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. 2016 Apr-Jun;9(2):126-36.
doi: 10.1016/j.optom.2015.10.005. Epub 2015 Nov 14.

Reliability of power profiles measured on NIMO TR1504 (Lambda-X) and effects of lens decentration for single vision, bifocal and multifocal contact lenses

Eon Kim  1 , Ravi C Bakaraju  2 , Klaus Ehrmann  3
Affiliations

Reliability of power profiles measured on NIMO TR1504 (Lambda-X) and effects of lens decentration for single vision, bifocal and multifocal contact lenses

Eon Kim et al. J Optom. 2016 Apr-Jun.

Abstract
in English, Spanish

Purpose: To evaluate the repeatability of power profiles measured on NIMO TR1504 (Lambda-X, Belgium) and investigate the effects of lens decentration on the power profiles for single vision (SV), bifocal (BF) and multifocal (MF) contact lenses.

Methods: Accuracy of the sphere power was evaluated using single vision BK-7 calibration glass lenses of six minus and six plus powers. Three SV and four BF/MF contact lenses - three lenses each, were measured five times to calculate the coefficients of repeatability (COR) of the instrument. The COR was computed for each chord position, lens design, prescription power and operator. One lens from each type was measured with a deliberate decentration up to ±0.5mm in 0.1mm steps.

Results: For all lenses, the COR varied across different regions of the half-chord position. In general, SV lenses showed lower COR compared to the BF/MF group lenses. There were no noticeable trends of COR between prescription powers for SV and BF/MF lenses. The shape of the power profiles was not affected when lenses were deliberately decentered for all SV and PureVision MF lenses. However, for Acuvue BF lenses, the peak to trough amplitude of the power profiles flattened up to 1.00D.

Conclusion: The COR across the half-chord of the optic zone diameter was mostly within clinical relevance except for the central 0.5mm half-chord position. COR were dependent on the lens type, whereby BF/MF group produced higher COR than SV lenses. The effects of deliberate decentration on the shape of power profiles were pronounced for lenses where the profiles had sharp transitions of power.

Objetivo: Evaluar la repetibilidad de los perfiles de potencia medidos con NIMO TR1504 (Lambda-X, Bélgica) e investigar los efectos del descentramiento de las lentes sobre los perfiles de potencia de las lentes de contacto monofocales (SV) bifocales (BF) y multifocales (MF).

Métodos: Se evaluó la exactitud de la medida de la potencia esférica utilizando lentes de vidrio monofocales de calibración BK-7, con lentes de seis potencias positivas y seis potencias negativas. Se realizaron cinco mediciones en tres muestras de cada una de las tres lentes monofocales y cuatro lentes bifocales/multifocales diferentes, para calcular los coeficientes de repetibilidad (COR) del instrumento. Se calculó el COR para cada posición de la cuerda, diseño de la lente, prescripción de potencia, y operador. Se midió una lente de cada tipo con un descentramiento deliberada de hasta ±0,5 mm, en intervalos de 0,1 mm.

Resultados: Para todas las lentes, el COR reflejó variaciones en las diferentes regiones de la posición de media cuerda. En general, las lentes monofocales reflejaron un COR menor en comparación a las lentes del grupo BF/MF. No se produjeron variaciones notorias del COR entre las prescripciones de potencia de las lentes monofocales y bifocales/multifocales. La forma de los perfiles de potencia no se vio afectada al descentrar deliberadamente todas las lentes monofocales y PureVision MF. Sin embargo, para lentes Acuvue BF, la amplitud entre el punto más alto y el más bajo de los perfiles de potencia reflejó un aplanamiento de hasta 1,00 D.

Conclusión: El COR a lo largo de la cuerda media del diámetro de la zona óptica se mostró dentro de la relevancia clínica, excepto en la posición central de la cuerda media de 0,5 mm. Los COR dependieron del tipo de lente, reflejando el grupo de lentes bifocales/multifocales un COR superior al de las lentes monofocales. Los efectos del descentramiento deliberado en la forma de los perfiles de potencia fueron significativos en aquellas lentes en las que dichos perfiles tenían unas transiciones de potencia más abruptas.

Keywords: Contact lenses; Lentes de contacto; Monofocales; Multifocales; Multifocals; NIMO; NIMO TR1504; Perfil de potencia; Power profile; Repeatability; Repetibilidad.

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Figures

Figure 1
Figure 1
(a) The front view of the NIMO TR1504 instrument (top-left); (b) software captured high resolution image showing the Schlieren fringes and superimposed lens diameter to assist with lens centration (top-right); and (c) a sample output of the color-coded radial power map (bottom).
Figure 2
Figure 2
Example of Acuvue BF lens when well aligned (left) and the same lens when deliberately decentered by +0.5 mm (right).
Figure 3
Figure 3
The COR for all the BF and MF designs (both operators) are presented here: Acuvue High Add BF (Operator 1: 1st row left; Operator 2: 1st row right), PureVision High Add MF (Operator 1: 2nd row left; Operator 2: 2nd row right), Acuvue Low Add BF (Operator 1: 3rd row left; Operator 2: 3rd row right) and PureVision Low Add MF (Operator 1: 4th row left; Operator 2: 4th row right).
Figure 4
Figure 4
The COR for all the SV designs (both operators) are presented here: Acuvue Advance SV (Operator 1: 1st row left; Operator 2: 1st row right), Clariti 1-day SV (Operator 1: 2nd row left; Operator 2: 2nd row right) and Focus N&D SV (Operator 1: 3rd row left; Operator 2: 3rd row right).
Figure 5
Figure 5
The overall COR of lens designs calculated for each prescription power in two regions of interest on the half chord of the optic zone: (i) central segment ≤ 0.5 mm and (ii) the half chord between 0.51 and 3.2 mm.
Figure 6
Figure 6
Power profiles of deliberately decentered BF and MF lenses: (a) Acuvue BF High-Add (top-left); (b) Acuvue BF Low-Add (top-right); (c) PureVision MF High-Add (bottom-left) and (d) PureVision MF Low-add (bottom-right).
Figure 7
Figure 7
Power profiles of deliberately decentered SV lenses: (i) Acuvue Advance SV (top-left); (ii) Clariti 1-Day SV (top-right) and (iii) Focus N&D SV (bottom).
Figure 8
Figure 8
The average difference in sphere power reading from NIMO measured at center and across ±0.5 mm decentration. *Statistically significant changes.
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