Perimetry in Intracranial Tumors

Dear Editor, In the article titled ‘Demographic Profile and Neuro-ophthalmic Manifestations in Primary Intracranial Tumors in Adult Patients: An Observational Study from a Tertiary Care Health Centre in Eastern India’,[1] authors have highlighted the importance of neuro-ophthalmic evaluation in intracranial tumour (ICT) patients. We appreciate author’s effort and research. We would like to highlight a few points about the importance of full field evaluation with Semiautomated kinetic perimetry (SKP) in ICT patients. Standard automated perimetry (SAP) evaluates the visual field (VF) up to 30° (temporally and nasally) from the fixation point whereas actual VF extends up to 90° temporally and 60° nasally from the fixation point.[2] SKP evaluates the actual VF peripheral isoptre with kinetic perimetric technique and retinal sensitivity in central 30° with static technique. Yamaguchi et al.,[3] documented a case of temporal crescent (TC) syndrome due to the lateral ventricular glioependymal cyst. Authors have highlighted the point that lesions situated in most anterior portion of striate cortex affect the monocular TC. A disadvantage of SAP programmes (30-2) is its inability to document the TC syndrome. Mejico et al.,[4] reported a case of cavernous angioma causing peripheral homonymous scotoma located between 40° and 60° from vertical meridian. SAP fails to show scotomas beyond 30°. Current perimetric practice pattern evaluates central 30° with SAP programmes in ICT.[1] In this study 41.5% of patients had VF defect. Pituitary adenoma was the most common ICT in this study. Probably charting peripheral isoptre with SKP might further increase the percentage of ICT patients showing abnormal VF. Bitemporal hemianopia respecting vertical meridian is a feature of chiasmal lesion (CL) in pituitary tumour. Incomplete and asymmetric visual field loss is also observed in pituitary tumors. Incomplete temporal field loss extends from superior periphery towards the horizontal meridian, respecting vertical meridian. Incomplete field loss at the edge of SAP chart is the apex of larger field loss in SKP. Eccentric fixation in SAP may mask small edge VF loss thus showing normal fields in spite of isoptre contraction. Astorga-Carballo et al.,[5] evaluated the features of 104 chiasmal syndrome patients. Full field evaluation with Goldmann perimetry in a pituitary macroadenoma patient showed left eye: temporal incomplete hemianopia, respecting vertical meridian and extending into inferior temporal quadrant. The right eye: complete temporal hemianopia and nasal field showing island of retained vision. An underlying vascular compression due to tumour displaced chiasma must be suspected in this patient. Right eye central scotoma is due to optic nerve compression and crossing of vertical meridian is due to delayed reaction time (fatigue). Pattern of VF loss in CL is determined by anatomical position of chiasma (prefixed, normal, postfixed) and the position of lesion (superior/inferior to chiasma). Chiasmal lesions may cause central VF loss in two situations, (i) anatomical variation cause optic neuropathy like VF loss (arcuate scotoma/central scotoma).in CL, (ii) compressive lesion on posterior chiasma (crossing binasal macular fibres) cause bitemporal hemianopic scotoma. To conclude, SKP is preferrable for visual field evaluation in ICT patients. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.