Physiology of cumulative defect curves; consequences in glaucoma perimetry

Staging Functional Damage in Glaucoma: Review of Different Classification Methods

Classification of glaucomatous visual field defects for different severity levels is important. The reasons for this are numerous, and include: to distinguish between healthy and diseased individuals, to have homogeneous grouping criteria when perimetry is used to define the severity of glaucoma, to adjust therapy on the basis of disease severity, to describe visual field conditions in a short and simple format, to monitor the progression of the disease, and to provide a common language for both clinical and research purposes. Many severity classification methods have been proposed, although none have had widespread use in clinical practice. Other methods, like the cumulative defect curve (Bebie curve), can be used to distinguish the type of visual field loss as diffuse, localized, or mixed. This article provides a review of the main classification methods that have been proposed in the past 40 years.

Enhanced Glaucoma Staging System (GSS 2) for classifying functional damage in glaucoma

PURPOSE

To introduce a new method, derived from the Glaucoma Staging System (GSS), for classifying glaucomatous visual field defects.

PATIENTS AND METHODS

Four sample groups composed respectively of 471 (sample #1), 128 (sample #2), 185 (sample #3), and 131 (sample #4) patients with either ocular hypertension or chronic glaucoma were considered. The GSS 2 uses both the MD and CPSD/CLV or PSD/LV perimetric indices to classify visual field defect in 6 stages and in 3 types (generalized, localized, and mixed). The formulas were determined using sample #1. A new borderline stage was created, on the basis of sample #2. The relationship between the PSD/LV and CPSD/CLV values was studied on sample #3 to verify the possibility of using the uncorrected indices instead of the CPSD/CLV. The relationship with other classification methods was studied on sample #4.

RESULTS

The GSS 2 showed a strong level of association with the AGIS and the Hodapp-Parrish-Anderson methods in staging defect severity. A good correlation was also found with a classification based on the Bebie curve.

CONCLUSIONS

The GSS 2 was able to correctly classify both damage severity and perimetric defect type in the sample studied, using either the corrected or uncorrected visual field indices. It is a quick and easy method, and its formulas can be introduced in any software.

Longitudinal and cross-sectional study of patients with early-onset severe retinal dystrophy associated with RPE65 mutations

PURPOSE

To quantify retinal function longitudinally and cross-sectionally in patients with autosomal-recessive early-onset severe retinal dystrophy (EOSRD) associated with RPE65 mutations.

SUBJECTS AND METHODS

The ocular phenotype was characterized in four children from three families up to the second decade of life, and in three siblings from one family aged 43-54 years carrying compound heterozygous or homozygous mutations in RPE65. Standard clinical examination included colour vision testing, fundus photography and Goldmann visual fields (GVF). Full-field ERGs (in all) and multifocal ERGs (in two patients) were also recorded. Visual performance and fundus appearance were compared to literature data.

RESULTS

In childhood, visual acuity (VA) ranged from 0.1 to 0.3, and GVF for target V4 was well preserved. VA and GVF were measurable in only one of the three adult siblings. Nystagmus was present in two of four children and two of three adults. Photophobia was absent in childhood and developed in adulthood. Funduscopic changes were discrete during the first decade of life in three of four children; one patient had clear macular changes already at age 5 years. All three adult siblings had distinct retinal changes including the macula. Bone spicules were not a feature. Residual colour vision was present in all patients with measurable VA. Rod ERGs were absent at any age; cone ERGs were detectable in early childhood. To date, VA data have been reported in 51 patients, visual fields in 29 patients, and a detailed fundus description in 34 patients. For all three parameters, data were comparable to the results in our patient cohort.

CONCLUSION

In childhood, patients with RPE65 mutations have better visual functions than typically seen in Leber congenital amaurosis. The phenotype shows a common progressive pattern with intrafamilial and interfamilial variation. The data suggest a preserved retinal morphology at young ages, arguing for vision-restoring gene therapy trials in childhood.

Short wavelength automated perimetry

Short Wavelength Automated Perimetry (SWAP) utilizes a blue stimulus to preferentially stimulate the blue cones and a high luminance yellow background to adapt the green and red cones and to saturate, simultaneously, the activity of the rods. This review describes the theoretical aspects of SWAP, highlights current limitations associated with the technique and discusses potential clinical applications. Compared to white-on-white (W-W) perimetry, SWAP is limited clinically by: greater variability associated with the estimation of threshold, ocular media absorption, increased examination duration and an additional learning effect. Comparative studies of SWAP and W-W perimetry have generally been undertaken on small cohorts of patients. The conclusions are frequently unconvincing due to limitations for SWAP in the delineation of abnormality and of progressive field loss. SWAP is almost certainly able to identify glaucomatous visual field loss in advance of that by W-W perimetry although the incidence of progressive field loss is similar between the two techniques. Increasing evidence suggests that functional abnormality with SWAP is preceded by structural abnormality of the optic nerve head and/or the retinal nerve fibre layer. SWAP appears to be beneficial in the detection of diabetic macular oedema and possibly in some neuro-ophthalmic disorders.

Localised changes in glaucomatous visual fields after trabeculectomy

BACKGROUND AND OBJECTIVE

Modern techniques of automated perimetry have shown that surgical reduction of intraocular pressure (IOP) may have a beneficial effect on the glaucomatous visual field. The purpose of the present study was to analyse and quantify the changes in the visual fields of glaucoma patients after trabeculectomy.

MATERIALS AND METHODS

Octopus visual fields of twenty-seven glaucoma patients were analysed. Change in visual field mean sensitivity (MS) was calculated to detect total field changes. A clinical and a statistical analysis of small clusters of test points were used to define whether local changes had occurred.

RESULTS

MS in the operated eyes improved significantly from 16.4+/-5.6 to 18.2+/-5.5 dB. The patients had on average 3.9+/-6.2 clusters where the retinal sensitivity had improved at least 5 dB and only 0.4+/-0.9 clusters where sensitivity had deteriorated at least 5 dB after trabeculectomy. 17 patients had more improved than deteriorated clusters postoperatively.

CONCLUSION

Statistically significant improvement was seen in the MS, but improvement was also found in small local areas of the visual fields after trabeculectomy.