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glaucoma. Keltner et al. (1993) developed a VF classification system for the Optic Neuritis Treatment Trial that also has been used in the Ocular Hypertension Treatment Study (OHTS).

SAP VF assessment: full-threshold strategy

Deciding which perimetric program to apply requires knowledge of both the pathology concerned and the characteristics of the various programs available. One can nonetheless affirm that the majority of ocular and neuro-ophthalmo- logical diseases affecting the VF can be studied analyzing the central VF with a 301 fixed grid of points set at 61 or at a variable density, using a III white target stimulus (program 30/2 or 24/2 Humphrey, G1/G2 or 30/2 Octopus) (Anderson and Patella, 1999).

The FT is the most suitable strategy to evaluate VF in glaucoma patients, except in certain cases (the elderly, patients who are particularly fatigued, etc.) when fast threshold strategies (Humphrey Fastpac, Octopus tendency-oriented perimetry [TOP] strategies) could be better.

In some cases with very advanced perimetric damage in which only a small area of residual central functionality remains, or in patients suffering from macular pathologies, the examination pattern can be focused on the central 101 field, with specific programs (10/2 and Macula for Humphrey and M1 or M2 for Octopus) and/or using a V target stimulus in the case of low-vision patients.

Before carrying out the examination, it is important to explain to the patient what automated perimetry is, how it is carried out, and its importance in diagnosing and/or treating the pathology with which the patient is affected. Indeed, the patient’s informed awareness is fundamental in order to obtain reliable and clinically useful results. It must not be forgotten that SAP is a subjective, psychophysical method in which collaboration between the patient and the person carrying out the examination is essential and the importance of the learning effect should also be taken into consideration (Kulze et al., 1990; Marra and Flammer, 1991) (Fig. 3).

In other words, the patient must ‘‘learn’’ to carry out an automated perimetry exam, and it is therefore always advisable to repeat the test if the results are in doubt or not consistent with the clinical situation. It is also necessary to consider the psychological behavior of the patient undergoing perimetry. In most cases, the patient is suffering from glaucoma and is aware of the chronic nature of the disease and the way it develops. Consequently, the VF examination often causes anxiety in that it represents the moment of verifying effective ocular conditions and progression of the disease. It is therefore up to the person carrying out the exam to reassure the patient and warn him that certain light stimuli may not be seen but that this does not necessarily mean having pathological implications.

Particular care must also be taken in the correct insertion of the data. As is known, the single perimetric exam results are compared with a normative database that takes into account the age of the patient. Therefore, an erroneous date of birth can lead to comparison with the wrong age group and the possibility of diagnosing nonexistent perimetric defects or masking real defects.

The pupil diameter influences the quantity of light reaching the retina and consequently its adaptation. It is therefore advisable to carry out and repeat a perimetric examination under the same pupil diameter conditions. Furthermore, normal perimetric data are gathered from subjects with nondilated pupils. Consequently, it is best to carry out an automated perimetry in physiological conditions, monitoring successive examinations for the constancy of the pupil diameter in order to ensure a correct comparison of the results obtained (Park and Youn, 1994).

Another important aspect is the use of optical corrections. For refractive defects of up to 1 spherical and/or cylindrical diopter, it is advisable not to use corrective lenses because the support of these can lead to artifacts that can compromise a correct clinical and statistical interpretation of the results (Zalta, 1989). In cases in which an additional optical correction is required, it is absolutely necessary to use lenses with metallic frames to avoid false ‘‘annular’’ scotomata due to the lens frame (Fig. 4). Anatomical anomalies such

as congenital or acquired ptosis, facial asymmetries, and prominent noses should always be noted in the exam report, because they may cause perimetric artifacts.

As mentioned above, SAP results represented a primary outcome in most of the clinical trials and population-based studies on glaucoma and ocular hypertension. Each trial adopted different criteria to define a glaucomatous VF defect (Heijl et al., 2008).

SAP VF defects assessment: OHTS criteria

In the OHTS, a reliable VF was considered to be abnormal if GHT and/or corrected CPSD global index results were outside normal limits (Po0.01 and Po0.05, respectively).

Borderline GHT results were not included as an abnormal field. These results were an indication that the results were suspicious but not clearly abnormal.

An OHTS VF was classified as reliable if none of the reliability indices (false-positive errors, falsenegative errors, or fixation losses) exceeded the 33% limit.

In OHTS, glaucomatous VF damage was defined as follows: two consecutively abnormal SAP test results, with at least one of the two abnormal tests being within the 6-month interval (Gordon and Kass, 1999).

Only few studies suggested the possibility that the VF index MD would be more likely than PSD to capture a generalized depression of sensitivity that may be a prominent feature of early glaucoma cases. The OHTS showed that PSD, but not MD, is a predictor of glaucoma development among ocular hypertensive subjects. PSD may be important for identification of early glaucoma cases. PSD was found to be a good predictor of the development of OAG in the EGPS (Miglior et al., 2007).

However, an average loss of 27.3% of retinal ganglion cells is necessary for the corrected PSD index of standard achromatic perimetry to fall below the 95% normal confidence limits (Kerrigan– Baumrind et al., 2000).

In another study, using SAP-SITA PSD at 95% specificity, the average percentage loss of rim area of the patients with glaucoma identified as