Determination of the Culture Time Point to Induce Corneal Epithelial Differentiation in Induced Pluripotent Stem Cells

BACKGROUND

Limbal stem cells (LSC) are progenitor cells in the ocular surface that renew the corneal epithelium. Limbal stem cell deficiency usually induces blindness through the loss of corneal transparency, and bilateral cases do not an accurate treatment because of the lack of an autologous source of stem cells.

METHODS

Induced pluripotent stem cells (iPSC) are promising for use in cell therapy because of their autologous origin and the capability to differentiate into corneal epithelial cells. However, there are not standardized protocols to achieve a complete corneal epithelial differentiation. We examined the expression of several markers in a human episomal iPSC line after an induction period from embryoid bodies.

RESULTS

Progenitor LSC and corneal epithelial differentiation markers, some extracellular matrix protein adhesion molecules, and wingless signaling pathway were studied. Overall, LSC progenitor and corneal epithelium differentiation markers increased after maintaining cell culture in specific conditions for 14 days, whereas pluripotency markers decreased.

CONCLUSIONS

Our approach indicated that the optimal time point to initiate iPSC differentiation into LSC and corneal phenotypes, with the use of specific medium, is from 14 days after initial embryoid bodies treatment induction.

Effect of Limbal Relaxing Incisions on Corneal Aberrations

PURPOSE

To study the effect of limbal relaxing incisions on corneal aberrations after phacoemulsification with aspheric intraocular lens (IOL) implantation.

METHODS

Forty-five eyes underwent microincision cataract surgery with on-axis phacoemulsification incision. These eyes were divided into two groups: limbal relaxing incision group (23 eyes) and control group (22 eyes). In the limbal relaxing incision group, a single limbal relaxing incision was performed on the steepest meridian of corneal topography and the degrees of arc were determined using the DONO-Donnenfeld nomogram. The eyes in the control group were operated on by microincision cataract surgery without limbal relaxing incision. Corneal topography and wavefront analysis over 6-mm pupil size were performed preoperatively and 1 month postoperatively in both groups. Target induced astigmatism vector, surgically induced astigmatism vector, difference vector, magnitude of error, flattening effect, and torque were analyzed using the Alpins vectorial method.

RESULTS

The limbal relaxing incision group showed significant reduction in topographic astigmatism by 51.87% of preoperative topographical astigmatism (P < .0001). The mean surgically induced astigmatism of limbal relaxing incision was 1.29 ± 0.71 diopters (D), which was close to the mean target induced astigmatism (1.33 ± 0.20 D), whereas the control group did not show a significant change in topographic astigmatism (0.17 ± 0.11 D; P = .73). Higher order aberrations of the cornea did not show significant change in either group except quatrefoil aberration, which significantly increased in the limbal relaxing incision group but not in the control group, with no significant difference between the two groups regarding corneal aberrations.

CONCLUSIONS

Limbal relaxing incision is an effective method in reducing corneal astigmatism with neutral effect on corneal aberrations.

Concise review: limbal stem cell deficiency, dysfunction, and distress

The cornea is the clear tissue at the front of the eye that transmits light to the retina at the back of the eye. The cornea is covered by an epithelium and surrounded by a narrow band of tissue known as the limbus. The limbus has two important roles in maintaining a healthy corneal epithelium. First, stem cells for the corneal epithelium reside at the limbus and not in the cornea. Second, the limbus acts as a barrier separating the clear avascular corneal epithelium from the surrounding vascular conjunctival tissue. A failure of these limbal functions can result in the painful and blinding disease of limbal stem cell deficiency. In this disease, the corneal epithelium cannot be maintained by the stem cells, and the corneal surface becomes replaced by hazy conjunctival tissue. There are many causes of limbal stem cell deficiency, such as burns to the eye, inflammatory diseases, and hereditary diseases. Current understanding of the pathophysiology of the disease is discussed here. In particular, understanding whether the limbal stem cells are lost or become dysfunctional or indeed whether the limbal microenvironment is disturbed is important when developing appropriate management strategies for the disease.

[A new method to test vertical ocular deviations using perilimbal light reflexes]

BACKGROUND

To develop a new diagnostic technique to determine vertical ocular deviations when the center of the pupil is covered by swollen eyelids in up- and downgaze.

