Journal of Clinical Ophthalmology and Research

: 2018  |  Volume : 6  |  Issue : 3  |  Page : 85--89

Repeatability of manual and portable handheld automated keratometric measurements in pediatric population

Kunal Kaushik, Amit Maitreya, Anuradha Raj 
 Department of Ophthalmology, Himalayan Institute of Medical Sciences, Swami Rama Himalayan University, Dehradun, Uttarakhand, India

Correspondence Address:
Anuradha Raj
Department of Ophthalmology, Himalayan Institute of Medical Sciences, Swami Rama Himalayan University, Jolly Grant, Dehradun, Uttarakhand


Background: The cornea is not only responsible for the majority of the refraction of the eye, but is also readily accessible for measurement and modification. The refractive power of the anterior corneal curvature can be measured by an instrument known as keratometer and various manual and automated keteratometers are available for this purpose. Objective: To study the comparison between keratometric measurements by Bausch and Lomb manual keratometer (MK) and Nidek KM-500 portable handheld automated keratometer (PAK) in pediatric age group. Methods: 404 eyes of 202 children of age between 5-16 years were examined. Three sets of readings of vertical, horizontal meridia and axis measurements were taken for each eye using both instruments. Results: The mean of average vertical, horizontal keratometry and axis readings using MK were 43.24 ± 1.52 D, 42.86 ± 1.47 D and 10.33 ± 36.47 degrees respectively. The mean of average vertical, horizontal keratometry and axis readings using PAK were 43.29 ± 1.41 D, 42.99 ± 1.34 D and 20.78 ± 12.39 degrees respectively. The mean of average keratometric astigmatism (KA) for MK and PAK were 0.661 ± 0.796 D and 0.663 ± 0.590 D respectively. The reliability coefficients of MK and PAK were 0.888 and 0.994 respectively for vertical meridia, 0.993 and 0.989 respectively for horizontal meridia, 0.973 and 0.963 respectively for axis measurements. Conclusion: Both the instruments had good comparability and repeatability. Keratometric measurements using MK and PAK were significantly similar. However, there was statistically significant difference in the axis measurements using both the instruments.

How to cite this article:
Kaushik K, Maitreya A, Raj A. Repeatability of manual and portable handheld automated keratometric measurements in pediatric population.J Clin Ophthalmol Res 2018;6:85-89

How to cite this URL:
Kaushik K, Maitreya A, Raj A. Repeatability of manual and portable handheld automated keratometric measurements in pediatric population. J Clin Ophthalmol Res [serial online] 2018 [cited 2019 Feb 20 ];6:85-89
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Full Text

Approximately two-third of the refracting power of the eye is supplied at the air/tear interface that lies on the front surface of the cornea which is generally referred to as the anterior refracting surface of the eye. The cornea makes major part of refraction of the eye.[1]

The refractive power of the anterior corneal curvature can be measured by an instrument known as keratometer and the procedure is known as keratometry. This refractive power is expressed in diopters (D).[2]

Various keratometers are commercially available for clinical use. Manual (Bausch and Lomb [B&L] and Javal–Schiotz), automated (autokeratorefractors, IOL Master) keratometers, and devices for simulated keratometry (corneal topographers) are the most common instruments used for this purpose.[3]

The B&L manual keratometer (MK) has remained essentially unchanged since 1932 and is most commonly used.[4] It helps in measuring the curvature of the central 3 mm (mm) of the cornea with readings ranging from 36 D to 52 D.[5]

Automated keratometers have gained widespread acceptance in the field of eye care since its inception in early 1980's. Most units of automated keratometer measure corneal curvature by projecting three beams of near-infrared light with light-emitting diode as a source in a triangular pattern onto a central corneal area of about 3–3.3 mm in diameter.[3] The readings range between 33.75 D and 67.50 D.[6]

MK has been used for years for the measurement of corneal curvature in adults. It requires patient's cooperation and many children are very uncooperative for this procedure. In these young uncooperative children, keratometry needs to be done while the child is sleeping, under oral sedation or general anesthesia with the help of portable automated keratometer (PAK). There are very few studies which have compared automated keratometer with MK in children.

Keeping this in mind, the present study was undertaken to compare keratometry measurements by MK and PAK in pediatric age group.

