Preop Exam


LASIK Evaluation and Eye Exam

Prior to any refractive procedure, a detailed examination and discussion of your options is most important. If any of the following tests or items are not included in your refractive surgery evaluation, we feel it is incomplete. This check list will help you define a quality refractive experience!

Eye Exam

After undergoing corneal mapping, your visual acuities are recorded, both with and without corrective lenses. Your muscle balance, pupil size, and eye dominance are measured. After dilation, the physical condition of your eyes is then further evaluated. The doctor will check your tear film, corneas, lenses, retinas, and optic nerves to rule out any presence of disease since refractive surgery must be performed on healthy eyes. The stability of your corneas will be assessed and the pressure inside your eyes will be measured.

Following the exam, the Doctor will discuss your eye health with you and your surgical options. If surgery is planned, a technician will review pre-operative and post-operative instructions. Your compliance with these instructions helps ensure the best possible result from your surgical procedure. A patient education coordinator will then discuss pricing and payment options and help you schedule your surgery date.

Pupil Measurement

How big your pupil gets in low light can be very important in evaluating how good your image quality at night is after refractive surgery. How your pupil is measured in your exam is very important. In the old days, we would use a penlight or other light source and compare the pupil with round circles on a card to estimate the pupil size in low light. This test was not as accurate as we would like because even a little bit of light from any source can make your pupil measure smaller than it truly is in low light. Modern day pupil size measuring technology involves either light amplification or infrared technology. Both can accurately measure your pupil size in low light without making your pupil artificially smaller while performing the measurement. After knowing what your pupil size is in low light conditions, the next question to ask is: “Will the laser treatment I have cover my pupil adequately in low light so as to maximize my quality of night vision?”

Corneal Topography and Corneal Tomography

Each cornea is unique, with very small amounts of irregularity, imperceptible to the examiner, even under a high powered microscope. Corneal topography can be a major factor in determining whether a patient can benefit from refractive surgery and is most often critical in helping to plan a follow up enhancement surgery for a patients’ optimum visual result. There are several systems for measuring the corneal shape, structure and thickness, each one giving the doctor a different view or type of information. Some offices only have one type of corneal map for their evaluation process.  Dr. Tylock has over 20 years experience working with these evolving technologies and currently utilizes Pentacam Tomography (Scheimpflug imaging), Orbscan II, Humphrey Zeiss Ocular Coherence Tomography (OCT) and Visx Wavefront™ and Analysis Systems.

Corneal Thickness Measurement

Corneal flap (lamellar) surgery itself has been performed for many years. It was first performed in the form of keratomileusis more than 60 years ago. Flap surgery has evolved into a more accurate surgery because of the laser. There are principles we learned from flap surgery even before the advent of the laser component. One important principle is that we know we do not want to thin a cornea too much. If we do, it could become irregular in shape and create an irregularity in vision that could be a problem. For this reason, it is very important to accurately measure the thickness of your cornea pre-operatively. Since we know the thickness of the flap we are going to make, the amount of tissue the laser is going to remove to get our correction, we always calculate to leave a safe amount of untouched tissue behind. Utilization of IntraLASIK allows our patients to maintain the highest level of safety since this technology allows for consistent customization of thinner, more uniform flaps not possible with a microkeratome and blade. This technology is especially important in patients who have higher corrections or thinner corneas.

Tear Film Analysis and Dry Eye Evaluation

Dry eye, very common among preoperative LASIK patients, is the most frequent risk factor patients have that can delay recovery following the LASIK procedure. The cornea is the area of your eye where refractive laser surgery is performed. It does not contain blood vessels. Instead, it gets nutrition from the tear film on the surface and the fluid inside the eye (aqueous). The pre-ocular tear film acts as an interface between the cornea and the outside environment. It provides a smooth, high quality refractive surface over the cornea, resulting in sharp, clear vision. The tear film also contains several natural substances that helps protect the ocular surface against infection.

If our exam and testing show that your eyes are dry, the doctor may elect to treat the condition prior to surgery. Frequent preservative free tear replacements throughout the day and use of different ointments at night are the first line of therapy. Other drops and medication combinations may be used. Punctal plugs are a way of plugging the tear drainage system that is extremely effective so that your own natural tears lubricate the surface of your eye and cornea longer. We have found that patients benefit from IntraLASIK since they have considerably less dryness postoperatively as compared to patients having traditional LASIK.

Cycloplegic Dilated Exam

There are two reasons to perform this part of the exam prior to refractive surgery. Most people understand that a dilating drop makes the pupil big. This is important because it provides our doctors with the clear view that is needed to perform a complete eye examination. The doctor will verify that the retina and internal eye structures are healthy prior to proceeding with surgery. The second reason is accommodation. Accommodation is the process your eyes use to focus up close to read. When you read, the lens inside your eye behind your pupil becomes more fat or curved. This curvature of the lens makes a person more nearsighted so they can read. During an eye exam when a person is looking at the eye chart, they can involuntarily try to focus on the eye chart and stimulate the accommodation response. If a person does this, they will measure more nearsighted (or less farsighted) than they really are.

So how do we handle this accommodation response in your exam? This is the second reason for the dilating drops. The drops called Cyclogyl or Mydriacyl not only dilate the pupil but it relaxes the muscle that changes the shape of the lens. This relaxing of the lens muscle process allows us to measure the true level of nearsightedness or farsightedness when your eye is in its totally relaxed state. Often we will find that someone is quite a bit less nearsighted than we thought they were. This test helps us maximize the chance that you will have a stable, unchanging correction after we are done with your laser vision correction. There are some types of dilating drops that make the pupil big but do not relax the lens. Just making the pupil big is good for an internal exam but it does not relax the lens and give us the important information necessary to deliver an accurate treatment to you.

To schedule a pre-LASIK eye examination, contact our vision correction center serving Dallas and Fort Worth, Texas today.


Tylock Eye Care & Laser Center offers CustomVue™ measurements and analysis, LASIK laser vision correction, PRK laser eye surgery, Wavefront™, WavePrint mapping, and IntraLASIK to residents of Dallas and Fort Worth, Texas. Tylock Eye Care & Laser Center is proud to serve the residents of Allen, Arlington, Bedford, Carrollton, Coppell, Dallas, Euless, Fort Worth, Frisco, Ft Worth, Garland, Hurst, Irving, Las Colinas, Mansfield, McKinney, Plano, Richardson and surrounding Texas communities.