The relationship between dioptric power and magnification in progressive addition lenses

Assessment of Visual Quality Improvement as a Result of Spectacle Personalization

Personalized spectacles customized according to an individual's facial anatomy were developed to provide enhanced visual performance and overall comfort when compared to standard spectacles. In this comparative crossover trial, each subject was randomly assigned to wear either personalized spectacles or standard spectacles for two weeks and then tried the second pair for another two weeks. Visual acuity and reading speed were measured, and visual quality and comfort were assessed using specific questionnaires. The correlation of the wearing parameters with the subjects' satisfaction was calculated. According to our results, the subjects wearing personalized glasses reported significantly less experience of swaying and significantly higher overall satisfaction compared to those wearing the control spectacles. At the end of the study, 62% of subjects preferred the personalized spectacles, and visual quality was the primary reason for their spectacle preference followed by wearing comfort. The difference from the ideal cornea-vertex distance was significantly lower when wearing the personalized spectacles compared to the control frames. In addition, the absolute value of the difference from the ideal cornea-vertex distance was significantly correlated with patient satisfaction. These results suggest that personalized spectacles, customized according to an individual's facial anatomy for the ideal wearing parameters, result in both visual and comfort advantages for wearers.

Interdevice agreement in the measurement of physiognomy parameters and frame angles to prescribe progressive addition lenses

CLINICAL RELEVANCE

Ophthalmic lens adaptation requires accurate measurements of physiognomy parameters and frame angles, with a great impact on subject vision, especially when personalised progressive addition lenses are prescribed.

BACKGROUND

The aim of this study is to describe interdevice agreement between different methods and traditional methods (frame ruler).

METHODS

The agreement of the interpupillary distance, nasopupillary distance and fitting point height measured with four devices (PD-5, OptiCenter, Visioffice and a frame ruler) and of pantoscopic and frame wrap angles measured with three devices (OptiCenter, Visioffice and Essilor standard ruler) was assessed in 21 healthy volunteers, by a Bland-Altman analysis; mean difference and limits of agreement (LoA) were calculated.

RESULTS

Frame ruler nasopupillary distance measurements showed limited agreement with PD-5 [-0.38 ± 1.03 (LoA -2.40 to 1.64) and 0.44 ± 1.02 (LoA -1.72 to 2.61)] and Visioffice [0.62 ± 1.24 (LoA -1.81 to 3.05) and -0.16 ± 1.72 (LoA -3.54 to 3.22)] measurements for the right and left eyes, respectively. Poor agreement was found for interpupillary distances (PD-5 [0.21 ± 1.47 (LoA -2.67 to 3.09)], OptiCenter [-0.05 ± 1.16 (LoA -2.32 to 2.22)] and Visioffice [0.46 ± 1.95 (LoA -3.36 to 4.28)]), fitting point height (OptiCenter [-1.27 ± 2.56 (LoA -6.27 to 3.75) and -0.92 ± 2.77 (LoA -6.35 to 4.51)] and Visioffice [-5.88 ± 6.21 (LoA -18.05 to 6.29) and -5.98 ± 6.12 (LoA -17.98 to 6.02)] for the right and left eyes, respectively) and pantoscopic and frame wrap angles (OptiCenter [-4.13 ± 3.75 (LoA -11.48 to 3.22) and -1.09 ± 0.60 (LoA -2.27 to 0.09)] and Visioffice [-6.18 ± 3.53 (LoA -13.10 to 0.74) and -1.93 ± 3.49 (LoA -8.77 to 4.91)], respectively).

CONCLUSIONS

These results suggest that measurements of physiognomy and frame angles are not interchangeable between assessed devices and that these differences could induce lens centration errors with a large impact on progressive addition lens prescriptions.

