BACKGROUND: The corneal sighting center is defined by the intersection of the line of sight with the anterior corneal surface and is usually found by measuring angle lambda, between the pupillary axis and the line of sight. It is to be determined if a measurement of the pupil offset in the corneal map of videokeratography might be used instead of angle lambda to provide a practical clinical method for finding the corneal sighting center. METHOD: Two-dimensional angle lambda measurements were made in a group of 17 young adult Caucasian subjects under natural pupil conditions, using an apparatus designed for this purpose, and were compared to measurements of the corneal sighting center position as located by videokeratography. RESULTS: The correlation between angle lambda as measured directly and the pupil offset as measured by videokeratography was 0.84, which is statistically and clinically significant. CONCLUSIONS: The position of the corneal sighting center may be found relative to the corneal reflex of a fixated light by using the distance and direction of the pupil offset in the corneal map of videokeratography, or indirectly by taking 0.6 times the same value and measuring in the opposite direction from the pupillary axis. The latter method does not require active fixation by the patient.

Adult↗

PubMedDate not supplied

The effect of endotoxin and endotoxin tolerance on inflammation induced by mycobacterial adjuvant.

Peptidoglycan, the substance in mycobacteria thought to be responsible for inducing adjuvant arthritis, and endotoxin (lipopolysaccharide or LPS) share many inflammatory properties. Since repeated administration of LPS produces tolerance, i.e., resistance to the toxic and inflammatory effects of LPS, we tested whether LPS and/or LPS tolerance might influence inflammation due to mycobacterial adjuvant. Male Sprague-Dawley rats were injected with Escherichia coli LPS or saline intraperitoneally and then challenged with 100 micrograms killed Mycobacteria butyricum (adjuvant) in the footpad. A single dose of 100 micrograms LPS three or 24 hours before adjuvant markedly, but transiently, reduced the local footpad swelling that begins within hours of the adjuvant injection and histologically resembles a sterile abscess. Animals that received multiple doses of LPS and were therefore tolerant or animals that received LPS 72 hours before adjuvant demonstrated adjuvant-induced footpad swelling nearly equal to controls. The anti-inflammatory effect of LPS was transient since footpad swelling in all groups was nearly comparable six days after the adjuvant injection and LPS failed to inhibit consistently the arthritis that develops two or more weeks after adjuvant injection. These studies establish that LPS can markedly inhibit the prodrome of adjuvant arthritis (footpad swelling due to M. butyricum), that inhibition of this prodrome does not prevent the subsequent development of arthritis, and that LPS tolerance diminishes this anti-inflammatory effect of LPS.

Animals↗

PubMedDate not supplied

Corneal power correction factor for photorefractive keratectomy.

BACKGROUND: Studies of corneal power changes resulting from photorefractive keratectomy generally rely on keratometer or videokeratograph measurements. These instruments convert corneal radius of curvatures values to optical powers by means of the single refracting surface formula, which incorporates an index of refraction value of 1.3375. This index approximates that of the tears but not the 1.376 index of the corneal epithelium or stroma. A hypothetical optical model was used to determine the most appropriate index to be chosen with respect to corneal power calculations relative to photorefractive keratectomy. METHODS: The contribution of each refractive element in the tear lens-corneal surface to the total power of the eye was calculated in order to identify which index of refraction was most appropriate for the corneal power calculation. RESULTS: The outer tear surface has significant optical power but the tear layer as a whole has nearly zero power due to the offsetting negative power of the posterior test surface. There is no significant difference in the effective power of light leaving the corneal anterior surface when considered with or without the tear layer. Photorefractive keratectomy changes the epithelium and anterior surface of the corneal stroma, but does not affect the posterior stroma or other ocular media. Hence the refractive index for the corneal epithelium or stroma of 1.376 should be used in converting radius to optical power values. The error in assuming a corneal index of 1.3375 is a constant proportion equal to 11.4% of the corneal power reading. CONCLUSIONS: Photorefractive keratectomy presents a situation in which the actual corneal refractive index of 1.376 should be used for correct corneal radius to power conversions. This may be accomplished by changing the index value in the instrument algorithm for keratometry and videokeratography to 1.376 or by adding a correction factor of either 11.4% of the regular reading to its value or multiplying by the factor 1.114. In other applications of keratometry or videokeratography, the index 1.3375 may be more appropriate.

Cornea↗