Diagnostic Eye Exams

Corneal Topography

Corneal topography maps the contour or the shape of the cornea. Cornea is a transparent, dome-shaped structure that covers the iris, the color part of the eye, and serves as the main refractive surface of the eye. This means that cornea is responsible for majority of the focusing the light entering the eye. Therefore, even a slight distortion to the shape of the cornea or a small disturbance to its clarity can potentially lead to significant visual loss.

At DuPage ophthalmology, we have the Pentacam, which is an advanced corneal topographical system that can perform point-to-point measurement of the corneal surfaces, both front and back - a unique feature not available in many other corneal topographers. Pentacam scans the cornea surfaces with a laser, and each eye usually takes less than 30 seconds, with no discomfort to the patient.

Pentacam provides vital data on the corneal contour, which is crucial in the preoperative evaluation of patients before undergoing laser vision correction (LASIK/PRK) or cataract surgery. In order to undergo LASIK successfully, cornea contour must be smooth and regular. Pentacam is a powerful diagnostic tool in detecting subtle distortions in the corneal shape, which could be signs of keratoconus or warping of corneal surface from chronic contact lens wear, making patient a poor candidate for laser vision correction or presbyopia correction.

Corneal Pachymetry

Corneal pachymetry measures the thickness of cornea. The normal corneal thickness at the center of the cornea is about 550 microns, little over half of a millimeter. If the cornea is too thick, it could be an indication that there is swelling in cornea, which could be a sign of corneal disorder, such as Fuchs corneal dystrophy. If the cornea is too thin, then it could indicate the presence of keratoconus or pellucid corneal degeneration, two corneal disorders characteritized by abnormally thinning of cornea.

Corneal thickness is also an important parameter in evaluating patients with glaucoma. When we measure the eye pressure in patients with glaucoma, we have to taking into account the corneal thickness. Given two glaucoma eyes with identical eye pressure, the eye with greater corneal thickness is less likely to sustain damage to its optic nerve than the eye with thinner cornea. In other words, having a thicker cornea is protective against glaucoma.

High-definition Ocular Coherent Tomography

High-definition ocular coherence tomography (HD-OCT) is the newest technology added to our ophthalmic diagnostic tool set. HD-OCT images the eye in cross sections, similar to the CT and MRI scans, but unlike CT and MRI scans, HD-OCT utilizes light to image the eye. Eye structures are organized in layers, many of which are transparent. After entering the eye, the light is bend and reflected by different layers of the eye, and the light waves then interact with one another, similar to how water waves in a pool bend and reflect light. The HD-OCT exploits the interference patterns from the light waves and generates cross-sectional images of the eye in exquisite clear and magnified detail.

The resolution of HD-OCT is phenomenal. At DuPage Ophthalmology, we have the latest HD-OCT system, RTVue, which can image the eye from front to back at a resolution close to 1/200 mm. This means that with RTVue we can see the structures inside of a living eye at a resolution of a light microscope, at which even the cell nuclei can be discerned. The testing time is short with RTvue, and each eye usually takes less than 30 seconds, with no discomfort to the patient.

Images from each exam are stored in our electronic medical record. As more images are acquired from the same eye over time, the RTVue’s computer software performs sophisticated statistical analysis to look for subtle anatomical changes. It is frequently the case that in many eye disorders that changes are first noticed on HD-OCT, long before the patient experiences visual changes. Prime examples are glaucoma and diabetic macular edema. In their early stages, these disorders can be easily detected on HD-OCT, while the patients are completely asymptomatic and the clinical signs are hard to discern.

The uses of RTVue are numerous. Most commonly, RTVue is used to detect glaucoma and macular disorders. It is especially useful in following the progression of glaucoma and macular degeneration. RTVue is very sensitive in detecting macular swelling, which can be a sign of significant diabetic retinopathy. RTVue is also useful in visualizing any disturbance to the surface of the retina, such as macular pucker, the wrinkling of macular surface, which can lead to visual distortion and loss of central vision. RTVue can also image the cornea and the lens of the eye in great detail. RTVue can detect subtle changes in the corneal tissue and corneal contour. It can also detect early cataracts. RTVue is invaluable in performing preoperative evaluation and post-operative assessment for laser vision correction and presbyopia correction.

Immersion A-scan and IOL Master

These two instruments are used to measure the axial length of the eye, from front to back (cornea to retina), which must be known accurately for calculating the proper power of the intraocular lens implant, which is to be placed in patient’s eye during cataract surgery. Immersion A-scan makes the measurement by sending sound wave under water, whereas the IOL Master does the same measurement by sending a laser beam into the eye. Both methods are considered the ‘gold standards’ in assessing the axial length of the eye.