 Materials and Methods

This observational cross-sectional study was approved by the institutional research ethical committee and was in accordance to the tenets set forth in Declaration of Helsinki. This study was conducted over 12 months from March 2015 to March 2016. A total of 404 eyes of 202 children aged between 5 and 16 years who presented for refraction and whose parents/guardians gave consent for examination were included in the study. Eyes with known congenital ocular abnormalities such as nystagmus, cataract, conjunctival or corneal pathology, irregular astigmatism, systemic ailments, and keratometry readings <36 D or more than 52 D were excluded from the study. Participants with a history of intraocular or extraocular surgery, contact lens usage, head tremors, and participants unable to cooperate for the procedure were also excluded from this study.


Demographic indices were recorded in case recording form that included age, sex, and address of the patient. Clinical assessment of the children included detailed medical history and ophthalmological examination including uncorrected and best-corrected visual acuity measured with the help of Snellen acuity chart, Hirschberg's test, extraocular movements, slit-lamp examination for anterior segment evaluation, and cycloplegic retinoscopy. Participants were examined after 30 min of use of homatropine and tropicamide and fundus examination using indirect ophthalmoscope was done. The keratometry measurements of vertical and horizontal meridia along with axis of horizontal meridia were performed using MK (B&Lomb, Japan) and PAK (Nidek KM-500 Japan) using the standard protocol.[6],[7]

Both the instruments MK and PAK were calibrated before the study using standard protocol.[8]

The following steps were undertaken for obtaining keratometry readings using PAK:

For recording measurement of the right eye, R button was pressed and the power was ON automatically. The patient was asked to watch the fixation light (red light) inside the measuring window. While looking into the observation window, the main body was moved until the size of target ring almost coincided with the outer circles of iris and the target ring became a concentric circle with the mire ring. When measuring window was brought around the focusing point (about 40 mm in front of patient's eye), the target ring started to blink and the blinking speed became higher as the focusing point got closer. When it was exactly focused, a beep sounded and the target ring disappeared to notify that the measurement was completed. The values displayed on the screen were noted, horizontal and vertical meridia were decided on the basis of the value of the axis; 180° axis was converted to 0 as per convention. For the left eye, L button was pressed and above said steps were repeated. After one set of reading, the patient was asked to close eyes for 5 min to restore stable tear film and to relax the child.[6] The PAK measurements were taken always by holding it in a vertical position.

Three set of readings were taken for each eye using MK and PAK by a single observer. The mean of three keratometry readings was calculated. Keratometric astigmatism (KA) was calculated as the difference between the steeper and the flatter meridian. The mean of KA was also calculated.

Statistical analysis

Data were expressed in term of mean ± standard deviation (SD). All statistical interpretation and analysis of results obtained were carried out using statistical software SPSS version 22 (Statistical Package for Social Sciences, version 22, SPSS Inc, Chicago, IL, USA) and Microsoft Excel. Continuous variables were presented as mean ± SD. Categorical variables were presented as absolute numbers and percentages. The comparison of normally distributed continuous variables between the groups was performed using paired Student's t-test. Nominal categorical data between the groups were compared using Chi- square test or Fisher's exact test as appropriate. Cronbach's alpha test was used to calculate the intraclass coefficient for repeatability. The P < 0.05 was considered statistically significant.


A total of 404 eyes of 202 patients were studied which included 116 (57.44%) males and 86 (42.56%) females (P = 0.349). The mean age of the children included was 10.94 ± 3.04 years [Table 1]. In males, the mean of average vertical and horizontal meridia readings was 43.08 ± 1.45 D and 42.67 ± 1.47 D, respectively. In females, the mean of average vertical and horizontal meridia readings were 43.46 ± 1.59 D and 43.13 ± 1.43 D, respectively [Figure 1].{Table 1}{Figure 1}

Comparison of keratometric readings obtained by both the instruments was made using following criteria:

The mean of the average of vertical and horizontal meridia readings was 43.24 ±1.52 D and 42.86 ± 1.47 D, respectively, using MK. The mean vertical and horizontal meridia readings using PAK were 43.29 ± 1.41 D and 42.99 ± 1.34 D, respectively. The mean keratometry measurements obtained by PAK were slightly steeper than that of MK, but the difference was not statistically significant as for vertical meridian and horizontal meridian (P = 0.609, 0.209), respectively [Table 2]The correlation coefficients for vertical meridia measurements obtained using MK and PAK in 1st, 2nd, and 3rd set of readings were 0.965, 0.966, and 0.972, respectively [Figure 2]a,[Figure 2]b,[Figure 2]c. The correlation coefficients for horizontal meridia measurements obtained using MK and PAK in 1st, 2nd, and 3rd set of readings were 0.949, 0.949, and 0.940, respectively [Figure 2]d,[Figure 2]e,[Figure 2]fOn comparing the mean of average KA, MK and PAK were 0.661 ± 0.796 and 0.633 ± 0.590, respectively, the difference between the two instruments was not statistically significant (P = 0.573). The correlation coefficients for KA measurements obtained using MK and PAK in 1st, 2nd, and 3rd set of readings were 0.907, 0.951, and 0.949, respectively [Table 3].{Table 2}{Figure 2}{Table 3}

