Visual Psychophysics

1. Visual Psychophysics Juan G. Santiago, MD Vitreo-Retinal Fellow Valley Retina Institute, P.A.

2. Retina • First step in the visual process is the absoption of light by the rod and cone photoreceptors. • The neural circuitry of the retina and higher visual cortex is active in the organization and processing of the photoreceptor signals.

3. Photoreceptors • There are 2 types of photoreceptors in the retina • Rods • Cones • Rods and cones operate differently • Rods are more sensitive to light than cones. • At low levels of illumination the rods provide a visual response called scotopic vision. • Cones respond to higher levels of illumination; their response is called photopic vision.

4. Photoreceptors • The eye contains about 6.5 million cones and 100 million rods distributed over the retina. • The rods and cones are not distributed evenly around the retina. • The density of the cones is greatest at the fovea, this is the region of sharpest photopic vision.

5. Photoreceptors • There are 3 basic types of cones in the retina. • These cones have different absorption characteristics as a function of wavelength with peak absorptions in the red, green, and blue regions of the optical spectrum. • α is SWS, β is MWS and γ is LWS. • There is a relatively low sensitivity to blue light. • There is a lot of overlap.

6. Photoreceptors • The optic nerve bundle contains on the order of 800,000 nerve fibers. • There are over 100,000,000 photoreceptors in the retina. • Therefore, the rods and cones must be interconnected to nerve fibers on a many-to-one basis.

7. Psychophysical Testing • Although electrophysiologic testing objectively measures cell layers and cell types in the visual pathway, it does not always allow testing of localized responses, and it may not be sensitive to small degrees of visual dysfunction. • Psychophysical tests can be exceedingly sensitive, but they are always subjective and are usually not tissue-specific because perception represents an integration of information processing by different parts of the visual pathway.

8. Psychophysical Testing Visual Acuity Visual Field Dark Adaptation Color Vision Contrast Sensitivity

9. Psychophysical Testing Visual Acuity Visual Field Dark Adaptation Color Vision Contrast Sensitivity

10. Visual Acuity • Most widely used measure of visual function. • Wide range of uses: • Assessment of refractive error • Screening for ocular health • Following the course of eye disease • Evaluating the effectiveness of medical and surgical treatment • Prescribing aids for the visually impaired • Setting vision standards for employment and driving

11. Visual Acuity Testing Snellen Chart ETDRS Chart

12. Visual Acuity Testing Tumbling E Chart Landolt C Chart

13. Psychophysical Testing Visual Acuity Visual Field Dark Adaptation Color Vision Contrast Sensitivity

14. Visual Fields • Most retinal diseases are readily diagnosed by ophthalmoscopy; hence, visual fields receive little clinical attention in the diagnosis or follow-up of retinal disorders. • The island of Traquair • Superior: 60 degrees • Nasal: 60 degrees • Inferior: 70-75 degrees • Temporal: 100-110 degrees

15. Visual Fields • Qualitative techniques • Confrontation testing • Amsler grid • Tangent screen • Quantitative techniques • Goldmann perimeter • Tübinger perimeter • Suprathreshold automated visual screeners (Fieldmaster 101 and Dicon units) • Octopus • HVF • SWAP • Microperimetry

16. Amsler Grid • The Amsler grid is viewed at14 in, using the central dot for fixation. Regions of metamorphopsia (C), scotoma (B), and blur (A) are noted.

17. Tangent Screen • A tangent screen field from a hysterical or malingering patient fails to show expansion of the visual field with doubling of both test object size and distance.

18. Quantitative Techniques • More important for follow-up than diagnosis. • Documentation of visual recovery after RD surgery, laser therapy and anti-inflammatory drug therapy is an important aspect of patient care.

19. Quantitative Techniques • Short wavelength automated perimetry (SWAP) • Uses a two-color increment threshold procedure (blue-on-yellow) to assess the functional status of short-wavelength-sensitive (SWS) mechanisms • Most applicable when early detection has important therapeutic application. • Microperimetry • Relatively new methodology for assessing visual fields that is especially helpful for central retinal disease.

20. Perimetry of Diffuse Retinal Diseases Visual Fields

21. Retinitis Pigmentosa • Earliest field defect: a group of isolated scotomata 20 to 25 degrees from fixation • Eventually these isolated defects coalesce into a “ring scotomata” affecting the midperiphery. • Peripheral field loss progresses, leaving a small, central island of vision. • Eventually, complete visual loss may occur.

22. Gyrate Atrophy Progressive peripheral visual field constriction

23. Diabetic Retinopathy • May be an ideal method for follow up of the disease due to diffuse retinal ischemia. • Field defect exist, even in the absence of observable retinopathy. • Central field defects present in 40% of eyes without visible retinopathy and in all diabetic patients with retinopathy • Central 10 degree SWAP is abnormal in diabetic patients without macular edema. • In diabetic children without retinopathy, light sensitivity is impaired in the midperiphery of the VF proportional to the degree of microalbuminuria.

24. Diabetic Retinopathy • FA of a patient with preproliferative diabetic retinopathy. Static sensitivities from Octopus perimetry are superimposed. Areas of good perfusion (G) have normal visual function. Areas of intermediate perfusion (I) have a moderate decrease of visual function, and nonperfused areas (P) have complete loss of visual function.

25. Diabetic Retinopathy • Average sensitivity of the retina decreases with decreasing perfusion, both for diabetic retinopathy (dots) and for branch retinal vein occlusion (diamonds).

