Intraocular pressure presentation in beh

Presentation

1. INTRAOCULAR PRESSURE Dr. NINA JHA GLAUCOMA FELLOW BEH

2. I ntroduction It refers to the pressure exerted by intraocular contents on the coats of the eyeball. Normal range : 10- 21mmHg. IOP rises approx 0.8 to 1mm Hg for every 1mmHg increase in episcleral venous pressure

3. How IOP is produced Aqueous produced by the ciliary processes in the posterior chamber that drain in angle of anterior chamber. (flow rate = 2.5 microliters/min) 1 . resistance to flow at the lens-iris interface 2 . resistance to flow at the angle of the anterior chamber pressure in the eye increases until the force pushing fluid out of the eye (i.e., the eye pressure) results in the same amount of fluid produced and enters the eye.

4. Intraocular pressure is created by aqueous formation which has two components : 1. A hydrostatic component from the arterial blood pressure and ciliary body tissue pressure. 2 . An osmotic pressure induced by the active secretion of sodium and other ions by the ciliary epithelium. • Normal IOP is pulsatile, reflecting in part its vascular origin and effects of blood flow on the internal ocular structures. The IOP is a dynamic function.Any single measurement of IOP is just a momentary sample and may or may not reflect the average pressure for the patient in that hour, day or week.

5. E quilibrium

6. F actors influencing IOP D emographic factors S ystemic factors O cular factors

7. D emographic factors A ge S ex H eredity

8. S ystemic factors D iurnal variation S easonal variation B lood pressure O besity P osture E xercise N eural hormones D rugs

9. D iurnal variation A verage of 3–6 mmHg in normal individuals M aximum pressure : morning hours M inimum pressure : late at night Higher IOP is associated with greater fluctuation and a diurnal fluctuation of >10mmHg - suggestive of glaucoma

10. W hy?

11. W hy?

12. S easonal variation W inter months

13. B lood pressure Normally , IOP fluctuates 1–3 mmHg as arterial pressure varies with each cardiac cycle. L arge swings in systemic BP- increase IOP

14. P osture S itting to the supine position -- IOP rise : 6 mmHg R apid increase -- reflects changes in arterial and venous pressure The episcleral venous pressure increase in the supine position

15. E xercise Strenuous exercise : T ransient reduction of IOP C aused by acidosis and alterations in serum osmolality

16. N eural factors Hypothesis --- No proof Sympathetic system Sympathectomy - A transient reduction in IOP A n increase in outflow facility from a release of catecholamines Parasympathetic system - Stimulation : reduces IOP - Cholinergic drugs lower IOP by increasing outflow facility

17. F ood and drugs I ncrease in IOP C orticosteroids C ycloplegic drugs Water D ecrease in IOP General anesthesia Marijuana Anti glaucoma

18. O cular factors R efractive error E ye movements E yelid closure I nflammation S urgery

19. R efractive error H igher IOPs : myopic Intraocular pressure also correlates with axial length

20. E yelid movement If the eye moves against mechanical resistance, IOP can rise substantially E yelid closure Forcible eyelid closure raises IOP by 10–90 mmHg Repeated eyelid squeezing reduces IOP Widening of the lid fissure increases IOP : 2 mm Hg

21. I nflammation Inflammation Reduced production of aqueous humour Decrease in IOP

22. S urgery IOP is reduced after ocular surgery. If outflow channels are affected by inflammation or by the surgery itself -- IOP can be elevated

23. M ethods of measurement

24. Technique s o f Measurin g IOP D irect method Manometry I ndirect method Tonometry

25. Manometry Invasive technique that precisely measures the pressure inside the eye Is the reference pressure by which all other tonometers are judged for their accuracy Is used most commonly As a laboratory technique in performing continuous pressure measurements over time Evaluating effect of physiologic and pharmacologic manipulations on pressure Studying aqueous humor dynamics in postmortem eyes

26. Manometry IOP is higher than the atmospheric pressure A small hollow needle inserted into the anterior chamber, will cause the aqueous humor to flow out through the needle The needle attached to a reservoir of fluid raised high enough to prevent any loss of aqueous-height of the column of fluid (calibrated in cm of water or mm of Hg) reflects the IOP

27. Digital Instrumental Tonomet r y

28. The Evolution of Tonometers 1826-William Bowman Digital tonometer as routine examination 1863-Alnrecht von Grafe Designed 1 st instrument to attempt to measure IOP 1865-Donders 1880-Preistly Further instruments followed – indentation type(no anesthesia was used till 1884) 1885-Malkalov 1 st Applanation tonometer 1905-Hjalmar Schiotz Indentation tonometer 1948,1955-Friedenwald Coefficient of ocular rigidity 1954-Goldmann Prototype applanation tonometer(constant area) 1972-Grolmann NCT Grant Electronic indentation tonometer Halberg Handheld tonometer

29. What is Tonometry ? Tonometry is an indirect method of measuring IOP with the help of specially designed instruments known as tonometers .

