Both of them use different technological methods and provide reliable anterior segment measurements.
This study included 219 eyes of 115 randomly chosen normal Egyptian subjects of both sex (68 male and 47 female) who meet the inclusion criteria, eleven eyes were not included due to exclusion criteria. All subjects were recruited from the outpatient clinics of the ophthalmology department, El-Agouza police hospital (age group:25-50 years old).
This comparative study between LENSTAR LS 900 and TOMEY TMS-5 showed high correlations and relatively good agreement between the two devices in measuring CCT, K-values (Kf, Ks and average K) and WTW corneal diameter in healthy eyes. However, the two devices cannot be used interchangeably except for average K values.
Caution must be used regarding CCT, Kf, Ks and WTW values produced by the two devices interchangeably because it may lead to misinterpretations of results. Consequently, it should be appropriate to use the same device for the follow-up of the patient. LENSTAR LS 900 gives slightly higher values for CCT, K-values (Kf, Ks and average K) and WTW diameter than TOMEY TMS-5.
No correlation was found between CCT values and all parameters measured by LENSTAR LS 900 and TOMEY TMS-5 (WTW, K-values, ACD and AL). Consequently, the later parameters can be excluded to have any effect on CCT values; CCT is an independent factor unrelated to other ocular parameters.
No correlation was found between K-values (Kf, Ks and average K)
and ACD while as axial length increases, the cornea tends to become flatter.
Regarding WTW corneal diameter, the difference between LENSTAR LS 900 and TOMEY TMS-5 must be considered in IOL formulas incorporating WTW data and in calculating phakic IOLs.
This study points that the normal WTW diameter is wider than the currently accepted range. Further studies are needed to update cutoff points for defining macrocornea and microcornea referenced in ophthalmology textbooks based on different devices used for measurement and differences in population.
Knowledge of the negative correlation between WTW corneal diameter and K-values may have an important application in choosing the right size of microkeratome suction ring in keratorefractive laser surgeries; corneas with a larger WTW diameter have a flatter surface (higher risk of
free cap). While age, gender, laterality and CCT have no effect on WTW
diameter
The shorter the axial length is, the smaller the WTW diameter would be. Furthermore, the smaller the WTW diameter of the patient is, the shallower the ACD would be. Therefore, a small WTW corneal diameter may be a predisposing factor for developing PACG and increase the risk of complications with phakic IOL implantation.
The results of this study are only applicable to healthy adult eyes with good vision and fixation. These results might not be applied to pediatric patients, patients with anterior segment eye disease such as keratoconus or eyes with previous surgery such as refractive procedures, corneal crosslinking and corneal transplantation. Thus, further studies are recommended with a larger sample size to address these considerations and to increase the power of this study.