Axial Length In Children Research Articles

Effect of axial length and keratometry measurement error on intraocular lens implant power prediction formulas in pediatric patients

To examine the relationship between axial length and keratometry measurement errors and intraocular lens (IOL) power calculations for pediatric eyes. The sensitivity of IOL power calculation to errors in axial length and keratometry measurements was computed as a function of axial length and keratometry for the SRK II, Hoffer Q, Holladay I, SRK/T, and Haigis formulas. The sensitivity of the IOL power calculation to an axial length measurement error is increased at 4 to 14 D/mm error in axial length in children compared with 3 to 4 D/mm error in axial length in adults. The error in calculation is 0.8 to 1.3 D/D error in keratometry measurement for both children and adults. Axial length measurement errors in pediatric eyes may lead to large errors in IOL power calculations.

Reliability and validity of the partial coherence interferometry for measurement of ocular axial length in children

To assess the validity and repeatability of partial coherence interferometry (IOLMaster) and A-scan ultrasound measurement of axial length (AL) in children. A prospective comparison of AL measurement made by the IOLMaster optical instrument (Carl Zeiss) and ultrasound A-scan (Alcon) was performed. A total of 20 children (11 male, nine female) were recruited into the study; the mean age of the sample was 11.4 years (range 6.2-15.8). Inclusion criteria comprised individuals <16 years, with no ocular pathology and no previous eye operations or allergy to topical anaesthetics. All measurements were performed by a single examiner. Data on validity show that, on average, a small measurement difference existed between these groups with the IOLMaster being 0.017 mm greater than A-scan ultrasonography. The 95% confidence interval for this difference encompasses zero, demonstrating that no significant systematic bias exists between the two-measurement techniques. Overall, IOLMaster reliability exceeded that of A-scan. This is evidenced primarily by the spread of the paired test-retest difference for A-scan compared to IOLMaster. The mean test-retest difference for A-scan was considerably larger than IOLMaster at 0.042 and 0.004 mm, respectively. The results show that IOLMaster was more accurate and reproducible than the contact ultrasonographic technique when used in children. Such results indicate that IOLMaster may be a useful tool in studies of eye growth and refractive development in children.

Fitting Age Related Reference Intervals to Ocular Axial Length in Children Using a Four-Parameter Curve Family

There exist a number of methods to determine age dependent reference intervals. Some of those are based on standard parametric classes of distributions like normal or lognormal and standard parametric classes of age functions like linear or polynomial of some order. Others are based on more flexible distribution classes like Box-Cox transformation of the normal distribution, which allows for skewness. There exist also purely nonparametric methods, where the bounds of the reference intervals are only assumed to be nondecreasing and they are directly estimated by a suitable error function without any distributional assumption. In this paper we propose a flexible four-parameter age function class for the reference interval bounds and a method to estimate those. The four parameters in the class have concrete meanings; starting value at age 0, asymptotic value at increasing age, time scale and shape. The function class satisfies some desirable properties, which are discussed. The estimation of the parameters in the model uses the same type of error function as in the purely nonparametric methods. With our method we also get an estimate of the distributional position of an observation for a new individual given its age. The method is illustrated by an application example, where a 90% reference interval for ocular axis length of children up to age 18 years are determined.

Fitting Age Related Reference Intervals to Ocular Axial Length in Children Using a Four-Parameter Curve Family

There exist a number of methods to determine age dependent reference intervals. Some of those are based on standard parametric classes of distributions like normal or lognormal and standard parametric classes of age functions like linear or polynomial of some order. Others are based on more flexible distribution classes like Box-Cox transformation of the normal distribution, which allows for skewness. There exist also purely nonparametric methods, where the bounds of the reference intervals are only assumed to be nondecreasing and they are directly estimated by a suitable error function without any distributional assumption. In this paper we propose a flexible four-parameter age function class for the reference interval bounds and a method to estimate those. The four parameters in the class have concrete meanings; starting value at age 0, asymptotic value at increasing age, time scale and shape. The function class satisfies some desirable properties, which are discussed. The estimation of the parameters in the model uses the same type of error function as in the purely nonparametric methods. With our method we also get an estimate of the distributional position of an observation for a new individual given its age. The method is illustrated by an application example, where a 90% reference interval for ocular axis length of children up to age 18 years are determined.

Ocular axial length in children with unilateral congenital cataract.

Ocular axial length and thickness were measured in 12 children (age 4 to 418 days, median 103 days) with unilateral congenital cataract who were referred to St. Erik's Eye Hospital during 1991-1994. The measurements were performed in both eyes with A-scan ultrasonography before cataract extraction. In 4 children measurement of the axial length was repeated 1 to 4 months after the unilateral cataract extraction. All eyes with congenital cataract were shorter than the normal fellow eye. The individual axial length differences showed a mean value +/- SEM of 1.03 +/- 0.16 mm. This difference was statistically significant (P < 0.01). In the 4 children where measurement of the axial length was repeated, the difference between the eyes after unilateral cataract extraction had become greater than before. In addition, the thickness of the cataractous lens was 0.63 +/- 0.17 mm (mean +/- SEM) less than the non-operated clear lens. This difference was statistically significant (p < 0.01). In conclusion, in children with unilateral congenital cataract the affected eye has a shorter axial length and a thinner lens.

Intraocular pressure and axial length in children

The intraocular pressure and the anteroposterior length of the eye are of great clinical importance for the diagnosis and management, before and after surgery, of congenital glaucoma. It is well-known that normal intraocular pressure in children is different from the normal levels in adults. We performed measurements of intraocular pressure and axial length in 141 children who had been admitted for eye problems other than glaucoma. The intraocular pressures were measured with the Perkins hand-held applanation tonometer at the beginning of general anesthesia. Simultaneously, A-scan ultra-sound measurements of the axial lengths of the eyes were made. In 10 children under the age of two years, the intraocular pressure was 11.85 +/- 1.35 mmHg. In 79 children from two to seven years, the intraocular pressure was 12.80 +/- 1.73 mmHg. In 52 children from seven to 15 years, the intraocular pressure was 13.31 +/- 1.79 mmHg. The axial lengths of the eyes in children under the age of two years, from two to seven years, and from seven to 15 years, were 21.31 +/- 0.97 mm, 22.04 +/- 0.92 mm, and 23.22 +/- 1.00 mm, respectively. These results were considered to be guidelines for measuring intraocular pressure and axial length in children suspected of having congenital glaucoma. The differences of intraocular pressures stated by other authors are due to early measurement of the intraocular pressure at the beginning of general anesthesia.

Congenital and traumatic cataract. The effect on ocular axial length.

Elongation of the eye is one of the drawbacks of implanting intraocular lenses in children. To evaluate possible effects of cataract and aphakia on eye elongation, we measured the axial length in children with unilateral aphakia (15 children with congenital cataract and 27 with traumatic cataract) and in children with bilateral congenital cataract (operated on in 14 cases and not operated on in eight cases). In all cases of unilateral aphakia, the aphakic eye was consistently longer than the normal fellow eye. Excessive eye elongation was related to corresponding reduction in visual acuity. The presumed rate of elongation was quantitatively expressed using the time elapsed since surgery and the age of the child. In bilateral congenital cataract, the axial length measured in aphakic eyes that were operated on was similar to that in eyes that were not operated on. We suggest that unilateral cataract or aphakia is associated with excessive eye elongation of affected eyes. Eye elongation seems to be related to amblyopia and poor vision rather than to aphakia.