30. Applanation Indentation Shape of deformation- TRUNCATED CONE Precise shape- variable & unpredictable Displace large intraocular volume Conversion tables based on empirical data used Prototype- Schiøtz tonometer Shape of deformation- FLATTENING Precise shape- constant Displace small intraocular volume Mathematical calculations for IOP Differentiated on the basis of variable measured

31. APPLAN A TION TONOMETERS No n - co n tact Air puff tonometry Pulse air Tonometry Contact Fixed area variable force Goldmann Perkins Fixed force variable area Maklakoff

32. D igital palpation O ldest method of rough IOP estimation  IOP is estimated by response of eye to pressure applied by finger pulp. Indents easily – low IOP Firm to touch – normal IOP Hard to touch – high IOP

33. Schiotz tonometer

34. Schiotz tonometer Hjalmer August Schiotz in 1905 The amount of corneal indentation by given amount of known weight (force)is measured to estimate I.O.P

35. A metal plunger that slides through a hole in a concave metal footplate The plunger, hammer, and needle weigh 5.5 g. This can be increased to 7.5, 10, or 15 g

36. B asis of indentation P lunger indents the cornea Baseline pressure / Steady IOP : P0 Pt. : Pressure during tonometry Tonometer measures Pt. The change from P0 to Pt is an expression of resistance an eye offers to the displacement of a volume of fluid ( Vc ). P0 is estimated from conversion tables

37. Schiotz tonometer : Technique Patient should be anasthetised with 4%lignocaine or 0.5% proparacaine With the patient in supine position, looking up at a fixation target while examiner separates the lids and lowers the tonometer plate to rest on the anesthetized cornea so that plunger is free to move vertically . Scale reading is measured. The 5.5 gm weight is initially used. If scale reading is 4 or less, additional weight is added to plunger. Conversion table is used to derive IOP in mm Hg from scale reading and plunger weight.

38. Advantages S imple Portab le Eas y to use Relatively inexpensive No need for SlitLamp or power supply

39. Factors Affecting Scleral Rigidity High Scleral Rigidity Hyperopia extreme myopia long standing glaucoma ARMD vasoconstrictors

40. Low Scleral Rigidity increasing age high myopia miotics vasodilators Postoperative after RD surgery ( vitrectomy , cryopexy , scleral band) intravitreal injection of compressible gas. Keratoconus Thyroid disease

41. S ources of error Corneal influences Steeper & thicker cornea -- falsely high IOP. Repeated measurements -- lower IOP. Moses effect Cornea may mold into space between plunger and hole in tonometer footplate, pushing up plunger and yielding a falsely high IOP reading

42. Limitations Instrumental errors Standardisation - testing labs for certification Mechanical obstruction to plunger etc. Muscular contractions Of extra ocular muscles increase IOP Accomodation decreases IOP Variations in volume of globe Microphthalmos High Myopia Buphthalmos It can be recorded in supine position only

43. Calibration The instrument should be calibrated before each use by placing it on a polished metal sphere and checking to be sure that the scale reading is zero. If the reading is not zero, the instrument must be repaired.

44. Sterilization The tonometer is disassembled between each use and the barrel is cleaned with 2 pipe cleaners, the first soaked in isopropyl alcohol 70 % or  methylated  spirit and the second dry. The foot plate is cleaned with alcohol swab. All surfaces must be dried before reassembling. The instrument can be sterilized with ultraviolet radiation, steam, ethylene oxide. As with other tonometer tips, the Schiotz can be damaged by some disinfecting solutions such as hydrogen peroxide and bleach.

