VIDEO fitting guide slideshow

PDF Fitting guide

To select curves:

• For K readings 7.1mm and flatter, select first trial lens 0.2mm steeper than the mean K reading

• For K readings from 6.0 to 7.0mm, select the first trial lens equal to the mean K reading

• For K readings 5.9mm and steeper, select the first trial lens 0.4mm flatter than the mean K reading (less predictable).

To select diameter:

Smaller diameters are required for central cones and larger diameters for decentered cones.

A larger diameter is often required for early cones and will also tend to make the lens ride higher.

The lens should hang off the top lid and be well clear of the lower limbus.

Option:Nissell K2

LINK to article

• The lens should remain centred over the pupil in primary gaze and maintain reasonable centration on blinking.

• The lens should move approximately 1-1.5mm on blinking to allow metabolites and tear debris to be removed from underneath the lens. The movement should be smooth and unobstructed in the vertical plane.

• Fluorescein facilitates the assessment of lens alignment viewed using the slit-lamp or a Burton lamp. The ‘fluorescein pattern’ intensity allows confirmation of either a steep or flat fit of the lens. One should note the fluorescein intensity in the centre of the lens, mid peripheral and periphery (Figures 1-5).

Good alignment	Steep	Flat	3 Point	Piggyback
figure one	figure two	figure three	figure four	figure five

• In fitting a RGP lens for a conical cornea, the ‘three-point-touch’ (Figure 4) is used to distribute the weight of the contact lens as evenly as possible between the cone and the peripheral cornea. With an apical contact area of 2-3mm aimed for.

• An over refraction should then be conducted to allow for the tear lens to be calculated. This measure gives further guidance on lens alignment. In a steep fitting lens (Figure 2) a positive tear lens results on over refraction, thus requiring less hypermetropic correction. This is often seen in apical clearance fitting, where the lens arches over the cone clearing the central cornea and resting paracentrally. Such a fit can be beneficial in reducing epithelial damage to the central cornea.

• A flat fitting lens (Figure 3) will result in a negative tear lens on over refraction. Here the lens is assumed to be fully on the cone and is characterised by a broad green band of lens clearance. This results in improved visual acuity due to the apical touch but may lead to increased apical changes and epithelial trauma.

• Ocular surface examination, including palpebral conjunctival and tear film assessment must be documented pre and post lens trial.

Once issued, review no earlier than 2/52 to allow the patient to adjust to the lens (Paul Rose notes that Px's whine and whinge much more when reviewed after 1/52)

WT 2+2 Max 8

Lenses must be worn for a minimum of 2 hours for each appointment

WT Max 12 hours (knowing the patient will overshoot this)

Review at 1/12 then 6/12 (since Px's usually miss this and return after 12/12)

Lenses Should last 24/12

Clean with a two step solution, ie Boston.