The Complete Approach To Glaucoma Evaluation

The Complete Approach To Glaucoma Evaluation, glaucoma, POAG, PAC, PACS, PACG

1. EVALUATION OF A GLAUCOMA PATIENT Dr. ANKITH NAIR

2. DEFINITION Glaucoma is a Chronic Optic Neuropathy with typical structural damage in the optic disc, usually accompanied by or leading to corresponding functional changes in the visual field 

3. Causes and risk factors No  identifiable cause for Primary glaucoma  Secondary Glaucoma has underlying causes like Tumor, diabetes, hypothyroidism, advanced cataract or inflammation R/f for Glaucoma include : Age Black race Diabetes Family history Eye injury or previous surgery Severe myopia Corticosteroid use, especially topical  High blood pressure Genetic factors (Congenital Glaucoma)

4. TYPES OF GLAUCOMA

5. SYMPTOMS OF GLAUCOMA  CLOSED ANGLE OPEN ANGLE GLAUCOMA  Symptoms develop slowly, and a person may not notice them until the later stages.  They include: Gradual loss of peripheral vision, usually in both eyes  and Tunnel vision 

6. HISTORY

7. Visual Complaints  Ocular symptoms Medical history Current topical medications Family history Allergies to medications Systemic medications Trauma/Surgical history History  

8. Components of a Comprehensive Eye Examination  

9. Visual Acuity and Refraction  Myopes at higher risk for POAG and Hyperopes at higher risk for PACD 

10. External Examination  To detect subtle hemangioma or dilated episcleral veins  indicating  Secodary cause  Ciliary Conjuctival Congestion --> Serious intraocular pathology (Acute Angle Closure) 

11. Ocular Motility  Patient having Amblyopia or Extropia  may change the management plan 

12. Pupil Examination  Glaucoma is usually an asymmetric disease, and demonstration of a relative afferent pupillary defect is an important diagnostic clue A dilated pupil may be a sign of angle closure

13. Slit-Lamp Examination   For signs of pseudoexfoliation (PXF), pigment dispersion, uveitis, or trauma  Pigment liberation following dilatation – Highly suggest PXF 

14. Intraocular Pressure Measurement  Measured at every visit  Desirable to obtain multiple readings throughout the day  Current gold standard --> Goldmann applanation tonometer  Corneal edema detected --> Underestimated  IOP Central Corneal Thickness – Affect IOP reading -->CCT Correction done 22mmhg is the cut off for Indian population  Water drinking test to predict peak IOP and IOP fluctuations 

15. GONIOSCOPY

16. POAG is a diagnosis of exclusion  Demonstration of open angle especially important in regions where PACD common   Gonioscopy is used to examine the A ngle of the anterior chamber  Best performed with Indentation  Gonioscope and 4 mirror type 

17. Testing conditions critical in determining Whether angle open or closed  Many angles open in bright room and long slit beam (image)  Ideal testing conditions  : Dim room illumination  Minimal intensity of slit lamp illumination  Low slit beam height  No pressure on eye with gonioscope  Wait 30-45s for pupil to dilate before deciding if angle open 

18. I f under these conditions, Posterior Trabecular Meshwork (PTM) not seen --> Pt. asked to look toward mirror to obtain “Over the hill view” of the angle  If >180 degree seen with such view, angle considered open  If not seen > Pt considered a PACS  Next > increase illumination and slit height to constrict pupil > Perform indentation with gonioscope> Look for other signs of pathology in the angle (Peripheral ant synechiae, signs of PXF, trauma, old hemmorhage, inflammation, new vessels)  If other signs absent, and angles open under conditions described above, then, in prescence of disc of field changes > diagnosis of POAG 

19. Role of Van Herrick tests and Angle Imaging  Suggested as a screening test for Angle closure  Negative test does not rule it out and positive test still requires gonioscopy  VH positive and raised IOP in combination is highly specific Angle imaging techniques like the US biomicroscope and ASOCT have not yet replaced gonioscopy and therefore not necessary for clinical use

20. OPTIC DISC AND NERVE FIBRE LAYER EXAMINAITON

21. Ideal – Magnified stereoscopic examination of disc – 60-90D lens or contact lens with Slit Lamp Stereo Photographs - Current gold standard Document disc findings with drawing or imaging for future comparison 

22. STRUCTURAL CHANGES  OF THE OPTIC DISC IN GLAUCOMA

23. Increased cup to disc ratio   Arbitrary statistical cut off of 0.7:1 - suspicious  Even more suspicious if vertically oriented  CDR --> Fallacious as disc size is not accounted for Size of disc estimated with a 60D lens.   Magnification factor for 90D lens is 1.41   “Normal” sized disc in India – Vertical diameter of 2.0mm  Get a feel of whether the disc is Small, Medium or Large  Ask “Is this disc physiologically allowed to have this sort of cup?”  CDR difference of 0.2 is suspicious  Increase in CDR over time is pathognomic for Glaucoma  Also can document the Rim to disc ratio in Superior, Supertemporal, Inferotemporal, Inferior and Nasal areas of disc  Rim : Disc <0.1:1 considered pathology until proven otherwise

24. Changes in NRR  NRR thickness follows the ISNT rule - (80%)  Change in this pattern is suspicious  Inferior rim thinner than temporal is highly suspicious  If the rim extends to edge for one clock hour – Notch  Notch is characteristic of glaucoma and produces a functional field defect too Hemmorhage that touches NRR is specific but not sensitive  Peripapillary choroidal atrophy is a soft sign of glaucomatous  damage  Significant if associated with other signs or if it increases in size 

25. Nerve Fibre Layer Defect Gold standard for examination  – Red free photography  Examined clinically using green filter on slit lamp or ophthalmoscope  The Inferior arcuate NFL - larger area and more clearly seen consistent with NRR thickness  Localized NFLD - Dark wedge that follows the pattern of NFL and increases width toward periphery  Strong predictive value for future functional changes Hemmorhage that touches NRR is specific but not sensitive  High specificity but low sensitivity.  Definite sign of pathology, but can occur in other diseases too. 