45. G oldman applanation tonometer

46. Biprism Probe: The two beam-splitting prism within the applanating unit optically convert the circular area of corneal contact into 2 semicircles

47. G oldman applanation tonometer International clinical standard C onstant -area applanation T he force necessary to flatten (or applanate ) an area of the cornea 3.06 mm in diameter Interobserver variability : 0–3 mmHg

48. P rinciple Imbert -Fick principle -T he pressure inside an ideal dry, thin-walled sphere equals the force necessary to flatten its surface divided by the area of the flattening P = F/A P = pressure F = force A = a rea

49. Cornea being aspherical , wet, and slightly inflexible fails to follow the law. Moisture creates surface tension (S) or capillary attraction of tear film for tonometry head. Lack of flexibility requires force to bend the cornea which is independent of internal pressure. The central thickness of cornea is about 0.55 mm and the outer area of corneal flattening differs from the inner area of flattening . It is this inner area which is of importance.

50. Procedure The patient is asked not to drink alcoholic beverages as it will lower IOP and not to take large amounts of fluid (e.g., 500 ml or more) for 2 hours before the test, as it may raise the IOP. The angle between the illumination and the microscope should be approximately 60°. The room illumination is reduced. A fixation light may be placed in front of the fellow eye. The tension knob is set at 1 g. If the knob is set at 0, the prism head may vibrate when it touches the eye and damage the corneal epithelium. The 1 g position is used before each measurement.

51. The palpebral fissure is a little wider if the patient looks up. However, the gaze should be no more than 15° above the horizontal to prevent an elevation of IOP. After instilling topical anaestheia , Edge of corneal contact is made apparent by instilling fluorescein while viewing in cobalt blue light. The biprism should not touch the lids or lashes because this stimulates blinking and squeezing. The patient should blink the eyes once or twice to spread the fluorescein -stained tear film over the cornea, and then should keep the eyes open wide. Do not to place any pressure on the globe because this raises IOP.

52. In some patients, it is necessary for the examiner to hold the eyelids open with the thumb and forefinger of one hand against theorbital rim. By manually rotating a dial calibrated in grams, the force is adjusted by changing the length of a spring within the device. The prisms are calibrated in such a fashion that inner  margin of semicircles touch when 3.06 mm of the cornea is applanated . The Intra ocular pressure is then read directly from a scale on the tonometry housing.

53. The fluorescein rings should be approximately 0.25–0.3 mm in thickness – or about one-tenth the diameter of the flattened area. The fluorescent semicircles are viewed through the biprism and the force against the the cornea is adjusted until the inner edges overlap.

54. Sources of error Instrument related

55. Sources of error Technique related

56. P otential errors Corneal factors - Thin cornea - Thick cornea - Astigmatism > 3 diopters - Irregular cornea F luorescein - Inadequate fluorescein - Too much fluorescein

57. P otential errors Procedure - Elevating the eyes > 15° - Repeated tonometry - Pressing on the eyelids or globe - Squeezing of the eyelids Observer bias (expectations and even numbers ) Tonometer out of calibration

58. Caliberation GAT should be calibrated periodically, at least monthly. If the GAT is not within 0.1 g (1 mmHg) of the correct calibration, the instrument should be repaired; however, calibration errors of up to 2.5 mmHg may still be tolerated clinically.

59. Sterilization Applanation tip should be soaked for 5-15 min in diluted sodium hypochlorite, 3% H2O2 or 70% isopropyl alcohol or by wiping with alcohol, H2O2, povidone iodine or 1: 1000 merthiolate . Other methods of sterilization include: 10 min of rinsing in running tap water, wash with soap and water, cover the tip with a disposable film, and exposure to UV light. Disposable tonometer tips may also be used

60. When using disposable tips, they have a smooth applanating surface. The acrylic disposable tips seem to be somewhat more accurate than the silicone ones. While disposable shields or tips may be safer than disinfection solutions.

61. It is possible to transfer bacteria, viruses, and other infectious agents with the tonometer head, including such potentially serious infections as epidemic keratoconjunctivitis , hepatitis B, and, theoretically, acquired immunodeficiency syndrome. Care must be taken to be sure any sterilizing solution has been completely rinsed off the tonometer tip, as some of these solutions may be toxic to the corneal epithelium, especially after LASIK or other corneal procedures. If the tonometer tip is not mechanically wiped after each use, epithelial cells may stick to the tip with the small but serious risk of transmitting virus.

62. Safety regulations No examination should be undertaken in case of eye infections (or) injured corneas. Only clean and disinfected measuring prism should be used. No damaged prisms should be used. If the measuring prism come in to contact with the cornea without the drum having previously been correctly set, vibration can occur in the feeler arm, which will produce unpleasant feeling for the patient. The tonometer tips should be examined periodically under magnification as the antiseptic solutions and mechanical wiping may cause irregularities in the surface of the tip that can, in turn, injure the cornea.

