LASIK Screening
This is the most important part of the specs removal surgery. At Indovision Cataract &n Laser Eye Centre, we make sure screening is done as per standard international protocols. The screening process may take around 2 hr while the LASIK surgery takes less than 13 mins.If you wear contact lenses, you need stop wearing them before your baseline evaluation. Contact lenses can lead to a change in shape of the cornea. Depending on the type of your contact lenses you need to stop wearing them. If you wear:Soft contact lenses: it is recommended that you stop wearing them 2 weeks before your baseline evaluation Rigid gas permeable lenses: Stop wearing at least 3 weeks before evaluation Hard lenses: These lenses affect the cornea the most. You should stop wearing at least 4 weeks before evaluation
THE TESTS INCLUDE
Auto refractometer test
Dilated refraction
Post mydriatic test (PMT)
REFRACTION
It is the most important part of LASIK screening. Even the best surgery may not give accurate results if the correct power of the eye has not been determined.
To ensure correct spectacle power, following tests are done:

Auto refractometer test

Dilated refraction

Post mydriatic test (PMT)
INTRAOCULAR PRESSURE (IOP)
Like blood pressure in the body, the fluid in the eye contributes to intraocular pressure (IOP). A balance is maintained in the in flow & outflow of fluids in the eye. The pressure created by this fluid or aqueous humor is called IOP. The normal IOP ranges from 11 to 21 mm of Hg. The intraocular pressure can be measured by non-contact tonometer (NCT).
- NCT – In this method, an air puff is directed on the cornea & compression of the cornea is determined. This helps to calculate the IOP of the eye. This is a screening method. Reliability of this test is slightly low.
- Applanation tonometer (AT) – This is considered as gold standard in measuring the IOP. Anesthetic drops are put in the eye. Eye is stained with fluorescein dye. Then a device is brought in contact with the cornea that helps to applanate (flatten) it. Reading is taken to measure IOP.
Importance of IOP measurement
Steroid drops are used after LASIK surgery. These steroid drops may lead to transient rise in IOP. For those who have Glaucoma (raised IOP), the LASIK surgery may not be suitable. Some people tend to develop a rise in IOP after use of steroid. These are known as steroid responders. For such patients’ adequate measures need to be taken.
THICKNESS OF THE CORNEA
Normal corneal thickness is around 530 microns. A minimum corneal thickness of 450 microns is needed to undergo LASIK. In a cornea which is less than 495 microns, should be treated with caution. Entire cornea is evaluated. The anterior & posterior curvatures of the cornea are determined. Any abnormal thinning or weakness of the cornea will eliminate you from any spec’s removal procedure.
SCREENING OF ANY PATHOLOGY IN THE EYE
LASIK can be done only in healthy eyes. LASIK should be avoided in eyes with any corneal pathology, glaucoma, retinal diseases & keratoconus. It is also contraindicated in systemic disorders like Lupus & rheumatoid arthritis.
RETINAL EVALUATION
A dilated retinal evaluation is mandatory for LASIK screening. In myopia, the length of the eyeball is more than normal length. This leads to a more stretched & thinned out retina. It is quite common to have fine breaks or holes in retina. Such holes need to be sealed before LASIK is done. Retinal holes when left untreated can lead to retinal detachment & permanent loss of vision.
DRY EYE TEST
LASIK involves making a flap in the cornea. While making a flap, the corneal nerves are also cut. This lead to dryness. The dryness usually improves over 3-6 months. During this time, lubricating drops will be prescribed to you. However, if you are suffering from dry eyes, you may not be a good candidate to undergo LASIK, as LASIK may aggravate dry eyes. Dry eye test to be done before LASIK.
- Shirmer’s test
- Tear film breakup time
Shirmer’s test
This test measures the amount of tear secretions. A bend filter paper with markings is placed in the lower lid. After 5 mins, wetting of the paper is noted. The amount of wetting grades the severity of dryness.
Tear film breakup time
The eye is numbed with anesthetic drops & stained with fluorescent dye. Appearance of a first random dry spot is noted. Normally dry spot appears after 15-35 seconds. If dry spot appears in less than 10 seconds, there is dryness.