26. Diabetic Retinopathy • Retinal hemorrhages and exudates of at least 3 to 4 degrees in diameter produce localized depressions in the visual field. • Macular exudation and edema cause irregular depression and flattening of static profile of the central field. • Visual sensitivity in Octopus static perimetry quantitatively correlate with retinal perfusion in preproliferative diabetic retinopathy. • The degree of retinal perfusion is more important in predicting visual field loss than the amount of proliferative retinopathy.

27. Diabetic Retinopathy • There is a correlation between the degree of retinopathy in type 1 diabetic patients and SWAP field loss. • PRP produces a marked concentric contraction of the visual field. • Central visual field sensitivity significantly depresses 1 week after treatment, but recovery of up to 95% occurs within 3 months.

28. Toxic Retinopathies • Tamoxifen • Even in the absence of retinopathy SWAP MD depresses proportional to the duration of therapy. • Vigabatrin (anti-epileptic drug) • Peripheral visual field losses in 30%. • Sildenafil (Viagra) • Substantial acute decrease in SWAP MD and milder decrease in MD on standard perimetry (case report).

29. Infectious Retinopathies • HIV-positive patients demonstrate significant localized as well as mean defects; even in patients with no infectious retinopathy. • More marked in patients with low CD4 counts.

30. Perimetry of Focal Retinal Diseases Visual Fields

31. Retinal Detachment • RD have sloping isopters on kinetic perimetry. • Helpful to differentiate from a retinoschisis, which is characterized by dense defects with steep margins, usually located supranasally. • Long-standing RD may produce steep isopters. • In shallow RD, assessment of he visual field may be more accurate than ophthalmoscopy in identifying the border of detached retina.

32. Retinal Detachment • Recovery of retinal sensitivity following long-standing RD is incomplete. • Cone function returns before rod function after successful surgical reattachment of the retina. • Central visual field defects occur following a high percentage of RD surgeries, especially with internal SRF drainage.

33. Choroidal Melanoma • Anterior melanoma • Localized constriction of the visual field. • Posterior melanoma • Dense scotoma with steep borders. • Choroidal nevus • No or subtle field defect (important in DDx)

34. Choroidal Melanoma • Small malignant melanoma of the posterior pole has been superimposed on the visual field obtained by Octopus perimetry. Because of the relatively coarse (6-degree) grid pattern of the perimeter, sensitivity is markedly reduced only at the center of the lesion.

35. Choroidal Metastases • Dense scotoma with steep borders • Visual field depression does not consistently correspond to tumor size or location. A 50-year-old patient with known breast carcinoma is referred for evaluation of a mass in the posterior pole of the right eye

36. Choroidal Metastases An inferonasal field defect in the right eye corresponds to the choroidal metastasis. There is also an unexpected dense bitemporalhemianopsia. A CT scan was requested for further evaluation.

37. Choroidal Metastases • A suprasellar mass is shown that is consistent either with pituitary tumor or metastasis.

38. Vascular Lesions • In BRAO and BRVO, the density of visual field defect is proportionate to the amount of ischemia.

39. BRVO • FA from a patient with a superior BRVO. Retinal sensitivities from Octopus perimetry are superimposed to show depressed function in the area of intermediate retinal perfusion (I). G, Area of good perfusion.

40. Inflammatory Diseases • Toxoplasmosis • Dense, irregular, steep-margined, isolated scotoma. • Syphilitic choroiditis • More diffuse depression of visual field function. • Vasculitis • Corresponding arcuate field defects to the vasculitis affected temporal arcades.

41. Idiopathic Retinal Vasculitis FA demonstrates leakage from the superotemporal retinal branch vein of the right eye. Goldmannperimetry shows an inferior arcuate field defect that corresponds to the affected region of the retina.

42. Perimetry of Macular Diseases Visual Fields

43. Macular Drusen • No effect on retinal sensitivity using standard techniques. • In SWAP, mean sensitivity of patients with soft drusen is significantly lower.

44. Age Related Macular Degeneration • Pigmentary AMD cause irregular shaped central scotoma with sloping margins and variable density. • May be bilateral, but often asymmetric. • Disciform macular degeneration causes a dense central scotoma. • Absolute scotoma associate strongly with choroidal scars (RR = 107.61) and RPE atrophy (RR = 9.97). [SRH RR=2.88, CNV RR=1.86]

45. ARMD Dense central scotoma corresponding to disciform macular degeneration.

46. CNVM – SLO Microperimetry Loss of fixation stability Decreased central retinal sensitivity

47. Cone Dystrophy • Progressive symmetric to slightly asymmetric central visual loss. • Central scotoma with relative sparing of the fovea.

48. Stargardt’s Disease • Two types of scotoma in microperimetry • Dense ring scotoma with stable fixation • Dense central scotoma with fixation shift.

49. Macular Cysts and Holes • Macular cysts may present without appreciable scotoma. • Macular holes produce dense scotoma with steep margins. • Microperimetry may be helpful in predicting the outcome of MH surgery • Visual outcome correlated with the maximum sensitivity adjacent to the hole • Absolute scotoma disappeared completely in 64% of patients achieving complete MH closure following surgery. • High incidence of inferotemporal and temporal peripheral field loss after uncomplicaed MH surgery.

50. Macular Hole Three-dimensional reconstruction of high-density macular grid (1-degree spacing) documenting steep absolute central scotoma of the left eye (A) and unaffected right eye (B).