Silicone Hydrogels Materials for Contact Lens Applications

Purpose: To assess current recommendations by optometrists for replacement frequency (RF) of silicone hydrogels (SH) and daily disposable (DD) contact lenses in Canada, determine rates of non-compliance with recommendations by both the optometrist and patient, and investigate reasons for non-compliance. Methods: Survey packages were sent to optometrists in Canada who had agreed to participate. Patients completed survey questions regarding demographics and contact lens wearing patterns, including recommended and actual contact lens RF. Optometrists were asked to provide lens information and their recommendation for RF. Fifty-eight optometrists returned 654 surveys, of which 578 were eligible for analysis. Results: Seventy percent of patients were female with a median age of 32 years. Lens type distribution was 18% DD, 35% two-week SH, and 47% one-month SH. Six percent were worn for extended wear. Daily wear median wearing time was 12 hours/day, a median of five days/week for DD, seven days/week for SH (two-week and one-month). Optometrists’ recommendations were non-compliant with the manufacturers’ recommended RF for 6% of DD, 35% of two week, and 2% of one-month patients. Patients were non-compliant with recommendations from both the manufacturer and optometrist for 12% of DD, 43% of two-week, and 31% of one-month lens wearers. The most common reason for non-compliance was forgetting which day to replace lenses. Fifty-six percent thought a reminder system would help with compliance. A higher proportion of compliant patients followed the RF because of confidence in their optometrist. Conclusions: Optometrists generally recommended RFs consistent with manufacturers’ recommendations for DD and one-month SH lenses but often recommended longer intervals for two-week SH lenses. Patients were most compliant when wearing DD lenses and least compliant when wearing two-week SH lenses. Communication between the patient and optometrists concerning the risks of non-compliance, or initiating a reminder system might improve compliance.

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Quality Control of Silicone Hydrogel Contact Lenses by Impedance Spectroscopy

MRS Proceedings ◽

10.1557/opl.2014.201 ◽

2014 ◽

Vol 1626 ◽

Author(s):

M. Torres ◽

K.S.V. Santhanam

Keyword(s):

Quality Control ◽

Phase Angle ◽

Contact Lens ◽

Contact Lenses ◽

Electrochemical Impedance ◽

Spectroscopic Method ◽

Impedance Change ◽

Impedance Measurements ◽

Silicone Hydrogel ◽

Silicone Hydrogels

ABSTRACTWe wish to propose an impedance spectroscopic method for the quality control of contact lenses by measuring the pore resistance. Silicone hydrogels are excellent materials for use as contact lenses and their on eye performance is dependent on salt intrusion characteristics which are related to the pore resistance and water uptake. When the contact lenses are placed on the eye, they are expected to permeate ions and molecules to maintain ocular health. The hydrogel pores control the permeability and can be viewed as a quality control parameter. Two models are considered here: in one, the contact lenses are considered as strong rigid films with no permeability. In another, the hydrogels are having ionic permeability. We designed a silicone hydrogel contact lens attachment holder that is amenable for electrochemical impedance measurements. The electrochemical impedance measurements were carried out in an inert medium of 0.1 M Na2SO4. The impedance measurement experimental parameters used were a) AC potential 10 mV rms b) frequency range 0.1-210 kHz and c) open circuit potential of 0.207 V. The impedance variation with frequency was constructed for a number of hydrogels. The ideally acceptable silicone hydrogel contact lenses showed an impedance change with frequency in a sigmoidal fashion with a characteristic phase angle (acceptable in the range of 70-75o). The hydrogel pore resistances for the acceptable contact lenses are in the range of 4.5-11 kΩ. When the impedance showed a linear decrease or no well defined phase angle, the contact lens is considered acting as an insulator-a test for rejection. A test of the model was done with several acceptable contact lenses in the market. This study revealed interesting aspects of the influence of pulsating electric field on the silicone hydrogels.

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