Rufina Chan

The repeatability and accuracy of axial length and anterior chamber depth measurements from the IOLMaster

Background: Axial length and anterior chamber depth have been measured clinically using conventional ultrasound biometry. Recently, a non‐contact device has become available to measure these parameters. This study evaluated the repeatability and accuracy of this device.

The Validity of a New Noncontact Tonometer and Its Comparison with the Goldmann Tonometer

Purpose. This study compared a new noncontact tonometer (NCT), the Nidek NT-4000 (Nidek Co., Ltd., Aichi, Japan), with a pulse detection feature; an earlier model, the Nidek NT-2000, without this pulse detection facility; and Goldmann tonometry. Methods. Thirty-one young subjects had their intraocular pressure (IOP) in one eye randomly measured by two NCT’s, followed by a Goldmann tonometer. The pulse detection mode used by the NT-4000 included synchronizing the IOP with the peak of the pulse (P-P), the middle of the pulse (P-M), or the bottom of the pulse (P-B). The order of measurements from these three modes was also random. Three consecutive readings were obtained from each mode/tonometer, and the mean was used for analysis. Results. Goldmann tonometry demonstrated the smallest variation from consecutive measurements (coefficient of variation, <4%), followed by the NT-4000 (coefficient of variation, <5% in various modes) and the NT-2000 (coefficient of variation, >5%). For the NT-4000, the mean IOP decreased from the highest in the P-P mode (16.1 mm Hg) to the lowest in the P-B mode (14.7 mm Hg), with the P-M mode in the middle. A significant difference was found among the IOP readings using the NT-4000 (in various modes), NT-2000, and Goldmann tonometry (repeated-measures analysis of variance, p < 0.01). More than 80% of the results from the NT-4000 were within 3 mm Hg of those from the Goldmann tonometry. Conclusions. The pulse detection feature from this new NCT could capture and monitor pulse waves, thus reducing the variations in the consecutive measurements. The NT-4000 also performed better than the NT-2000 when compared with the Goldmann tonometry.

Effect of cycloplegia on axial length and anterior chamber depth measurements in children

Background:  Cycloplegia has been shown to have no effect on axial length measurement made with the IOLMaster in adults. The current study aimed at evaluating the effect of cycloplegia on axial length and anterior chamber depth (ACD) measurements made with the IOLMaster and an ultrasonic biometer in children.

The validity of a digital eyelid tonometer (TGDc‐01) and its comparison with Goldmann applanation tonometry – a pilot study

Purpose:  To determine the intra‐ and inter‐examiner repeatability of a new eyelid tonometer, and its agreement with Goldmann applanation tonometry (GAT).

Intra‐observer and inter‐observer repeatability of Anterior Eye Segment analysis system (EAS‐1000) in anterior chamber configuration

Background:  Anterior chamber configuration can be assessed via optical or ultrasonic techniques. Scheimpflug photography is a non‐invasive method measuring the anterior segment. The Anterior Eye Segment analysis system, EAS‐1000, utilises the Scheimpflug principle and was found to have good repeatability. Previous repeatability studies, however, have had limitations in their design. The current study investigated the intra‐observer and interobserver repeatability of the EAS‐1000.

Effect of posture and artificial tears on corneal power measurements with a handheld automated keratometer.

Purpose: To study the effect of posture and artificial tears on handheld automated keratometry. Setting: Department of Optometry and Radiography, Hong Kong Polytechnic University, Hong Kong, China. Methods: Thirty‐five subjects were recruited to have corneal curvature measurement in 1 eye (randomly selected) by a Medmont topographic keratometer and a Nidek handheld keratometer. In handheld keratometry, the measurements were taken with the subject in a sitting and lying posture (both with and without the use of artificial tears). The sequence of measurements was randomly assigned, but the application of artificial tears was always the last. The steepest and flattest corneal curvatures were compared between the 4 conditions. The corneal power was converted to orthogonal power vector components and rectangular Fourier form (M, J0, J45) for another comparison. Results: There was a significant difference in the steepest and flattest meridians between the 4 conditions (P<.01). However, the mean difference between the handheld keratometer and the topographic keratometer was less than 0.50 diopter, and the intraclass correlation coefficient (ICC) was very high (0.96), indicating good clinical reliability. When analyzed in rectangular Fourier form, the difference was also significant but the ICCs were lower (0.97, 0.89, and 0.64 for M, J0, and J45, respectively). The greatest difference was when subjects were in the lying posture and had received artificial tears. Conclusions: Handheld keratometry provided different results from topographic keratometry. The difference was greatest with the use of artificial tears. Cataract surgeons should take this into consideration, especially when using the handheld keratometry in the operating theater in patients under general anesthesia. Results show that the power vector method is best for studying corneal shape.

Effect of instrument rotation on handheld keratometry

Purpose: To study the effect of instrument rotation on handheld automated keratometry. Setting: Department of Optometry and Radiography, The Hong Kong Polytechnic University, Hong Kong SAR, China. Methods: In 33 recruited subjects, corneal curvature in 1 eye (randomly selected) was measured using a Medmont topographic keratometer and a Nidek handheld keratometer. In handheld keratometry, measurements were obtained holding the instrument in the upright position and rotating it anticlockwise 5 degrees, 10 degrees, and 15 degrees and then clockwise 5 degrees, 10 degrees, and 15 degrees. The sequence of measurements was randomly assigned. The steepest and flattest corneal curvatures as well as the axis along the flattest meridian were compared in different conditions. The corneal power was converted to vector representation (M, J0, J45) for a second comparison. Results: There was a significant difference in the steepest and flattest curvatures in different conditions (repeated‐measures analysis of variation, P<.05). However, the mean difference between handheld and topographic keratometry was approximately 0.25 diopter (D) for the steepest curvature and 0.05 D for the flattest curvature regardless of the direction and amount of rotation. The intraclass correlation coefficients were nearly 1, which indicated good clinical reliability. The mean difference in axis determination followed the direction and amount of rotation. With vector representation, the difference between the devices increased with the amount of rotation, especially J0 and J45. Conclusions: Handheld keratometry was in agreement with topographic keratometry. However, practitioners should adjust the axis manually according to the direction and amount of rotation. The difference between handheld and topographic keratometry increased with the rotational effect, which was seen with vector representation. Practitioners are advised to use the handheld keratometer in the upright position.

Morning glory syndrome.

Morning glory syndrome is a congenital optic disc anomaly in which much of die excavated colobomatous optic disc is filled with glial tissue. Ocular complications may include strabismus, reduced visual acuity and retinal detachment and it may have systemic associations as in Aicardis syndrome. A patient widi monocular morning glory syndrome and reduced visual acuity is reported. The pattern reversal visually evoked potential was reduced and the latency increased in the affected eye.

Should Orbscan pachometry be performed before or after Goldmann applanation tonometry

Purpose:  To compare the Orbscan central corneal thickness (CCT) values before and after intraocular pressure (IOP) measurement with Goldmann applanation tonometry in young normal adults.

Epiretinal membrane with macular pucker

Background: Epiretinal membranes are a common finding in people over the age of 50 years. Clinically, they usually cause minor visual distortion. However, in some patients, there may be a significant visual loss and/or metamorphopsia and surgery may be required in more severe cases.