26. So, the diagnosis of glaucomatous changes in the ON is usually based on a combination of the above signs

27. IMAGING TECHNIQUES FOR EXAMINING THE OPTIC DISC These instruments lack specificity and sensitivity for routine clinical use Provide valuable clinical information

28. VISUAL FIELD

29. Integral part of a full ophthalmic evaluation  Available techniques   To test the full field (including confrontation, tangent screen, Goldmann perimetry and automated perimetry),   To assess just the central field of vision, such as the Amsler Grid , Bjerrum Tangent screen Manual and/or automated visual field testing is subjective  Abnormalities in the visual field - sign of damage anywhere in the visual system   Assess whether or not a visual field defect matches the appearance of the disc and retina, or fits with other clinical signs Test each eye separately -Non-congruous defects in each eye could be missed as the normal areas of field in one eye overlap the defects in the other eye

30. Early glaucomatous visual field defects are subtle and easily missed  Even with modern automated and sensitive visual field analysers , not evident until at least 30% of the retinal ganglion cell axons that make up the optic nerve are lost  Two major types of perimetry  Kinetic perimetry - detection of moving targets  Static perimetry - detection of a stationary target Static testing > Kinetic perimetry  To detect glaucomatous field loss, important to test for differences in the superior and inferior hemi-fields and hunt for defects such as a nasal step  Emerging technologies in visual field testing include:  Short-wavelength (blue–yellow) automated perimetry (SWAP)  Frequency doubling technology (FDT) perimetry  Motion displacement perimetry (MDP) 

31. Features of Glaucomatous Visual Field Defects  Relatively specific glaucomatous visual field defects

32. CONFRONTATION TESTING

33. AMSLER CHART TESTING Can be used to detect subtle central defects as well as paracentral defects  Patients hold chart at comfortable reading distance from their uncovered eye and stare at the central spot of the grid  Ask them to identify and then point out any areas where the grid is missing or distorted ​ Missing areas may suggest paracentral glaucomatous visual field loss, whereas distortion is more common with macular disorders 

34. STANDARD AUTOMATED PERIMETRY Constant size stimulus against a constant background illumination presented in varied light intensities at particular points according to testing strategy and minimum intensity necessary for detection of stimulus recorded as threshold of that particular point May be performed as a threshold or suprathreshold analysis With suprathreshold analysis, the intensity of the stimulus target is not reduced to the level of detection/non-detection. A threshold analysis is more sensitive, but takes longer and is more susceptible to detecting artefacts  

35. GOLDMANN PERIMETRY Enables kinetic visual field testing, and generates a permanent record of the visual field, making it more sensitive, reproducible, and better for detecting change overtime Consists of an illuminated hemispheric bowl upon which target spots of light are shone  Moved from non-seeing regions to seeing regions   Kinetic testing  Examiner  moves the target where they choose throughout a test, Observe that the patient's eye is fixating on the fixation spot, Communicate with the patient and document isopters between seeing and non-seeing regions to produce an exact drawing of visual fields  For static testing, the test target can be projected statically at a single location and the brightness increased until the patient responds that the target has been seen

36. THRESHOLD VS SUPRATHRESHOLD TESTING SUPRATHRESHOLD  Definition: Presents stimuli well above expected thresholds Application: Quick assessment for screening purposes THRESHOLD  Definition: Determines the lowest intensity stimuli detectable. Application: Quantifies and characterizes visual field defects More sensitive, but takes longer and  more susceptible to detecting artefacts

37. SAP Analysis provides the following : Patient data and reliability indices  Pictorial grey-scale plot of the visual field  Plot of raw data sensitivities for each test spot  Global indices (in dB) indicating how the height and shape of  Patient's hill of vision deviates from normal.  Mean deviation gives the average difference between the patient's overall visual field sensitivity compared to a normal  Pattern standard deviation gives the standard deviation of the tested spot deviations from normal   Total deviation plot , with a probability map  (indicating the likelihood for each missed point that it is abnormal)   Pattern standard deviation plot , together with its probability map  Analyses of change in visual field sensitivity with time 

38. The key feature of a glaucomatous visual field defect is an abnormality on the Pattern Standard Deviation plot, which also shows on the total deviation plot A field defect on the TDP, in the absence of a defect on the PSDP, can be due to glaucoma , but is more likely to be due to media opacity Field defect  more extensive on the TDP than on the PSDP may indicate co-morbidity (e.g. cataract and glaucoma)

39. CONCLUSION Diagnosis of established glaucoma at a stage where treatment can prevent blindness involves the strategy of case detection. This requires comprehensive eye examination, including slit lamp, IOP, gonioscopy, and detailed disc and retinal examination on all patients. Automated Perimetry should be obtained for all suspects

40. REFERENCES Evaluation of a Glaucoma patient – Ravi Thomas et al  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3038503/ Visual field testing. A practical guide - Pubmed https ://www.ncbi.nlm.nih.gov/pmc/articles/PMC3588129/

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