63. P erkins tonometer It uses same prisms as Goldmann It is counterbalanced so that tonometry is performed in any position The prism is illuminated by battery powered bulbs. Being portable it is practical when measuring IOP in infants / children, bed ridden patients and for use in operating rooms.

64. Draeger Tonometer Draeger tonometer is similar to Perkins It has a different set of prisms It operates with a motor.

65. MacKay- Marg tonometer A movable plunger (1.5 mm in diameter) that protrudes slightly from a surrounding footplate or sleeve M ovements of the plunger are measured by a transducer and recorded on a paper strip.

66. MacKay- Marg tonometer This instrument is useful for measuring IOP in eyes with scarred, irregular, or edematous corneas because the end point does not depend on the evaluation of a light reflex sensitive to optical irregularity, as does the Goldmann tonometer . It is accurate when used over therapeutic soft contact lenses.

67. T onopen  Portable Battery operated Same principle as that of Mackay- Marg tonometer It is particularly useful in: community health fairs on ward rounds children irregular surfaces measuring through an amniotic membrance patch graft to read from the sclera

68. Tono -Pen tends to overestimate the IOP in infants so its usefulness in congenital glaucoma screening and monitoring is somewhat limited. In band keratopathy where the surface of the pathology is harder than normal cornea, the Tono -Pen tends to overestimate the IOP A disposable latex cover which is discarded after each use provides infection control.

69. Pneumotonometer  or pneumatic  tonometer It is like Mackay- Marg tonometer . The sensor is a air pressure like electronically controlled plunger in Mackay- Marg tonometer . It can also be used for continuous monitoring of IOP.

70. It gives significantly higher IOP estimates. It has a sensing device that consists of a gas chamber covered by a polymeric silicone diaphragm. A transducer converts the gas pressure in the chamber into an electrical signal that is recorded on a paper strip. The gas in the chamber escapes through an exhaust vent between the diaphragm and the tip of the support nozzle. As the diaphragm touches the cornea, the gas vent is reduced in size, and the pressure in the chamber rises.

71. Maklakov tonometer Designed in 1885 I.O.P is estimated by measuring the area of cornea that is flattened by a known weight. It is different from others in that the known force is applied and the area of applanation is measured constant force rather than constant area

72. Patient in supine position and cornea anaesthetized A layer of dye is applied to the cornea Dumb-bell-shaped metal cylinders with flat end plates of polished glass Diameter of 10 mm The surface of the weight is painted with a dye, such as mild silver protein ( Argyrol ) mixed with glycerin . Instrument is allowed to rest vertically on the cornea for 1 sec Circular white imprint on the endplate is measured and I.O.P. is calculated by using conversion table for corresponding weights(5,7,10 &15gms)

73. Intraocular pressure is measured in grams per square centimeter and is converted to millimeters of mercury by dividing by 1.36. widely in Russia and China This instrument displaces a greater volume of aqueous humor and thus IOP readings are more influenced by ocular rigidity. It does not correct for corneal bending, capillary attraction, or tear encroachment on the layer of dye. Many instruments similar to the Maklakow device have been described,like the Applanometer , Tonomat , Halberg tonometer , and GlaucoTest .

74. The Ocuton tonometer Hand-held tonometer Works on the applanation principle Probe is so light that it is barely felt Needs no anesthetic in most patients It has been marketed in Europe for home  tonometry   Useful to get some idea of the relative diurnal variation in IOP if the patient or spouse (etc.) can learn to use it.

75. I mpact rebound tonometer(I-care) A new and updated version of indentation tonometer A very light, disposable, sterile probe is propelled forward into the cornea by a solenoid T he time taken for the probe to return to its resting position and the characteristics of the rebound motion are indicative of the IOP S creening purpose

76. Transpalpebral (through Eyelid) Diaton Tonometry Diaton Tonometer measures intraocular pressure through the Eyelid It is regarded as a simple and safe method of ophthalmotonometry Transpalpebral tonometry does not require topical anesthetic drops. Hence, there is very little risk of infection Compared with the current standard of Goldmann applanation tonometry and Tono -Pen, recent data suggests that transpalpebral tonometry via the Diaton tonometer is clinically useful device for measuring IOP in routine eye exams

77. Transpalpebral (through Eyelid) Diaton Tonometry Although requiring practice of the technique, transpalpebral tonometery has been described as sufficient for clinical use and it may have applications in the home-monitoring of intraocular pressures Use of transpalpebral tonometry may be indicated in those for whom Goldmann tonometry is not indicated such as in children, those with corneal pathology, or those who have had corneal surgery

78. Hand-held Diaton tonometer with Test and Training Eye case

79. Position of the Transpalpebral Diaton Tonometer Tip on the Eyelid with No Contact with Cornea or use of Anesthesia

80. N on contact tonometer A pplanates the cornea by a jet of air N o direct contact between the device and the surface of the eye

81. P rinciple The force of the air jet increases rapidly and linearly with time. E mis sion of a collimated beam of light reflected from the central cornea received by a photocell . The time required to produce the peak reflection is directly related to the force of the air jet and thus to the counterbalancing IOP .

