Comparing Height Data For Four Topographers

Staff
1/6/2014

Researchers from the University Medical Center Gronigen, in the Netherlands, performed a cross-sectional study to compare the ability of clinical corneal topographers to describe the shape of the anterior cornea for optical modeling. Unfortunately, test-retest variability hampered a detailed description of the anterior corneal shape at the level of individual subjects, and interdevice variability compromises the exchangeability of the devices.

The anterior corneal shape of healthy subjects was assessed with four topographers (Atlas Placido disk, Galilei dual Scheimpflug, Orbscan scanning slit and Pentacam single Scheimpflug). Exported height data were fit with Zernike polynomials. Mean values with the standard deviation, interdevice variability and test-retest variability were determined for the defocus Z(2,0), astigmatism Z(2,–2) and Z(2,2), coma Z(3,–1) and Z(3,1) and spherical aberration Z(4,0) coefficients for 5.5 mm and 8 mm diameters.

At 5.5 mm, the single Scheimpflug topographer showed the smallest coefficient of repeatability: 0.31 μm for defocus Z(2,0); 0.40 and 0.34 μm for astigmatism Z(2,–2) and Z(2,2), respectively; 0.15 and 0.11 μm for coma Z(3,–1) and Z(3,1), respectively; and 0.08 μm on spherical aberration Z(4,0); the other topographers showed up to 10 times larger coefficients of repeatability. The (unsigned) mean differences were in the range of 0.20 to 1.21 μm for defocus Z(2,0); 0.02 to 0.31 μm and 0.06 to 0.42 μm for astigmatism Z(2,–2) and Z(2,2), respectively; 0.03 to 0.18 μm and 0.03 to 0.35 μm for coma Z(3,–1) and Z(3,1), respectively; and 0 to 0.14 μm for spherical aberration Z(4,0). The Placido-disk topographer and single Scheimpflug topographer data corresponded best. Similar trends were found at 8 mm.
J Cataract Refract Surg 2013; 39:1570-1580.

De Jong T, Sheehan M, Dubbelman M, Koopmans S, et al.

Debridement-scaling: Procedure Reduces Dry-Eye Symptoms
Results of a study from Massachusetts suggests debridement-scaling of the line of Marx and the lower keratinized lid margin provides statistically significant symptom relief of evaporative dry-eye disease and improves meibomian gland function.

Patients symptomatic for and diagnosed with evaporative dry eye who also evidenced anteroplacement and a thickened LOM were alternately and consecutively assigned to the test (n=16) or control (n=12) group. Mean age of the patients was 55.9 ±15 years in the test group vs. 53.7 ±15.3 years in the control. Symptoms were evaluated with the Standard Patient Evaluation of Eye Dryness questionnaire; a minimum of 6/28 was required for admission to the study. Meibomian gland function was also evaluated and the LOM was stained with lissamine green to determine thickness and location.

The stained LOM and the width of the keratinized lower lid margin in the test group were debrided-scaled using a stainless steel, foreign body, golf club spud. All patients were required to abstain from other lid treatments, with exception of artificial tears and warm compresses, and monitored for changes in symptoms and MG function approximately one month later.

There was a significant improvement in symptoms and MG function one month post-debridement-scaling in the test group. The controls evidenced no significant change in either parameter. Patient baseline mean pre-debridement-scaling symptoms were 13.4 ±4.6 (test) vs. 13.9 ±5.5 (control). At one month post-debridement-scaling, symptoms were 10.5 ±3.8 (test; population level statistic <0.0001) vs. 14.3 ±7.5 (control; population level statistic >0.05).  The baseline mean pre-debridement-scaling number of functional MGs was 2.6 ±1.3 (test) vs. 2.7 ±1.5 (control) and 3.8 ±1.4 (test; p=0.0007) vs. 2.4 ±1.1 (control; p>0.05) one month later.
Cornea 2013;32:1554-1557.
Korb D, Blackie C.