The Optic Disc:That Which Must Be Understood in Glaucoma and The DDLS

Jeffrey D. Henderer, MD

Optic Nerve Exam

Why examine?

• The tissue at issue
• Glaucoma usually has a characteristic feature – cupping (rim thinning)
• Can have other associated findings
  • Disc hemorrhage
  • Rim thinning/pallor/notching
  • Vascular alterations

Optic Nerve Exam

• Disc size/shape
• Rim size/shape
• Cup size/shape/depth
• Peripapillary atrophy
• Disc hemorrhages
• NFL defects
• Vascular changes

Optic Nerve Exam - Benefits

• Disc damage (nerve fiber layer damage) may precede visual field defect
  Sommer, et al. Arch Ophthalmol 1991;109:77
• Disc may be stable while the field fluctuates

Optic Nerve Exam – Disc Size

• Population-based glaucoma surveys indicate larger discs may be a weak risk factor for glaucoma

  • Disc area
    Quigley, et al. J Glaucoma 1999;8:347
  • Vertical disc diameter
    Healey, et al. Am J Ophthalmol 1999;128:515

   

Optic Nerve Exam – Cup Size

• Cup size is related to disc size
  Healey, et al. Aus N Z J Ophthalmol 1997;25(S1):S99
• This must be considered when evaluating for pathologic cupping
• May underestimate the severity of glaucoma in cases of focal rim thinning or notching

Optic Nerve ExamProblems

• Variable inter-observer agreement
  Lichter. Trans Am Ophthalmol Soc 1976;74:532
  Tielsch, et al. Ophthalmology 1988;95:350
  Varma, et al. Ophthalmology 1992;99:215
• Physiologic cupping
  • Large nerve area
  • Normal rim, vessels, peripapillary region
    Jonas, et al. Am J Ophthalmol 1989;107:137
• Variable cupping patterns can not be quantified readily by a simple cup/disc ratio
• Neuroretinal rim area remains constant while disc area and cup area differ across racial groups
  Tsai, et al. J Glaucoma 1995;4:248
• So rims get thinner as discs and cups get larger
  

Theoretical Rim Area by Optic Nerve Diameter

Optic Nerve Exam - Techniques

Can a scale be developed that grades according to rim thickness as well as corrects for disc size?

The Disc Damage Likelihood Scale

• Uses knowledge of disc size (vertical disc diameter) to stage disc damage according to rim thickness
• Nerve diameter usu. 1.25 – 2.25 mm
• Rim/disc ratio
• Eight stage scale
• Based on clinical exam

Optic Nerve Exam - Techniques

How do you exam the optic nerve?

• Direct ophthalmoscopy (magnification)
• Indirect biomicroscopy (stereo)
• Optic nerve photos (stereo)
• Imaging systems
  • Confocal scanning laser tomograph (HRT)
  • Scanning laser polarimeter (GDx)
  • Optical coherence tomography (OCT)

   

   

Measuring Disc Diameter

• Vertical optic nerve diameter
• Technique
  • Slit lamp
  • 60D, 66D, 78D or 90D lens
• Vertical slit beam to create trapezoid of light
• Beam > 1 disc diameter wide
• Adjust length of beam to match vertical “height” of the nerve
• Scleral canal to scleral canal
• Read length of light column from the continuous scale on the slit lamp
• Multiply this length by a conversion factor
  • Lens specific
  • Manufacturer specific

   

   

Conversion Chart

Vertical Disc Diameter

• African-Americans 1.81 mm
• Caucasians 1.69 mm
• Male = Female
  Pearlman, et al. AAO poster 2000

Determine Thinnest Rim/Disc Ratio

Rim/Disc Ratio and DDLS

Estimating Disc Pathology by R/D Ratio

Does the DDLS Work?

• Inter and intra-observer reliability superior to cup/disc ratio
  Henderer, et al. AJO 2003;135:44
• Correlation with VF better than HRT 1
  Bayer, et al. AJO 2002;133:758
• Less influenced by ancillary test results than c/d ratio
• Equally likely to detect progression

Future Project

• Correlate DDLS with VF and compare to c/d ratio

Confounders/Problems

• Axial length
• Refractive error (3 diopters)
• Tilted nerves
• Rim thinning in a new area

Conclusions

• Optic nerve evaluation critical for glaucoma management
• Pattern of rim thinning in the context of nerve diameter crucial
• The DDLS is a useful tool for describing the optic disc