Gonioscopy and methods to assess anterior segments

Gonioscopy

1. Gonioscopy and methods to assess anterior segments.IOP and various methods of IOP Measurements Bipin bista 2 nd year Resident-ophthalmology National medical College & Teaching Hospital

2. GONIOSCOPY HISTORICAL BACKGROUND In 1907, Trantas visualised the angle in an eye with keratoglobus by indenting the limbus . Later termed gonioscopy. Salsmann later introduced goniolens in 1914 1919, a steeper lens was introduced by Koeppe Trancoso contributed by developing gonioscope for magnification and illumination of the angle. Goldmann introduced gonioprism Barkan established the use of gonioscopy in the management of glaucoma

3. Principle of Gonioscopy In healthy eyes, angle cant be visualised d/t optical principle known as Critical angle. Basically, when a light passes from a medium with greater to lesser refractive index, (r) is larger ( i ) but when (R) is equals to 90 ( i ) is said to attain critical angle. When ( i ) exceeds the critical angle, light is reflected back to first medium. Cornea-air interface is 46 thus light coming from anterior chamber angle exceeds critical angle, thus the solution is to eliminate this interface by using a goniolens or gonioprisms

4. Direct Gonioscopy Direct gonioscopy is performed with a Koeppe Lens , a Dome-shaped 50D lens requiring an optical coupling solution . Kept in patient’s cornea in supine position. Now a days its use has been reserved for the operating room using an operating microscope to examine children and perform certain surgical procedures.

5. Indirect gonioscopy Use of goniolenses with built-in mirrors to facilitate visualisation of irido -corneal angle. These lenses reflect light originating from the opposite side of the aqueous humor . Zeiss lens and Goldmann lens .

6. Goldmann lenses It has three build-in mirrors each provide different levels of magnifications. Curved surface is filled with coupling solution and placed in anaesthesized cornea. Ask to look upward and place the inferior rim of the lens into the lower fornix. Then is asked to look forward, and is evaluated with slit-lamp in narrowed beam Lens can be rotated to examine either clock hours of the angle.

7. Zeiss lens Four mirror lens Doesn’t require coupling solution. Allows visualisation of all four quadrant. Indentation gonioscopy can be performed. Initially the angle is assessed without indenting and then by dynamic compression. Indentation is possible d/t smaller contact surface of this lens in compare to corneal surface. Be careful in applying pressure : posterior displacement of peripheral iris and widening of the anterior chamber angle.

8. Gonioscopic Grading System Knowing the gonioscopic anatomy of the angle : Identify the landmarks. Estimate the width of the angle between peripheral iris and the cornea. Evaluate the insertion Contour of iris Degree of posterior TM pigmentation.

9. Shaffer System Described in terms of angular width in degrees of the anterior chamber angle. Estimated by making two lines , one from the point of insertion to Schwalbe’s line and another from the iris surface of insertion.

10. SHAFFER ANGLE GRADING SYSTEM GRADE NUMBER ANGLE WIDTH DESCRIPTION CLOSURE 4 45-35° Wide open Impossible 3 35-20 Wide open Impossible 2 20 Narrow Possible 1 < 10 Extremely narrow Probable Slit Slit Narrowed to slit Probable Closed Closed

11. SPAETH SYSTEM Provides more complete description of the anterior chamber angle. Level of iris insertion Geometric angle formed by the intersection of a line tangential to the trabecular meshwork with surface of iris at Schwalbe’s line Peripheral iris contour Degree of depigmentation of TM.

12. SPEATH SYSTEM Insertion of the iris    A: anterior to trabecular meshwork    B: behind Schwalbe’s line    C: posterior to scleral spur    D: deep into ciliary body face    E: extremely deep    Width of the angle    Ranges between 10° and 40°    Iris configuration    s: steep    r: regular    c: concave    Pigmentation of the posterior pigmented meshwork at the 12 o’clock position    Pigmentation is graded from 0 (no pigmentation) to 4 (heavy pigmentation)

13. Van Herick’s Method Using Slit lamp alone to estimate the anterior chamber angle width. Thin beam of light is projected 60 plane to the eye from temporal field. Estimate corneal thickness to the peripheral part of the anterior chamber.

