Correlation of retinal nerve fiber layer thickness and visual fields in glaucoma: a broken stick model.
OBJECTIVE
To determine the retinal nerve fiber layer (RNFL) thickness at which visual field (VF) damage becomes detectable and associated with structural loss.


METHODS
Retrospective cross-sectional study.


METHODS
Eighty-seven healthy and 108 glaucoma subjects (1 eye per subject) were recruited from an academic institution. All patients had VF examinations (Swedish Interactive Threshold Algorithm 24-2 test of the Humphrey Visual Field Analyzer 750i) and spectral-domain optical coherence tomography RNFL scans. Comparison of RNFL thickness values with VF threshold values showed a plateau of VF threshold values at high RNFL thickness values and then a sharp decrease at lower RNFL thickness values. A broken stick statistical analysis was used to estimate the tipping point at which RNFL thickness values are associated with VF defects. The slope for the association between structure and function was computed for data above and below the tipping point.


RESULTS
The mean RNFL thickness value that was associated with initial VF loss was 89 μm. The superior RNFL thickness value that was associated with initial corresponding inferior VF loss was 100 μm. The inferior RNFL thickness value that was associated with initial corresponding superior VF loss was 73 μm. The differences between all the slopes above and below the aforementioned tipping points were statistically significant (P < .001).


CONCLUSIONS
In open-angle glaucoma, substantial RNFL thinning or structural loss appears to be necessary before functional visual field defects become detectable.
Department of Ophthalmology, Harvard Medical School, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts.
Tarek
T
Alasil
Harvard Medical School, Boston, Massachusetts.
Kaidi
K
Wang
Department of Ophthalmology, Jules Stein Eye Institute, University of California, Los Angeles, California.
Fei
F
Yu
Department of Ophthalmology, Harvard Medical School, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts.
Matthew G
MG
Field
Department of Biostatistics, Massachusetts General Hospital, Boston, Massachusetts.
Hang
H
Lee
Department of Ophthalmology, Harvard Medical School, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts.
Neda
N
Baniasadi
Department of Physics and Astronomy, Vrije Universiteit, Amsterdam, Netherlands.
Johannes F
JF
de Boer
Department of Ophthalmology, Jules Stein Eye Institute, University of California, Los Angeles, California.
Anne L
AL
Coleman
Department of Ophthalmology, Harvard Medical School, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts; Harvard Medical School, Boston, Massachusetts. Electronic address: Teresa_Chen@meei.harvard.edu.
Teresa C
TC
Chen
D000368:Aged; D000465:Algorithms; D003430:Cross-Sectional Studies; D017889:Exfoliation Syndrome / Q000175:diagnosis; D005260:Female; D005902:Glaucoma, Open-Angle / Q000175:diagnosis* / Q000503:physiopathology; D006801:Humans; D007429:Intraocular Pressure; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009412:Nerve Fibers / Q000473:pathology*; D009901:Optic Nerve Diseases / Q000175:diagnosis* / Q000503:physiopathology; D012165:Retinal Ganglion Cells / Q000473:pathology*; D012189:Retrospective Studies; D041623:Tomography, Optical Coherence; D014065:Tonometry, Ocular; D014786:Vision Disorders / Q000503:physiopathology*; D058609:Visual Field Tests; D014794:Visual Fields / Q000502:physiology*