Comparison of physiognomy and frame angle parameters using different devices to prescribe progressive addition lenses

Clinical relevance: Accurate measurement of several physiognomy parameters (interpupillary, nasopupillary and fitting height distances) and frame angles (pantoscopic and frame wrap angles) is essential for prescribing progressive addition lenses for presbyopic patients.Background: Few reports have described the repeatability of different devices commonly used to conduct essential measurements for prescribing progressive addition lenses.Methods: Interpupillary, nasopupillary (at far and near distances) and fitting point heights were measured three consecutive times in 21 healthy volunteers with four devices (traditional frame ruler, PD-5 interpupilometer, OptiCenter, and VisiOffice). Pantoscopic and wrap frame angles were also measured three times with Essilor standard pantoscopic ruler, Opticenter and VisiOffice.Results: The frame ruler, PD-5 and Opticenter showed better repeatability for interpupillary and nasopupillary distance (co-efficient of variation close to 1%, within-subject standard deviation or Sw < 0.50 mm) measurements at far and near distances than Visioffice (co-efficient of variation > 2%, Sw > 0.50 mm). Fitting point heights measurements showed worse repeatability with all devices (frame ruler: co-efficient of variation close to 5%, Sw = 0.46 mm; Opticenter co-efficient of variation > 5%, Sw > 0.80 mm; Visioffice co-efficient of variation > 10%, Sw > 1.50 mm). Pantoscopic angle measurements showed very low repeatability with the ruler and Opticenter (co-efficient of variation > 25%, Sw > 1.90 mm). The frame wrap angle showed unacceptable repeatability values with the ruler (co-efficient of variation > 10%, Sw = 0.49º) and Visioffice (co-efficient of variation > 60%, Sw > 2.50º), but acceptable repeatability with Opticenter (co-efficient of variation < 1%, Sw = 0.05º).Conclusions: Interpupillary and nasopupillary distance measurement showed acceptable repeatability with all the assessed methods; however, these measurements alone are no longer sufficient for free-form progressive addition lens prescription, which requires fitting point heights and pantoscopic and frame wrap angle measurement. Such measures display a lack of repeatability that could induce centration errors and could affect vision and/or adaptation of the user.

Near Points of Convergence and Accommodation in a Population of University Students in Iran

PURPOSE

To determine the distribution of the near point of convergence (NPC) and near point of accommodation (NPA) in a young student population in Iran.

METHODS

The subjects were selected using a cluster sampling method. All students underwent optometry tests, including visual acuity measurement, refraction, and cover test, as well as ophthalmic examinations. The NPC and NPA were measured using an accommodative target (near Snellen chart).

RESULTS

Of 1,595 students, the data of 1,357 were analyzed. The mean NPC and NPA in the total sample were 7.25 cm (95% confidence interval [CI], 7.02 to 7.48) and 9.99 cm (95% CI, 9.69 to 10.29), respectively. Older age was associated with an increase in the NPC, which increased from 6.98 cm in 18-20 years olds to 9.51 cm in those over 30 years. The NPA was significantly associated with age and refractive errors in the multiple linear regression model, increasing from 9.92 cm in 18-20 years olds to 11.44 cm in those over 30 years ( P = 0.003). Hyperopic eyes had lower NPA than myopic and emmetropic eyes ( P = 0.001). In younger age groups, the mean accommodation amplitude was lower than the mean Hofstetter value. Moreover, with age, especially after 30 years, the mean values surpassed those determined using the Hofstetter formula.

CONCLUSION

The NPC values in this study were lower than those previously reported for identical age groups. The Hofstetter formula is not always an accurate predictor of the accommodation amplitude in the Iranian adult population.

Simulating real-world scenes viewed through ophthalmic lenses

We present a comprehensive procedure to simulate real-world scenes viewed through ophthalmic lenses. Such a method enables us to anticipate the effects on image formation of the following combined undesired optical defects typically found in ophthalmic lenses: blur, distortion, and chromatic aberration. Additionally, it helps in comparing the expected scenes seen with different lens designs. The procedure is based on the following steps: (1) to calculate the distortion and local dioptric matrix associated with a set of different gaze directions; (2) to estimate point spread functions (PSF) associated with these matrices; (3) to compute the joint action of distortion, chromatic aberration, and PSF field on the scenes. We illustrate this procedure with two +5D spherical lenses: a moderately good performance lens and a highly degrading one. The method is suitable to evaluate ophthalmic lenses in a virtual reality framework.