14. Van Herick’s Grading Anterior chamber depth as a proportion of corneal thickness Description Grade Comment ≥ 1 Peripheral anterior chamber space equal to full corneal thickness or larger 4 Wide open    ¼ -1/2 Space between one-fourth and one-half corneal thickness 3 Incapable of closure    1/4 Space equal to one-fourth corneal thickness 2 Should be gonioscoped <   1/4 Space less than one-fourth corneal thickness 1 Gonioscopy will usually demonstrate a dangerously narrowed angle

15. Occludable angles Based on the Spaeth classification an iris with an insertion of either A or B or an angle with a very steep approach and angle widths measuring between 10° and 20° may benefit from a Yag laser peripheral iridotomy . The superior angle is the narrowest of the four quadrants and the inferior angle is usually the widest except in patients with the pseudoexfoliation syndrome where this rule does not apply due to the presence of zonular laxity

16. T onometry

17. What is Normal ? It may be defined as that pressure which does not lead to glaucomatous damage of the optic nerve head. Unfortunately, such a definition can’t be expressed in precise numerical terms.

18. Role of IOP in Glaucoma Central role It is the only known modifiable factor that has been to show delay in progression in both ocular hypertensive and glaucoma.

19. Setting up a target IOP Mild disease : RNFL with Normal Visual Field :20% reduction in IOP , Below 18 mmHg. Moderate : VF abnormalities in one hemifeild but not within 5 fixation : 30% reduction , below 15 mmHg. Severe : field loss within 5 of fixation : 50% IOP reduction set IOP below 13 mmHg.

20. Factors affecting IOP FACTORS ASSOCIATED WITH ELEVATED IOP WITH IOP REDUCTION Supine Position Valsalva maneuver Elevated episcleral venous pressure Sympathomimetics and anticholinergic agents in narrow angles Ketamine and succinylcholine Caffeine Hyperthermia Blinking (10mm), Eyelid squeezing(90mm), Upgaze , Strabismus surgery. Prolonged exercise Pregnancy Metabolic acidosis Alcohol intake Marijuana General anaesthetics.

21. Tonometers and tonometry Two basic types of tonometers : Indentation Applanation

22. Indentation Schiötz tonometer was introduced in 1905 Displaces a relatively large Intraocular volume

23. Applanation tonometry Goldman applanation tonometry works on Imbert -Fick priniciple . States that an external force (W) against a sphere equals the pressure in the sphere ( p t ) multiplied by area flattened ( applanated ) by the external force (A). W= P t × A

24. Technique Tip has built in bi-prism which is transparent. Cornea is anaesthesized and fluorescein is applied. Tonometer head is applied to surface of the cornea and a variable force is applied using a sensitive spring using a dial.

25. Limitations Astigmatism greater than 3 diopters . Can be avoided by taking 2 measurements 90 apart – vertical and horizontal axes at rt. Angle. Careful in corneal abrasion and decompensation by anaesthesia. Potent source of infection : cleaned with hydrogen peroxide or with 70 % isopropyl alcohol. Calibration of instrument should be done twice in a year.

26. Tono -Pen Small strain gauze with annular applanation . Easy to use Portable Digital readout Used over bandaged contact lens, gas filled eyes after vitrectomy . Disposable covers Costly

27. Non contact Tonometer ( Airpuff ) Applanation achieved by a column of air Sensor detects applanation . No anaesthesia or sterilisation is required. Not portable Requires maintenance

28. pneumotonometer Slightly convex tip, resting on a cushion of air. Portable Position independent Used in irregular corneas and soft contact lenses. Expensive Sanitation is difficult.

29. Rebound tonometry Measure IOP without anaesthesia. Measures IOP by a force produced by a small plastic probe as it rebounds from cornea. Comfortable among all and highly reproducible Better applied in Paediatric cases.

30. Cycloscopy Direct visualisation of ciliary processes under special circumstances, such as iridectomy , wide iris retraction, aniridia , aphakia .

31. High resolution ultrasound biomicroscopy Low frequency allows deeper penetration low resolution Echoes are produced from interfaces of fluids and tissues. Frequency of 20 to 50 MHz

32. Fluorophotometry Standard technique to know the rate of aqueous outflow post status drug application as well . Instilling fluorescein drops in Anterior Chamber and the cornea and evaluating via emission scans.

33. Tonography Means of estimating the outflow facility by raising the IOP with an electronic indentation and observing the decay curve in the IOP over time, which is continuously recorded on a paper strip. Inferred in Freidenwald Tables.

34. OCT of anterior segment AS-OCT uses 1310-nm wavelength , posterior – 820 nm Higher resolution

35. Measurement of episcleral venous pressure Uses a thin membrane stretched over the tip of a hollow applanating head, filled with water or air. Normal : 8 and 11 mmHg. Measured at a distal junction of aqueous and episcleral veins.

36. Pachymetry Assessment of Central corneal thickness Easy, portable and widely used. Influences types of tonometry to be used Shows prognostic value for patients with ocular hypertensives .

37. Reference: 1.Glaucoma – Shield Textbook of Glaucoma 6 th edition 2.Curbside Consultation in Glaucoma : Steven J. Gedde 3.Myron yanoff and jay s duker4 th edition THANK YOU