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					DIAGNOSES OF GLAUCOMA

      D R HASNAIN U L HAQ
          EYE SU RGEON
                     HISTORY

 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.
                 VISUAL ACUITY

 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.
                   (Tonometry)


 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)


 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)


 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.
                    (Perimetry)


 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.
        TYPES OF TONOMETRY

SHOITZ TONOMETRY
APPLANATION TONOMETRY
OTHERS
        APPLANATION TONOMETRY

 Goldman applanation tonometer: 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.
APP TONO
APP TONO
MIRES
 Goldmann's
 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
 eyepiece.
                       IMBERT-FICK LAW


 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
               Indentation tonometry

 Among all the indentation tonometers, the Schiøtz tonometer,
  introduced into clinical practice at the beginning of the century,
  soon became very popular. It was used worldwide until the advent
  of the Goldmann applanation tonometer. With the Schiøtz
  tonometer, 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 Friedenwald nomogram 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 Schiøtz tonometer may be
  used, but correction of the scale readings according to the individual
  E value, is imperative.
Schiotz tonometer
                       tonopen

 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.
                      continue

 pneumotonometer contact device: The device is
 operated similarly to the handheld tonopen
 tonometer, 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 tonopen tonometer.
                       continue

 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.
                        digital

 Tactile finger applanation over the closed eyelid by a
 skilled eye doctor is an age-old traditional method
 utilized by the experienced practitioner
                    Gonioscopy


 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.
             TYPES

 INDIRECT
 DIRECT
                           Stuctures in angle

   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 Schlemm which 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.
goniscopy
P of gonio
Gonioscpic view
goniscopy
G view
G view
                 Optic nerve exam

 This is the most important test for the diagnosis of
  glaucoma
 You can see the disc and see cd ratio
                                   Opn exam

   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.
                        Vf test

 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.
                Types of vf testing

 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.
Humphery perimeter
Pattern of visual loss
Arcute scotoma
Nasal steps

				
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