The mean of axis measurements obtained using MK was 10.33 ± 36.47° and using PAK was 20.78 ± 12.39°. On comparing these values, there was statistically significant difference between the two instruments (P = 0.01) [Table 4].{Table 4}

Repeatability of manual keratometer and portable automated keratometer

The intraclass correlation for vertical meridia, horizontal meridia, and axis measurements using MK were 0.888, 0.993, and 0.973, respectively, the mean of SD within sessions were 0.05, 0, and 0.868, respectively. The intraclass correlation for vertical meridia, horizontal meridia, and axis measurements using PAK were 0.994, 0.989, and 0.963, respectively, the mean of SD within sessions were 0, 0.03 and 1.350, respectively [Table 5].{Table 5}


The PAK is handheld instrument designed to provide rapid and precise estimate of keratometry in adults. Although there have been few published reports, in which PAK was used for young children. The portability and ease of use of PAK suggest its utility in screening of young children.

The MK has been the gold standard keratometer since years. In the present study, both the meridia were slightly steeper in females than males by a difference of <0.5 D, but this difference was statistically nonsignificant as P value for vertical meridia and horizontal meridia were P = 0.287, 0.325, respectively. Similarly, Iyamu and Osuobeni concluded that females had slightly higher mean of average corneal curvature measurements; however, there was no statistically significant difference. Lam reported the difference of more than 0.5 D when the instrument was held at the orientation of 15° or more as compared to the vertical plane, and they also concluded that the PAK should be used in a vertical position to obtain accurate measurements which was applied in the present study also.[9]

They also suggested that the tendency for females to have steeper meridia may be linked to the fact that females have shorter axial length than males.[10]

In the present study, on comparing MK and PAK using three criteria which were mean of the two keratometric readings, correlation between the keratometric readings and mean KA, the results showed no statistically significant difference. These results were in concordance with Jarvis et al. who compared the accuracy of PAK with MK on the basis of mean difference of astigmatism between the two meridia which was 0.0189 ± 0.5878 D and average keratometry reading was 0.0318 ± 0.5878 D with no statistically significant difference (P > 0.001).[11] Ale Magar reported mean difference between MK and automated keratometric readings was not statistically significant which was same as reported in the present study.[12] Hammack in their study reported correlation coefficient of 0.97 on the linear regression analysis of the individually automated keratometer compared with MK keratometry readings which was comparable to the various coefficient values obtained in the present study.[13] Similar findings were reported by Ramakrishnan and Naik[14] and Elliot et al.[15]

Sunderraj reported statistically significant difference of 11° in the measurement of the axis by automated keratometer in comparison to MK (P< 0.001) which holds true for the present study also where difference was about 10.45°.[16] Halberg et al. also reported statistically significant difference between MK and automated keratometer in axis measurement.[17]

The intratest reliability test in this study indicated good repeatability of MK and PAK for vertical, horizontal meridia and axis measurements which were 0.888, 0.993, 0.973, and 0.994, 0.989, and 0.963, respectively. Jarvis et al. also reported the intraclass correlation for average MK and PAK keratometry reading as 0.981 and 0.995, respectively, which was similar to the present study results.[11] Similarly, Chang et al. reported good reliability of the mean keratometry reading by automated keratometer.[18] Similar findings were reported by Iyamu and Osuobeni[19] and Noonan et al.[20]

Limitations of the study

The study had following limitations: (1) the study only included children with age >5 years and (2) children with various ocular pathologies were not included as well.

Keratometry measurements using MK and PAK showed good reliability using intraclass correlation for horizontal and vertical meridia. Both the instruments (MK and PAK) provided significantly similar keratometric readings for horizontal and vertical meridia. However, the study shows that the axis measurements obtained using both the instruments were not interchangeable. Hence, automated keratometer offers precision in measuring the keratometric values for various purposes such as IOL calculation and contact lens fitting in children where MK is not possible.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


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