Rigid gas permeable contact lenses
Rigid Gas Permeable Contact Lenses (RGP) are made from plastic polymers that allow the flow of oxygen to the eye. At Ezekiel Eyes we specialise in all types of contact lenses. Practitioners who attempt to do contact lens practice with any degree of seriousness have a detailed knowledge of rigid gas permeable fittings.
Rigid Gas Permeable are especially beneficial for patients with astigmatisms, patients who have deposits on the soft contact lenses, patients with dry eyes, patients with keratoconus, post-graft, post laser, post PRK, post RK, traumatised corneas, etc.
Rigid Gas Permeable are easier to clean than soft contact lenses and better deposit resistant.
Boston XO is the brand name of the material we at Ezekiel Eyes utilise for the majority of our rigid gas permeable contact lenses, including lenses for keratoconus, orthokeratology and post surgical contact lenses.
Boston XO (BXO) is our material of choice due to its excellent material properties. The official material name is Hexafocon A.
BXO has an oxygen permeability index of 100, one of the highest in the Boston family of materials. This means a higher percentage of oxygen passing through the lens and reaching the cornea to maintain good corneal health.
Wettability is a measure of the area covered by a drop of liquid on the lens surface. This is closely related to the surface tension forces of the contact lens surface. The more wettable the contact lens material, the more area the drop of liquid will spread. It is very difficult to develop a testing standard that accurately predicts the on-eye wetting performances as tear film components vary significantly from person to person. However, in a laboratory setting, the BXO material was able to outperform the older gas permeable materials.
Durability (Hardness, Modulus, Toughness)
The durability of the contact lens is dependent on the combination of hardness, modulus and toughness of the contact lens material.
Hardness (index of 112) refers to the resistance of a material to indentation. This ensures that the surface of the contact lens is free from any depression on the surface which may affect the long term comfort of the contact lens. One every day example of this property is dropping the rigid gas permeable contact lens on a hard surface without causing any dents on the contact lens surface.
Modulus refers to the amount of force applied to a contact lens material to deform (or cause strain within the lens) until breakage occurs or until the deformation reaches some predetermined point. BXO has a modulus index of 1500MPa. This index ensures that the force applied to the contact lens, from the front of the eyes, does not change the original shape of the contact lens. Any deviation from the original lens curvature will affect the visual outcome.
Lastly toughness (2.6MN/m3) refers to the amount of energy a contract lens can absorb before the material is broken or flexed to some predetermined deformation point. This quality is closely related to contact lens handling and cleaning, as the force of handling and cleaning motion may cause excessive strain or flexure on the contact lens.
Ultraviolet (UV) radiation absorber in the contact lens reduces the amount of UV reaching the underlying structure of the eye, but does not offer total protection. Protective eyewear (such as sunglasses) is still recommended for maximum protection.
This advance treatment on the contact lens increases the wetting surface of the contact lens, which may improve the comfort of the wearer.
The BXO material offers super-permeability and is as dimensionally stable as older generation gas permeable contact lenses of much lower oxygen permeability.
The surface of gas permeable contact lenses has unique properties such as an ionic charge on the surface and the increased energised surface due to the addition of silicon. Therefore to maintain comfort and to prevent the surface from drying, the lens surface should be free from deposits. The Boston range of solutions has been formulated to work with the unique surface properties of the Boston materials.
Boston Advance Cleaner
The Boston Advance Cleaner is specifically designed for newer materials like the BXO, which are more prone to lipid deposits. This is due to the negatively-charged surfaces attracting the positively-charged lipid and protein components found in the tear film. The Boston Advance Cleaner contains friction-enhancing agents to help mechanically break down the adhesion between the deposits and the lens surface without damaging the lens surface. The ‘soap-like’ (surfactant) property of the solution then envelops the lifted deposits which prevent the deposits from rebinding onto the lens surface.
Boston Advance Comfort Formula Conditioning Solution
The Boston Advance Comfort Formula Conditioning Solution provides disinfection and improves wettability for the BXO material. Water attracting polymers in the solution are attracted to the contact lens surface which makes the lens surface more ‘moist’. This allows the lens to wet better and stay wetter longer in between blinks. This, in turn, decreases lens surface drying and help repel deposits until the tear film coats the lens to maintain lens wetting. The solution also contains disinfecting agents, which are effective is destroying harmful microorganism on the lens surface.
Boston One Step Liquid Enzymatic Cleaner
The Boston One Step Liquid Enzymatic Cleaner is used once a week to remove stubborn deposits and improve contact lens wearing comfort. The enzymatic cleaner works together with the disinfecting step. Maintaining lens cleanliness helps maximises the contact lens life and also to maintain wearing comfort.
Boston Rewetting Drops
Over time, as a result of environmental factors, deposit formation or inadequate blinking, the smooth layer to tears attracted to the lens surface will gradually break down. When tear film continuity is not maintained the lens surface can dry out. Protein and lipid deposits make use of these dry spots to attach themselves to the lens surface, causing discomfort and reduce wearing time. The Boston Rewetting drops utilizes electrolytes that bind onto the dry lens surface to rewet the lens, prevent deposition and extend the contact lens wearing time.
At Ezekiel Eyes we pride ourselves on quality service and utilising quality products for our patients. One of the contact lens suppliers we utilise is Geflex Laboratories.
Gelflex Laboratories is accredited with:
– ISO 13485:2003 – Medical Devices Quality Management System.
– Annex V of MDD 93/42/EEC (CE mark for Europe)
– ISO 14971:2007 – Medical Devices – Application of Risk Management to Medical Devices.
– Therapeutic Goods Act 1989 – The Manufacturing Principles
– Therapeutic Goods (Medical Devices) Regulations 2002 – Product Quality Assurance
– Conditions specified in Certificates AU Q00130/01 and MR Q00050/01
– A registered foreign manufacturer of contact lenses with US FDA