Dioptric Value Research Articles

Low‐grade myopia in children with regressed retinopathy of prematurity

Myopia is a frequent sequelae of retinopathy of prematurity. The mechanism for myopia development in children born preterm is not well understood. From a group of 33 myopic preterm children we selected those who had regressed retinopathy and myopic values < or = 5 D. Seventeen children met our criteria. Of them, 10 patients could be re-examined. Factors related to myopia development were analyzed and compared to a control group of 12 children born fullterm with emmetropia or low hypermetropia, as well as another group of 10 fullterm children with myopic values < or = 5 D. The age of children ranged from 9 to 14 years in all groups. The mean birth weight in myopic premature children was 1249.3 g. Higher keratometric diopter values were found in myopic premature children than in emmetropic fullterm children (p < 0.05) and myopic fullterm children (p < 0.05). Increased axial length values were observed in myopic fullterm children when compared to myopic premature children (p < 0.05) In children born preterm the corneal refractive power seems to play a major role in myopia development.

Conversion of keratometer readings to polar values

Corneal astigmatism is a complex entity that has direction and magnitude. This study reports a new method to describe corneal astigmatism within the with- and against -the-rule concept. Each net astigmatism of the maximal power M in the meridian α may be divided into two dioptric components: a with-the-rule astigmatism projected on the 90-degree meridian and an against-the-rule component projected on the 180-degree meridian. The former figure has the dioptric value M × sin2α, the latter M × cos2α. The polar value is defined as the difference between these magnitudes: M × (sin2#x00D7; - cos2α). The polar value calculates the balance between the with- and against-the-rule components for any given net astigmatism. The entire model allows an exact description of surgically- induced with- or against-the-rule astigmatism following cataract extraction. The advantage of the model is that a corneal astigmatism may be expressed by a single figure. The system enables each surgeon to evaluate the contribution of the preoperative astigmatism, incision type, suture technique, and postoperative treatment on the final astigmatism. This in turn allows the surgeon to estimate a number of different surgical techniques empirically. By disposing of and choosing between several known techniques the surgeon may be able to minimize final astigmatism even in cases of significant preoperative astigmatism.

Permeability of the blood-retinal barrier in myopia. An analysis employing vitreous fluorophotometry and computer simulation.

Vitreous fluorophotometry was performed in 165 eyes of 93 cases with various degrees of myopia. The age range was 10-39 years. On background of the significant correlation between the refractive diopter value and the length of vitreous cavity, a simulation model for myopia has been established for assessing the permeability of the blood-retinal barrier. Significant negative correlations between the diopter and P-in and the diopter and D-p were found, indicating that by increasing degree of myopia, the functional disorder of the blood-retinal barrier and the liquefaction of the posterior vitreous gel progress. From the comparative study between eyes with slight myopia and eyes with emmetropia, a significant increase in the length of the vitreous cavity and P-in was found in the former, whereas no significant difference was observed in D-p. Therefore, it is suggested that the functional disorder of the blood-retinal barrier in myopia produces the liquefaction of the posterior vitreous gel.

The effect of spherical aberration of contact lens to the wearer.

To determine the influence of the spherical aberration of a contact lens on the total spherical aberration of the eye-contact lens system, appropriate formulas are derived. By comparing the total spherical aberration of the eye without a contact lens with that found when a contact lens is in place, it is shown that the spherical aberration of the eye is determined, almost entirely, by the first refracting surface (either cornea or contact lens). The amount of aberration when converted to a dioptric value shows the relative effects clearly.

Ophthalmic changes from age of 10 to 18 years. A longitudinal study of sequels to low birth weight. I. Refraction.

A report is given on refractive changes (delta R) from age of 10 to 18 years. The 1979 follow-up comprises 137 persons who had earlier (around 1970) participated in a larger investigation into ophthalmic sequels to a low birth weight (n = 539). In general (127 out of 137), there is a shift towards lower dioptric values (increase in refraction). Seven remained static while three showed a slight decrease in refraction (0.25-0.5 D). Adult emme- and hypermetropia show a median delta R about 0.7 D (increase) during adolescence, against median values of 1.7 and 2.5 D in juvenile myopia, of ex-prematures and full-terms respectively. With a median delta R of 1.2 D, 'myopia of prematurity' occupies an intermediate position (21 eyes of 13 subjects). Except for this subgroups, there is no evidence that low birth weight has influenced refractive distribution. With a (planned) skewing towards myopia, the 1979-sample cannot be considered epidemiologically representative, as was the original 1970-material. Concerning the latter, the 18-year incidence of myopia is given as 17.6% for ex-prematures and 13.1% for fullterms (minimum figures, based on school medical records).

Effects of hyperbaric air pressure on keratometry.

Following reports of vision blur by scuba divers at depth below 100 feet, keratometric readings were taken on volunteers inside a hyperbaric chamber at the USAF School of Aerospace Medicine. It was found that as the pressure within the chamber increased, the corneal reading showed an increased dioptric value. This change in refractive condition also occurred in measurement on test steel balls. Whether this dynamic response was due to increased atmospheric index, or displacement of instrument optics, was explored.

Optimum Diopter Value for a View-finder of Photographic Camera

(1972). Optimum Diopter Value for a View-finder of Photographic Camera. Optica Acta: International Journal of Optics: Vol. 19, No. 5, pp. 343-345.

RETINOSCOPY AT A DEFINITE DISTANCE

The art of retinoscopy is based theoretically and practically on the maintenance of a known distance between the eye of the patient and that of the retinoscopist. The length actually chosen is based on habit and convenience, and may be, and frequently is, modified to suit unusual circumstances. The dioptric effect of this distance is, of course, well known: Compensation is made (for infinity) by subtracting from the retinoscopic findings the number of diopters which is the reciprocal of the distance in meters. The observer places before the eye of the patient a lens which will cause the emergent light to come to a focus at some convenient and accurately measured distance. The reciprocal of this focal length (in meters) yields the dioptric value of the lens which causes parallel light to be focused at that specific distance; and this dioptric value subtracted from the lens actually in place yields