Rigid lens verification and evaluation

1. Rigid lens verification and evaluation Week 14

2. Rigid lens verification • After taking all the measurements, fitting a trial lens, and ordering the lens, we must verify the lens once it is received. • We do this to make sure the parameters we ordered are correct. • We do this BEFORE we dispense the lens. • The parameters we verify are: • Power • Base curve • Diameter • Center thickness

3. Rigid lens verification Power verification lensometer • The power of the lens must be checked for accuracy the same way we verify a pair of spectacles before dispensing to the patient. • We do this by using the lensometer. • The lens is placed convex side up on the lens stop of the lensometer. • You measure the lens the same way as a pair of glasses, the lens will be spherical.

4. Lens verification Base curve verification radiuscope • Base curve is just as important as power and diameter and must be verified. • To verify the base curve is what we ordered, we use the radiuscope.

5. Lens verification Using the radiuscope radiuscope • The lens holder is removed and ONE drop of water is placed in the “depression”. The lens floats on top of the drop of water, convex side up.

6. Lens verification Using the radiuscope • The lens holder is put on the table with the water and lens in it. • This must be placed so the green light from the radiuscope is directly on the center of the lens. • The table can be rotated and shifted to center the green light.

7. Lens verification Using the radiuscope • Look through the eyepiece and focus the star shaped mire by turning the knob on the right. • Use the knob on the left to move the number scale to zero. • There is a small knob under the eyepiece to focus the number scale.

8. Lens verification Using the radiuscope • Once the star is in focus and the number scale is at zero. • Measure the base curve by turning the star focusing knob away from you. The star will disappear and then will come back into focus, the scale reading will also move away from zero. • Once the star comes back into focus, use the fine focus knob.

9. Lens verification Using the radiuscope • When the star mire comes into focus the 2nd time, it may not be centered. • You can center the star by rotating the table to bring the star into center again.

10. Lens verification Using the radiuscope • The base curve is read by the position of the number scale line. • This is in radius of curvature and is in mm’s. • There is a conversion chart to convert to diopters, which is how we order BC. • This reading is about 8.41

11. Lens verification Diameter verification V gauge & pd ruler • The diameter of the lens must be verified before fitting it on the patient. • To do this, you can use a pd ruler and measure the diameter or a “V” gauge. There is a channel in the shape of a “V” in the ruler. • The lens is dropped in the channel and when it stops, the diameter is read on the side of the ruler in mm’s.

12. Lens verification Center thickness verification Radiuscope & thickness gauge • Center thickness of the lens is important, especially if you specified a thinner or thicker lens than the norm. • Lenses are generally fit as thin as possible for better O2 permeability. Keep in mind a high powered convex lens will be thick to begin with, so you may want to see what the lab can do to make the lens thinner. • To verify the thickness, we use a radiuscope,if it has a thickness gauge on it or a thickness gauge.

13. Lens evaluation • After the lens is verified, we inspect for scratches, chips and warping and then put it on the patient’s eye for evaluation. • We evaluate by checking: • Positioning and movement • Condition • Visual acuity • Flexure • Residual astigmatism • Comfort • Fluorescein pattern • Corneal and eyelid integrety

14. Lens evaluation flexure VA and residual astigmatism • Flexure occurs when the lens “bends” over the cornea (astigmatic ridge) when the patient blinks. • We can check for this with keratometry. With the lens on the eye, after the patient blinks, the mires will change. This happens because the lens bends in a different shape over the cornea. • We can also check for this with retinoscopy. With the lens on the eye, flexure is evident when the reflex suddenly changes after blinking. • Check the VA and make sure it is what you expected it to be, if not, over refract and make modifications. • If there is astigmatism not corrected for by the “tear lens”, this may be residual astigmatism. This is not corneal or refractive astigmatism but lenticular astigmatism and is caused by the crystalline lens. • This should have been dealt with before fitting with a trial lens. Residual astigmatism is usually tolerated if it is less than the amount of the spherical power.

15. Lens evaluation Positioning and movement • The lens should always move 1mm upon blinking. If there is no movement, the lens is too tight. If the lens is moving all over or too much, it is too flat. • The lens should be positioned over the pupil, centered. The lid attachment fit should be under the upper lid but centered over the pupil and move at least 1 mm after blinking.

16. Lens evaluation comfort Fluorescein patterns • New gas perm lens wearers may take up to 6 weeks to build up tolerance for the lens but if an established wearer that complains of discomfort or pain, you have to find out why. • What are some reasons a patient will complain of pain? • Fluorescein can stain the tears so you can evaluate the tear film under the lens. • If you encounter a dumb bell shape pattern, this signifies a large amount of astigmatism and you may need to modify with a change to the BC, D or making the lens a bi toric. • A bi toric has 2 base curves, one horizontally and one vertically. This is typically used with large amounts of astigmatism, -3.00D or more.

17. Lens evaluation Fluorescein patterns Flourescein patterns

18. Fluorescein patterns

19. Fluorescein patterns

20. Fluorescein patterns • It is important to remember that even though the lens has a steep or flat fit does not mean that it is a bad fit. • lens is steep or flatbecause that is the way you chose to fit the lens. The tear lens is making up for the cylinder that was not ground into the lens. There is supposed to be a fluorescein pattern. • When evaluating the fluorescein pattern, you should know what to expect before looking under the slit lamp. If you fit an apical fit, the lens should fit tight, just not too tight !

21. Lens evaluation Corneal integrity Corneal abrasion • This is regarding the patient that has already worn CL’s. • Always inspect the cornea before fitting with new lenses. • Check with fluorescein under the slit lamp for any staining, scratches, ulcers, erosion, and or edema that may prevent the patient form wearing lenses. • Tear film integrity should always be tested as well. • These types of problems need be heal before wearing lenses. • All of the above should be evaluated in the exam, well before the fitting starts.

22. That’s it ! See you next time for lens modifications!