There is no discomfort associated with the testing, except that the patient’s face might get a little wet from the saline used with the immersion A-scan. Therefore, we ask patient not wear clothes that they do not wish to get wet during immersion A-scan.

The testing time shorter with IOL Master, with each eye taking less than 30 seconds to complete, whereas immersion A-scan takes a few minutes with each eye. However, immersion A-scan is more reliable than IOL Master in eyes with dense cataracts.

At DuPage Ophthalmology, every patient undergoes testing with both instruments in her preoperative cataract evaluation. Accurate measurement of the length of the eye is a crucial element in attaining excellent surgical outcome. When both testing methods give nearly identical data, the surgeons are more confident in the outcome of surgery. As the old saying goes, measure twice, cut once. It remains true today.

Refraction

Refraction is the procedure of measuring the glass prescription, in order to correct refractive error (which includes near-sightedness, far-sightedness, and astigmatism). In some cases, refraction is also performed to determine the best possible visual acuity an eye can attain and serves as a crucial tool in pinpointing the cause of visual impairment. At DuPage Ophthalmology, we use the finest refractive system available to measure for the best glass prescriptions, for both far and near. The system, EPIC, is completely automated and provides a consistent setting for accurate assessment of refractive error every time. For most patients, refraction with EPIC can be completed in less than five minutes.

Fundus Photography

Fundus photography is used to capture digital images from the back of the eye - the retina, the macula, and the optic nerve. At Dupage Ophthalmology, we have one of the most advanced and reliable digital fundus camera that can capture highly detailed images from the back of the eye, and in many cases, without having to dilate the pupil with eye drops. The resolution of the images is of high-definition quality, and the computer software accompanying the camera further enhances the quality of images.

Fundus photography is commonly used to capture images from eyes with macular degeneration, glaucoma, or diabetic retinopathy. Serial fundus images are also useful in following the clinical course of patients suspected of developing glaucoma and patients with large nevi (freckles) in the back of the eye. The images are reviewed by the doctors and stored in our electronic medical records for future comparison. At DuPage Ophthalmology, we routinely take ocular digital images in cases of glaucoma, glaucoma suspect, diabetes, choroidal nevi, and macular degeneration in order to provide the best care to our patients.

Specular Microscopy

Specular microscope images primarily the inner layer of the cornea, called endothelium. The corneal endothelium maintains the clarity of cornea by constantly removing water from the cornea. With aid of a computer, specular microscope can calculate the density of endothelial cells of the cornea. Higher the density, healthier the cornea is, and more resilient the cornea is to the manipulations from intraocular surgery (i.e., cataract surgery). Specular microscope can also measure the thickness of cornea, which is an indirect metric on the health of corneal endothelium. The main use of specular microscopy is to check the status of the corneal endothelium and to be part of the preoperative risk assessment of intraocular surgery.

Automated Visual Field Testing

Visual field testing is used to assess the peripheral (side) vision, which can be affected in glaucoma or diseases involving optic nerve and the central nervous system, such as optic neuritis, multiple sclerosis, strokes, and brain tumors. By plotting and analyzing the pattern of loss in peripheral vision, the visual field testing assists the doctor in locate the pathology that is afflicting the patient.

At DuPage Ophthalmology, our visual field machine is completed automated, and with the aid of an attached computer, the testing is tailored to each patient. After reviewed by the doctor with the patient, the results of the visual field are stored in our electronic medical record system. With each new testing, the computer compared the most recent findings with results from previous tests by using sophisticated statistical analysis software, to check for progression in the patient’s condition. We typically performed visual field testing annually to semi-annually in most glaucoma patients. However, in some patients, frequent testing is performed as their clinical conditions warrant.

Holladay IOL Consultant

Holladay IOL Consultant is Internet-based computer software, which we use to calculate the power of intraocular lens for each patient prior to cataract surgery. Modern cataract surgery has become a highly precise operation, especially with the advent of advanced intraocular lens implants (toric, multi-focal, and accommodating lens implants). Modern intraocular implants, whether conventional or advanced, are marvelously engineered and meticulous manufactured. However, without an accurate and precise method of determining which lens implant is best for each patient, even the finest intraocular lens would not function optimally if it were inserted into an eye that is not inappropriate for the lens implant.

At DuPage ophthalmology, to attain consistently excellent surgical outcome, we use the Holladay IOL Consultant, the most sophisticated calculating software for selecting intraocular implants. Like many other online software, Holladay IOL Consultant is continually improved and periodically updated. In addition, Holladay IOL Consultant also has the statistical tools that allow us to continually review and analyze our surgical outcomes. With Holladay IOL Consultant we have consistently attained excellent surgical results in our cataract patients