Practitioners > Lens Types
Neil Cox - Moorfields Eye Hospital, United Kingdom
ROSE K Lens
Heralded as "a quantum leap forward in the evolution of lens design for the condition" of keratoconus the ROSE K lens has become the world's most frequently prescribed gas permeable contact lens for keratoconus.
Unlike traditional contact lenses, the complex geometry built into every ROSE K contact lens closely mimics the cone-like shape of the cornea for every stage of the condition.
The result is a more comfortable fitting lens for patients and better sight (visual acuity).
The ROSE K lenses' complex geometry has only become possible since computer-controlled contact lens lathes were developed to cut sophisticated oxygen permeable polymers to the right shape.
The ROSE K lens has a number of features that make it ideal for keratoconus:
"A quantum leap forward in the evolution of lens design for the condition."
Patrick Caroline, FAAO - Director of Contacts Lens Research at the Oregon Health Services University, Portland, USA
Standard lens designs with fixed optical zones (OZ) do not ideally fit the cone shape of keratoconus patients. Figure 1 shows a standard lens that will yield unwanted pooling at the base of the cone and peripheral bearing that can seal off and cause corneal problems.
Figure 2 demonstrates the benefits of a smaller optical zone to fit the cone contour. The design results in little tear pooling at the base of the cone and shows an even distribution of tears under the lens.
The ROSE K system has set optical zones to maximize vision while maintaining good corneal health.
ROSE K2 Lens
Paul Rose further refined the ROSE K lens to take into account the unusual corneal shapes of keratoconus patients, which require abnormal curves on the back of the lens to fit the cornea optimally. This new lens is known as the ROSE K2 lens.
With normal corneas the shape does not change dramatically from the center out, but tends to change evenly in predictable amounts, and therefore with normal corneas the back surface of the lens can be designed with small incremental changes (e.g. eccentricity) over most of the lens with a peripheral curve at the edge. Usually, this will achieve reasonable alignment with the cornea and a good fit.
However, to achieve optimum alignment with the cornea in keratoconus patients, many curves are required on the back surface of the lens, and adjacent curves are often very different. Particularly in steeper cones, several curves are often required within the patient's pupil zone to achieve a good fit over the central area of the lens. Unfortunately, each one of these curves gives rise to a slightly different focal point at the back of the eye. This causes the patient to experience ghosting around the object that they are viewing (like a TV with poor reception) and this is worse the bigger the pupil is because more curves on the back surface of the lens come within the patient's pupil zone. Therefore night driving where the pupil is larger is very difficult for keratoconus patients. These multiple focuses are called aberrations.
The ROSE K2 lens minimizes these aberrations by applying very small changes to the curves on both the front and back of the lens in an attempt to bring the light passing through the lens within the pupil zone to a single point.
Following extensive trials, the best combination of aberration control curves have been developed for computerized digital lathes to cut these very complex curves for the ROSE K2 lens to give the best focus.
The ROSE K2 lens marks a significant improvement in optical quality over the original ROSE K design and is available from most ROSE K manufacturers and distributors internationally.
ROSE K Post Graft Lens
Menicon also markets the ROSE K Post Graft Lens for patients who have undergone penetrating keratoplasty. This lens is designed for postoperative recovery and improvement in vision.
The ROSE K Post Graft lens is available from most ROSE K manufacturers and distributors internationally.
ACT (Asymmetric Corneal Technology)
By nature, the keratoconic cornea is asymmetric, where the inferior quadrant is frequently significantly steeper than the superior portion, causing the GP lens to lift off at 6 o'clock (see illustration E).
ROSE K lenses incorporating ACT are designed to accommodate this asymmetry (good edge lift at 3, 9 and 12 o'clock but lift at 6 o'clock). The inferior quadrant of the lens is steeper than the superior quadrants, providing a more accurate fit at 6 o'clock, which makes the lens more comfortable and stable (see illustration F) and often provides superior vision. ACT is independent of the primary base curve and edge lift value and is available for ROSE K, ROSE K2, ROSE K2 IC, and ROSE K2 Post Graft lens designs.
A spherical ROSE K lens (symmetric) fitted on this asymmetric keratoconic cornea fits well at 3, 9 and 12 o'clock but causes the lower edge to lift off at 6 o'clock.
Incorporating ACT into the design significantly improves the fit at 6 o'clock, making the lens more comfortable and stable, providing superior vision.
ACT Grade #1 (0.7mm)
Slight edge stand off with pooling at or around 6 o'clock (between 5 & 7 o'clock). Specify ACT grade #1
ACT Grade #2 (1.0mm)
Moderate edge stand off with pooling and possible bubble at or around 6 o'clock (between 4 & 8 o'clock) the tear meniscus may also start to break up on blinking. Specify ACT grade #2
ACT Grade #3 (1.3mm)
Severe edge stand off or lift off (tear meniscus breaks up) at or around 6 o'clock. Specify ACT grade #3.
Note: Other grades of ACT are available (0.4mm to 1.5mm), please consult your ROSE K distributor.