What is the filter that you need to use for the fluorescein pattern of RGP fitting?
Using a cobalt blue filter over the illumination system is required. In addition, using a yellow barrier filter (i.e., Wratten #12 or Tiffen #2) will result in greater fluorescence, especially with RGP lens materials that have ultraviolet blocking agents (Figs.
How do I choose a base curve for RGP contact lenses?
For a larger lens, flatten each meridian by another 0.25D to avoid excessive vaulting. For a smaller lens, steepen each meridian by a 0.25D. The base curve for a 9.0mm diameter lens would be 42.00D/44.25D or 8.04mm/7.63mm.
How do I choose a contact lens base curve?
Base curve : Select the base curve which is 0.4 – 0.6 mm flatter than the flattest ‘K’ for smaller lenses and 0.6 – 1.0 mm flatter for larger lenses. 6. Fit the contact lens to the respected eye and leave the patient to wait for 15-20 minutes to settle the lens well.
How do you evaluate RGP fit?
Lens movement is one of the key characteristics of an ideal RGP fit. The lens should move around 1 to 1.5mm with each blink. The movement should be smooth and unobstructed in the a vertical plane, indicating a near alignment fit. Lens movement occurs either as a response to the eyelid force or by upper lid attachment.
What is thumb rule in contact lens?
A simple rule of thumb exists. For every 0.05mm that the BOZR is steeper than K, the tear lens power increases by +0.25D. Therefore you must counter this by adding -0.25D to the power of the contact lens.
What is the flattest K?
Flat K reading is the reference point to find the base curve. When the GP lens is is fit on K it refers to the selection of a base curve that matches the flattest K reading. Other GP fitting philosophies may recommend fitting flatter or steeper than K.
Is higher base curve flatter or steeper?
The base curve is the radius of the sphere of the back of the lens that the prescription describes (the lower the number, the steeper the curve of the cornea and the lens, the higher the number, the flatter the curve of the cornea and the lens).
What is rule of thumb in contact lens?
How is RGP diameter measured?
The RGP Contact Lens Diameter Gauge or V-Gauge, is used to determine the diameter of a rigid contact lens. The contact lens is dropped into the V shaped channel of the gauge. The exact outside diameter is read at the point where the lens stops.
How much astigmatism can RGP correct?
A bitoric RGP lens should be fit, because the anterior surface of the lens will correct the 4 D of residual astigmatism. Large amounts of corneal astigmatism (>3 D) require a back toric surface for lens stability, fit parallel to the corneal curvature (ie, fit ”on K” in each meridian).
What is sagittal depth?
Sagittal depth actually refers to the entire contact lens from the center of the lens to the plane that the edges circumscribe. Various brands of scleral contact lenses allow you to manipulate the sag in different ways in order to achieve the desired vault over the cornea.