DIAGNOSES OF GLAUCOMA. DR HASNAIN UL HAQ EYE SURGEON. HISTORY.
DIAGNOSES OF GLAUCOMA
DR HASNAIN UL HAQ
The most common type of glaucoma, primary open angle glaucoma, is hereditary. If members of your immediate family have glaucoma, you are at a much higher risk than the rest of the population. Family history increases risk of glaucoma four to nine times.
Field of vision changes are one of the first symptoms to surface in glaucoma patients. By the time central vision is affected, glaucoma is already too far advanced with almost all peripheral vision permanently lost. A visual acuity test measures a patient’s ability to see far away or up close. For this test, you may be asked to read from an eye chart. The visual acuity test uses an eye chart with letters and images to measure vision ability at various distances.
The tonometry test measures the eye’s intraocular pressure (IOP). The test is used in the detection and diagnosis of glaucoma. Usually drops are used to numb the eye before the doctor or technician uses a special device to measure the eye’s pressure. The tonometry test takes only minutes to perform and does not cause any eye pain.
Ophthalmoscopy is used to examine the inside of the eye, focusing on the retina and optic nerve. In a darkened room, the physician will dilate the pupils before magnifying the patient’s eye using an ophthalmoscope (an instrument with a small light on the end). This allows the physician to look at the shape and color of the optic nerve. If this test reveals an optic nerve that looks unusual.
Gonioscopy is a painless eye test that determines whether the area where fluid drains out of your eye (the drainage angle) is open or closed. It is often done during a routine eye examination, depending on your age and whether or not you are at high risk for developing glaucoma. Although the causes of glaucoma are not well understood, if the drainage angle becomes damaged, blocked, or clogged, pressure may increase inside the eye.
A perimetry glaucoma test measures all areas of your vision, including your peripheral vision. At the end of the test, a printout shows if there are any areas of vision loss. Loss of peripheral vision is often an early sign of glaucoma. Early detection is key in successful glaucoma diagnosis and treatment.
Goldman applanationtonometer: the "gold standard" instrument attached to the slit lamp biomicroscope used in all eye doctors' offices. It requires a cobalt blue light source and a small droplet of fluorescein on the ocular surface. A tiny pressure sensor attached to a spring-loaded arm is gently placed against the tear film, and the doctor or technician reads the pressure through the microscope under the blue light.
proposal, with a diameter of 3.06
mm. The applanated area can be observed
by means of a BIO microscope. The partition
of the image is created by two prisms arranged edge to egde.. Simultaneously,
the exerted force can be read
on a scale which is projected into the observation
The Imbert-Fick law states that ‘pressure is equal to the force per unit area of applanation for a spherical container’, assumed to be infinitely thin, dry and perfectly elastic in form.
The cornea is, however, a rigid structure which has an average thickness of 540μm, and a tear-moistened outer surface.
Nevertheless, by selecting a circular zone 3.06mm in diameter the smallest area of applanation (7.35mm2) is attained while still giving accurate results, introducing a relative error in IOP of only 2.5 per cent.
This is due to the balance between the four forces acting on the cornea on applanation:
Force of probe + Tear capillary action = IOP + Ocular rigidity
Furthermore, once the density of mercury (13.6g/cm3) is considered in the final calculation, an easy conversion is produced in which 1g of weight equates 10mm of hg
Among all the indentation tonometers, the Schiøtztonometer, introduced into clinical practice at the beginning of the century, soon became very popular. It was used worldwide until the advent of the Goldmannapplanationtonometer. With the Schiøtztonometer, a plunger produces a corneal indentation, the depth and the volume of which are dependent on the IOP and the distensibility of the ocular walls. Since the degree of distension is constant (scleral rigidity or E), it can be calibrated to obtain the true IOP. The E value can be determined by performing two scale readings with two plunger loads. Using the Friedenwaldnomogram and conversion tables, the exact IOP value is obtained. Other tables that give a single reading, in IOP values (mmHg), relate the tonometer reading to an "average eye" with average scleral rigidity. Such tables may under or over-estimate the true IOP. In conclusion, when more reliable instruments are not available, the Schiøtztonometer may be used, but correction of the scale readings according to the individual E value, is imperative.
Tono-Pen handheld electronic contact tonometer: This widely used, portable, handheld device runs on hearing aid batteries and calibrates digitally with the push of a button. It requires a disposable sterile cover for each patient. The sterile device tip is gently placed against the tear film by the doctor or technician, and the pressure reading appears on the digital readout simultaneous to a faintly audible beep.
pneumotonometer contact device: The device is operated similarly to the handheld tonopentonometer, but due to its larger size, it's not readily portable. It requires a continuous gas supply and separate gauge container with analog readout attached to a long tube and pressure probe. This is an older technology and has largely been replaced by the handheld tonopentonometer.