PATIENTS AND METHODS

In upgaze (downgaze) the reflex of a diagnostic lamp held at about 50 cm distance from the patient is observed on the lower (upper) limbus. In the case of an asymmetric reflex, prisms are used to obtain symmetrical reflexes. The amount of prisms indicates the size of the vertical misalignment. In five healthy volunteers, the angles of vertical changes of gaze position were plotted against the prism size needed to recenter the perilimbal reflex.

RESULTS

There was a linear correlation between the amount of upgaze changes in degrees and the strength of prisms used for compensation in degrees. This linear correlation was also found in downgaze. For both the correlation coefficient was r = 0.98 +/- 0.01. In upgaze the slope of the average regression line was 0.55 +/- 2.3 degrees, in downgaze - 4.1 +/- 0.8 degrees. A prism of 1 degrees corresponds in upgaze to a vertical deviation of about 1.3 +/- 0.14 degrees, in downgaze to a deviation of about 1.1 +/- 0.07 degrees.

CONCLUSIONS

These results demonstrate that the perilimbal light reflex test is suitable for measuring simulated vertical ocular deviations. Therefore, the test may also be used in patients with vertical deviations who cannot be measured with classical methods. The method is more exact for measurements in upgaze.

Comparison of protein kinase C subtype expression between normal and aniridic human ocular surfaces: implications for limbal stem cell dysfunction in aniridia

Frozen sections of corneoscleral buttons from normal and aniridic donors were stained with hematoxylin and periodic acid-Schiff, monoclonal antibodies AE-5 and AK-2 (to cornea-specific K3 and K12 keratins, respectively), and AM-3 (to conjunctival goblet cells) as well as with subtype-specific antibodies to seven different protein kinase C (PKC) subtypes, the signal transduction isoenzymes increasingly implicated in the regulation of cell growth and differentiation. Compared with the normal cornea, the aniridic cornea showed decreased AE-5 and AK-2 stainings, increased AM-3 staining, attenuated Bowman's membrane, invasion of new blood vessels, and limbal epithelial hyperplasia. In the normal tissue, the corneal epithelium expressed PKC alpha, lambda, and zeta; the limbal and conjunctival epithelia expressed additional PKC gamma. Conjunctival goblet cells expressed only PKC lambda. Within a given epithelium, different PKC subtypes had different cell-layer distributions. In the aniridic tissue, some of the four normally expressed subtypes were expressed in different cell layers, especially at the limbal region. PKC beta and PKC delta, which were normally weakly expressed, were markedly up-regulated. These results support the conclusion that the aniridic cornea does indeed manifest features of limbal stem cell deficiency with decreased corneal epithelial phenotype and increased conjunctival epithelial phenotype. Different capacities of proliferation and differentiation may be affected by the differential expression of PKC subtypes by different cell layers of normal ocular surface epithelia. The aberrant expression of PKC subtypes in aniridia may thus result in abnormal proliferation and differentiation noted in its ocular surface epithelia. Because limbal stem cells are the ultimate source of corneal proliferation and differentiation, we postulate that limbal deficiency in aniridia is a result of abnormal limbal stem cells.

Infrared thermography of the tear film in dry eye

Infrared ocular thermograms were recorded for a group of 36 dry eye patients and for 27 age- and sex-matched controls. Mean ocular surface temperature was greater in the dry eye group (32.38 +/- 0.69 degrees C) compared with the control group (31.94 +/- 0.54 degrees C; p < 0.01). In addition, there was a greater variation of temperatures across the ocular surface in the dry eye group, illustrated by the difference in temperature between the limbus and the centre of the cornea (0.64 +/- 0.20 degrees C in dry eye patients compared with 0.41 +/- 0.20 degrees C in the control group; p < 0.001). This parameter was also shown to be greater in dry eye patients who displayed either a fast tear break-up time or a poor Schirmer's test result. Infrared thermography is a non-invasive and objective technique that may prove a useful research tool for study of the tear film, its deficiencies and its various treatment modalities.

Dellen causing disappearance of Vogt's limbal girdle (II): A compressive phenomenon?

The cornea remains clear and avascular partly as a result of the compactness of the stromal lamellae. Loosening of these lamellae promotes loss of corneal transparency and peripheral vascularisation. Conversely, increased compactness of corneal tissue may possibly result in resorption of certain peripheral opacities. We report a case in which increased corneal compactness, produced by dellen formation, resulted in the disappearance of a type II Vogt's limbal girdle.

The limbal palisades of Vogt

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