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Biomedical subjects

R A Krefman

Publications and source records attributed to R A Krefman.

8 recordsLinked to original sources
PubMed1995

Lined multifocal wearers prefer progressive addition lenses.

BACKGROUND: Despite reported successes with progressive addition lenses, lined multifocals remain the lens of choice for previous lined multifocal wearers. METHODS: To explore the feasibility of switching lined multifocal wearers to PALs, in a prospective clinical trial we interviewed 265 lined multifocal wearers, prescribed a new PAL (Varilux Comfort) and then interviewed them again to compare the lens types and patient preferences. RESULTS: PALs ranked significantly higher than lined multifocals for all questions and were preferred by 92 percent of the patients. CONCLUSIONS: PALs should be the lens of choice for previous bifocal wearers.

Adaptation, Ocular↗
PubMed1991

A comparative evaluation of Readables to single vision lenses.

Emmetropic presbyopes are often prescribed single vision lenses for near or intermediate work. These lenses limit the usable range of clear vision especially in advanced presbyopia. Readables, a special purpose PAL that emphasizes intermediate and near vision extends the usable range by providing appropriately changing power over the middle 28 millimeters of the lens. A crossover design, randomized controlled clinical trial was undertaken to determine if Readables were perceived to provide better function than the single vision reading lens. Readables were preferred by a ratio of 25:2 and scored significantly better in lens performance measures. The design benefits of Readables are appreciated by the presbyopic patient.

Adult↗
PubMed1983

Two additional benefits of dark glasses on rod vision in patients with congenital achromatopsia.

The visual performance of nine rod monochromats was measured with photopic stimuli viewed through filters that attenuated the ambient illuminance. In kinetic perimetry experiments, eight of nine patients showed substantially larger visual field size under the experimental as compared to the control conditions. In increment threshold or brightness-matching experiments, long wavelength sensitivity was shown to be enhanced under the experimental conditions.

Adolescent↗
PubMed1982

Visual improvements with red-tinted glasses in a patient with cone dystrophy.

A patient with cone dystrophy empirically discovered that his vision improved when a red filter was placed in front of his eyes. The present study documents the conditions under which his visual acuity and field improved and shows that the patient's vision is mediated by the night vision photoreceptors, the rods. Increment threshold functions examined the benefits (and limitations) of red glasses to the patient's vision.

Adult↗
PubMed1981

Reversed telescopes on visual efficiency scores in field-restricted patients.

Low vision aids have not been successfully prescribed for many people with peripheral visual field loss. Visual field and visual acuity measurements for four field-restricted subjects were made with and without field-expanding reversed telescopes. The calculated visual efficiency was not significantly improved with such devices; therefore, their value remains in question.

Glaucoma↗
PubMed1981

Reverse Galilean telescopic spectacles in unilateral aphakia.

Minimizing aniseikonia in unilateral aphakia is often a difficult task. A case is presented in which a patient preferred a reverse Galilean telescopic spectacle of his own design to a contact lens. The design of the spectacles and the patient's visual performance with them are described. A reverse Galilean telescopic spectacle should not be excluded from the therapeutic alternatives in unilateral aphakia.

Aphakia, Postcataract↗
PubMed1980

Working distance comparison of plus lenses and reading telescopes.

Low vision aids used in the spectacle plane may be either plus lenses or telescopes focused for near. The plus lens has a shorter working distance than a near point telescope of the same equivalent power. A relationship between the anterior focal length (fv) of the near point telescope and the equivalent focal length (fe) of a thin lens of equal power can be derived from the formula fv = (mag) (fe). This formula provides a basis for determining what equivalent powers are equal and interchangeable between the two types of aids. Furthermore, the advantages of the increased working distance afforded by the near point telescope can be defined.

Eyeglasses↗