The airpuff noncontact tonometer, which generally requires no anesthetic drop, is widely used in doctor's offices, clinics, and screening facilities. It is very safe due to the "no touch" technology, but it often produces falsely elevated readings, particularly in patients who squeeze their muscles upon anticipation of the air puff. The patient simply sits then places their chin in a rest while looking straight ahead, while the operator activates the air puff mechanism while aligning each eye individually.
Tactile finger applanation over the closed eyelid by a skilled eye doctor is an age-old traditional method utilized by the experienced practitioner
To determine whether a person has open angle glaucoma or narrow angle glaucoma we examine the angle. This is the area at the edge of the iris (the colored part of the eye) where it joins the white part of the eye (sclera). The front of the eye (cornea) makes it impossible to view this directly. In order to see the angle it is necessary to use a contact lens with a mirror.
Pupil. Visible with the gonioscope if dilated.
Iris. Colour varies between individuals.
Iris root/insertion. The last roll of the iris may obscure the view of the ciliary body
Ciliary body. Longditudinal muscle. Colour varies between individuals - may be pale brown, grey or dark.
Scleral spur. Protrusion of sclera into anterior chamber. Attached to ciliary body posteriorly and trabecular meshwork anteriorly.
Trabecular meshwork. Multilayered network of fenestrated lamellae and endothelial cells draining aqueous into Canal of Schlemmwhich may visible when full of blood (e.g. in hypotony or when excess force applied to sclera during gonioscopy. Most of the drainage occurs via the posterior, more pigmented, portion of the trabecular meshwork. There are variations in colour but usually grey with varying degrees of pigmentation.
Schwalbe's line. Delineates the anterior edge of the trabecular zone and represents the termination of Descemet's membrane. Very fine glossy white line.
Posterior surface of Cornea. Observe limbal loops.
This is the most important test for the diagnosis of glaucoma
You can see the disc and see cd ratio
one of the hallmarks of glaucoma is the optic nerve damage, which is characterized by cupping of the optic nerve. Even a normal optic nerve has a small amount of cupping. However, the patients with glaucoma tend to have larger cupping than normal subjects. the cup-to-disc ratio of normal subjects is typically around 0.2 to 0.3 . The cup-to-disc ratio is often measured both in the vertical and horizontal position to estimate the amount of cupping and amount of optic nerve damage (. The cup size is simply the area of the optic nerve that is not occupied by the optic nerve fibers (an empty space). However, with glaucoma, there is progressive loss of optic nerve fibers, and consequent increase in the cup size of the optic nerve. When an eye doctor says there is a cup-to-disc ratio close to 1.0, this refers to almost complete cupping and an advanced damaged optic nerve from glaucoma. Conversely, if the cup-to-disc ratio is 0.3 or less, then this refers to a relatively healthy looking optic nerve. While there is no one cup-to-disc ratio that separates normal from glaucoma, the cup-to-disc ratio greater than 0.6 or 0.7 is suspicious of glaucoma and often requires further testing to rule out glaucoma. As glaucoma progresses, the cup-to-disc ratio enlarges (as more optic nerve fiber dies off), and the patient may start to develop peripheral vision loss. A small fraction of glaucoma patients, if detected late or inadequately treated, may become blind in one or both eyes with a complete loss of optic nerve fibers.
A visual field test is a method of measuring an individual's entire scope of vision, that is their central and peripheral (side) vision. Visual field testing actually maps the visual fields of each eye individually. The visual field test is a subjective examination, requiring the patient to understand the testing instructions, fully cooperate, and complete the entire test in order to provide useful information.
Confrontation visual field testing typically is used as a screening visual field test. One eye is covered while the other eye fixates on a target object, such as the doctor's open eye, while the doctor stands or sits directly in front of you. You then are asked to describe what is seen on the far edges or periphery of your field of view. As an example, your eye doctor may hold up different numbers of fingers within your peripheral field of view and ask how many can be seen while you continue to fixate on the doctor's eye.
Automated Perimetry: Various forms of automated perimetry tests measure your responses to the presence of objects in different areas of your field of view. While your head is held still, usually with a chin rest inside a large bowl-like instrument, you stare (fixate) on a source of light straight ahead. A series of random lights of different intensities are flashed in your peripheral field of vision. You then press a button or use other means to indicate your response when you perceive the computer-generated light suddenly appearing in your field of view. If you are unable to see objects in an appropriate portion of your field of view, then you may have a blind spot indicating vision loss
Frequency Doubling Perimetry: Frequency doubling is based on an optical illusion that uses vertical bars of contrasting colors such as black and white appearing on a screen. These bars appear to double in number when they alternately flicker at higher frequencies, a phenomenon thought to be due to the unique response of specific light-sensitive cells (photoreceptors) within the eye's inner back lining (retina). Inability to see vertical bars at certain frequencies could indicate optic nerve or other types of eye damage with accompanying loss of vision in certain areas of the visual field.