Full field perimetry in occipital lobe lesion.

Kedar et al.[1] in their article titled “Visual fields in neuro-ophthalmology” have mentioned that standard automated perimetry (SAP) has replaced Goldmann perimetry (GP) in clinical practice amidst fears that peripheral visual field defects may be missed. They have highlighted the fact that GP still has a role in neuro-ophthalmological clinical practice.

The pattern of visual field defects help in localizing site of the lesion in visual pathways. Limitation[2] of static perimetry are decreased efficiency in delineating complex lesion that extend into peripheral field, and localizing lesions within the occipital lobe. In occipital lobe lesion structural-perimetric correlation is less certain. A routine assessment of central 30o with SAP may miss homonymous peripheral scotomas. So a full-field perimetry (SAP with GP) is indicated in this lesion.

Pituitary tumors and craniopharyngiomas may occasionally require full-field perimetry during initial evaluation or follow-up. Hormone secreting pituitary tumors may cause steroid induced open-angle glaucoma. Such patients may present with glaucomatous and neuro-ophthalmological features causing diagnostic dilemma. Choudhari et al.[3] described a case of 43-year-old male patient who had pituitary adenoma, normal intraocular pressure (IOP), open angles, thin bleb, and thin neuroretinal rim. Probable diagnosis is hormone secreting pituitary tumor with steroid-induced glaucoma. Full-field perimetry at initial workup would have provided a better picture in this patient.

Automated combined kinetic and static perimetry[2] may miss very small defects in the central 30o. Brain and eye's adaptive strategy may be an explanation for this anomaly. Microperimetry (MP) is capable of eliminating adaptive strategy (eccentric fixation, fixation instability) thereby unmasking early scotomas seen in glaucomatous (central) field defect. Ratra et al.[4] in their article titled “Comparison between Humphrey Field analyzer and Microperimetry 1 in normal and glaucoma subjects” have mentioned that MP shows high sensitivity in detecting field defects in contrast to the conventional perimetry which shows limited precision, repeatability, and low sensitivity to small scotoma especially in the presence of low vision. The fixation analysis and surveillance of MP is far superior with auto-tracking of eye movements and correction for loss of fixation. SAP is the current standard in glaucoma diagnosis. Upto 20-40% of retinal ganglion cell (RGC) loss occurs prior to scotoma detection. Cerebral plasticity and RGC plasticity may be an explanation for this anomaly. Peripheral scotoma may have a potentiating effect on the central reserved visual field. Armaly-Drance technique (ADT) uses Goldmann type perimeter with supra-threshold static perimetry to test for central field defects and both supra-threshold static and kinetic perimetry to examine the peripheral field with emphasis on the nasal and temporal periphery. This technique revealed a high sensitivity and specificity which make it suitable for clinical and survey screening. An additional modification is to use V4e isoptre nasally to rule out crowding of peripheral nasal isoptres. Probably combination of ADT and MP may unmask early scotoma.

To conclude, a combination of full-field perimetry[5] and MP may avoid diagnostic pitfalls in neuro-ophthalmology-glaucoma clinical practice. Probably current preferred perimetric practice pattern requires re-evaluation.