The effect of corneal light scatter on vision after penetrating keratoplasty

Abstract

Purpose: To determine the effect of corneal light scatter on vision after penetrating keratoplasty (PK).

Design: Cross-sectional study.

Methods: setting: Cornea service at Mayo Clinic, Rochester, Minnesota. study population: Sixty-one eyes with clear grafts at 14.6 +/- 10.5 years after PK; 12 eyes with late endothelial failure (LEF) at 19.7 +/- 6.4 years after PK; 41 normal eyes. observation procedures: PK. main outcome measures: Backscatter from different depths of the cornea was measured by a custom scatterometer; intraocular forward light scatter was measured with a stray light meter; high-contrast visual acuity (HCVA) was measured by Early Treatment Diabetic Retinopathy Study (ETDRS) or Snellen chart; mesopic and photopic low-contrast visual acuity (LCVA) were measured with a 10% contrast chart.

Results: Backscatter from the anterior, middle (stroma), and posterior thirds of the cornea was higher in clear grafts compared with normal (P < .001), and higher in grafts with LEF compared with clear grafts (P < .001). Corneal stromal backscatter from clear grafts correlated with time after keratoplasty (r = 0.21; P = .006; n = 61). Forward light scatter was higher in eyes with clear grafts compared with normal (P < or = .006), and higher in eyes with LEF compared with clear grafts (P < or = .01). Corneal stromal backscatter from clear grafts correlated with HCVA (r = 0.34; P = .02; n = 52), mesopic LCVA (r = 0.36; P = .01; n = 28), and photopic LCVA (r = 0.57; P < .001; n = 28). Forward scatter in eyes with clear grafts correlated with photopic LCVA (r = 0.38; P = .04; n = 26).

Conclusions: Light scattered from the cornea increases with time after PK and is associated with decreased high- and low-contrast vision.

Figure 1. Corneal backscatter after penetrating keratoplasty (PK)

Backscatter was measured by using a custom scatterometer in clear grafts 14.6 ± 10.5 years after PK (n=61), in grafts with late endothelial failure 19.7 ± 6.4 years after PK (n=12), and in normal (unoperated) corneas (n=41). Backscatter from the anterior, middle and posterior thirds of the cornea was higher in clear grafts compared to normal (P<0.001), and was higher in grafts with LEF than in clear grafts (P<0.001). Backscatter was expressed in scatter units (SU).

Figure 2

The relationship between corneal backscatter and time after penetrating keratoplasty. Backscatter from the middle third (i.e. corneal stroma) of the cornea of clear penetrating grafts increased with time after keratoplasty (r=0.21, P=0.006, n=61). Backscatter was expressed in scatter units (SU).

Figure 3. The relationship between visual acuity and corneal backscatter after penetrating keratoplasty

Backscatter from the middle third (i.e. corneal stroma) of the cornea of clear penetrating grafts correlated with low-contrast visual acuity (LCVA) measured under mesopic (r=0.35, P=0.01, n=28) and photopic conditions (r=0.57, P<0.001, n=28). Backscatter was expressed in scatter units (SU), and LCVA was expressed as the logarithm of the minimum angle of resolution (logMAR).

Figure 4. The relationship between corneal backscatter and intraocular forward light scatter after penetrating keratoplasty

Backscatter from the middle third (i.e. corneal stroma) of the cornea of clear penetrating grafts correlated with intraocular forward light scatter (r=0.41, P<0.001, n=35). Backscatter was expressed scatter units (SU).

Figure 5. The relationship between visual acuity and intraocular forward light scatter after penetrating keratoplasty

Photopic low-contrast visual acuity (LCVA) correlated with intraocular forward light scatter (r=0.38, P=0.04, n=26). LCVA was expressed as the logarithm of the minimum angle of resolution (logMAR).