Circadian rhythm: corneal curvature and refractive changes after wearing contact lenses.

The ciradian rhythm of habitual contact lens (PMMA) wearers is characterized by steepening of corneal curvature and increasing myopia after lenses have been worn during the day and flattening of corneal curvature and decreasing myopia after lenses have been removed overnight.

Astigmatism after contact lens wear.

With-the-rule astigmatism increased by more than 3 D in 2 habitual long-term wearers of contact lenses after they abruptly stopped wearing their lenses. Reducing wearing time gradually over a 2- to 3-month period caused less than 1 D increase in with-the-rule astigmatism in 2 other long-term wearers. All 4 persons had worn polymethylmethacrylate contact lenses for 12 or more years.

Strabismus measurements in the Siamese cat.

Anatomical and neurophysiological studies suggest a relationship between "abnormal" visual pathways and strabismus found in the Siamese cat. A telephotographic method for measuring eye positions in these cats reveals that newborn Siamese cats have a conspicuous exotropia appearance. Adult animals appear to have esotropia, orthophoria, or exotropia, which can be intermittent.

Combat spectacles: military testing of a new spectacle frame.

An improved spectacle frame has been developed for use during periods of extreme physical activity, particularly by military personnel during combat operations, and which can be used under protective face masks and headgear. The frame has a wrap-around shape, made of nylon with a contoured, recessed bridge and safety lens groove. U-shaped bridles snap on the frame front and an adjustable, interlocking strap fits over the bridles and passes under a protective mask sealing area. Field tests were conducted with 1231 soldiers at 12 military installations. Over 90% of those tested found combat spectacles were comfortable to wear, extremely durable, compatible with headgear and superior to existing military eyewear.

Accidental exposure to sarin: vision effects.

Two men were accidentally exposed to vapors of sarin, a cholinesterase inhibitor and extremely toxic nerve gas. Diagnosis was confirmed by depressed cholinesterase activity, and fixed extremely miotic pupils. No other signs or symptoms developed and neither man required treatment. Recovery to normal cholinesterase activity was gradual over a 90-day period. Pupillary reflexes were not detectable until 11 days after exposure; the miotic pupils dilated slowly over a 30-45 day-period. Eye pain and blurred vision did not occur; visual acuity and amplitude of accommodation were improved for several weeks. Other functions not affected significantly were intraocular pressure, visual fields, color vision, heterophorias, and vergences.

Corneal refraction: relative effects of each corneal component.

The refractive power of the cornea may change after wearing contact lenses and as a result of disease or surgery. Each corneal component that contributes to the refractive power was analyzed and their relative significance was determined by comparing the refractive effects of a 10% change. In order of magnitude, the effect of a 10% change in each component was as follows: anterior corneal curvature (4.87 D), index of refraction (1.87 D), depth of anterior chamber (1.20 D), posterior corneal curvature (0.62 D) and corneal thickness (0.01 D). Refractive changes are the result of increases and decreases of each component and the total effect is the sum of the individual changes in each component.

Vision and ocular changes following accidental exposure to organophosphates.

The most conspicuous short-term effects of exposure to organophosphates are miotic pupils and a reduced visual field. Two men accidentally exposed to vapors of sarin, a cholinesterase inhibitor and extremely toxic nerve gas, showed these effects but no adverse effects on near- or far-visual acuities, oculomotor functions, intraocular pressure or color vision. However, reports of other accidental exposures to organophosphorus compounds suggest that there are visual and ocular changes, including myopia and decreased visual acuity.

Changes in corneal curvature associated with contact lens wear.

Brief answers are given to 5 complex questions about the corneal curvature of contact lens wearers. Short-term (circadian) and long-term (withdrawal) changes are significant time variables which are often overlooked.

The effects of external ocular irritation on intraocular pressure.

Riot control agents (tear gases) cause intense eye irritation and reflex squeezing of the eyes. The intraocular pressure under these circumstances is unknown but animal and human studies of ocular irritation and forces acting upon the eye indicate a transient increase in intraocular pressure which is not necessarily detrimental to vision.

Long-term effects of extended wear lenses: changes in refraction, corneal curvature, and visual acuity.

Extended wear lenses (Scanlens 75) +4.25 to -10.00 D were worn monocularly by 19 patients for an average of 5.4 years. The other eye of each patient was either emmetropic or amblyopic and no lens was worn. Both eyes were tested after lens removal and again 2 days and 7 days later. No significant differences in refraction, keratometry, or visual acuity were found between the experimental and control eyes. The amount of changes in both groups was not clinically significant: refractive changes averaged less than 0.37 D, keratometric changes averaged an equivalent 0.25 D, astigmatism increases were less than 0.25 D, and visual acuity was fully correctible to previous best visual acuity with spectacles in all cases.

Evaluating the effects of wearing contact lenses: morning and afternoon testing.

Corneal steepening and myopic increases are characteristic of diurnal variations which affect habitual wearers of contact lenses. Testing before insertion of lenses and after wearing lenses for 8 hours provided a good indication of the magnitude of diurnal changes in 35 individuals.

Adaptation to hydrogel contact lenses: variations in myopia and corneal curvature measurements.

Forty patients wearing lenses (soflens) were examined regularly for 3 months. During the first month the mean myopia gradually increased to 0.12 D more myopia and increased linearly to 0.50 D more myopia at 3 months. The mean corneal curvature flattened during the first 3 weeks, but steepened to about 0.37 D at 3 months. The process of myopia changes are not attributed solely to the anterior corneal curvature, but may also be the result of variations in the posterior corneal curvature, corneal thickness and index refraction as well as a change in the depth of the anterior chamber.