82. A dvantage of non contact tonometer C an be operated by non-medical personnel U seful in mass screening D oes not absolutely require topical anesthesia N o direct contact between the instrument and the eye C orneal abrasion I nfection transfer

83. Reichert Ocular Response Analyzer A n air puff tonometer that directs the air jet against the cornea M easures two pressures at which applanation occurs - One : air jet flattens the cornea as the cornea is bent inward “Resting pressure” Next : T he air jet lessens in force and the cornea recovers

84. D ifference between the two -- corneal hysteresis measure of the viscous dampening biomechanical properties of cornea

85. Dynamic contour tonometry Kanngiesser “ different concept ” P rinciple that by surrounding and matching the contour of a sphere ( or a portion thereof ), the pressure on the outside equals the pressure on the inside .

86. SENSIMED contact lens-based system embedded strain gauges detects corneal curvature changes at the limbus that occur in response to changes in IOP. records readings for 90 seconds/8.5 minutes/ up to 144 measurements in a 24-hour period. collected data can be transferred wirelessly to a computer via Bluetooth.

87. OCT Tonometry Non-contact tonometry using optical coherence tomography (OCT) is currently under development. It works as a force being applied to the cornea and simultaneous measurement of the corneal reaction. In the case of OCT tonometry , the force applied to the cornea can be : -air pressure in the form of a high pressure jet -a shock or acoustic wave - low pressure air using air pumped into a sealed chamber around the eye (like scuba mask).

88. Clinical Value Of Tonometry - In the diagnosis of Glaucoma- not in its diagnostic potentiality but in judging the response to antiglaucoma medications -In cases of Sub acute angle closure glaucoma ,if halos and blurring of vision are present along with raised IOP  then it supports the diagnosis and calls for gonioscopic examinations - In Chronic angle closure glaucoma with glaucomatous optic disc changes and typical field defects,in addition to the history of repeated congested episodes, gonioscopic examination confirms findings and tonometry would be little more than confirmatory. -But in cases with vague history,equivocal disc ,atypical field defects and with uncertain gonioscopic findings,tonometry plays a crucial role in diagnosis

89. Tonometry for Special Clinical Circumstances Tonometry  on Irregular Corneas The accuracy of Goldmann and Tono -Pen tonometers and the noncontact tonometers is limited in eyes with irregular corneas. The pneumatic  tonometer  has been shown to be useful in eyes with diseased or irregular corneas . Tonometry  over Soft Contact Lenses Pneumo   tonometry  and the  Tono -Pen can measure with reasonable accuracy the IOP through bandage contact lenses. Pneumotonometer correlates well with manometrically determined IOP, whereas the Tono -Pen consistently underestimates the pressure.

90. Tonometry  with Gas-Filled Eyes Intraocular gas affects scleral rigidity, rendering indentation tonometry unsatisfactory. Pneumatic tonometer and Tono -Pen used. A pneumatic tonometer underestimates Goldmann IOP measurements in eyes with intravitreal gas Tono -Pen compares favorably with Goldmann readings. Both instruments significantly underestimated the IOP at pressures greater than 30 mm Hg .

91. Tonometry  with Flat Anterior Chamber IOP readings from the Goldmann applanation tonometer , pneumotonometer , and Tono -Pen do not correlate well with manometrically determined pressures. Tonometry  in Eyes with  Keratoprostheses In patients at high risk for corneal transplant rejection, implantation of a keratoprosthesis is now a viable option for vision rehabilitation . Most keratoprostheses have a rigid, clear surface, it is impossible to measure IOP by using applanation or indentation instruments. In such eyes, tactile assessment appears to be the most widely used method to estimate IOP.

92. R eferences Becker-Shaffer’s diagnosis and therapy of the glaucomas – 8th edition Principles and practice of Ophthalmology , Albert and Jakobiec , 3rd edition Glaucoma – American academy of O p hthalmology 2015-2016